car falling on face on accelleration

**Toasty** · 05-23-2009

Long time no type fellas!

Working on diagnosing my 99 L67 - wife caled home day before yesterday and said car was not wanting to start well, and when it did start, it wasnt wanting to stay running. i by feathering the gas, etc she got it home, but it did sound like it was missing, at least a bit, the idle was rough, but smothed out mostly before hitting the rev limiter in park. Left it sit yesterday, today, it starts alright, and drives SLOWLY ok, but if i give it gas it wants to fall flat on its face. if i keep in the gas, it does keep going, though it sounds much more quiet than it should (wierd--especially since there are a few pinholes in the resonator-?)

Here's what I know so far -
Bone stock
Car has 200K now, probably about 15K on new plugs/wires, MAF sensor, Fuel pump.

i think the fuel filter has about 25K on it, but not for sure.
when scanning it this morning while driving with the LS1M i was getting occasional misfires on a few different cylinders, but mostly 3 and 5, maybe a few on the others.

after i got done with my short test driving this morning, i pulled a P0171, lean on bank 1 code.

What should I be checking first?

If there are readings that i can pull with the LS1M that would help, let me know and i will test and post them up--- thanks!!!

**Toasty** · 05-23-2009

did a little more scanning, at least with it sitting still--

at idle, LTFT's are @ 16.4 !!!
at idle, STFT's are @ 20.6 !!!

If I increase throttle fast, STFT's zero out immediately, car bogs down and acts like it wants to die. If i increase trottle slowly, it doesnt bog down/want to die.

perhaps this helps?

**Sabrewings** · 05-23-2009

Possibly a bad O2 sensor, a bad MAF, or a vac leak.

Wait, are those numbers positive or negative?

**Toasty** · 05-23-2009

... Those were POSITIVE

**Bio248** · 05-24-2009

you have a vacuum leak with those fuel trims. fix that.

**Toasty** · 05-24-2009

Would an exhaust leak before the rear o2 or a clogged cat cause the high fuel trims?

**blueguy** · 05-24-2009

Well...an exhaust leak would most likely effect it but not that much IMO...Like Bio said...you got a vacuum leak somewhere...find that shiz and fix it and re-scan

**Toasty** · 05-24-2009

Either the vac leak is on the back side of the motor or its the intake manifold gasket... Top lines around the SC are fine.

**Bio248** · 05-24-2009

get a can of carb spray. when you find it the cars idle will change noticeably.

**Toasty** · 05-24-2009

Tried with brake cleaner, didn't find anything on the topside/ SC or BBV....

**Bio248** · 05-24-2009

brake cleaner wont work. carb spray. you need something flammable.

**Toasty** · 05-24-2009

i may have to start by replacing vac lines/fittings one by one... used brake cleaner and/or wd40 and noticed no change whatsoever. saw a few of the rubber ends that were cracked a bit, but they werent leaking. (both brake cleaner and/or wd40 should be a decent subsitute for the carb cleaner, right?

would a bum MAP sensor cause a vac leak? i swear i hear something back there, but cant determine if it is vacum or the EGR... but i have no MAP codes, only the system too lean P0171 occasionally (it's not coming back on immediately after clearing.

**Bio248** · 05-24-2009

EGR is a good suspect. the lines sometimes crack. even the line at the LIM can go bad.

**Toasty** · 05-24-2009

Are you suggesting that the EGR is the cause of the problem or just the noise I hear?

What should normal readings for both o2's, map and maf be?

If the fuel filter were restricted, that could cause the computer to try and compensate, thus raising the LTFT's or no?

**Bio248** · 05-25-2009

when the fuel trims are locked at the most positive they can go like that then you have a vacuum leak.

**Toasty** · 05-25-2009

Would a bad map sensor cause a vac leak since it connects to a vac line? What should the map reading be on the scan?

**Toasty** · 05-25-2009

well, i've tested everthing that i can as far as vac lines go. i know the fuel trims seem to be maxed, but perhaps could that be from not enough fuel pressure? (so the pcm commanding more fuel to compensate?) I think im gonna get the car over to a repair shop and have them look into fuel pressure, etc, and see if they see a vac leak somewhere. if it's a relatively easy/inexpensive fix, it's cool, but if it's intake manifold gaskets, i dont think i'm gonna sink the money into the car at this point

**Toasty** · 05-27-2009

well... shop called. i had a sneaking suspicion of what the problem might be. I was right - it was a bad fuel pump (which i replaced in august) sure enough, bad fuel pump and clogged filter !!!

here's to hoping there isnt anything else amis!

**JoshMcMadMac** · 05-28-2009

Originally Posted by Toasty

well... shop called. i had a sneaking suspicion of what the problem might be. I was right - it was a bad fuel pump (which i replaced in august) sure enough, bad fuel pump and clogged filter !!!

here's to hoping there isnt anything else amis!

If you recently replaced the fuel pump, I would wager it was just the filter that needed replaced but the shop went for the pump first...and has charged you for both.