90' Suburban 5.7L fuel pressure range

[RSchevy4x4]

Stumbled across this site just recently while doing some research, and found some awesome posts! You guys rock. I was hoping someone would have or know the fuel pressure spec's for a 90' chevy suburban 4x4 5.7L. with TBI ? ? ?

I've had problems years ago with this suburban going through fuel pumps about every 80K miles. (The truck now has 195K and is still in outstanding condition.) So recently, when I stoped getting fuel delivered to the TBI unit, I immediately changed out my fuel pump and strainer in the tank, along with a fresh fuel filter. Historically, thats fixed it every time. This time no luck. I even changed out the pump relay and the pressure regulator inside the TBI (as they are easy to get to and fairly inexpensive). Still no luck. The gaskets in the TBI unit are all new and there seems to be no visible fuel leakage at all.

Per a couple other posts, I inspected all wiring to and from the tank for burnt wires, or anything of the sort, and everything checks out fine. I even ran a continuity check on the pump wiring inside the tank before installing the new one, and the wiring is all good. As a last effort, a good friend recommended changing out the oil pressure sending unit, as that's also tied inline to the fuel pump wiring. If faulty, it could *possibly* effect fuel delivery. The part was cheap, so I did, and still no luck. Now short of replacing the TBI injectors themselves (which I did about a year or 2 ago), there's nothing left to replace. Right?

I've read many of the other posts in this forum and have checked cap, rotor, coil, etc... and have great spark. I checked the ECM with a code reader and the system passes ok with a continuous "12" flashing wich means system pass. From what I can see, I'm just not building up enough fuel pressure. With a fuel pressure guage inline and the key turned to ON, the new pump runs audibly for 2 to 3 seconds, and pressure builds up to about 10 to 13 lbs and stays there as long as the pump is running. Once the pump stops, that 10 to 13 lbs of pressure drops to zero immediately. While cranking, there's no fuel being delivered into the TBI ports. On occasion the pump will kick back on for 10 to 15 seconds or more, but never build pressure above 10 to 13lbs.

Other posts indicate fuel pressure should be up above 50 or between 55 and 65ish, but I'm assuming thats for the fuel injected 350's. Is it different for factory TBI applications?

Has anyone experienced this similar problem, or have any other suggestions? Is there any part or component that I've overlooked?

Any help would be greatly appreciated.


Thanks a bunch!

-Ryan

[planedude]

plug off your return line and try to start it. The pressure should be around 12. If this fixes it your pressure regulating unit is faulty.

[RSchevy4x4]

Planedude, Thanks for the tip! I finally had a chance to get under the suburban today and give this a try. Unfortunately, I plugged off the return line and had the same indications.

With key on, the pump runs for about 3 seconds, and quickly builds up to between 10 and 12 lbs. then shuts off and the pressure drops back down to zero.

I also noticed that while cranking the engine over that pressure drops dramatically down to about 3 of 4, but always bounces back up to 12 so long as the pump is running.

Any other thoughts?

Thanks again for all your help.

Ryan

[2000CAYukon]

When you turn the key off, pressure should not drop to zero. This is an indication that the fuel pressure regulator is not doing it's job.

3 to 4 PSI while cranking is also too low. This could be the fuel pressure regulator or a bad pump.

//2000CAYukon

[RSchevy4x4]

Finally, I got it fixed.

As luck would have it, my Ignition Control Module was bad inside the distributor. When I pulled the old one out to inspect it, I noticed the factory original "GM" stamping on the top of it. Who'da thought that after 195K miles it would have the original ICM.

At any rate, I threw in a new one and the suburban is back up and running again.


Hope this can be of help to anyone else with similar indications.

Thanks again to everyone for your help and suggestions.

Ryan