Let's talk about fuel issues -- Fuel Pressure Drop under Acceleration

[TexasBlownV8]

Sorry to hear that! Fuel problems suck.

What fuel system components are you running? BAP, FP, injectors, etc? Have you data logged yet?


BP

GT500 pumps with KB dual BAP, 80# injectors, dual 10ga. power feeds.
Been running the setup over a year with no issues.

Just a little incidental datalogging so far, nothing definitive; Returnless FPDC at idle is right around 0.5 (not good), whereas normally it'd be like .18 or something. LTFT driving on highway were both over 20; unusual, too. Fuel pressure appeared to be normal during that time.
Noticed on my last "test run" that afr goes full lean when I give it heavy throttle.

I checked the FRPS yesterday and I think it is ok. (compared PCM's reading with my separate fuel gauge setup.)
Changed fuel filter, it was clear and clean.

Testing pumps by unplugging one fpdm at a time and listening for the pump primes (did one side, waiting for awhile to test other one). I suspect one side is not working or there is a hose/flow issue. Both FPDM's are getting 12v power.

 

[petersonb]

GT500 pumps with KB dual BAP, 80# injectors, dual 10ga. power feeds.
Been running the setup over a year with no issues.

Just a little incidental datalogging so far, nothing definitive; Returnless FPDC at idle is right around 0.5 (not good), whereas normally it'd be like .18 or something. LTFT driving on highway were both over 20; unusual, too. Fuel pressure appeared to be normal during that time.
Noticed on my last "test run" that afr goes full lean when I give it heavy throttle.

I checked the FRPS yesterday and I think it is ok. (compared PCM's reading with my separate fuel gauge setup.)
Changed fuel filter, it was clear and clean.

Testing pumps by unplugging one fpdm at a time and listening for the pump primes (did one side, waiting for awhile to test other one). I suspect one side is not working or there is a hose/flow issue. Both FPDM's are getting 12v power.

The only time I ever saw .50 for FPDC at cruising speeds, the hose from the top of the fuel pump was loose (i.e. the pump was running full speed, but just pumping the gas right back into the fuel tank).

When I had a bad pump, it was only .50 when I would go WOT; otherwise, it was only higher than normal.

I, too, would suspect an internal-tank leak somewhere. The good news is that it would be pretty obvious if it were!


BP

 

[TexasBlownV8]

Sounds like both pumps are priming (unplugged and tested each one, they both prime).

Well that's my next step: pop open the tank and see if I can see any flow/hose issues.

There may be a secondary GT500 pump setup that I can swap-in and try (if 'someone' can find it).

 

[petersonb]

Well that's my next step: pop open the tank and see if I can see any flow/hose issues.

Sounds like both pumps are priming (unplugged and tested each one, they both prime).

Well this will be hard to describe, but the sound when they prime:

Is it a high pitched whine, followed by the sound of it "grabbing" fuel? (tone dropping)



BP

 

[TexasBlownV8]

I re-testing priming, one side, then the other.
They sound the same, and each side builds about 27-29 psi of engine-off pressure by itself.
The sound is more like a mild growling, not really a whine.

I compared the sounds to the stock pump in my V6, and the sound is somewhat different. That pump just sounded more solid, it that makes sense. Different frequencies, too, of sound.

I think there might be a hose or leaking issue in the gt500 pump hat.

 

[petersonb]

Ah, good point. No, not high really pitch. More like a growling noise for a few seconds. Sounds like it grabs fuel right away, Now that I think about it, I might have heard a little gurgling at one point, which could be bad.
I'll compare the sounds to my v6. I've never really paid attention to the sound, other than hearing it and knowing the pump(s) have primed.

When the hose was loose/leaking on mine, it was always a low-pitched priming sound, like gurgling, as you describe.

I suspect a hose inside.

Heads up, submersible fuel line from Gates is ~$20 a foot on Amazon.


BP

 

[TexasBlownV8]

In addition to the hose, the clamps are what kind? I know they're not the normal worm clamps.

Using your pictures in this thread, where did you find leakage?
I know you said there was blockage in the checkvalve and then in the T cone.

 

[petersonb]

In addition to the hose, the clamps are what kind? I know they're not the normal worm clamps.

Using your pictures in this thread, where did you find leakage?

First, two things:

1) Worm clamps shown in the picture are NOT the correct kind, and are no longer being used.

2) I have a Walbro single fuel pump, so your setup will be slightly different.



Now, the hose became detached from the pump where the yellow arrow points. That's when I was at .50 FPDC all of the time, and very lean AFR.

It could also leak at the clamps (yellow circles).

These are the clamps which I'm using now, and the same style as the ones which I'm using now.


BP

 

[TexasBlownV8]

Gotcha. Thanks. There's enough fuel where I should be able to raise up the hat a little and peek inside and see what's going on when it pumps. Manuel (Lito) made a post or two about that, somewhere (he's my tuner, too).

Before I take that route, I am going to confirm a couple other things, and snag a quick datalog. I have older good logs, I'd like to see what the PCM is seeing and trying to do.

