Dropping fuel pressure at WOT

[BluHoe96]

Ok, so after I have gotten my tranny rebuilt I was heading home from work. All of a sudden the truck bogs out. So I let off the throttle. After laying in traffic for 20 min the bogging occurs at part throttle too as well as WOT. Took it home and let it sit for a day.

Next day checked the fuel pressure:
Key turned and ignition off - 62 psi
Ignition on at idle - 50-52psi

So I assumed that my fuel pressure was good. Pulled the MAF and sprayed the crap out of it with MAF cleaner as well as the IAT and the harnesses. Got a little more throttle response out of the truck after doing this. I figured great!

This morning after my hour drive to work accelerating out of the toll booths the truck bogs a little bit again at 3/4 throttle. Got to work and hooked up the fuel pressure gauge again. Same a reading at idle and with key on. Then decided to drive with the gauge in.

Took off at WOT and saw the gauge drop to about 28 psi! Part throttle she sits at about 40 psi. So I am definitely not maintaining my pressure.

What is my fuel pressure supposed to be during engine load? Do I have to maintain above 60 psi all the time? How else can i further troubleshoot to confirm that it is my fuel pump and not my regulator, voltage to pump, etc? I just want to make sure my pump is crap because I just changed it last year and only have about 25k miles on it. And I HATED doing it!

 

[AtomicHoe094]

i wouldnt do any more wide open shots man, running too lean isnt good. haha

 

[retorq]

No leaks that you can see?? When I swapped the pump in my 95 the lil flex tube in the tank had a pin hole in it ... was fine at idle but under load it effected flow and pressure enough to not run right.

 

[BluHoe96]

Yea I wish I had a way right now to see my afr, but don't have a tool right now. I guess to properly go through everything I will have to drop the tank regardless. Sux...

 

[gregsb]

Either you have a leak or restriction in your supply line or your fuel pump is not operating correctly.

When was the last time you changed your fuel filter? If it is old and partially clogged then that can cause a reduction in pressure.

When you shut down your truck does the system still hold pressure? If not then you have a leak somewhere.

If it does hold pressure then I would suspect the fuel pump assembly. I had the small hose that goes between the pump and the sending unit fail on a brand new ACdelco pump so it may not be the pump itself.

Hope this helps some.

 

[BluHoe96]

Thanks that sounds like the same hose retorq said he had a pinhole in. When I shut off the truck it takes a minute for the pressure to climb to 58 psi and 2 minutes for it to climb up to 62 psi. That part to me seemed good. This tells me my regulator is good or no?

 

[gregsb]

If you are maintaining pressure then your regulator, injectors and the overall integrity of the fuel system is good. Which pretty much points to delivery as the culprit either a restriction i.e. clogged filter or pressurizing system i.e. fuel pump.

Here are some links that might help you in your diagnosis:
http://www.aa1car.com/library/fuel_pump_diagnose.htm
http://www.motor.com/magazine/pdfs/022003_11.pdf

 

[99 2dr]

Mine had the same pin hole as retorq. Started and ran great as long as it had a full tank of fuel. Have you tried filling the tank and taking note of the fuel level when the problem occurs?

 

[gpracer1]

I would go the easiest cheapest way first. Sounds like the fuel filter, and if not at least you will have a new filter on it to rule out.

 

[BluHoe96]

Mine had the same pin hole as retorq. Started and ran great as long as it had a full tank of fuel. Have you tried filling the tank and taking note of the fuel level when the problem occurs?

It does it no matter what the level. I topped it off Monday when it did it first, and it did it less severe today with the tank at half. It seems to do it though at the end of my 1.25 hr. commute and less time if I am sitting in traffic. Could this be the fuel pump harness heating up and impeding voltage?

I would go the easiest cheapest way first. Sounds like the fuel filter, and if not at least you will have a new filter on it to rule out.

Have a NIB one on my passenger seat waiting to go in this afternoon. I will see if the situation improves after this.

 

[retorq]

That's what mine looked like ...

 

[gpracer1]

It does it no matter what the level. I topped it off Monday when it did it first, and it did it less severe today with the tank at half. It seems to do it though at the end of my 1.25 hr. commute and less time if I am sitting in traffic. Could this be the fuel pump harness heating up and impeding voltage?



Have a NIB one on my passenger seat waiting to go in this afternoon. I will see if the situation improves after this.

 

[BluHoe96]

I know updates have slowed down because of work. Hopefully I can get a chance to do the fuel filter this afternoon. One thing I have noticed though is that I am consistently getting the sputtering/stalling about 45 min into my hwy. drive. If I could hook up a fuel pressure gauge while doing hwy. speeds I'd be set.

We'll see how things pan out after the fuel filter install...

 

[BluHoe96]

Throttle response has change for the BETTER with change of the fuel filter. Engine performance has definitely improved. I can goose the throttle now with no sputtering. However I think I still have a problem.

When I goose the throttle from cruising at 30 mph and do a 2nd gear drop the truck just hangs up and hangs out between 3-4 rpm and goes nowhere. Again tranny was just rebuilt so don't think it is that. I guess; 1) I have to see how the truck performs on my commute to work tomorrow and ; 2) I have to measure the fuel pressure on that 2nd gear drop I experience the hang up at. Hopefully I can do this during the week if I have time.

 

[BluHoe96]

Still doing the same thing sputtering after a long commute. This time though after the ff change had enough power to not allow the truck to go in limp mode. This morning got P0420 after just getting going? How can i confirm whether my cats are good?

 

[BluHoe96]

Ok! So yes, things are leaning towards a weak fuel pump! I managed to screw on the fp gauge when the truck was sputtering on the way to work. This is what I found:

That was at idle! For some reason my iphone was having problems taking video, but at half throttle I was dipping to about 15 or so psi (its hard to read in the dark and through the windshield where the pump was hanging out the hood.) These pressures are not apparent when the truck is running fine. They are at 60-62 psi at idle and 15-25 at throttle. Could it be the harness heating up over time and a voltage loss feeding the pump? Is it common for a pump to progressively go bad after time spent being on? What are the fuel pressures supposed to be at different conditions other than idle?

I mentioned earlier I did the pump already a little over a year ago. I DON'T WANT TO DO THIS AGAIN! I managed to get an Airtex fuel pump that also comes with the harness pigtail. It was considered Advanced Auto Parts' Premium Brand. Is this any good or will it crap on me in another two years? Should I just wait a couple days and order the AC Delco? What is a good fuel pump that people have had experience with.

BTW, at the fuel relay during the low fp condition, this was my voltage:

 

[AtomicHoe094]

walbaro is a good one but im not sure if they make one for are trucks thats drop in..

ACdelco would be the logic and best way to go, buy it on ebay. or just buy a really nice warranty on the new one at the parts store, these pumps tend to go A LOT!

 

[BluHoe96]

What is it that makes the pumps go? Why are these any different from other pumps? Is it the vendors for our vehicles? If I get a walbro how did you make it fit in the sender? Is it fatter or skinnier than a stock pump?

 

[gpracer1]

Well its either the pump or the regulator (which is in the manifold and part of the spider). Either one sucks to replace.

 

[retorq]

When I did my pump replacment the pump was different (longer I think) and I hacked up my bucket like most of the LS based guys that run Walbros did ... if you do a search at performancetrucks you'll find a few pics ...