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...


Quote Originally Posted by Reptile View Post
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.


Quote Originally Posted by Sabrewings View Post
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.


Quote Originally Posted by blue91gtp View Post
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.


Quote Originally Posted by Sabrewings View Post
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.