I need a little help please.
Thread Starter
Pro
Joined: Aug 2010
Posts: 734
Likes: 10
From: South East Coast Florida
I need a little help please.
My son has a 1996 box stock no mods I believe LT-4 Vette and it keeps throwing these two codes P0171 ans P0174 we have put a new fuel filter on it and run a couple of Sea Foam fuel treatment cleaner in the tank to no avail. Also we can't find any vacuum leaks anywhere. Cleaned the MAF. Fuel pump shows good pressure. Sometimes it will run a couple of days great before trowing the codes. Any help or thoughts will be greatly appreciated.
Pete
Pete
Melting Slicks
Joined: Nov 2005
Posts: 3,322
Likes: 141
From: Green Valley Arizona
These are the lean codes for both banks; a '96 has four O2 sensors; have you checked the condition of the two pre-cat O2's?
If they are originals...suggest changing all of them.
How old are the plugs & wires?
If they are originals...suggest changing all of them.
How old are the plugs & wires?
Thread Starter
Pro
Joined: Aug 2010
Posts: 734
Likes: 10
From: South East Coast Florida
Ya' that's probably the next step to try, Wanted to try all the easy stuff first, Ya know maybe somebody has run into this problem and fixed it easily. I didn't want to just start throwing parts at it. But thanks for your suggestions. I'll give it a try. Thanks Lanny
Pete
Pete
Last edited by Z06pete; Dec 22, 2015 at 06:09 PM.
Team Owner
Joined: Sep 2003
Posts: 25,344
Likes: 2,727
If you are to the extent of what you feel you're capable of diagnosing and checking it might be very advisable to have it professionally scanned before just throwing parts at it.
This time of year everyone is lacking cash and you might just find someone that is willing to work with you. Do you know anyone that has a capable scanner rather than just a "code reader"?
These codes can be chased for hours by knowledgeable folks, it might be good to do some freeze frames on the faults. When do the codes present themselves after a "cold start"? I'd maybe check that for the next few days and several drives. Can you establish a pattern?
Miles?
This time of year everyone is lacking cash and you might just find someone that is willing to work with you. Do you know anyone that has a capable scanner rather than just a "code reader"?
These codes can be chased for hours by knowledgeable folks, it might be good to do some freeze frames on the faults. When do the codes present themselves after a "cold start"? I'd maybe check that for the next few days and several drives. Can you establish a pattern?
Miles?
Thread Starter
Pro
Joined: Aug 2010
Posts: 734
Likes: 10
From: South East Coast Florida
If you are to the extent of what you feel you're capable of diagnosing and checking it might be very advisable to have it professionally scanned before just throwing parts at it.
This time of year everyone is lacking cash and you might just find someone that is willing to work with you. Do you know anyone that has a capable scanner rather than just a "code reader"?
These codes can be chased for hours by knowledgeable folks, it might be good to do some freeze frames on the faults. When do the codes present themselves after a "cold start"? I'd maybe check that for the next few days and several drives. Can you establish a pattern?
Miles?
This time of year everyone is lacking cash and you might just find someone that is willing to work with you. Do you know anyone that has a capable scanner rather than just a "code reader"?
These codes can be chased for hours by knowledgeable folks, it might be good to do some freeze frames on the faults. When do the codes present themselves after a "cold start"? I'd maybe check that for the next few days and several drives. Can you establish a pattern?
Miles?
Thanks for your your input.
Pete
Burning Brakes
Joined: Dec 2005
Posts: 805
Likes: 11
From: Hickory Flat Ga
I just went through a P0171 DTC. The fact that both codes are present means both banks of cylinders are being doused with excess oxygen. Both sensors do not fail simultaneously.
The most common cause is a vacuum leak on the intake manifold triggering both upstream HO2S to read lean. This causes a greater than 20% addition of fuel to the trim ratios firing the codes. It's cooking your cats at this level so use sparingly.
Logic dictates with both banks lean (too much unmetered air) you could also clean the MAF. But most the time it's a brittle hose cracked where you can't see it. Again a smoke machine works best to find the leak. With a scanner you can spray carb cleaner on a COLD motor and look for a change but prefer a propane tube for safety. The system is operating exactly as designed to alert you to a problem. You have to search for the source and restore the correct 14.7 to 1 ratio or this car will bitch harder than a red-headed girlfriend sitting home on Saturday night.
The most common cause is a vacuum leak on the intake manifold triggering both upstream HO2S to read lean. This causes a greater than 20% addition of fuel to the trim ratios firing the codes. It's cooking your cats at this level so use sparingly.
Logic dictates with both banks lean (too much unmetered air) you could also clean the MAF. But most the time it's a brittle hose cracked where you can't see it. Again a smoke machine works best to find the leak. With a scanner you can spray carb cleaner on a COLD motor and look for a change but prefer a propane tube for safety. The system is operating exactly as designed to alert you to a problem. You have to search for the source and restore the correct 14.7 to 1 ratio or this car will bitch harder than a red-headed girlfriend sitting home on Saturday night.
Last edited by tlong; Dec 23, 2015 at 12:28 PM.
