Hey guys. I really need answers here. I've been chasing this for a year and Im at my wits end. When the engine is cold, And for about the first 10 minutes of running it wont make revs above 3000. It coughs and farts and backfires. Then after the temp is up the problem goes away. Now I know more fuel is in the mix when your cold. At least its supposed to be. The other reason im thinking im lean is this....My flowmaster gets so hot it heats up the gas tank to the point where the fuel starts to boil. The tank pressure is enourmous. The venting system works cause I checked all that. But the amount of heat produced cant be normal. Plus the fuel pum is just screaming when the gas is hot and its a holley high flow. Im running about 58psi under wide open throttle. If im lean how do I tell. Theres no codes and the car runs great when its warmed up. I also changed to that after market MAF that seems to be popular around here. Please guys I need some Ideas here

Thanks

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

 

What do your spark plugs look like?
What is your inital timing set at?
Do you have a pressure guage or scanner that you can hook up to the car and find out what your real fuel pressure is?
Have you had your injectors cleaned?

Sounds like you may have a vacuum leak when cold, or some other warm-up problem in open loop. Look at the tech articles first and see if you can find something.

[This message has been edited by 89gta383 (edited July 05, 2001).]

 

My initial timing is at 12 degrees. I have a fuel presure guage on the furel rail. But this doesint necesarily mean I have enough fuel flow does it?

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

 

[QUOTE]Originally posted by EDGE:
[B]My initial timing is at 12 degrees.

[QUOTE/]

Holy Crap! No wonder. Your timing is WAAAAY to far advanced for running an aftermarket PROM. I would return it back to stock 6* btdc and see if that helps your problem. I bett he cars a dog at high RPM too.

Retard....

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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

 

Hey your right. The cars sucks at high rpm, it wont pass 5000

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

 

The timing may have a lot to do with that, but also the stock TPI setup is only capable of 5500 RPM anyhow.

If your timing is so far advanced, then the computer is sensing detonation at probably 3000 rpm on up and retarding the advance curve.

Set it back to stock 6* btdc and give it a try. Then go back and try 8* (only if you run premium fuel). It will run a whole lot better.

Oh, BTW- At least you know how to use a timing light, unlike some people around here.

Most people answer with "how do i know where my timing is at?"

So at least you have a head start.



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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

 

Lol. Thats funny about the timing light. You can speak tech with me dont worry I had the whole car apart and did everything myself to it. So any ideas you can think of would be great. Oh by the way. I noticed that when the car starts farting and popping and backfiring at 3000 there a real strong fuel odour almost like its not getting burned. But after the warm up its fine. Hope that gives you anothe idea

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

 

I definitely agree with the timing observations made by others. I also think you're running too rich rather than too lean in open loop and the fuel from rich misfire is igniting in your exhaust system, causing the hot muffler and gas. That's pretty dangerous, and I'd back off the fuel pressure by about 5psi also. If it still does it, back it down some more.

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1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, Accel coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley AFPR, ported plenum,
Ruger P95DC, hot wife, new oil filter, thick rubber floormats.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

 

Can to high a fuel preassure actually cause to rich a mixture? I thought the fuel preassure just aided in atomization. Thanks for all the input. Keep in mind however that I dont get any codes at all. And is the fuel mix controlled differently in closed loop?

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

 

Absolutely - For a given size injector (lbs/hour), the amount of fuel injected is entirely determined by the injector pulse width (time the ECM holds it open) and the fuel pressure. While higher fuel pressures do provide better atomization, they also cause the injectors to dump alot more fuel into the engine for a given pulse width. Your computer is sensing this in closed-loop operation with the O2 sensor and correcting it accordingly. In open-loop operation it relies on stock fuel curves but since you modified the system the pulse widths are too long for your fuel pressure. I'm suprised you haven't gotten a code for too rich exhaust, but these devices don't always function properly. Furthermore, excess fuel pressure is hell on the fuel pump. Disconnect the battery, back the fuel pressure off at least 5-8psi., and try that for awhile. Hope this helps.

 

Thanks so much for all your input. This is the first things are actually starting to make sense to me. Ill try this and keep you posted. So do you think this may be a contributing factor to the boiling fuel from massive exhaust heat. Cause the heat shield is in place

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

 

Definitely. I'm just glad it didn't build up enough gas to blow the muffler (heard that happen before) and damage you or your ride. Any time it pops through the exhaust under load be sure to check for a misfire, overly rich combustion, or timing that is off. I think you may have all of the above. Hope this helps.

 

Hey Guys thanks a lot for the help. My timing was at 8 degrees so i backed it to 6. Then I set the fuel preasure to 55lbs with the vacuum line off. It was at 62lbs before. Now the son of a b&#@% goes like snot. She chirps between gears, and halls right on through to 5200 RPM. What a difference in performance. Once again thanks. Now my final question would be should i leave well alone, or bump the preassure up just a bit?

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1987 T/A GTA 5.7L, Bored .020 and ported for .202 valves, edelbrock headers, flowmaster exhaust, JET STAGE II chip, Comp CAM, Adjustable fuel pressure, Airfoil, K&N filter, B&M stage 2 shift kit, and a home depot ram air(Hey it looks good and it works)

 

If it's running better either leave it alone or lower it some more. I wouldn't raise it a bit from 55psi.

 

Actually, 55 may be too high still. These cars tend to be programmed on the "rich" side by GM and the last thing most "basically stock" engines need is more fuel.

Also, too high of fuel pressure will shorten the life of your fuel pump and possibly your injectors. If you need more fuel than 50 psi, I suggest looking else where (ie. modify the eprom or go to larger injectors). Changing the fuel pump on these cars is not a fun job.

 

You can get a o2 sensor gauge to read lean/rich for $75 from www.sdsefi.com