Endless P0171- some new hope - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 09-21-2009, 05:20 PM   #1
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Default Endless P0171- some new hope

The '98 SSEi.
P0171- is a lean burn in the bank. more air than gas when firing.

The story without end.

Months ago, extra air appeared on my boost gauge. At idle. -7.5 instead of pegged at -10. Been steadily checking, spraying carb cleaner, and replacing all vacuum lines and connectors over months. Finally started getting intermittent appearance of P0171. It usually comes on when I kick it over, or shortly thereafter. Plus it occurs when the engine is cold. I don't believe it has ever happened after the car is at temperature.

New development.

Finally fed up, took it to a dealer (that hurt, having to do that). They said no vacuum leaks, but it needed a new fuel pump. 39psi. $800, thanks, but I'll take a shot at it. Put in a Delphi pump, which looked exactly like the one I took out. Also replaced the screen/bag. (my fuel filter is 3 months old, and had no effect on the problem, before or after)

Afterwards, turned the key to ON to fire up the pump. Got out of the car to find the fuel pressure gauge at 45 psi. Better, but not quite. The spec for '96-'99 is 48-55psi. But then I thought of something. So I stood over the gauge, while I had the wife turn the key to the ON position. All within 5 seconds or so, the gauge jumped to 52-54 psi, and i got a hissing sound somewhere around where the MAP sensor stuff is, and (I think) the EVAP purge valve.The psi dropped to 45.

I can repeat this continuously, over and over again. And the same thing happens. I never noticed it before, because I didn't jump out of the car fast enough.

It gets even better. If I leave the gauge on for an hour or so, with the car turned off, the fuel pressure drops to 10psi.

Notes:

The battery cables are not clean, they are virtually new and cleaned, with particular care fixed to the engine block and starter.

During this long period, I measured my charge circuit as fine, but discovered the battery was a swelled pig. Replaced it with a maximum cranker. I haven't tested the alternator separately. And don't know how to find out how much current is reaching the fuel pump. When i use the a/c or power windows or brakes, the boost gauge moves even higher.

I have had 3 OEM gas caps on this thing. Never have I gotten the sweet sound of good tank pressure, when I removed the cap to fill the tank.

There has never been a performance interrupt problem. No uneven idling, no misses, no stalls, and the fuel pressure blows right into and through the pressure zone on throttle.

Sorry this is long, but I wanted to put out as much info as possible.

Qs

- Fuel system isn't my strong point, particularly how the EVAP system works with it to get rid of the vapors. What'* going on here?
- Chilton'* tells me to check a few items, if the rail loses pressure when the car is off. The first thing is the "check valve". I saw no valve on the entire pump assembly, only the pulsator. Is that the check valve?
- If I paint the car black, will it rid me of this neverending "White curse" episode?

ANY thoughts or help will be appreciated. After this, my last task before mods start is the SC coupler and snout. As long as i have been trying to figure this out, they may fall off before i get to them.

Thanks.

charlie
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Old 09-21-2009, 08:35 PM   #2
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I just spoke to a Pontiac Dealer'* Service Dept. and was told that the correct fuel pressure on a 96 SE is 40.5 to 47 PSI. Seems like the 98'* & up had a higher spec
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Old 09-21-2009, 08:40 PM   #3
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I think the bleed down in pressure is fairly normal too. I have problem with the p0171 code too. I'm intrigued with the possibilty of the Evap system. I've not heard of this before but it gives me something else to check.
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Old 09-21-2009, 10:00 PM   #4
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I just spoke to a Pontiac Dealer'* Service Dept. and was told that the correct fuel pressure on a 96 SE is 40.5 to 47 PSI. Seems like the 98'* & up had a higher spec
I would double check that. Per Chilton'*....

1986-1995 41-47psi, except 1995 L36

1995 L36 and 1996-1999 48-55 psi

This is only for your initial ignition state ie key ON, engine OFF. When you actually kick the engine over, the fuel psi should drop anywhere from 3-10 psi, due to the lower manifold pressure.

