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Old 11-07-2005   #61
george88gta
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Re: engine pings

Quote:
Originally Posted by nblanchard
colder plugs... didn't I suggest that earlier in the thread? hmmmm
You sure did! Since I am using the plugs specified for this engine, I was looking for another reason for the problem. There has to be something I am missing. Everything is supposed to be to spec so the plugs shouldnt be the reason. Another option would be to change to a 180 thermostat. Of course, the fuel containing 10% ethanol could have changed the performance parameters.
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Old 11-07-2005   #62
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Re: engine pings

in my experience... ethanol is a good thing... Sunoco 94 has ethanol
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Old 11-07-2005   #63
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Re: engine pings

Was the fuel pressure checked as the car drove? Weak fuel pumps (or bad/worn/dirty injectors) can cause fuel dribble which will result in improper mixtures that may result in lean pinging.

As for ethanol, I've read it has a lower energy content per unit volume as compared to gasoline, so while it may raise the octane of the fuel, you might not get as much energy out of the same unit volume of the fuel as a fuel with less ethanol. In my experience, the best drag strip results have come about with fuel that was not laced with ethanol in order to enhance octane. The best results I ever got was with Esso's 92 octane (back before they reformulated and ended up with 91). I also get distinctly poorer gas mileage with Sunoco's 94.
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Last edited by TripleTransAm; 11-07-2005 at 11:39 PM.
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Old 11-08-2005   #64
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Re: engine pings

Quote:
Originally Posted by TripleTransAm
Was the fuel pressure checked as the car drove? Weak fuel pumps (or bad/worn/dirty injectors) can cause fuel dribble which will result in improper mixtures that may result in lean pinging.

As for ethanol, I've read it has a lower energy content per unit volume as compared to gasoline, so while it may raise the octane of the fuel, you might not get as much energy out of the same unit volume of the fuel as a fuel with less ethanol. In my experience, the best drag strip results have come about with fuel that was not laced with ethanol in order to enhance octane. The best results I ever got was with Esso's 92 octane (back before they reformulated and ended up with 91). I also get distinctly poorer gas mileage with Sunoco's 94.
I replaced the fuel pump early this summer, the old one was getting really noisey. I also installed a new sending unit/pickup and strainer while I was in there. Injectors are also new this year ( ACCEL 24 pound injectors). I dont think they are leaking, the fuel pressure holds when you turn off the engine. If they were leaking, I believe that you would see the fuel pressure drop off rapidly. I can get a hose made up so I can tape the fuel pressure guage to the windshield to observe the fuel pressure while driving. The engine was pinging beore I made these changes so they didnt have any effect on the problem.The folks at Hypertec indicated that the ethanol may be part of the problem. Back to the EGR valve, should I be getting a "check engine" light with the vacumn hose removed from the valve?
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Old 11-08-2005   #65
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Re: engine pings

Quote:
Originally Posted by george88gta
I replaced the fuel pump early this summer, the old one was getting really noisey. I also installed a new sending unit/pickup and strainer while I was in there. Injectors are also new this year ( ACCEL 24 pound injectors). I dont think they are leaking, the fuel pressure holds when you turn off the engine. If they were leaking, I believe that you would see the fuel pressure drop off rapidly. I can get a hose made up so I can tape the fuel pressure guage to the windshield to observe the fuel pressure while driving. The engine was pinging beore I made these changes so they didnt have any effect on the problem.The folks at Hypertec indicated that the ethanol may be part of the problem. Back to the EGR valve, should I be getting a "check engine" light with the vacumn hose removed from the valve?
Yes you should btw, what is your compression ratio?
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Old 11-08-2005   #66
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Re: engine pings

Quote:
Originally Posted by fearthisgta
Yes you should btw, what is your compression ratio?
Compression ratio is 9:1:1, not nearly high enough to be having this problem.
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Old 11-08-2005   #67
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Re: engine pings

