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Old 09-30-2015   #1
quickbird144
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Missfire/popping at idle gremlin

Been having this issue since late 2012. Replaced just about everything at the time and still no change.

2 years later, a new engine, bunch of things replaced and it's still there. 87 gta. Originally 350 tpi but swapped over to a stealth ram vortec 350 a month ago. Replaced fuel pump today with Racetronix kit.

With the EST wire unplugged, it's still there but not as profound, plug in the EST wire and it amplifies it. Idle surges and it even cut off on me while driving a few times, but stated right back up.I can't for the life of me figure this out, especially on a new engine. Replaced every sensor except for the coolant temp switch and knock sensor but they tested good with meters and respond appropriately when data-logging. Replaced ESC module, coil, complete new distributor, ECM with PROM, new injectors, new TPS and IAC. Cold start it doesn't seem as bad but after it's warmed up it gets pretty bad.

Here's a video of what it's doing. This is with EST connected.
https://youtu.be/mVIBfbnv1fc

Last edited by quickbird144; 09-30-2015 at 07:25 PM.
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Old 09-30-2015   #2
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: Missfire/popping at idle gremlin

After all of that, I would probably pull the C100 plug, I think it's called, at the firewall and clean all the pins. Wipe all the grease off and clean the pins gently. Apply new grease and see if that helps. Just about everything goes through that plug. It has to be something basic since it does it open loop. Like the TPS signal getting lost at that plug. You've eliminated vacuum leaks and such. Bad cam lobe. I'm guessing no codes since you didn't mention any. Timing chain off one tooth could cause it, distributor timing too advanced, something like that. You've already been there though. Yeah, try the plug I guess. I had it get corroded on my car once. Lost the outside air temp on the Corvette.
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Old 10-01-2015   #3
quickbird144
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Re: Missfire/popping at idle gremlin

Thanks for the quick reply. I do not get any codes. I've been driving around with the EST connector disconnected because that's the only way I can drive the car and it's my daily. I didn't mention that when I bought a brand new autozone distributor it somewhat helped but didn't eliminate my problem. I'll try cleaning the C100 connector. I feel like I have it isolated to a ignition/spark issue but still clueless.
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Old 10-03-2015   #4
MunsonGTA
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Re: Missfire/popping at idle gremlin

I had a similar issue where the car wouldn't even want to start unless my est bypass was disconnected. The distributor was wayyyy off. How does the motor sound inside the engine bay? Is it running real rough? Does it clear up after 2500 rpm while driving?
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Old 10-03-2015   #5
quickbird144
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Re: Missfire/popping at idle gremlin

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Originally Posted by MunsonGTA View Post
I had a similar issue where the car wouldn't even want to start unless my est bypass was disconnected. The distributor was wayyyy off. How does the motor sound inside the engine bay? Is it running real rough? Does it clear up after 2500 rpm while driving?
I've played around with the timing and did the whole drop the distributor at #1 TDC many times. It's always dead on. Inside the bay the engine sounds good but reacts to the miss, it'll shake here and there. To be honest it seems like it clears up around 1500 rpm. Anything above that and it's smooth. I did a datalog with DataMaster and everything looks fine there.

I did notice however my ECM power connector that comes off the positive battery cable gets very hot. Comes from the battery into a fusible link then one wire goes into a weather-pack connector and the other goes to the ECM fuse mounted on the driver side radiator. My battery to starter wire is definitely questionable as it has some splits and cuts. Will be replacing it.
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Old 10-03-2015   #6
rhomanski
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Re: Missfire/popping at idle gremlin

If that ECM power connector is that hot, you need to look at that wire. If it has a high resistance short to ground, it will get hot, your computer won't get the power it needs, and it will run crappy.
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Old 10-06-2015   #7
86TA355SR
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Re: Missfire/popping at idle gremlin

Nothing is more frustrating than an issue like you're going through. You can spend hours looking/working on stuff and get nowhere.

It's got to be something electrical at this point.. Especially since it hasn't been any of the easier stuff/normal suspects.

Please keep us updated.