From there it'* a mental crapshoot for me. Temperature, barometric pressure, the Idle air control (IAC), and a host of things get involved which contribute to action by the regulator.

Hoping against hope, what my system is doing wrong is this..... it powers up with key ON to 52-54. But it should stay there. Instead I hear that purge/leak (whatever) and the pressure drops, but to the normal idle operation range. So it'll kick over and run right, but the PCM is seeing a low fuel pressure/lean burn for a turnover, and/or low pressure/lean burn for a cold engine idle. I don't remember ever getting the P0171 on a start or run where the engine was at operating temperature.

That may sound like I know what'* going on, but i don't. The EVAP vacuum circuit is in this somewhere.

Quote:
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I think the bleed down in pressure is fairly normal too. I have problem with the p0171 code too. I'm intrigued with the possibilty of the Evap system. I've not heard of this before but it gives me something else to check.
Maybe some bleeddown. But there is supposed to be a "check valve" somewhere that stops backflow. And if you have good fuel tank pressure (as in a tight gas cap, line connections, and pump sealing) there is no place for the fuel to pressure down. It would seem to me (the last physics i had was 40+ yrs ago) that the entire fuel system would have be pressure tight for the fuel and evap system to function properly.

P0171 is a not-too-bad in an L36. But a lean burn in an L67 that you want to mod, is a KR bad dream, with a chipped piston waiting down the road.
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Old 09-21-2009, 10:42 PM   #5
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I think the bleed down in pressure is fairly normal too. I have problem with the p0171 code too. I'm intrigued with the possibilty of the Evap system. I've not heard of this before but it gives me something else to check.
Oh, I forgot. And one thing you might check for P0171 (if you haven't already heard it 100 times the battery cables. the fuel pump runs off of your alternator. If the charging circuit is intermittently disrupted in any way (or stressed charging a zombie battery) an older fuel pump is the likely candidate to suffer in performance. Clean 'em. Scrape 'em down to clean copper. Peel back a bit of rubber and check under that, too.

And the ground cable from the positive terminal to the ground on the base of your engine is by far the most important one to clean and clean the connection post.It'* a bugger to get to on a '96, but ya have to do it. You'll save yourself a world of future pain. An 18 inch 13mm(i think) wrench does the trick, or anything you can rig up like that, if you are tool poor like me.
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Old 09-22-2009, 08:25 AM   #6
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Hi guys...

If you search on my name and that code you'll find lots of info. I feel like I bought the code in the past.

Having fought it a few times, here'* the "usual suspects" that I've found.

Fuel pressure. 40+ is fine. The spec from 96+ is 48-52 but it'* not that important. I've yet to find 48+ with all new components.

Corrosion inside the battery cable. If your terminals at the battery were nasty and you cleaned them, look where the strands head into the sheath, if they are corroded that'* a possibility. Swapping cables out for new is the only way to fix that issue.

Grounds, when doing grounds, clean the ones on each front fender (by battery and horns), clean the one ground on the back side of the block, down behind the oil filter. (Easiest to access through the wheel well).

Vaccum connectors: remove the airbox and replace the vacuum connection rubber chunks of hose at the charcoal canister. Check that the hose from the evap soleniod marked "CAN" does indeed go to the canister. Check the U bend on the other side hose going to the throttle body (this is a commonly cracked piece). Injector O -rings could be a potential, but carb clean testing would pick this up.

Throttle body gasket, check for vac leaks

EGR tube. There'* a tube from the EGR that heads under the throttle body, this is a flimsy piece of tinfoil. These crack right at the end where the holding piece pushes on it to keep it seated. To know if this is an issue, remove the tube from the EGR/LIM and hold up to light inspecting closely. These cracks can be tough to find.