Quote:
Originally Posted by george88gta
Compression ratio is 9:1:1, not nearly high enough to be having this problem.
Meant to post this earlier. Seems that there are potential problems resulting from ethanol.
"There seems to be a few possible problems. One is that ethanol makes
the engine run leaner, causing performance problems. Another is that
the ethanol increases the fuel volatility, making vapor lock a problem.
Also, ethanol can dislodge some deposits in the fuel system and block
the flow." I will try to get the entire article and post a reference to it.
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Old 11-09-2005   #68
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Re: engine pings

I agree about the ethanol thing... whenever I'd switch to a fuel laced with ethanol, my cars would start funny for the few tankful or two, then no problem. Now, for my WS6 to start 'funny' is a BIG DEAL... this car starts on the same number of crank revolutions every single freaking time, no matter what the outside temperature or how long the car sat.

Anyway, back to the original topic:
About the whole EGR thing, I thought of something last night. Please understand that I do not wish to insult your mechanical knowledge of our cars in any way, so please don't take this in that manner: are you sure it was the vacuum line to the EGR that you disconnected? I say this because many many years ago I mistook the vacuum line to the FPR as the line to the EGR (or was that vice versa, I can't remember). Anyway, being my first TPI, I visually mixed up the two (being used to the EGR valves on carb'ed GMs). If you removed the vacuum line to the FPR, you might have just added some 10 psi to the fuel pressure since the FPR uses low vacuum to determine the need for higher rail pressures (ie. WOT, resulting in a richening effect).

Again, please don't be insulted by my suggestion, it is not my intent to insult.
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Old 11-09-2005   #69
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Re: engine pings

Quote:
Originally Posted by TripleTransAm
I agree about the ethanol thing... whenever I'd switch to a fuel laced with ethanol, my cars would start funny for the few tankful or two, then no problem. Now, for my WS6 to start 'funny' is a BIG DEAL... this car starts on the same number of crank revolutions every single freaking time, no matter what the outside temperature or how long the car sat.

Anyway, back to the original topic:
About the whole EGR thing, I thought of something last night. Please understand that I do not wish to insult your mechanical knowledge of our cars in any way, so please don't take this in that manner: are you sure it was the vacuum line to the EGR that you disconnected? I say this because many many years ago I mistook the vacuum line to the FPR as the line to the EGR (or was that vice versa, I can't remember). Anyway, being my first TPI, I visually mixed up the two (being used to the EGR valves on carb'ed GMs). If you removed the vacuum line to the FPR, you might have just added some 10 psi to the fuel pressure since the FPR uses low vacuum to determine the need for higher rail pressures (ie. WOT, resulting in a richening effect).

Again, please don't be insulted by my suggestion, it is not my intent to insult.
No problem, but I am sure that it was the EGR. I had replaced the FPR with a billet adjustable regulator so I am quite clear as to EGR and FPR. The vacumn hose on the EGR is a real pain to reinstall since it is bured under the plenum, not fun on a hot engine. Also, the vacumn hose on the EGR comes from the solenoid down by the base of the distributor, another fun place to work. I hooked up a hand held vacumn pump to the EGR valve and the damn thing wont hold vacumn. According to the shop manual, the valve should hold 10 inches of vacumn for at least 20 seconds. Guess I have to fix that before I go any further. Wonder if I should have had a "check engine" light all along. I have a backup PCM with a stock 350 chip, maybe I will install that to see if I get the EGR code.
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Old 11-09-2005   #70
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Re: engine pings

Yep, you obviously know the difference between the FPR and EGR.

I didn't quite know how to go about proposing this suggestion, so I'm glad you didn't get offended, especially since it seems you're familiar with the under-plenum area.

EGR problems and pinging go hand in hand, it seems, so I think I'll be checking the same thing out on my own car (it's always pinged a little much for my liking - most likely things started seizing up from all the time the car sat around motionless for the first 6 years of its life - I don't get any codes thrown either! I always thought it was fuel pressure).
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Old 11-09-2005   #71
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Re: engine pings

Quote:
Originally Posted by TripleTransAm
Yep, you obviously know the difference between the FPR and EGR.

