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Old 04-19-2011   #1
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
90 gta 5.7 tpi problems?? any help?

Has anyone came across a problem like this... My 90 gta 5.7 tpi was running great...all the sudden it started acting up... It will start but when you throtle it it stalls... Changed timing chain plugs wires cap rotor oxygen sen throtle body ignition control mod... I did change the computer it ran good for 2 days then back to the same thing... Swapped comp 2 more times and still the same! It sounds like it sucking air like crazy... Checked for vacume leaks found none... Its almost like its starving for fuel... Have pretty much narrowed it down to a fuel prob... But have perfect fuel presure... Any help would be apprciated!!
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Old 04-19-2011   #2
83 fxdg 90
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Re: 90 gta 5.7 tpi problems?? any help?

check engine on all the time or on then turns off after running a while or not on at all
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Old 04-19-2011   #3
YumikoGTA
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Re: 90 gta 5.7 tpi problems?? any help?

Well you did a lot of things to the engine so the problem could be a lot of things. But if you say it sounds like air or vacuum sound, just be sure that you have connected all of the vacuum hoses correctly to the plenum. There are four or five of them that connect to it. One for the brake on the rear area of the drivers side. Two near the rear on the passengers side, one under the plenum close to the front and then there is one that attaches to the passengers side close to the front, I think that one is a head vacuum line, because it attaches the other end to the passengers side valve cover (if I remember correctly). Also make sure that just because the hoses are all connected to the plenum seem ok, make sure that the hoses are also connected correctly at the other ends as well.

Other types of vacuum leaks can occur perhaps like if the intake is not connected properly, anywhere in the line from the air filter to where it connects into the front of the plenum, or the gaskets that are between the plenum and the pipes or the pipes that go into the intake manifold are missing, loose or damaged from incorrect assembly. Checking for vacuum leak is perhaps the easiest and cheapest thing to check so I would do that one first.

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Last edited by YumikoGTA; 04-19-2011 at 12:21 PM.
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Old 04-19-2011   #4
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

If you think it's fuel related, it would be either the fuel pressure regulator or the pump. Is the vacuum line connected to the regulator? It could have developed a hole in the diaphragm inside the regulator, letting the pressure drop under throttle. The pump could have lost a blade from the impeller. It would give pressure but would not give enough volume. It would also make a lot more noise. It's in the tank, see if that's where your noise is coming from. The best would be to hook up a gauge to the fuel rail and manipulate the throttle by hand and see what your pressure is doing at idle and at throttle. How old is the pump? Most will die somewhere around 160,000 miles.

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Old 04-19-2011   #5
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

Ron... Thanks! Have checked pressure while throtling pressure is great new pump already filter as well... It was running great after comp change after most things were changed then it went back to doing the same!! Possible electrical issue or prom chip??? I get no change on diognostic comp when I test the oxy sen lead coming from comp it reads 398 even when you test it by touching postive post on battery with finger same with neg post
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Old 04-19-2011   #6
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

Sounds like you may have already found your problem. On my scanner while the engine is running the O2 sensor reading is always changing. If you have a multimeter check the resistance between the sensor plug and the computer. Look the computer plug over good, make sure that pin hasn't been pushed out of the plug. Now, that's if it goes closed loop. Does yours go closed loop? Does it set any codes? It's speed density isn't it? Do you have headers? Have you changed to a three wire sensor yet? Come back.

Regards,

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Old 04-26-2011   #7
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

@ Ron got something funky going on with the electrical... unplug the oil pressure switch and the gage goes to max pressure... have found a cink in the fuel line ( part of the sending unit) still checking things... o2 sen still doing the same! did test the injectors at the connector and got a strange outcome! the light on the tester at start was giving rapid flashes the one solid light for a sec... not sure what up with that... but headed thru the wiring now! was thinking maybe changing the pick up coil... its looking really rusty has almost no gap at the tabs! any thoughts??
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Old 04-26-2011   #8
merc3065
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Re: 90 gta 5.7 tpi problems?? any help?