PS=I went through an ignition issue years ago-high RPM miss. Spent an entire season chasing it. All the normal suspects checked out ok. Module checked good. Believe it or not, it wasn't. I swapped it and all of my issues were gone. Put the bad one in my dad's Buick-the way he drove, he'd never notice! Up to that point, I'd never heard of a module doing that-most just die and the car won't start.

Guess what I'm saying is that it wasn't what I expected.
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Old 10-06-2015   #8
quickbird144
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Re: Missfire/popping at idle gremlin

I'm definitely at a loss now. Did what is commonly known as the "big 3" wire upgrade, and miss is still laughing at me. Replaced the battery to starter cable, upgraded the battery to chassis cable to a 4ga and upgraded the battery to alternator cable to a 4ga as well. I've put a DVM on the ECM power feed from the battery and get battery voltage with ign on engine off and just over 13v with car running with no spikes or anything.

Even when I log with DataMaster it shows voltage in the 13.5v range. It's not running lean, no codes. I just don't get it.

I bought a brand new not reman distributor and still had the miss so I returned it and have been using my oem one that I've had ever since I got the car a few years ago. One thing is for sure though, when the car is dead cold, the miss is almost non-existent, as it warms up it gets worse.
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Old 10-07-2015   #9
rhomanski
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GTA Year: 1988
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Re: Missfire/popping at idle gremlin

I'd say remove the computer and use a meter to check all the wiring. Start with the grounds. Several are under the dash I think. Where you live the moist air can cause corrosion on the grounds.

With my second car many years ago, I added fog lights. I used the headlight ground to mount the relay. 10 years later, my engine started to die at odd times. I walked around the front once when it was running crappy and saw one headlight dim. I started checking the headlight ground and it fixed it. I moved the relay to a different spot. The headlight was seeking ground through the computer circuit. Causing the engine to die. That was on an 85 Dodge I bought new. I still have it. It has a very primitive computer with a feedback carburetor.
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Old 10-08-2015   #10
MunsonGTA
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Re: Missfire/popping at idle gremlin

Well it could be an issue that is rarely heard of, but happened to me. I actually had my balancer seperate from itself and spin. The outer metal piece with the timing mark moved about 4 inches. We couldn't get my car to run worth a damn. After replacing the balancer, car ran great.

As far as the timing goes, what I would do is the thumb test. Pull the #1 plug and bump the motor over until it really blows your thumb off. It'll do it twice, you want the harder of the two blasts of air. When that happens, pull the distributor cap and see where the rotor is pointing.
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Old 10-09-2015   #11
quickbird144
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Re: Missfire/popping at idle gremlin

I stumbled across and old school trick. The dollar bill test as it's commonly known. With engine running at idle, you put a dollar bill or piece of paper or even a rag up to the exhaust pipe. If it wants to suck it in, you have a exhaust valve problem. Whether burnt or staying open, etc. My dollar bill was going nuts. When I recently built this engine I took a stab at adjusting valves for the very first time. Used a video I found on YouTube for the adjustments. Also the heads were completely rebuilt.

I set the valves on the engine stand with each piston at TDC and left it at that. Never revisited them. I have a pretty strong feeling they may be out of proper adjustment now. Especially since there is a well known method that's used to adjust valves called EOIC (exhaust opening, intake closing) that I had no clue about.

Last edited by quickbird144; 10-09-2015 at 10:59 AM.
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Old 10-09-2015   #12
DynoDave
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Re: Missfire/popping at idle gremlin

Using the dollar bill to "view" exhaust pulses can work, but on a car with an exhaust that is not true/pure straight duals (no shared pipes, no shared cats or mufflers) it's a little more difficult to pickup on the reverse pulse. Still, a quick and easy diagnostic check that might get you started in looking in the right direction.
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Old 10-09-2015   #13
quickbird144
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Re: Missfire/popping at idle gremlin

Quote:
Originally Posted by DynoDave View Post
Using the dollar bill to "view" exhaust pulses can work, but on a car with an exhaust that is not true/pure straight duals (no shared pipes, no shared cats or mufflers) it's a little more difficult to pickup on the reverse pulse. Still, a quick and easy diagnostic check that might get you started in looking in the right direction.
Forgot to mention I have longtubes that run into an x-pipe to SLP lm1 mufflers. So I guess not quite a true setup. I adjusted the valves with the car running and it made absolutely no change.