I didn't quite know how to go about proposing this suggestion, so I'm glad you didn't get offended, especially since it seems you're familiar with the under-plenum area.

EGR problems and pinging go hand in hand, it seems, so I think I'll be checking the same thing out on my own car (it's always pinged a little much for my liking - most likely things started seizing up from all the time the car sat around motionless for the first 6 years of its life - I don't get any codes thrown either! I always thought it was fuel pressure).
I know what you mean about getting offended. Some folks just know everything and cant be helped. Been around too long to have an attitude like that. All help and comments are appreciated. Anyway, back to the pinging. I swapped in the other PCM with a stock 350 chip and reattached the vacumn line to the EGR. Car actually ran well, but not as aggressive as it was with the Hypertec chip. Today was cold and rainy and I didnt expect any pinging. Also did not get a "check engine" light. After driving for about a 1/2 hour, I stopped and removed and plugged the vacumn line from the EGR. Very slight pinging and no "check engine" light. So I guess the mystery deepens as to why no "check engine" light. Maybe the EGR is working just enough to prevent throwing a code, and removing the vacumn line cant be detected. Not looking forward to it, but I am going to replace the EGR and the EGR solenoid, it is right next to the distributor and gets hit every time I screw around with the timing ( when you loosen the distributor hold down). I also have a new set of colder plugs ( NGK V Power), but I will hold on to them until after the EGR replacement.
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Old 11-09-2005   #72
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Re: engine pings

Quote:
Originally Posted by TripleTransAm
Yep, you obviously know the difference between the FPR and EGR.

I didn't quite know how to go about proposing this suggestion, so I'm glad you didn't get offended, especially since it seems you're familiar with the under-plenum area.

EGR problems and pinging go hand in hand, it seems, so I think I'll be checking the same thing out on my own car (it's always pinged a little much for my liking - most likely things started seizing up from all the time the car sat around motionless for the first 6 years of its life - I don't get any codes thrown either! I always thought it was fuel pressure).
Speaking of fuel pressure. I am not convinced this is as big an issue as folks like to make it out to be. When I first replaced the regulator it was out of adjustment and the engine wouldnt start . Opened it up to 42 psi and the engine started right away. I have had the pressure up to as high as 50 psi with no effect on the pinging or performance. It is my opinion that once you achieve the right pressure to obtain proper atomization, adding pressure doesnt do much for a stock or mild engine. Of course, as you install power adders to the engine you will need more fuel, but I think bigger injectors is the proper way to ensure you get the fuel you need, not just increasing pressure. Some folks claim that increasing the pressure above the stock parameters, will increase wear on the pump. Having gone thru a pump change, I prefer to avoid anything that would cause premature pump failure.
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Old 11-09-2005   #73
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Re: engine pings

You said it, regarding the pump replacement! While I'm still on the original pump in my GTA, I did watch firsthand what a metric pain it was to remove and replace the pump on my WS6 under warranty (the fuel level sender wore out at the very top of the resistive range, with the tank full - below 3/4 full it was perfect). This was back when I had a great relationship with my dealer and they'd let me assist with any work on my cars, since they were not very knowledgeable about F-bodies due to their relative rarity up here (unfortunately, this dealer has since closed). Anyway, there was much swearing and frustration involved.

In the case of my GTA, on some cold mornings or after I haven't used the car for a week or so, my fuel pump priming sound a little tortured. Much like when a battery is weak... instead of a sharp consistent 2 second long whizz, it's more of an irregular buzz. So either something is making my pump 'bind' (like a clogged sock?) or the pump motor itself is weak. On my to-do list one of these days (sticking a fuel pressure gage to my windshield as I drive around).

I suspect the reason why you weren't seeing much change in your car's behaviour with fuel pressure changes was due to the car possibly correcting itself through pulse-width changes to make up for any richening or leaning due to pressure changes. I guess the only way to really tell would be to check the BLMs and Integrator values to see how FPR changes would affect them. But I suppose there would be a threshold where the injectors just wouldn't be working right due to excessive or too low pressures, so at that point there would be nothing the ECM could do to adapt.

