Thread: Interesting issue I cannot seem to figure out....

On my black GTP. For awhile now if I go WOT, I get a **** ton of KR (like damn near 10 degrees!) and my O2s will be in the 820-850s. Now if I roll into the throttle, even go 3/4 throttle my O2s will be in the 920s with no KR but as soon as I push it all the way it goes into the low 8s and I get a ton of KR. Obviously I haven't been driving it WOT because i'm afraid of damaging the motor. I need to figure this out and fix it. I've been scanning with my Scanmaster of course.

Heres what i've done. I just swapped fuel rails because my old ones were causing a vacuum leak, swapped fuel injectors (same stock L67 style, lower mileage), new fuel filter. The only other things i think it could be is thew FPR or the fuel pump since its original with 143,000 miles on it. Anyone ever have a fuel pump do similar things? Could a bad FPR do this too? I'm baffled at this point. I don't want to drop the $$$ on a fuel pump if it doesn't absolutely fix 100% of my problem. My vac leak is fixed and good. I would of thought that would of been the problem but even after resetting the computer the problem is still there.

Any ideas? Thoughts? Suggestions?

Are your STFTs and LTFTs locking in at 0 every time you go WOT? Make sure to look at it both when you roll into the throttle and when you punch it.

False Knock? How are your motor mounts...if they are really bad you might try replacing them. Also check the DP...when I went WOT a couple times scanning I got almost 9* and was like ?!?!? On a 3.4" with a XP Cam setup??!?! Not happening...turned out my DP from my Pacesetters was making contact on the Front Sway Bar...flipped it upside down and it cured it right up

Hope you figure it out man.

do you tune out a lot of your torque management? when we were tuning my car we had to keep raising the thresholds on everything because otherwise i would get a bunch of KR. once we finally got everything high enough i was only pulling like 1* or KR when i stabbed it and got a downshift.

Originally Posted by Sabrewings

Are your STFTs and LTFTs locking in at 0 every time you go WOT? Make sure to look at it both when you roll into the throttle and when you punch it.

I can check this, what will this determine?

Originally Posted by bluegtp91

False Knock? How are your motor mounts...if they are really bad you might try replacing them. Also check the DP...when I went WOT a couple times scanning I got almost 9* and was like ?!?!? On a 3.4" with a XP Cam setup??!?! Not happening...turned out my DP from my Pacesetters was making contact on the Front Sway Bar...flipped it upside down and it cured it right up

Hope you figure it out man.

Motor mounts are fine. So is downpipe clearance (sway bar flipped). Before all this the car was well tuned and getting 0 degrees of KR. Ever since this issue all of a sudden popped up, its been showing lean and lots of KR.

I really don't think its false judging by the O2s, i'm 99% sure its fuel

Originally Posted by Reptile

With O2's that low, it's got to be pointing toward a fueling issue. The only way to diagnose the pump is to hook a gauge up to the fuel rail and see if it's holding pressure. Make sure that the pump and the FPR is still healthy.

Hey Brian, can you tell me how to do this test? I do have a fuel pressure gauge that hooks up to the schrader.

Originally Posted by Bio248

do you tune out a lot of your torque management? when we were tuning my car we had to keep raising the thresholds on everything because otherwise i would get a bunch of KR. once we finally got everything high enough i was only pulling like 1* or KR when i stabbed it and got a downshift.

The car is or was well tuned before by Overkill. The car has remained the same mod wise. This issue sorta popped up. The TQ managment from what I can see is taken care. The tune has been on it for a couple years, along with the goodies.


I'm damn tempted to swap FPR or pump next.

The wierd part is when my FP went out on my White GTP (around 130,000 miles) it showed no signs of weakness or anything. I drove it to work fine. That evening when I went home to get it wouldn't start. Lucky for me the dealership was down the street with the pump I needed. Oddly enough, my 1993 GP SE fuel pump went out the same damn way!

Thanks for the help guys I need to get this straightened out...

BTW, the car is slightly modded and has been this way for awhile and was tuned good. Basically it has...

-Thrasher CAI w/ 9" K&N Cone
-DUB 3.25" Pulley
-ILGPC Intercooler w/ VW Rad., GM Pump, 3/4" lines, Cobalt SS Filler T w/ 5 psi cap
-JimmyC 3" Catless Downpipe
-180 Degree T-Stat
-Autolite 104s @ .054
-Denso O2 Sensor
-Overkill Tuned PCM

Everything else is stock...

Originally Posted by Iron Indian

I can check this, what will this determine?

If a car was tuned in the winter and the trims are much more negative in the summer, at WOT the LTFT could lock in at a negative number which will cause lower O2s. That's why it's important to have your whole tune spot on so your LTFT locks at 0 when you go WOT and your O2s stay where they should be.

Originally Posted by Iron Indian

The weird part is when my FP went out on my White GTP (around 130,000 miles) it showed no signs of weakness or anything. I drove it to work fine. That evening when I went home to get it wouldn't start. Lucky for me the dealership was down the street with the pump I needed. Oddly enough, my 1993 GP SE fuel pump went out the same damn way!

