Alright. Well. I just got me an 88 Firebird. It was originally a 5.0 car, and now it is a 350 TPI out of a 92 F-body. Well. Its got a few kinks in the engine. It runs great and sounds great. For the most part.

First, and I am hoping this will solve a few of the other problems it has, it will not build and hold fuel pressure. Let me explain. I turn the key on to start it, and I can hear the fuel pump. It won't ever shut off. It will run til the battery dies. Thats with the car off. I can hear, under the intake, something leaking. Now, fuel isn't spraying out or anything, i just kinda sounds like an air leak. What could it be? A bad fuel pressure regulator? I started it up, and with a small spray bottle, sprayed all around the intake and on the injectors, and I get no bubbles, and it doesnt suck gas down into the intake either.

Now, its running very rich, idles horribly, dies at stop lights, and eats gas. But, as long as you are on the gas, it runs really well. Infact, I had it keeping up with an lt1 Camaro ...but thats not the point.

Now, The MAF Sensor is popping up as being bad, as is the TPS, both of which I am going to get very soon. I know the MAF and TPS will both help the idle and mileage.

Also, since this is a 92 motor in an 88 car....what do I do about the MAP sensor? 88's didnt have them from what I can tell. So, how would I fix the obvious vacuum leak? Im not even really sure where it hooks up. Lol


Now, if it helps any, the car has a ported and polished upper intake, new lower intake, headman headers (looks like shorties maybe) and diff. heads ( not sure brand or how well the supposedly flow).

Help is needed quickly, as this is my daily driver right now. (thank god I dont have to drive far to work)

 

The car will either have a MAF or a MAP, not both. One is MAF fuel management, the other is speed density. GM switched from MAF to SD in 90. Obviously the car is running the 88 FI system. The noise you hear from under the intake is probably the fuel pressure regulator. It wll normally put off a hissing noise as fuel passes through it. The hissing may also be a vacuum leak in the line from the back of the plenum to the regulator. This would explain your rich idle.

I am curious though as to why your fuel pump doesnt shut off after two seconds with key on engine off. Youll need to look at the FP control system to see whats been done to cause the pump to run on. How do you know its not holding pressure? Have you checked it with a gauge? If there wasnt fuel pressure the engine wouldnt run.

Why do you think you need to replace your MAF or your TPS, are there trouble codes? Have you tested these parts? You can test TPS with an analog volt meter or a lab scope. Sweep it slowly through its range and watch for glitches or drop outs. Set it at .45-.55 volts at idle and verify that it reads about 4.5 at WOT. You can check MAF voltage with a scanner.

Several things will cause rich running. The fact that it runs okay with throttle tells me it probably isnt getting vacuum to the fuel pressure regulator or that it has a bad TPS. I do not advocate throwing parts at a problem. Until you perform some diagnosis, you have no idea what is actually wrong and guesses can get very expensive.

 

Yeah, after a tad bit of research I realized the maf/map thing.

To be honest, I have not tested the pressure to see what its holding. I will in the morning. I know the pressure is good though, because ( I know this thing has a proper name, i just dont know it) when you press that little valve on the fuel rail, it sprays fuel all over the place. But, the noise is for sure coming from the pressure regulator.

It has the codes for the TPS and for the MAF. The kid who owned it, put a cold air intake on the thing, and completely through out the MAF, and had it in a box in the car ( sold me the car cause it was getting like 5 miles to the gallon, put that on there, and it gets like 17.)(looking back, with it getting the improvement in mileage, maybe the computer just needed time to catch up and realize) So, maybe it was damaged in the bouncing around in the box. And I will check the TPS when I get the chance tomorrow.

 

Be sure to check fuel pump circuit. The pump sould turn off after 2 seconds with the key off. Do you have a good repair manual for the car?