I would expect, however, that open-loop operation would be affected because the O2 sensors wouldn't be read.

Anyway, this is all an educated guess based on the relationship between WOT vacuum and fuel pressure regulation at the FPR... these cars are supposed to run rich from the factory at WOT, and I've read about the boosting of fuel pressure at WOT to arrive at this richening. I'm sure I read this somewhere, I just can't remember where.


As for not throwing an EGR code, if I recall correctly the ECM monitors EGR operation based on a switch. If the ECM is ordering the EGR to do one thing and the switch reflects this, everything is okay. If the ECM orders the EGR to do something and the switch doesn't change, then the ECM panics and throws a code.

Now, what I cannot remember without looking at my manuals later tonight at home is: where is this switch located? Is it on the solenoid, purely to make sure that the solenoid is working right, regardless of the state of the EGR valve itself? Or is it actually on the valve itself, to make sure the bugger actually moved when the solenoid was ordered to do its thing? In the latter case, the switch would have to be pretty fubar'ed in order to not feed back the proper info to the ECM.

Or maybe the ECM is faulty? ECMs can fail 'softly', without throwing codes... in my case, my original ECM's detected TPS readings plateau'ed at 1.5 volts or so, even though the actual voltage at the TPS was able to hit the full 4.7 volts or whatever the max was, I forget. In other words, the TPS voltage swung nicely from .5 to max, but the ECM would only read from .5 to 1.5 and then remain at 1.5 all the way to WOT. So maybe in this case, the EGR solenoid is being ordered to do something and the ECM always thinks it's getting the desired response from the diagnostic switch, due to some internal problem?

To know for sure, you'd have to execute the full diagnostics in the manual.
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Old 11-09-2005   #74
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Re: engine pings

Quote:
Originally Posted by TripleTransAm
You said it, regarding the pump replacement! While I'm still on the original pump in my GTA, I did watch firsthand what a metric pain it was to remove and replace the pump on my WS6 under warranty (the fuel level sender wore out at the very top of the resistive range, with the tank full - below 3/4 full it was perfect). This was back when I had a great relationship with my dealer and they'd let me assist with any work on my cars, since they were not very knowledgeable about F-bodies due to their relative rarity up here (unfortunately, this dealer has since closed). Anyway, there was much swearing and frustration involved.

In the case of my GTA, on some cold mornings or after I haven't used the car for a week or so, my fuel pump priming sound a little tortured. Much like when a battery is weak... instead of a sharp consistent 2 second long whizz, it's more of an irregular buzz. So either something is making my pump 'bind' (like a clogged sock?) or the pump motor itself is weak. On my to-do list one of these days (sticking a fuel pressure gage to my windshield as I drive around).

I suspect the reason why you weren't seeing much change in your car's behaviour with fuel pressure changes was due to the car possibly correcting itself through pulse-width changes to make up for any richening or leaning due to pressure changes. I guess the only way to really tell would be to check the BLMs and Integrator values to see how FPR changes would affect them. But I suppose there would be a threshold where the injectors just wouldn't be working right due to excessive or too low pressures, so at that point there would be nothing the ECM could do to adapt.

I would expect, however, that open-loop operation would be affected because the O2 sensors wouldn't be read.

Anyway, this is all an educated guess based on the relationship between WOT vacuum and fuel pressure regulation at the FPR... these cars are supposed to run rich from the factory at WOT, and I've read about the boosting of fuel pressure at WOT to arrive at this richening. I'm sure I read this somewhere, I just can't remember where.


As for not throwing an EGR code, if I recall correctly the ECM monitors EGR operation based on a switch. If the ECM is ordering the EGR to do one thing and the switch reflects this, everything is okay. If the ECM orders the EGR to do something and the switch doesn't change, then the ECM panics and throws a code.

