Hi. I posted this in the TPI section, but figured I may get an answer here as well. So here it is. About 3 months ago, I purchased a 1990 Pontiac Firebird Formula for my 16yo son. It's a 5.0L TPI motor with an automatic behind it. It has developed a problem. At highway speed, it runs horrible. It won't get out of it's own way. It seems to hit a wall at about 2300 rpm. At first I suspected a bad fuel pump. I checked pressure at the rail and here's what I found. The book calls for 37-43 psi when first energizing the fuel pump. I have 40psi. It then calls for a 3-10 psi drop when the car is running. At IDLE I have about 37psi. I checked for proper flow and that is fine. I ran the gauge under the hood and to the cowl so I could watch it while driving it. The car cruises at 72mph 1700 rpm with about 37psi. When you get in it and try to accelerate, the gauge is all over the place. Pressure varies from 35 to 52/55psi and on occassion, hits 60psi. As soon as you get off the throttle, it stabilizes again at about 37psi. When I brought it back home, it was ideling in the driveway in park at about 37/40psi. If I blipped the throttle to rev it, pressure would jump to about 50psi and then return to the 37/40psi as soon as the idle came back down. I think the regulator is bad and needs replaced. What's your opinions? Thanks in advance for your help.

 

Well being that the pressure rebulator for these cars is vacuume controled the pressure will vary a bit. I personally havnt tested my fuel pressure while running so i really cant say exactly what it should dbe doing under various circumstances but i dont see anything i wouldnt expect there. Maby lets take this one back to the beggining? What exactly do you mean by the car wont get out of its own way?

 

The car seems to hit a rev limiter at about 2200 rpm or so. I replaced the fuel filter, air filter and the fuel pressure regulator. Changing the regulator stabilized the pressure. It pulls fine off the line to that 2200 rpm range and then starts to bog and surge. Can't get it through that dead spot. I also pulled the cap and checked the cap, rotor and visually checked the top of the distributor. Nothing really out of the ordinary. Any thoughts?

 

Have you tried checking the timing? Do you have any check engin light or codes stored?

 

Haven't checked the timing yet. I had an "occassional" light. I got a code 32, egr code. I may be wrong, but the egr shouldn't effect the car running at highway speed. Going to pull a plug or two tonight when I get home and see what they look like...ie...rich, lean, normal.

 

this is the same exact problem i have. i mean exact! but when i get to speed i can down shift to get the car above that 2300 mark. and it runs ok above that. i changed plugs wires cap and rotor, as well as the fuel filter. still no change. did you get your problem fixed?