With the O2 sensor flat lined, it'll cause the car to run like crap. It will go into limp home mode which will generally cause the car to run rich and idle funny. Oil pressure shutoff switch is at the back of the block behind the distributor, Oil pressure sensor relay is down by the oil filter (that will cause the pressure gauge to max as it has no resistance).

Sounds like the injector harness is working properly.

Is the service engine soon light on? If so, what is the stored code?
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Old 04-26-2011   #9
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

that the whole prob... its throwing no codes at all! it did throw a code 42 i believe when i unhooked the timing advance to set the timing but went off after it was plugged back in... could it be possible that maybe the sending unit is bad?? cause it to run rich? my # 1 and 2 plugs are fouled out not sure on the rest!
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Old 04-27-2011   #10
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

update... went thru the wiring... didnt find anything to off... ended up being a bad ecm board that was new... swaped it with another new one i had laying around good to go... as far as the o2 sen... it was just the scaner was giving false readings in the analog but was reading fin in the graph... so good to go on that... fixed the cink in the fuel line... found the distributor to have a hair line crack in it... replaced dis and pick up coil, car is running better now but now the fuel pressure is reading 30 psi at start then drops to 26... think the the fuel pump burned out from restriction possibly... maybe fuel regulator is bad... changing the fuel reg first! any thoughts??
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Old 04-28-2011   #11
merc3065
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Re: 90 gta 5.7 tpi problems?? any help?

quite possible that the regulator is bad, you can check that "relatively" easy.

If there's a tear in the diaphragm, then you need a new regulator.

That kink may have caused higher back pressure.

Also, replace the 2 fouled plugs.
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Old 04-30-2011   #12
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

this car is killing me... lol droped the tank found a fuel restriction near the pump... got that straightened out still running the same maybe going put the new pump in for sure... but not sure... found the the feul gage used the last time was bad... used the first one and got 50 psi then drop to 47... tested power to pump... is good! volume seems good too! going to try blowing out the fuel line all the way to the rail and see if there is any other restrictions! tested injectors again... they are working great! any ideas out there??
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Old 04-30-2011   #13
YumikoGTA
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Re: 90 gta 5.7 tpi problems?? any help?

Well if you have removed the fuel pump already, you should just put in a new one, unless you know for sure when the last time this has been replaced and it has only been recently For obvious reason, if you just put it back the old one, you never know if it will stop working soon. Since you have removed the fuel tank already, this is something that you should only want to do once or twice in the entire time that you own this car because it is a very work intense repair, well for me at least. I can not do this one by my self and need either help from my husband or my friends who are mechanics.

Also you say that you found a restriction near the fuel pump. So what was the restriction?

Yumiko

Quote:
Originally Posted by jibbio View Post
this car is killing me... lol droped the tank found a fuel restriction near the pump... got that straightened out still running the same maybe going put the new pump in for sure... but not sure... found the the feul gage used the last time was bad... used the first one and got 50 psi then drop to 47... tested power to pump... is good! volume seems good too! going to try blowing out the fuel line all the way to the rail and see if there is any other restrictions! tested injectors again... they are working great! any ideas out there??
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Last edited by YumikoGTA; 04-30-2011 at 07:23 PM.
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Old 04-30-2011   #14
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

yeah... im just gonna replace the pump... it was replaced not to long ago... but with all the restiction going on who knows how long the old one will carry on! the restriction was a cink... got it cleared with a coat hanger... worked wonders! you are certainly right on the tank... if you drop it you may as well replace something new! just wish the sending unit wasnt so pricy or id replace that as well... its becoming such a lil money hole! lol my mechanic is happy tho... least he a friend and get i the friend price!
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Old 04-30-2011   #15
YumikoGTA
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Re: 90 gta 5.7 tpi problems?? any help?