Now, what I cannot remember without looking at my manuals later tonight at home is: where is this switch located? Is it on the solenoid, purely to make sure that the solenoid is working right, regardless of the state of the EGR valve itself? Or is it actually on the valve itself, to make sure the bugger actually moved when the solenoid was ordered to do its thing? In the latter case, the switch would have to be pretty fubar'ed in order to not feed back the proper info to the ECM.

Or maybe the ECM is faulty? ECMs can fail 'softly', without throwing codes... in my case, my original ECM's detected TPS readings plateau'ed at 1.5 volts or so, even though the actual voltage at the TPS was able to hit the full 4.7 volts or whatever the max was, I forget. In other words, the TPS voltage swung nicely from .5 to max, but the ECM would only read from .5 to 1.5 and then remain at 1.5 all the way to WOT. So maybe in this case, the EGR solenoid is being ordered to do something and the ECM always thinks it's getting the desired response from the diagnostic switch, due to some internal problem?

To know for sure, you'd have to execute the full diagnostics in the manual.
Well, I changed my pump because it was groaning and took a while to bring up fuel pressure. Figured it was time, better than failing out on the road. You are going to drive me in to the manual on this one. BLM's and Integrators? Can these be read on an AutoXray scanners. Are these available to view on OBDI? I have not gone thru the entire process as outlined in the manual. I jumped in at the point where you check to see if the EGR valve can hold vacumn, ignition off. Before I rip off the plenum, I will run thru the entire test, just to be sure. As for O2 sensors, these cars have only one. Not sure what the solenoid contins, but there is a relationship with the park/neutral switc to enable EGR. Scanner indicates correct operation, but I will check the adjustment. Sure starting to miss my old cars with mechanical/vacumn advance.
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Old 11-10-2005   #75
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Re: engine pings

Quote:
Originally Posted by george88gta
Speaking of fuel pressure. I am not convinced this is as big an issue as folks like to make it out to be. When I first replaced the regulator it was out of adjustment and the engine wouldnt start . Opened it up to 42 psi and the engine started right away. I have had the pressure up to as high as 50 psi with no effect on the pinging or performance. It is my opinion that once you achieve the right pressure to obtain proper atomization, adding pressure doesnt do much for a stock or mild engine. Of course, as you install power adders to the engine you will need more fuel, but I think bigger injectors is the proper way to ensure you get the fuel you need, not just increasing pressure. Some folks claim that increasing the pressure above the stock parameters, will increase wear on the pump. Having gone thru a pump change, I prefer to avoid anything that would cause premature pump failure.
some people would disagree with that, check out this

http://www.thirdgen.org/newdesign/faq/thirdgen.shtml

scroll down to where you see a bunch of red numbers and see what it says about bumping up fuel pressure.
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Old 11-10-2005   #76
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Re: engine pings

Quote:
Originally Posted by MunsonGTA
some people would disagree with that, check out this

http://www.thirdgen.org/newdesign/faq/thirdgen.shtml

scroll down to where you see a bunch of red numbers and see what it says about bumping up fuel pressure.
Thanks for the info. I stand corrected since someone went to the trouble of charting performance on a dyno. Cant argue with that. I was going by "seat of the pants" performance and I did not notice any change in pinging nor did the car seem to run any better or worse until I got back down to less than 42psi. Since they only changed pressure, I am assuming that the increased performance was due to additonal fuel being injected in to the cylinders. Wouldnt that affect the rich/lean sensing at the O2 sensor?
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Old 11-10-2005   #77
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Re: engine pings

well i think what it is... is that GM didn't tune the car for it's full potential. They made it for a nice all around street car that gets pretty good gas mileage. When you add the extra fuel pressure, you're giving the car would it could have truely had from the factory. Whether the car reads it differently at the O2 sensor, i don't really know. I would think the car would sense the change and adjust everything accordingly.
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Old 11-10-2005   #78
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Re: engine pings

Quote:
Originally Posted by george88gta
Since they only changed pressure, I am assuming that the increased performance was due to additonal fuel being injected in to the cylinders. Wouldnt that affect the rich/lean sensing at the O2 sensor?

