PROBLEMS WITH A 1990 5.7 AUTO

[BUDROW2]

IT WILL NOT IDLE AT RUNING TEMP IN DRIVE BUT WILL BE A LITTLE ROUGH IN PARK AND NEUT. HAVE TRIED A COMPLETE TUNE UP PLUGS, CAP, ROTOR WIRES, EVEN A NEW DIST. ALSO TRIED IAC ,ECM,CLEANED TB , CHECKED TB FOR VAC LEAKS,DID A SMOKE TEST AT TEMP AND STONE COLD,CHECKED TB FOR A BAD GASKET OR WATER LEAK INSIDE BUT STILL NOTHING OH YES I TRIED A AFTER MARKET PROM FOR PERFORMANCE (PIGIE BACK) ON COMP ,ANY MORE IDEAS WOULD BE FUN THING TO TRY ,THANK FOR YOUR HELP



BUDROW2

[Fast Freddie]

check your injectors. pull the electrical clip off one, and use a digital ohm meter on the two pins in the top of the injector. you shoud get a reading of about 16.2 ohms. im saying that from memory so hopefully someone will correct me if i'm wrong.

[BUDROW2]

THANKS FOR YOUR HELP ,I TRIED ALL NEW INJECTORS ,AND A COMPLETE TUNE UP AND THE PROBLEM IS STILL THERE COULD IT BE ONE BAD INJECTOR ? DO I HAVE TO CHECK EACH INJ . FOR THE 16.2 OHMS

[Fast Freddie]

yes. each injector seperately. mine was doing about the same thing and 8 new injectors from www.tpis.com fixed it up really nice.

[BUDROW2]

THANK YOU I WILL GET ON IT IN THE MORNING ,

TYVM

[milehigreg]

Have you checked the resistance of your injectors? What did you find? I recently went through a crank/fire/stall condition and it turned out to be the injector on # 8 cylinder basically shorted to ground. It is a very simple check. Give it a shot if you haven't and let us know what you find.

Also, this thread should probably be in the C4 Technical and Perfrormance section. Moderators?

[Hib Halverson]

Is this because of misfire at idle or too low an idle speed?

How many miles are on this engine?

What kind of duty cycle has it sustained while you've owned it?

Did this problem develop slowly or one day did you wake up to find it incapible of idling in drive?

[BUDROW2]

well thank you for your reply ,i checked the ohms at each injector all were about the same 17.9 to 18.3 hot and cold ,to my understanding that should be ok ? i am about ready to invest in another set of injectors ,these are G. M. SO THEY SHOULD BE OK BUT THEY SCREW UP TO. now im ready to try the tps ,just got it today .this acts like a miss as it is idleing but then it will idle smooth for a few then bam it shuts off ,i am to the point of ajusting it with a 44mag ,but not quite yet .thanks for your help
budrow

[BUDROW2]

hi hib : just trying to answer your question , it acts like a miss fire at idle but i cant seem to locate it it will run really good above idle and at road speed ,only at idle it starts to mess up ,if you read all of the things i have tried im not lacking much ,we put it on a snap on computer and it has no codes ,but that dont mean much
,no miss fires plus all the new stuff we tried to no avail . it has had a pretty good life with only 85 thousand on it, not driven on sunday to the track nor towed . the third owner now te car belongs to a really good friend , so it is in good hands for what ever it needs and thats a little help .

[XLR8]

Originally Posted by milehigreg

...... this thread should probably be in the C4 Technical and Perfrormance section. Moderators?

I agree... hold on everyone!

Jane Ann

[Hib Halverson]

Before you buy injectors, you need to run the fuel pressure diagnostics listed in the factory service manual. That will give you a much better idea as to whether or not it's an injector problem or not. If that leads you to bad injectors, replace them as necessary.

Also, try running some aggressive injector cleaner.

Buy three bottles of Red Line Complete Fuel System Cleaner. Use it one bottle per tankful of fuel for the next three fill-ups.

[BUDROW2]

we did a fuel pressure test and even drove with it hooked up ,fuel pressure ok ,no pulseing or drop in pressure,we kind of ruled that out but who knows , thanks for your help , oh by the way we did the fuel cleaner in the tank twice ,and changed the fuel filter again

[jmccloud]

You likely have either a leaky PCV valve or EGR.
The PCV valve is so cheap, just replace it. And check its hoses for brittle cracks; replace if you can get them.
The EGR could be stuck or its control malfunctioned. I don't know how your year works; some have a vacuum solenoid that can fail so it could be only the solenoid. Even if the solenoid is good, the diaphragm in the EGR can fail. Any year can suffer from carbon in the seat (my fail mode on my '95 Blazer).
To find whether the EGR is functional; apply vacuum to its source to assure full movement and closure (cycle it a few times and see whether it seats at a uniform position). If you have a good schematic, trouble-shoot the solenoid wiring and function.
Good luck and please post when you solve it!

[Key West Jack]

1. Sounds like a vaccum leak. Check all vaccum hoses very closely, especially the pcv hose where it makes a 90* bend (inside the bend).

2. If no problem then I would agree it is in the egr circuit. 90s have a vaccum solinoid that controls the egr. It is located aft of the rad hose inlet on the intake manifold. Chances are it is the egr valve itself. I cant stress this enough, get a Delco form the dealer, aftermarket sellers have no idea what you need and their relacement books do not give the correct valve.

Good luck, don't get frustrated you will fix the problem. Jack

[BUDROW2]

THANKS GUYS ,WE DID CHECK THE E G R VALVE AND HOSES AND WE DID A SMOKE TEST ON THE ENGINE HOT AND COLD ENGINE ,NOW TO TRY THE SOLINOID FOR THE EGR HUMMMMM MAYBE IS IT ELECT,AND VACUM HAVE TO CHECK THAT
THANK AGAIN BUDROW