Ok so you mean that the fuel line has a bend in it or something? So a coat hanger can fix this? Also if you replace the fuel pump, you should also replace that strainer that connects to the bottom portion of the fuel pump also. You may also want to get the "o" ring for the top of the fuel tank from the GM Dealer. I suggest this because the "o" ring that comes with the new fuel pump is made up of soft rubber only. We used it on my GTA but the problem is when we slid the "o" ring clamp tight, it caused the soft rubber "o" ring that came with the fuel pump to disfigure and hang into the fuel tank in one area. We could not see this because it was on the inside. We found out when we filled up my GTA with fuel and it started to leak out from the top of the gas tank. So when we took it back out to see what was wrong, we could see that the soft rubber "o" ring just was hanging on the inside of the fuel tank in one area. This allowed fuel to escape past the area where the "o" ring was not in place correctly. I ordered the new "o" ring from the GM Dealership and it it has some sort of metal internal frame which keeps it strong under pressure from when you slide the metal "o" ring clamp back into place. These "o" rings from GM are pretty inexpensive, only a few dollars so it is worth it in my opinion.

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Old 04-30-2011   #16
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

Okay, trying to troubleshoot from so far away is very difficult. In the first post, you said replacing the computer fixed it for two days. Was that all that was done at that time? If so, that would point to something in or near the computer. You mentioned a loud vacuum leak. Have you ruled out a warped intake manifold? Is the car MAF or MAP?

Did you check the connectors at the computer? Sometimes pins can get bent or pushed out of the connector and then the subsequent changes won't help. Sometimes a wire will get broken and you won't be able to see it easily.

If you get a propane torch, don't fire it up, but turn it on and spew propane near the intake you can hear the idle change if there is a leak. Three things make a car run, fuel, spark, and air. One is not right. Fuel seems to be good. Check air and spark. Sometimes changing something will fool you. Coincidences happen. You change something and it starts running right, you think you fixed it. Then it goes back to running bad and you think your computer has burned out again. When in actuality, it's just that your idle air valve freed up for a couple days.

Assuming the computer is good, it has to be something the computer is not monitoring. Most of the air is not monitored. Most of the spark is. The throttle body on these will get dirty and cause problems. Right behind the throttle plate. The idle air can cause problems. Maf can really cause problems. Sometimes gently tapping on the sensor will cause it to change. That means the sensor is bad. The relays get intermittent and cause problems. Just keep looking and thinking and come back.

Regards,

Ron.
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Old 05-01-2011   #17
jibbio
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GTA Year: 1990
GTA Engine: 350 TPI Automatic
Re: 90 gta 5.7 tpi problems?? any help?

a little update... @ Ron... It has a MAP sensor... which seems to be good! a tiny vacuum leak was found on the manifold gasket... putting a new gasket in... did find 2 of the injectors to be at only 4 omhs... did some research and i think that if the injector are only around 4omhs it can cause the computer to shut down or something... changing the 2 injectors... fuel pump is fine... didnt have to drop the tank... the previous own was apparently a hack and cut thru on the top! any thoughts anyone? oh and the o2 sen is still acting funky... did test the wire... no breaks in it... possible the prom...and am swaping the ecu yet again just to be sure... will see after the injectors are changed then the new ecu will go in!
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Old 05-02-2011   #18
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Re: 90 gta 5.7 tpi problems?? any help?

replace the O2 sensor, they are cheap enough. Stick with AC Delco for the part, NGK can go bad quickly if the motor isn't running it's best.
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Old 05-03-2011   #19
jibbio
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GTA Year: 1990
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Re: 90 gta 5.7 tpi problems?? any help?

Quote:
Originally Posted by merc3065 View Post
replace the O2 sensor, they are cheap enough. Stick with AC Delco for the part, NGK can go bad quickly if the motor isn't running it's best.
have replace o2... the problem is the lead going to the computer... anyways HUGE update on car.... It ended up being 2 bad injector... they were only omhing at 4! who knew... now to figure out why the o2 readings on the scaner are funky! thinking possible prom chip??
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Old 05-03-2011   #20
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Re: 90 gta 5.7 tpi problems?? any help?

can you check resistance on the O2 wire for continuity?

See if you can locate the O2 wire and trace it back through the harness if you suspect the O2 wire is shot.

The funky readings could have been from the bad injectors. Also, if you had bad injectors etc, its a possibility that the O2 sensor is contaminated and needs replacement again. They are fragile...
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