I'm inclined to think that the O2 sensor would pick up the difference in mixture and correct the delivery via changes in the injector pulse widths. However, at WOT, from what I understand the ECM goes into a sort of open loop, not paying attention to the O2 sensors (only one on our cars, more in later years). I think it's because the O2 sensors are not wideband units, and would be useless in the A/F ratios that are obtained during WOT operation. Apparently it does take into account how the engine was behaving just before going into the WOT cell (15? I forget, it's been a while) as a basis for what to do during the open loop WOT operation, but I suppose fiddling with the pressure would skew the actual outcome somewhat in a manner that the ECM could not predict.

The way I see it, the calibrations were engineered to deliver a certain amount of fuel at a certain injector pulsewidth based on a pre-assumed amount of fuel pressure. So if we would change this and the ECM would disregard O2 sensor input like when at WOT, I don't see how it would have any other way of compensating. I also believe the factory err'ed on the side of caution and these things run overly rich out of the box with factory calibrations.

The BLM and integrators are the way the ECM keeps track of how to adapt the basic pre-programmed factory tables. My Diacom scan software can pick these up off the ALDL stream. The goal is usually to maintain the proper A/F ratio in different driving conditions. There is a great explanation of how this works somewhere on the Internet on a Buick GN/T-type related site, but here is the basic jist...

There is a 'matrix' of 15 (or some number like this) "cells" which each represent a certain driving condition, aligned in a 4x4 (or something similar) fashion. Moving along one direction involves changing load on the engine (throttle opening, etc.) and along the other direction it involves RPM or something similar. So, at low RPM low load, you'd be in a low cell, like 1 or 2 (I think 1 is idle, can't remember). You can see what cell you're operating in via Diacom or some similar scan s/w.

You could be operating in cell 2 and jump on the gas and suddenly find yourself in cell 4, then as the RPM climbed you might jump to cell 8 then 12, etc.

Within each cell, there is a stored BLM and Integrator... the Integrator is a short term correction, whereas the BLM is a long term (slower acting) correction. Both numbers, when applying no change whatsoever to the original calibrations, sit at 128, with a maximum swing to 255 and 0 in either direction. As you sit at a light idling with the ECM operating in cell 0, if you read BLM and Integrator at 128 each, that means the ECM is not adjusting the mixture from the factory calibrations at all.

In this scenario, if for some reason the ECM detects (via the O2 sensor(s)) that things are a little lean in this cell, it bumps up the integrator slowly. I don't believe the integrator is allowed to reach 255... long before then, the ECM will decide to bump up the BLM and reset the integrator back to 128. The process continues, with the ECM hoping to get the BLM such that the integrator is as close as possible to 128 (since it's the short term correction, and you want the long term correction to be as accurate as possible right off the bat).

If there is a vacuum leak, the engine may continue to operate normally without a hint of problem because it's been able to adapt to this extra air by internally offsetting the original calibrations. Sometimes it's something stupid like an exhaust leak letting in outside air into the exhaust stream during low pressure pulses, sometimes it's an actual vacuum leak.

Anyway, once you hit cell 15 or 16 (whatever WOT is), I think it looks at how things were behaving at the cell immediately before that and to keep things safe, the lack of manifold vacuum kicks the fuel pressure up about 10psi. More fuel pressure at a certain pulse width means more fuel actually pushed through the injector, within limits.



In the case of my GTA, I noticed recently that at idle and slightly off idle, the BLMs tend to be very high. Once moving (even at slow city speeds), things are right on. So this has me wondering if there isn't a need to go around the plenum and manifold and tighten things up or change gaskets (last change was in late 1994), because of a very small vacuum leak. Or possibly a gunked up IAC letting in too much air at idle? Anyway, my BLM in that cell is very high (140s?) and soon it will hit the threshold that the ECM uses to throw a "too lean" trouble code.