Thanks for the help guys I need to get this straightened out...

That is how my fuel pump went in my old Buick. Drove around all day and when I went to start it...nothing. Just one of things I guess...

Originally Posted by Sabrewings

If a car was tuned in the winter and the trims are much more negative in the summer, at WOT the LTFT could lock in at a negative number which will cause lower O2s. That's why it's important to have your whole tune spot on so your LTFT locks at 0 when you go WOT and your O2s stay where they should be.

Well, it is a Overkill PCM...isn't there something for a generic temp. setting or a factory temp. setting in the PCM? Just wondering as I don't know tuner systems very well...

No matter how it's tuned any car is subject to fuel trim shifts due to temperature changes. That's why the stock tune is so bad because it has to cover so many different possible environment temps.

Either way, it's a quick check. If it's 0 at WOT the problem is elsewhere.

Before I start let me say that last night I tried a spare FPR I had laying around. When I first starting driving it I had 0 KR and my fueling was in the 920s. Aboubt 2 miles down the road with the same test, the problem came back again. Dipping into the mid/low 800s and an assload of KR. I donno what the likely hood of 2 bad FPRs are, but i'm thinking slim to none since I don't common here the going bad on here or ClubGP. Hell, I don't even know how they die to begin with. Read on...

Originally Posted by Reptile

Shawn, hook your gauge up to the rail and see what it pumps up to with the key on, should be about 59ish psi....see if it bleeds down over a few seconds, it should stabilize and hold pressure. Running the engine will have about 52-55 psi at idle. While looking at this, pull the vacuum line off of the FPR, it should spike up to around 60 again as this puts it at full pressure.

Bear in mind that if you have a weak pump it could show on the low side all over the place. FPR is easier to replace or swap out, so I would start there.

If you haven't touched anything on the car tuneweise and mechanically other than the alky, It's got to be something in the fuel delivery system.

Here are my findings this morning...

Key On Engine Off: 44psi

Key Off Engine Off: 39psi (5 minutes) and I think still dropping

Running in Park at Idle: 45psi

Running in Park at Idle w/ Vac Line off FPR: 54 psi


I noticed my numbers are a bit off of yours. I assume thats what the specs call out? I could of sworn years ago on my White GTP I got the same numbers as i'm getting off the black car. I'd go compare it now but I have PRJs with no Schrader Port. I really need to buy a FP gauge for my fuel rails, its been on my to do list forever. I wish a BOLT IN schrader was availible for a 1/8 NPT hole.

Anyway, let me know what you think. Read on below too, I check out a few other things too....

BTW, this is the Black GTP, not my White one. The Black one has literally not been touched mod wise in years. No alky on it.

Originally Posted by Sabrewings

If a car was tuned in the winter and the trims are much more negative in the summer, at WOT the LTFT could lock in at a negative number which will cause lower O2s. That's why it's important to have your whole tune spot on so your LTFT locks at 0 when you go WOT and your O2s stay where they should be.

I check my LTFT and it was at +1 locked. Not 0, but close. IIRC, wasn't the acceptable range between +3 through -3?

The way this problem is acting, its running out of fuel. I really don't think tuning is the issue sense it ran fine 4 other seasons. The O2s seem to dip lower and lower the faster I go, KR builds too. Like its running out of fuel.

BTW, I checked my Inj. Pulse Width and they were at 19-21 which is about maxing out injectors. Like I said, before this issue popped up it was KR free and fine. I could easily see the PW up higher if the Fuel pump wasn't keeping up with it. Thats my only theory and i'm probably wrong too. I'm still on stock GTP injectors and they should be plenty for what little the car has done to it.

Originally Posted by blue91gtp

That is how my fuel pump went in my old Buick. Drove around all day and when I went to start it...nothing. Just one of things I guess...

And with that said, has ANYONE had a pump gradually go out, show signs of weakness? I for one can say I have not, at least not on a electric FP. Anyone?

Well, it is a Overkill PCM...isn't there something for a generic temp. setting or a factory temp. setting in the PCM? Just wondering as I don't know tuner systems very well...

I have no idea, all I know its a pretty spot on tune. Better than I could ever do it.

Originally Posted by Sabrewings

No matter how it's tuned any car is subject to fuel trim shifts due to temperature changes. That's why the stock tune is so bad because it has to cover so many different possible environment temps.

Either way, it's a quick check. If it's 0 at WOT the problem is elsewhere.

I answered you above I think. Heres a question for you... Could the LTFT be effected by a weak fuel pump OR something not right in the fuel system? Keep in mind, i've reset my computer a couple times trying to cure this. I think it has maybe 50 miles on it now.

How can I get my LTFT to 0? I'm no tuning guy, so I really have no clue. Thats right, I have a DHP powertuner and I have no idea how to use it. I'm kinda skeptical this is the issue. I hope i'm wrong, but things never seem to go easy for me.

