I have a 1985 trans am with tpi,. when it is cold it hesitates severely. My mechanic told me it was the fuel pump/ When the car warms up it runs fine/ Is there anyway I can raise the fuel pressure without replacing the fuel pump? And in case I have to replace the fuel pump, is there anyone who has a procedure for that? Thanks.

 

I dont believe it is the pump. Get a guage and test it. It would be doing it all the time. Maybe a bad cold start injector??? Never dealt with the cold start injector before. Any codes? Raising the pressure would help a failing pump die quicker anyway.

 

Car runs fine when warm though, so I will ask him Monday if thats something worth checking. Thanks.

 

How can I check the fuel pressure?

 

I think the cold start gets it started, but does not have anything to do with it staying running. If it were the pump, should act up all the time.

 

Connect a guage with a long enough line to the scrader valve on the pass. side fuel rail.(looks like a bicycle tire valve). Tape the guage to the windshield, and go for a ride. The pressure should stay steady at WOT. If its dropping, you are volume limited, and the pump is probably bad. The pressure should be approx. 36-38 psi at idle and go to about 43-45 at wot, and not drop.

 

Oh, to just check the pressure, have the gauge hooked up, and with the car idleing, disconnect the vacuum line off the regulator. This reading is what your pressure is. This is not going to help you. You have a hesitation problem.

 

I talked to my mechanic tonight and he checked the fuel pressure, it is very low at idle when cold and normalizes when it warms up. it is right where it is supposed to be at WOT. I asked him about a cold start injector and he said the car wouldn't start at all if it was bad.

 

I looked online and there is a cold start valve. That might be it, it is hard to start when cold.

 

Yea, thats what I thought about the cold start inj. too. ...Just wasnt really sure.

 

well I drove the car today and it hesitated for awhile, when it got up to temperature the check engine light came on then went off when I hit the gas. It took about 20 minutes of driving till it improved, but it ran o.k., at least it was driveable after 20 minutes, but I had to drive it for 20 minutes to get it driveable .
When I jump on it, even when cold, it does not bog or hesitate, only when its at idle and you get on the gas. So I am hoping that it is not the fuel pump. I know this car has a knocks sensor, could that be a possibility? I will look into the cold start injector valve further. It is getting proper fuel pressure at idle and at WOT, but it gets very low fuel pressure at low rpms when driving., even when warm and gets above where it supposed to be at higher rpms. I don't know what it could be.

 

Retrieve the code from the ECM, now that the CE came on.

 

no codes came up, fuel pressure is normal when warm, but not when cold, the cold start injector won't cause that. How much will it cost to replace the fuel pump at a reputable shop?

 

ok 2 codes came up this time, the first is code number 34
Mass Air Flow Sensor
voltage is too low

next code 44
oxygen sensor lean

 

Have you thought about the fuel pressure regulator? diaphram spring may be getting weak.

 

no I haven't, what would tell me that, thats the problem?

 

I can't tell you what the problem is, you haven't posted having checked it, that's why I asked, it's the only thing left in the fuel system. if it's not that then you've come full circle back to the fuel pump, the regulator is easier to change.