In this fashion, I really appreciate electronic controls. In 2002 I went nuts trying to detect a vacuum leak in my '78 that had me adjusting the mixtures in the carb to silly settings just to compensate... and I still think I need to rebuild the carb this winter, as I still feel things may be too lean (hard to tell from the plugs, because it's probably not lean at all RPM or temperature ranges). With electronic controls, I could have had the ECM tell me right away if things were too lean.
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/Steve
'87 GTA
'98 WS6
'78 T/A
2006 Dodge Daytona R/T

Last edited by TripleTransAm; 11-10-2005 at 04:42 PM.
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Old 11-10-2005   #79
george88gta
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Re: engine pings

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Originally Posted by TripleTransAm
I'm inclined to think that the O2 sensor would pick up the difference in mixture and correct the delivery via changes in the injector pulse widths. However, at WOT, from what I understand the ECM goes into a sort of open loop, not paying attention to the O2 sensors (only one on our cars, more in later years). I think it's because the O2 sensors are not wideband units, and would be useless in the A/F ratios that are obtained during WOT operation. Apparently it does take into account how the engine was behaving just before going into the WOT cell (15? I forget, it's been a while) as a basis for what to do during the open loop WOT operation, but I suppose fiddling with the pressure would skew the actual outcome somewhat in a manner that the ECM could not predict.

The way I see it, the calibrations were engineered to deliver a certain amount of fuel at a certain injector pulsewidth based on a pre-assumed amount of fuel pressure. So if we would change this and the ECM would disregard O2 sensor input like when at WOT, I don't see how it would have any other way of compensating. I also believe the factory err'ed on the side of caution and these things run overly rich out of the box with factory calibrations.

The BLM and integrators are the way the ECM keeps track of how to adapt the basic pre-programmed factory tables. My Diacom scan software can pick these up off the ALDL stream. The goal is usually to maintain the proper A/F ratio in different driving conditions. There is a great explanation of how this works somewhere on the Internet on a Buick GN/T-type related site, but here is the basic jist...

There is a 'matrix' of 15 (or some number like this) "cells" which each represent a certain driving condition, aligned in a 4x4 (or something similar) fashion. Moving along one direction involves changing load on the engine (throttle opening, etc.) and along the other direction it involves RPM or something similar. So, at low RPM low load, you'd be in a low cell, like 1 or 2 (I think 1 is idle, can't remember). You can see what cell you're operating in via Diacom or some similar scan s/w.

You could be operating in cell 2 and jump on the gas and suddenly find yourself in cell 4, then as the RPM climbed you might jump to cell 8 then 12, etc.

Within each cell, there is a stored BLM and Integrator... the Integrator is a short term correction, whereas the BLM is a long term (slower acting) correction. Both numbers, when applying no change whatsoever to the original calibrations, sit at 128, with a maximum swing to 255 and 0 in either direction. As you sit at a light idling with the ECM operating in cell 0, if you read BLM and Integrator at 128 each, that means the ECM is not adjusting the mixture from the factory calibrations at all.

In this scenario, if for some reason the ECM detects (via the O2 sensor(s)) that things are a little lean in this cell, it bumps up the integrator slowly. I don't believe the integrator is allowed to reach 255... long before then, the ECM will decide to bump up the BLM and reset the integrator back to 128. The process continues, with the ECM hoping to get the BLM such that the integrator is as close as possible to 128 (since it's the short term correction, and you want the long term correction to be as accurate as possible right off the bat).

If there is a vacuum leak, the engine may continue to operate normally without a hint of problem because it's been able to adapt to this extra air by internally offsetting the original calibrations. Sometimes it's something stupid like an exhaust leak letting in outside air into the exhaust stream during low pressure pulses, sometimes it's an actual vacuum leak.

Anyway, once you hit cell 15 or 16 (whatever WOT is), I think it looks at how things were behaving at the cell immediately before that and to keep things safe, the lack of manifold vacuum kicks the fuel pressure up about 10psi. More fuel pressure at a certain pulse width means more fuel actually pushed through the injector, within limits.