Checked compression on the first 2 cylinders on each side as the rear 2 would be nearly impossible to get to with the headers. First 2 on driver side came in at 160, first 2 on passenger side were 160 and 170. Plugs looked okay. 2 on the driver side looked a little lean.

Doesn't explain the dollar bill test but I definitely have a misfire somewhere. Back to the drawing board.
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Old 10-09-2015   #14
86TA355SR
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Re: Missfire/popping at idle gremlin

Since you've had this issue prior to the new motor and assuming it's assembled properly, I'd start with electrical items. Like mentioned prior, grounds. Specifically, ignition system.

Did the old motor have a HSR? If not, did it miss with the TPI?

What cam is in the new motor?

ECM/PROM burned for it?

Forgive the basic questions, I ask for a reason-once spent a lot of time helping a guy and all his issues were because he failed to mention he was running a stock PROM-on a 383 mini ram motor!

How the hell did he forget something like that?
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Old 10-10-2015   #15
quickbird144
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Re: Missfire/popping at idle gremlin

Just dropped in a brand new distributor today. Now every sensor on the engine is new. I recently went over all the grounds that go to the back of each cylinder head and re-did them. All other grounds have been checked. I pulled out my service manual and went over the ECM pinout with what should have what volts with ignition on engine off and with engine running, everything was in spec.

Old engine was TPI. Miss started a few years back. Later on a ended up getting a tune and the miss went away completely for awhile. Then it was off and on but with the new engine it's more frequently.

Have a 93 LT1 F-body cam in the new motor. It has 30lb injectors that came with my HSR (bought complete, intake was new but injectors were used). So with that said it does have a tune for everything.

Sometimes it's the basic questions that are important. I'm almost all out of options now. The only other thing that could possibly be in question is the injectors since I don't know the history of them. I bought some Bosch 3 21lb injectors for the TPI years back, and threw them on the HSR originally
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Old 10-11-2015   #16
rhomanski
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Re: Missfire/popping at idle gremlin

I'm guessing you have headers. Did you put a heated o2 sensor in it?
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Old 10-11-2015   #17
quickbird144
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Re: Missfire/popping at idle gremlin

Quote:
Originally Posted by rhomanski View Post
I'm guessing you have headers. Did you put a heated o2 sensor in it?
Sure do. Brand new heated one.

I'm starting to think it may be injectors.
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Old 10-11-2015   #18
MunsonGTA
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Re: Missfire/popping at idle gremlin

It could be the injectors. Did you double check your timing using the thumb method I mentioned?
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11.16 at 123 mph.
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Old 10-11-2015   #19
quickbird144
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Re: Missfire/popping at idle gremlin

Quote:
Originally Posted by MunsonGTA View Post
It could be the injectors. Did you double check your timing using the thumb method I mentioned?
I did something even more fool proof. Took #1 plug out and took valve cover off. Watched the valves and as soon as intake side came up I looked in the plug hole and saw the cylinder coming up and verified it with my balancer at 0.
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Old 10-12-2015   #20
rhomanski
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GTA Year: 1988
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Re: Missfire/popping at idle gremlin

You stated you've changed the injectors a couple times. You stated you've changed the prom with a new tune. Engine timing is good. Distributor is good. All the sensors are new. What have you done to the air intake? Could you have a small leak. I guess the throttle body is clean. Could the throttle plate bushings be leaking? Is the air filter new? You said the fuel was good, if air is good, that leaves the spark and timing again. Something in the wiring harness. I've got an '88 but it uses the same computer as yours because it was built before the anti theft was ready. So I have to make sure I get an '87 computer and chip.

Try and think back, did this start when something was changed? Some sensor or something. My Dad once had a Dodge pickup with a little tick. Everything he did made it worse. He asked me to get the head redone so I pulled it. Didn't help. Turned out to be the auto parts store had V8 distributors in 6 cylinder boxes. When they checked their stock they had 15 in the wrong boxes. The rebuilder did that with the last shipment. That'll make for a bad day. After another good distributor it ran perfect. Too bad his health had deteriorated so badly he couldn't use it anymore by then.
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