 

[petersonb]

Gotcha. Thanks. There's enough fuel where I should be able to raise up the hat a little and peek inside and see what's going on when it pumps. Manuel (Lito) made a post or two about that, somewhere (he's my tuner, too).

Before I take that route, I am going to confirm a couple other things, and snag a quick datalog. I have older good logs, I'd like to see what the PCM is seeing and trying to do.

Without removing the fuel hat, i was able to tell that the pump wasnt sending anything out by disconnecting the fuel line at the top (outside) of the hat after it primed. There wasnt very much fuel in the ine immediately after it "primed" so i was pretty sure it was disconnected inside. YMMV

Let us know what you find!


BP

 

[TexasBlownV8]

Hm, I'm not so sure I have a fuel issue at this point.
Instead, I think the PCM may be saying "wait a minute! You're in a system failsafe mode, and cant rev past 3k rpms!". Here's why I think it may be a pcm-induced situation.

Recently, I installed a GT instrument cluster (the car was a v6, and I still was using the v6 cluster). The car has no abs and no tcs; the GT cluster is looking for abs and tcs and is displaying warnings and flashing lights about them both, along with the brake system. I am thinking that the cluster 'errors' are being reported on the CAN and the PCM is picking them up, and limiting power as a result, for 'safety'. Today, I disconnected the battery and put the v6 cluster back in, both to rule out the cluster as a possible issue and to do a real clean of KAM (I'd reset the pcm, reload tune, etc, and that didnt help before). So then I decided to do some datalogging, and compare some of the fuel-related values with previous datalogs I have from last year. First thing I noticed was that I was able to easily get over that 3k rpm limit, and ran up to 5k without issues, with afr around 13 and around 2/3 to 3/4 throttle. This was a huge improvement. I took a few other light-throttle jabs, and afr seemed to be a little high, but in looking at the datalogs, I think it was ok. Haven't gone wot yet, as I want to think about this some more.
But at this point, I'm not sure I have fuel system issues. Just may be a cluster than needs programming!

 

[petersonb]

Hm, I'm not so sure I have a fuel issue at this point.
Instead, I think the PCM may be saying "wait a minute! You're in a system failsafe mode, and cant rev past 3k rpms!". Here's why I think it may be a pcm-induced situation.

Recently, I installed a GT instrument cluster (the car was a v6, and I still was using the v6 cluster). The car has no abs and no tcs; the GT cluster is looking for abs and tcs and is displaying warnings and flashing lights about them both, along with the brake system. I am thinking that the cluster 'errors' are being reported on the CAN and the PCM is picking them up, and limiting power as a result, for 'safety'. Today, I disconnected the battery and put the v6 cluster back in, both to rule out the cluster as a possible issue and to do a real clean of KAM (I'd reset the pcm, reload tune, etc, and that didnt help before). So then I decided to do some datalogging, and compare some of the fuel-related values with previous datalogs I have from last year. First thing I noticed was that I was able to easily get over that 3k rpm limit, and ran up to 5k without issues, with afr around 13 and around 2/3 to 3/4 throttle. This was a huge improvement. I took a few other light-throttle jabs, and afr seemed to be a little high, but in looking at the datalogs, I think it was ok. Haven't gone wot yet, as I want to think about this some more.
But at this point, I'm not sure I have fuel system issues. Just may be a cluster than needs programming!

Good find.

To me, its weird that youd be at .50 duty cycle in limp mode. My understanding is that .75 is thr "error" number. I would have expected duty cycle to be normal (low) if the car were in limp mode. As for the gauge cluster doing something weird, i have no clue about that. Could very well be.

What were the duty cycles like with the v6 cluster?


BP

 

[TexasBlownV8]

The duty cycle reading was from a different pid value than the one I should be reading. Looking at the right values, it seems to be fine (like 18% at idle).
It shouldn't be the cluster at all (as Manuel told me, too).

I dont know what it is exactly yet, but I did suspect some bad fuel may have been put in the other day (I drained most of it yesterday, but dindt get all of it). So there's a mix of mostly-new 93 octane now, but probably still about 10-20% of previous fuel, too. Then if the fuel was bad, and it was trying to adapt and learn with it, that wouldn't work out.
I went for a drive, and giving it gas from slow speeds or from a stop, and the car still wants to stumble and goes very lean, especially when boost is around 1-2 psi. But I can get her going and then give it some gas and she hauls just fine, although I'm not in it WOT at all at this time.
I'm starting to think it was the gas, or some other issue, like maybe a vacuum leak or plugs (although she idles fine, and I would expect running rich if there was a vacuum or bpv issue)


Update...Booyeah!!! Sally is back! (problem was the BPV; it was stuck in the WOT position.)

 

[petersonb]

Update...Booyeah!!! Sally is back! (problem was the BPV; it was stuck in the WOT position.)

Awesome! Yep that will do it, haha.


BP

 

[lito]

Sally?

 

[TexasBlownV8]

That's the blue car's name

And thanks again, Manuel, for the advice and assistance.

 

[lito]

Oh, as you never introduced her to me as such, hehe.

No problem, do those comparison logs to see how it improves with the W/M whenever the weather allows it.