Maf sensor, it'* one of the first things the FSM tells you to check. Car can run fine etc but if it'* dirty etc, clean it up. While the FSM checks it first, I check it last unless there'* a code. Reason being is the test is to unplug it. This test can give you a false positive because it makes the engine run off tables instead of real airflow data. This can richen the mixture and mask the code. Then you get a new maf and still have the code, that'* no fun.

Start off with those things and see if that works for you.
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Old 09-22-2009, 05:36 PM   #7
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Hi guys...

(snip)
Fuel pressure. 40+ is fine. The spec from 96+ is 48-52 but it'* not that important. I've yet to find 48+ with all new components.
(snip)

(snip)
EGR tube. There'* a tube from the EGR that heads under the throttle body, this is a flimsy piece of tinfoil. These crack right at the end where the holding piece pushes on it to keep it seated. To know if this is an issue, remove the tube from the EGR/LIM and hold up to light inspecting closely. These cracks can be tough to find.
(snip)
Bill... thanks for the stop-by.

i was wondering about the fuel pressure. there have been guys with pressure 10-15psi low, before any problem presented itself. If I can kick the car over and the pressure responds properly in synch with the throttle, what else would I want from the fuel supply..

My cables are the cleanest parts on my car. Over the past few years, I know we've seen an incredibly wide range of problems resulting from corroded battery cables. Over the past 6+ months, I have virtually cleaned my entire engine and connecting parts with carb/choke cleaner or brake cleaner, looking for leaks..

But today, here'* the question...

If I reach around the crosspipe, and spray brake cleaner on the EGR line, and where it goes into the LM.... and the exhaust becomes a dense acrid white smoke....

Do ya think that means anything?

I haven't pulled it yet, so i don't know what it is made out of. But like you said, it looks like aluminum. Aluminum is resistant to radiant heat, not conductive heat like it would get from laying on the crosspipe.

Thanks bigtime for your help.

<all>PS, FYI, I used brake cleaner because I was out of carb cleaner. Do this sparingly. Many brake cleaners, when combusted are highly catalytic (acidic), and rough on gasket edges,sensors etc. Plus, if you take a nice huff of the exhaust, you will likely get a headache for a few hrs.
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Old 09-23-2009, 08:14 AM   #8
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Well CM.. it'* been my experience that I was always unable to get anything in that area for good testing. If your exhaust changes, then something is occuring, no doubt there.

I'd pull out the ole 13mm and check it out. There'* a good chance you'll be LBO'less soon.

If you get the tube out w/o pulling the TB, .... that'* a mastered art.
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Old 09-24-2009, 10:33 PM   #9
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Well CM.. it'* been my experience that I was always unable to get anything in that area for good testing. If your exhaust changes, then something is occuring, no doubt there.

I'd pull out the ole 13mm and check it out. There'* a good chance you'll be LBO'less soon.

If you get the tube out w/o pulling the TB, .... that'* a mastered art.
Hah! I had to chuckle at myself. I thought it was going to be a chipshot. I unbolted the pipe, and came to a quick conclusion that the TB was coming off. I didn't really look at the new part, it has the accordian cast, but you can't bend it. The one i took out you could easily shape with your hands. There'* definitely some steel in the replacement, and it was too long, and wide to slip in. Worked it around with tools. I'll be real surprised, if I don't have to do it again, it'* really roughed up.

Yeah. That area is a big intersection of suspects. under area of the TB, the EGR pipe, and the LIM.

I'm goin' out now and carefully put the TB and the rest back on. But I'm not so cocked sure it'* the EGR anymore. The LIM gasket is overdue. I was waiting til i had the time to do the */C, put new bearings in the snout, and replace the jingling coupler.

We'll see.

The story might not be over, but i know where it'* generally located.
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Old 09-25-2009, 08:07 AM   #10
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I've actually been successful w/o taking off the TB. But I had seen a bunch and had the shallow swivel socket for the job. If you suspect a leak under the TB, it could be the SC to LIM or TB to SC gasket as well.
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