Vacuum leak??? P0171 code
10-21-2008, 10:33 PM
#1
Vacuum leak??? P0171 code
Ok, I need some input here:
I just wrapped up a rebuild for a local guy who had a couple cracked pistons. All stock parts back in the car, back to 100% stock, stock tune, everything. The car was denied warranty at a dealership, so I had to re-build the motor from a box of parts, I didn't do the teardown. Motor started right up beautifully, and runs nice and normal. Only issue i'm having is what I believe to be a vac leak. Car doesn't want to idle smooth when cold, and once its warm, its manintaing a smooth idle but has to go into the 30% range on STFT to get there. Throws a constant P0171 fuel trim lean code. O2 readings are basically lean all the time, even when driving, it swings back up but drops right back and holds lean.
If you blip the throttle at idle, the car takes a second to smooth back out, it has to trim itself back to 30% or more to be smooth, but once it gets there it seems fine.
Just looking for more ideas on this, I've gone over most of the obvious stuff, but I could have missed something or overlooked an item. What have you guys got for me? Thanks.
I just wrapped up a rebuild for a local guy who had a couple cracked pistons. All stock parts back in the car, back to 100% stock, stock tune, everything. The car was denied warranty at a dealership, so I had to re-build the motor from a box of parts, I didn't do the teardown. Motor started right up beautifully, and runs nice and normal. Only issue i'm having is what I believe to be a vac leak. Car doesn't want to idle smooth when cold, and once its warm, its manintaing a smooth idle but has to go into the 30% range on STFT to get there. Throws a constant P0171 fuel trim lean code. O2 readings are basically lean all the time, even when driving, it swings back up but drops right back and holds lean.
If you blip the throttle at idle, the car takes a second to smooth back out, it has to trim itself back to 30% or more to be smooth, but once it gets there it seems fine.
Just looking for more ideas on this, I've gone over most of the obvious stuff, but I could have missed something or overlooked an item. What have you guys got for me? Thanks.
10-21-2008, 10:44 PM
#4
Umm, its stock airbox, and it wont run smoothly or idle down right... I haven't seen a CAI do that.
Wouldn't it throw a code?
From what I understand, the O2 was replaced before I got involved with the car, but it was also a badly blown engine at the time. I could pull it and check I guess, that was one of the ideas I was thinking about tonight.
Wouldn't it throw a code?
From what I understand, the O2 was replaced before I got involved with the car, but it was also a badly blown engine at the time. I could pull it and check I guess, that was one of the ideas I was thinking about tonight.
Last edited by ItalianJoe1; 10-21-2008 at 10:44 PM. Reason: Automerged Doublepost
10-21-2008, 10:46 PM
#8
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Umm, its stock airbox, and it wont run smoothly or idle down right... I haven't seen a CAI do that.
Wouldn't it throw a code?
From what I understand, the O2 was replaced before I got involved with the car, but it was also a badly blown engine at the time. I could pull it and check I guess, that was one of the ideas I was thinking about tonight.
Wouldn't it throw a code?
From what I understand, the O2 was replaced before I got involved with the car, but it was also a badly blown engine at the time. I could pull it and check I guess, that was one of the ideas I was thinking about tonight.
10-21-2008, 10:47 PM
#9
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10-21-2008, 10:47 PM
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Umm, its stock airbox, and it wont run smoothly or idle down right... I haven't seen a CAI do that.
Wouldn't it throw a code?
From what I understand, the O2 was replaced before I got involved with the car, but it was also a badly blown engine at the time. I could pull it and check I guess, that was one of the ideas I was thinking about tonight.
Wouldn't it throw a code?
From what I understand, the O2 was replaced before I got involved with the car, but it was also a badly blown engine at the time. I could pull it and check I guess, that was one of the ideas I was thinking about tonight.
10-21-2008, 11:14 PM
#11
Hard to say, the car surges under throttle, but I put new rings in, so I haven't really pushed the car hard at all, break-in and all that good stuff...
Ehh, he had a bad sensor, which would spike once in a while, causing the "fuel cut" as he called it.
This car has full stock exhaust now, but it didn't the last time I saw it before the motor got taken apart. So anything is possible. I guess i'll have to get under there and take a look. Doesn't sound like an exhaust leak at all though, car is perfectly quiet and stock sounding.
Last edited by ItalianJoe1; 10-21-2008 at 11:14 PM. Reason: Automerged Doublepost
10-21-2008, 11:17 PM
#13
Also, car is only holding about 17 in/hg at idle, not 20ish like most stock cars.
10-21-2008, 11:19 PM
#14
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I was doing that somewhat tonight, but it was pretty dark, so I gave up. I think I hear a vac leak sometimes, but then I don't... I pushed each injector down, felt all around everything, all the **** I could think of...
Also, car is only holding about 17 in/hg at idle, not 20ish like most stock cars.
Also, car is only holding about 17 in/hg at idle, not 20ish like most stock cars.
10-21-2008, 11:33 PM
#18
Who, you??
Oh, BTW...
SHUT THE **** UP!!
Weird, mine was the diamond stuff, stock sleeves and ****, but huge vac, more than stock. Unless it was because of the fresh valve job and stuff, but its wierd that mine was higher and your build was lower.
Oh, BTW...
SHUT THE **** UP!!
Weird, mine was the diamond stuff, stock sleeves and ****, but huge vac, more than stock. Unless it was because of the fresh valve job and stuff, but its wierd that mine was higher and your build was lower.
Last edited by ItalianJoe1; 10-21-2008 at 11:33 PM. Reason: Automerged Doublepost
10-22-2008, 04:06 AM
#21
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Whoa....This whole topic is exactly where i needed to start...Car has been stock and ran good(07 SS/SC) and when i took off the air box i hit the 171 all the time. I added OTT stage one and Vibrant down pipe and now getting 171,1101,AND 300. Has anyone come up with a fixing for this...O and i am having boost issues as well....
1st pull 15-18 pounds like i should(have a 2.8 pulley)
2nd pull14-15 pounds
3rd pull-hits 14-15 and pulls it down to twelve and holds it
Any help?
1st pull 15-18 pounds like i should(have a 2.8 pulley)
2nd pull14-15 pounds
3rd pull-hits 14-15 and pulls it down to twelve and holds it
Any help?
10-22-2008, 04:42 AM
#23
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I was doing that somewhat tonight, but it was pretty dark, so I gave up. I think I hear a vac leak sometimes, but then I don't... I pushed each injector down, felt all around everything, all the **** I could think of...
Also, car is only holding about 17 in/hg at idle, not 20ish like most stock cars.
Also, car is only holding about 17 in/hg at idle, not 20ish like most stock cars.
If you have access to HPTuners, open VCM Scanner and connect to the PCM. Enter the area with the icon ON/OFF (the place where you can adjust idle manually) and check commanded idle to actual idle. Also note idle spark at the same time. If either actual idle is higher than commanded or they are the same and you are pulling consistently negative timing at idle, its probably a vacuum leak.
If you are running any open air crankcase breathers, get rid of them. Keep the PCV system closed until the problem is diagnosed.
10-22-2008, 08:15 AM
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Sorry i know that doesnt help your issue Joe