Originally Posted by agrazela

Yes, the FP on my topswapped 98 LeSabre just got weaker and weaker, instead of dying all at once. And it did just what yours is doing: cause massive KR when I punched it and max the IPW's because it was trying to pump fuel but couldn't because the pressure was tapering off at high load.

Fuel pressure values at idle were just at the low end of spec, but one tell was that the FP after keyoff would continue to drop gradually over time instead of settling down and holding. (Kind of like it sounds yours is doing.)

I went through all the same diagnostics, checking all the lines for leaks, replaced the FPR, etc. Ultimately, I replaced the pump (in my case with a TRE-340), and all my fueling problems went away.

I suspect the checkvalve / backflap (or whatever the heck it's officially called) in the pump went bad / stopped sealing well. The pump could flow, but it just wouldn't get up to or hold high pressure.

Good post! So it is a possibilty, interesting. For my leak down test, how long did you do yours for? I think i'll perform the same test on mine too. Let me know...

With mechanical gauge: my keyon FP was ~47psi. About 5 min after keyoff it had dropped to ~40psi. After an hour it was at like 30 psi. After overnight there was no pressure left on the gauge. It should hold some pressure even overnight.

Another thing it was doing was, idle FP was ~41 psi (a tad low); when I'd rev it by hand it would go up to ~45-ish, then when I let off it would drop down to 32-33 psi or so before returning back to 40-41.

Then I got an electronic FP sensor; here's what it was doing at WOT, before and after the pump swap:


This data is all in WOT (MAP ~100), collected through a/d converter on the PowrTuner. Note also that this data was collected (and the pump replaced) before I topswapped (i.e., L36); WOT fuel pressure is higher now, of course with an L67 FPR seeing boost.

As RPM (thus MAF, thus fuel demand) went up, the original pump was petering out badly on fuel pressure. With a new pump, fuel pressure stays solid all the way across. WOT KR went away, and IPW's backed off from near-static.

Originally Posted by agrazela

With mechanical gauge: my keyon FP was ~47psi. About 5 min after keyoff it had dropped to ~40psi. After an hour it was at like 30 psi. After overnight there was no pressure left on the gauge. It should hold some pressure even overnight.

I'll try and do a longer test tonight and post up results.

Another thing it was doing was, idle FP was ~41 psi (a tad low); when I'd rev it by hand it would go up to ~45-ish, then when I let off it would drop down to 32-33 psi or so before returning back to 40-41.

Mine don't do that. If I rev mine it raises to close to 50 psi and goes bad to 44 psi. No sudden dips, no nothing.

Then I got an electronic FP sensor; here's what it was doing at WOT, before and after the pump swap:


This data is all in WOT (MAP ~100), collected through a/d converter on the PowrTuner. Note also that this data was collected (and the pump replaced) before I topswapped (i.e., L36); WOT fuel pressure is higher now, of course with an L67 FPR seeing boost.

As RPM (thus MAF, thus fuel demand) went up, the original pump was petering out badly on fuel pressure. With a new pump, fuel pressure stays solid all the way across. WOT KR went away, and IPW's backed off from near-static.

Thanks for the info. I wish I could do the same test but I have no way of doing so unfortuneitly.

UPDATE:

Ok I hook up my FP gauge at the rail, ran the car for a few minutes, and killed it. I'll keep an eye on the pressure for several hours, see what happens. When I started this test it was at 40 psi @ 7:00pm.

By the way, I did the rev test again and its not working like it was before. When I would rev it it would barely raise and fluctiuate. I had someone hold the car at 3,000 RPMs while I watched the gauge, it went from an idle 44 psi to fluttering 43-44 psi. I tested it again at 4,000 RPMs, same results. Should the FP raise and stay higher than the FP at idle while being at a certain RPM?

Originally Posted by Reptile

Shawn, I tried calling you back, but left a message. Sorry I didn't get to you sooner on the issue. Pumps have been known to get weak over time, yes. Another issue to look at would possibly be the Pump Resistor if you have never touched that. It could be restricting the voltage to your fuel pump at WOT. I believe there is a mod to bypass it temporarily by bending a connector on the pump relay. Before you go to drastic actions, do a search on that and see if it fixes your problems at WOT.

On the fuel trims issue, + or - 3 at idle and cruise is deemed acceptable, but you always want your car to lock in at 0 at WOT. The car knows that something isn't right, so that's why it's trying to add fuel by possibly raising the IPW on the injectors.

Keep a cool head, and you'll find the problem!

HTH

I was about to PM you to thank ya for calling me, i got your message. I was gonna call you back but i've been trying to juggle several things all day long.

As for the pump resistor, I have them bypassed on both GTPs, I have for years, they suck! LOL. Good thought though, I never even thought of mentioning that I had done that in the past! As for the mod, it bending tab 85 on the relay.

Hope to figure this out soon...