Fallout

First off I just got finished browsing through about 230 posts related to fuel system questions from the search engine. Several have complained about similar problems to what I am experiencing but I have eliminated most of the fixes which have worked for them.

I am trying to help a friend diagnose a fuel system problem in his 2002 Chevrolet K1500 with a 4.8. The truck is stock and has 80k on it. We initially scanned it with HPTuners and it was running very lean so much so as it was retarding timing under normal driving due to the lean condition. Then approximately 10k ago his cat. converters went bad and had to be replaced. We think it was due to his lean condition.

Problem recently worsened with him having problems with hard to start and audible detonation under load. Hooked up a fuel pressure gauge initially no pressure present. Key on pressure builds to 40-45 lbs then drops off rapidly back to 0. While engine was running pressure maintained at 45 lbs and dropped off towards WOT. Checked for signs of Gas in the vacuum reference tube on FPR none present but had a new FPR laying around so changed it. Still same problem. Started suspecting pump was going bad and he planned on upgrading fuel system anyway so ordered and installed a new intank Walbro 255 (bucket modified). Now key on pressure hits 50-55 lbs and then rapidly drops off to zero.

We checked the Small o-ring on the fuel pressure regulator (as suggested by previous posts) and even put a known working fuel pressure regulator etc. from my 2001 chevy on it and still same exhibits the same problem.

The bed was off the truck so we pulled the return line off the sending unit and checked for fuel being returned. Fuel was returning while it was running and just to make sure it was not the Fuel pressure regulator leaking we plugged the return line and started it pressure was running at 100 lbs so we quickly shut it off and the pressure leaked down quickly again.

I have a couple of questions for those who have more experience with this than I do....

Could a stuck injector cause the system to bleed down so rapidly? (I know a recent post doesnt seem to think so but we are spinning our wheels). We are going to pull the plugs in the morning and check for signs of fouling to see if we can isolate the problem.

If it is not an injector will the fuel pressure regulator allow the fuel to return back down the feed line through the fuel pump? We resused the factory "ribbed" hose with a hose clamp as was suggested by previous posters?. I am going to check this for cracks in the morning as well.

I have tried throwing more fuel at it in HP tuners but no matter how much I add (ve and pe) it still runs lean.

I apologize for the long winded post but its late and I am tired...

Rafedial

iTrader: (7)

See if you can isolate the problem, seems like you already ruled out alot. You are showing symptoms of faulty injector(s). If you can, locate a set of noid lights to see if the ground through the PCM is good for each injector. Also check resistance across the injectors (need factory ohms specfications).

bigbadwolf54

iTrader: (14)

I think that he is having a fuel pressure bleed down problem, the fuel pressure should rise up to 50ish and remain there with the key on engine off and remain around 50 with the key off for a good amount of time. If no external leaks are found this indicates either an injector leaking down or the check valve in the factory fuel pump is ruptured...I am not familiar with the walbros yet so I can't help with that one. I would go back over the fuel pump install and double check/pressure check if possible the supply and return hoses. If an injector is bleeding pressure down that fast it is usually accompanied with other symptoms like misfires.

Fallout

Well we pulled the fuel rail and the injectors were not leaking. As a last resort we pulled the fuel sending assembly out and half submerged it in the tank of gas and keyed it on. Fuel is spewing out of the bottom of the factory ribbed hose. Evidently the hose clamp did create a good enough seal. Now to get some in tank fuel hose and see if that fixes the problem. Thanks for the replies.