I've been watching the Long term trims pretty close lately, as well as KR (always watching that), and I have noticed that even with air temps being around 15-25F, I am getting some KR, usually about 1-2 degrees, in the upper RPMs at WOT. I've also noticed that the LTFTs are locking in at about 12.5, which if I understand, it means that its adding fuel to compensate for a lean condition.

My first thought is that I am running lean due to a weak fuel pump, what kind of pressures should I have? Also, I don't have a fuel pressure gauge, where would I find one of those?

I have a 3.4" pulley that has been sitting around for a long time, and would like to get it on, but I want to take care of this KR first.

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-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

your ltft is 12.5 at WOT? they should be close to 0. have you changed your fuel filter?

I changed it last summer, how often should it be changed? I've maybe put like 6,000 miles on.

_________________
-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

it should be fine unless you got some real bad gas. Not sure where to find a fuel pressure gauge specifically, but that should be your next step

No, they should be zero at WOT no matter what. LTFTs lock in for WOT as soon as you pass about 7K in the MAF range (typically between 6K and 8K anyway) So your problem is with tuning the lower MAF range and getting that in check. You have to have a tuner to do this. Do you have one or have access to one? When those are close to zero then you will be locking in those zeros. If you continue to do any WOT runs at +12.5 you can kiss your pistons goodbye basically. The other thing you need to look at are your injector pulse widths. I doubt that you are maxing those out yet, but it could tell you a lot. I would suggest getting a fuel pressure gauge form Jegs or something. I used theirs for a long time. Just have to tie it in to the fuel line. I think you can use the Schrader valve to do it if I remember right. Can't remember what size that is though, someone correct me here. Fuel pressures should be about 45-55 idle IIRC and increase with throttle up to 65-80ish (can't remember the exact numbers, but I'm sure I'll be corrected if they are wrong, this is ball park)

Here you go:
http://www.jegs.com/i/JEGS/555/41013/10002/-1

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2000 SLE

Ok, I think I will order that gauge. As for a tuner, I don't have one, or know anyone that does. Although, I have been reading a lot about HPtuners lately, and would like to buy it. I just don't have $500 to spend on one right now. Does that gauge come with the fuel line? or do I need to get that separately?

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-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

To tie into the Schrader valve on the fuel rail, you need a Scrader valve removal tool (looks like a small screwdriver with a "notch" in the end) to remove the valve innards. Then you need an adapter, AN-4 to whatever NPT pipe thread the gauge (or sender) is.

Then of course, a gauge. And if you want to look at it inside the car, some length of hose between the adapter and the gauge. Unless you're using an electronic sender to e.g., an Aeroforce.

That JEGS gauge looks like nothing but a gauge; no adapter, hose, Schrader tool.

I have the Schrader tool, AN-4 to 1/4" NPT adapter, and 1/4" NPT 0-100 psi stainless steel fluid-filled gauge. No length of hose on that, though, so you'll basically only be able to test idle fuel pressure. Although in my experience, if the pump's going out, you can tell due to low fuel pressure at idle.

Shoot me a PM if you want to borrow all that.

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2004 Buick Lesabre Limited, Gran Touring
Bone Stock

1998 Buick Lesabre Limited, Gran Touring
Retired

PM Sent.

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-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

I was finally able to test the fuel pressure a few minutes ago, thanks to agrazela letting me borrow his pressure gauge

At key on, it was 47 psi. At idle it was 41 psi, and when I revved it, it would jump up a few psi, and then settle back down to about 40. Would these be the symptoms of a bad FPR?

_________________
-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

Those pressure readings are at the very low end of spec, and suggest in my experience, along with your scanned symptoms, a weak (but not yet entirely dead) pump.

Question: when you rev and then let off, does it dip below 40-41 (like maybe into the 30-35 psi range), then go back up and settle around 40?

Also: after running, then keyoff, monitor residual pressure over time. Does it drop a few psi in a few minutes then hold steady for hour(s)? Or does it drop fast, and/or continue to drop away with time?

Granted all these symptoms could be the FPR, and everyone with a weakening pump really wants it to be the FPR , but unless you see or smell fuel inside the vac line running to the FPR, it is likely not the FPR.

You can see here what was happening with my original weakening pump vs. an aftermarket replacement:


This data is all in WOT (MAP ~100), collected with an electronic sensor and a/d converter on the PowrTuner; I chose first gear data because the shift point is highest and it shows the greatest effect; namely, that as RPM (thus MAF, thus fuel demand) goes up, the original pump was petering out badly on fuel pressure. With a new pump, fuel pressure stays rock solid all the way across. WOT KR went away, and IPW's backed off from near-static.

_________________
2004 Buick Lesabre Limited, Gran Touring
Bone Stock

1998 Buick Lesabre Limited, Gran Touring
Retired

I know that when I let off it, it didn't drop down, it just went back up a 1-2 psi.

I didn't check to see what it does after I shut it off, but I'll do that tomorrow if I have a chance. Im assuming you mean that I should shut the car off, and leave the key off and see what it does?

Changing the fuel pump requires dropping the tank right? I will definitely be doing it myself. If I can handle the LIM gaskets, I can handle that.

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-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

That's right. Record pressure at time zero, 5 minutes, 15 minutes, 1 hour, 8 hrs, something like that.



I believe the 2000+ H-body has a fuel pump access hatch under the rear seat, like all years of Grand Prix have. No need to drop the tank and should make the job 10x easier.

_________________
2004 Buick Lesabre Limited, Gran Touring
Bone Stock

1998 Buick Lesabre Limited, Gran Touring
Retired

Ok that sounds good, I will be gone to the relatives for a while tomorrow, hopefully I can get it done up to an hour, then by the time I come back it will be 8 hours.

I'm very glad to hear I don't have to drop the tank. I have a FSM, so I'll be using that to do it. This is all assuming that I determine that the fuel pump is indeed the problem, which its looking like it is.

_________________
-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

I think I have a fuel pump sitting around here somewhere that is still good if you need one. Sure there are a couple out there closer to you though.

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2000 SLE

hans did a youtube write up to replace the fuel pump.....

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-Juan

No bonnie!
93 s10 ex cab: 2.8: t5: exhaust: tbi mods. 5.3, 76mm, and a D.r cam on a stand

I might be interested in that. I'll let you know.

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-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

I thought he did a video on the FPR.

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2009 G8 GT - White Hot


FMS Custom Cam, Yank 3600 SS, 1LE (ZL1) 3.91, SLP Longtubes, Magnaflow cat-back, Rotofab CAI, tuned via HPTuners
415/391

It's for the fuel sender. The fuel pump is part of that assembly isn't it?

http://www.youtube.com/watch?v=-7cY_IPCVfI

_________________
-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

I left the gauge on over night, and here's what I got.

0 min - 37 psi
5 min - 42 psi (I don't know how it went up, but it did)
30 min - 42 psi
2 hours - 17 psi
12 hours (this morning) 0 psi

_________________
-Tom

2003 Silverado Ext. Cab - Charcoal - 128,000 miles - Stock...for now.
2000 SSEi - Gone, but not forgotten.

Yes.

That looks pretty normal for FP at the rail while it is sitting. That's only a function of if it is bleeding off quickly or not. Meaning you might have a leak somewhere if it didn't hold. Looks fine. But I still don't think that can tell you if you have a FP problem while it is running. You have to go out and run it and see if the pressure goes up as you increase the TP%. Should.

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2000 SLE