In the case of my GTA, I noticed recently that at idle and slightly off idle, the BLMs tend to be very high. Once moving (even at slow city speeds), things are right on. So this has me wondering if there isn't a need to go around the plenum and manifold and tighten things up or change gaskets (last change was in late 1994), because of a very small vacuum leak. Or possibly a gunked up IAC letting in too much air at idle? Anyway, my BLM in that cell is very high (140s?) and soon it will hit the threshold that the ECM uses to throw a "too lean" trouble code.

In this fashion, I really appreciate electronic controls. In 2002 I went nuts trying to detect a vacuum leak in my '78 that had me adjusting the mixtures in the carb to silly settings just to compensate... and I still think I need to rebuild the carb this winter, as I still feel things may be too lean (hard to tell from the plugs, because it's probably not lean at all RPM or temperature ranges). With electronic controls, I could have had the ECM tell me right away if things were too lean.
I will have to drag out the manual on my AutoXray scanner to see if these parameters can be read. Dont get me wrong, these cars and especially the newer OBDII cars are definitley better performers and can be tuned/adjusted to meet most situations. I am working on installing a 6.0 liter 2002 Chevy truck engine in my 1955 convertible. Actually looking forward to the install and the tuning. Anyway, the parts didnt show up today so I will be putting this off until next week. I did check vacumn and I have 19-20 inches of vacumn so I dont think I have a vacumn leak. Do you know the correct routing for the vacumn lines coming from the EGR solenoid? One line goes to the EGR valve and the other line goes to the cruise control. Is this right? A bit off topic, on your 78 check the butterfly shaft in the base of the carb. The aluminum carb base wears and the hole for the shaft gets oval and will leak vacumn. Remove the return spring and see if you can move the shaft in the hole. If the shaft moves, other than rotating, the hole is worn and needs to be fixed.This can be fixed with a bronze bushing. If memory serves me right, a Briggs and Stratton 5hp valve guide will work.
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Old 11-10-2005   #80
TripleTransAm
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Re: engine pings

Quote:
Originally Posted by george88gta
Do you know the correct routing for the vacumn lines coming from the EGR solenoid? One line goes to the EGR valve and the other line goes to the cruise control. Is this right?
No clue. I'd have to check the shop manual tonight (also, I have my WS6 with me today so I can't run downstairs to the parking garage and check it out in person).

Honestly, I've gotten so spoiled with these EFI cars that I forgot there even was a set of vacuum hoses to worry about to begin with (like, to the A/C controls, the cruise control, the FPR, the EVAP system, etc.)... might be a good idea for me to check them out over the winter storage, the car IS 18 years old after all!

Thanks for the suggestion on the throttle shaft for my '78, I didn't think of that! My gut feeling had been that things are incredibly gunked up inside the small passages, since occasionally dousing the carb with carb cleaner tends to improve things for a while. I'm also going to be testing every temperature-vacuum switch and diaphragm (EGR, choke pull-off, distributor advance, etc.) looking for any other source of leakage, just in case. But I never considered the worn throttle shaft bushings before. Luckily I have 6 other spare carbs to steal parts from, so I might swap bases if I don't want to go through the hassle of re-bushing the shaft (will it still be numbers-matching if I do this? ). Again, thanks for the suggestion!

Excellent project you have going there on your '55! Please keep us updated in a separate thread, I certainly am interested in how things will work out.

No argument on the OBD-II being the more powerful of the PCMs, but sometimes I find myself inundated with all the stuff that can be read off the PCM with OBD-II. Also, it seems that with the version of Autotap I have, the more parameters the software requests from the PCM, the slower the speed of frames I can pull out. I don't know if this is an OBD-II limitation or simply my older Autotap, but I like how our 3rd gen f-body ECMs dish everything out without giving us the choice, so you're guaranteed to get all the available info without worrying about slowing down the stream. That's why I prefer snooping around 3rd gen F-body ECMs more than on my WS6 (and on my Mercury Marauder as well - still haven't figured out the knock sensor count logic on THAT car!).
__________________
/Steve
'87 GTA
'98 WS6
'78 T/A
2006 Dodge Daytona R/T
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