91 Firebird runs HORRIBLY

91, 5.0L H.O., 2bbl TBI, 134K mi., suddenly runs horribly.
Starts easily from cold. Idles okay a few seconds, then starts repeatedly
surging then nearly stalling in about 3 second interval until stalls
completely. Injectors produce nice cone shaped stream, though I would not
call it a mist. Watching injectors during this idle mode, while near
stalling, injectors produce heavier spray, then lighter during surge. When
engine warms up, idles smoothly. Opening throttle, engine will rev okay
after brief stall.

When placed in gear, sputters and usually stalls unless I pump gas pedal.
Pumping lightly keeps engine running. With Heavy pressure, usually stays
running, but barely fires, engine won't rev, and car won't accelerate.
Pumping gas lightly but rapidly will get eventual acceleration. When
engine gets good and warm, something seems to "click" (figuratively, not
audibly) and engine takes off like no problem. Also, sometimes during
sputter mode, flooring pedal will sometimes get "click" mentioned above.

ECM gives lean O2 sensor warning only. With ECM open, and measuring O2
sensor amp output, during smooth idle, voltage fluctuates between about
1.8 and 3 volts about once per second. Haven't monitored in rough idle.
Checked fuel pressure with engine off and fuel pump relay bypassed at
about 4.5 PSI steady. Fuel flow looks reasonable, though I didn't measure
it precisely. Intake manifold vacuum is a steady 20 in. Hg during smooth
idle.

New plugs last year, though originals looked clean.
All vacuume lines okay. Since trouble, have replaced (all original 134K):
fuel filter, dist. cap / rotor, O2 sensor, H2O temp sensor, and EGR valve.
Nothing has helped at all. Tired of pouring money. Need help. Somebody
please?

Smokin Leroy

In article <3b4d2ccc311b4a8beaebe4cb56228028 (AT) localhost (DOT) talkaboutautos.com>,
smokinleroy (AT) cableone (DOT) net says...

Haven't monitored in rough idle.
Checked fuel pressure with engine off and fuel pump relay bypassed a about
4.5 PSI steady. Fuel flow looks reasonable, though I didn't measure
it precisely.

Have you removed the IAC valve from the TBI unit and made sure the pintle
isn't all gummed up? It sounds like your IAC isn't working right.

4.5 PSI fuel pressure seems kinda low. The TBI injection is suppose to have
around 13 PSI.


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__________________________________________________ _______________
Dennis Smith

-1971 Trans Am - 455 H.O. - M21 4speed - Cameo white/blue stripe-
< http://ps2page.tripod.com/my71ta/tapage.html >
-1973 Trans Am - 455 - TH400 auto - Buccaneer red-
-1984 Trans Am - 5.0 L - TH700R4 auto - Royal blue/silver aero-
__________________________________________________ _______________

Doesn't the AIC only control idling? Fuel pump is looking more and more
like the culprit to me.

SL

In article
<8df8f07118c60296ee3690b3b52bc204 (AT) localhost (DOT) talkaboutautos.com>,
smokinleroy (AT) cableone (DOT) net says...

Doesn't the AIC only control idling? Fuel pump is looking more and more
like the culprit to me.

You said the idle surges up and down which usually indicates a dirty IAC
valve.


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__________________________________________________ _______________
Dennis Smith

-1971 Trans Am - 455 H.O. - M21 4speed - Cameo white/blue stripe-
< http://ps2page.tripod.com/my71ta/tapage.html >
-1973 Trans Am - 455 - TH400 auto - Buccaneer red-
-1984 Trans Am - 5.0 L - TH700R4 auto - Royal blue/silver aero-
__________________________________________________ _______________

Maybe you have some bad gas in the tank. Try adding about two bottles of
"heet" to the gas tank and see if that makes a difference. It won't hurt
the car and it is cheap.

I'm not saying the IAC can't be bad, but the problem happens not just
during idle. A close relative with extensive automotive training says 4.5
PSI fuel pressure sounds really low.

SL

Already been through a full tank and now half way through another.

Already been through a full tank and now half way through another.

In article <e8038644c5002bb534a635200de6aad8 (AT) localhost (DOT) talkaboutautos.com>,
smokinleroy (AT) cableone (DOT) net says...

I'm not saying the IAC can't be bad, but the problem happens not just
during idle. A close relative with extensive automotive training says 4.5
PSI fuel pressure sounds really low.

You may have two problems then. 4.5 PSI is very low. Even carburetors run
around 6-7 PSI. The TBI setup in your car should run around 13 PSI.

Have fun changing the fuel pump. Its right above the rear axle. You have to
disconnect the exhaust and shocks to lower the rear axle down to drop the
gas tank. It would have been nice if there was an access hole in the floor
above the gas tank under the carpet...

__________________________________________________ _______________
Dennis Smith

-1971 Trans Am - 455 H.O. - M21 4speed - Cameo white/blue stripe-
< http://ps2page.tripod.com/my71ta/tapage.html >
-1973 Trans Am - 455 - TH400 auto - Buccaneer red-
-1984 Trans Am - 5.0 L - TH700R4 auto - Royal blue/silver aero-
__________________________________________________ _______________

There might be residual water in the tank. I'm going through something
similar. I have gone through 4 tanks with putting fuel injector cleaner
every other tank and an additional 2 tanks with including "heet". The
"heet" seems to be helping. It might not fix the problem in your car but
it might help to rule out bad gas. I hope that everything works out for
you.