1991 trans am, 305 TPI with 5 speed..

Car runs like a bat out of hell on first start of the day till it warms up..when it warms up i get to about 2200 RPM and it starts to bog..if i barely touch the gas pedal i can take her to 4500 RPM no problem no bogging..but if i stomp it it just bogs at about 3000-3500 and actually decelerates..also i get an intermittent check engine light which is oxygen sensor lean but it goes away after about 5 minutes. I just changed my fuel pump and filter about 2 months ago, left me sit..never ran right since then but the problem got worse..with the engine warm i checked my fuel pressure: when i turn the key i get 41 PSI when the pump primes and it drops quickly, if i cycle the key on and off it stays up a little longer, at idle i get 36 PSI and if i crack the throttle it stays relatively the same..i just chaged my plugs and wires..running Borg warner super mag wires and NGK V Power plugs..idles really smooth, also has a pretty bad valve tap that happens only when it warms up..i don't think that is related to my problem but correct me if i am wrong. Also it is using alot more fuel than it should i believe, drove it 24 miles and used a quarter tank of gas..which does not make sense if it is running lean..i was thinking it might be the cheap 60 dollar Airtex pump i put in but the fuel pressure seems to be within spec? 40-47 PSI with the pump primed and engine off and said it should drop 3-10 PSI with the car idling..also i took it down the drag strip and i ran a 16.76 at 83 mph and i ran a 14.5 at 95 mph before this all happened so i dont know what the hell is up..any help would be nice and appreciated..car is all stock besides my dynomax 3 inch cat back which was put on like 10 years ago.

 

anyone?

 

I'd say partially/intermittent failure of fuel pump.

 

Could it possibly be that the fuel pump has decreased performance when it gets hot? The car runs great for 5-10 minutes before it starts to act up. Did some more pressure tests with the car..car was at operating temperature..36 PSI at idle, 42 PSI when the key is cycled, it holds if cycled 3 or 4 times, and about 45 PSI when the throttle is cracked wide open up to 4500 RPMs..could it be that the pressure is ok and within spec but the volume of fuel is diminished when the pump gets hot causing my problem? Fuel regulator seems to be functioning properly..no restrictions in the fuel delivery system..this is the only thing i can think of, i was thinking about buying a holley fuel pump that is rated at 69 gallons per hour versus this airtex 40 gallons per hour, any input is greatly appreciated.

 

Pretty sure holley pumps are made by Walbro. Other than that my car acted up just how you said above 70 deg outside temp,and my gas tank used to get incredibly hot. Changed out the pump with OEM, problem dissapeared, I attacked my problem like a parts swapper, and got lucky.

 

Update: fuel pressure regulator is good..did a fuel pump volume test, unhooked the fuel line and ran it into a bottle, alldata says one half pint in 15 seconds and in 15 seconds my 1 pint bottle was overflowing so my pressure and fuel volume are both within spec and good. This all leads me to think one of my oxygen sensors are bad and that would explain why it runs good before it goes into closed loop. Any thoughts?

 

Could be dying injectors, fuel pump, or even coil.

Hook up the fuel pressure gauge and make it so that you can see it through your windshield while you're driving. Watch it AND the road. That will tell you if your fuel pump is giving up the ghost.

 

Who installed the fuel pump? Airtex pump? no no no

The one inch piece of rubber fuel line between the pump and the steel line must be of the right grade. #6
I have seen this many times before. It starts to deteriorate just setting in fuel. Watch. . . wait one month and you will see the pressure fall off to zero immediately when you turn off the engine.

buy the bosch pump that comes complete with small section of rubber hose and new sock. your car will work fine once again!

 

OK. I just ordered a new NGK O2 sensor since it was only 20 bucks. I figured it was logical since alot of my symptoms point towards it. I knew the airtex pump was a bad idea lol, the 60 bucks was so enticing thought..shoulda spent 70 on the bosch. but the only thing that i dont get is that the fuel pump seems to be fine and running better than a factory one, about a pint and a half of volume every 15 seconds and pressure is good so this leads me to believe the fuel pump is fine. If the O2 sensor doesn't fix it i will do some more diagnostics on the fuel pump. Also my car used like a half a tank of gas to go like 50 highway miles..this coupled with everything really screams O2 sensor at me for some reason. I will try to pressure test while driving the car tomorrow morning and see where that gets me. Thanks for all the help..also is there anyway to force my car to run in open loop even when it is warmed up? thanks in advance