Confusing Lean Code Problem
Thread Starter
Teching In
Joined: Jan 2013
Posts: 27
Likes: 0
From: Dallas, TX
Confusing Lean Code Problem Stock LS1 swapped into my 2000 S10 pickup.
I have had a codes PO171 and PO174 (I know, a lot of threads on those and I have read most). I've done a lot of research on this subject and have not found a solution. All intake gaskets have been replaced, and I have visually inspected all PCV hoses and they do not appear to be leaking.
I was using the stock aluminum LS1 MAF, and after reading that it could be the MAF causing the codes, I swapped it out with the MAF from the 4.3L V6 from the motor I pulled out of the truck. The MAFs look identical except the 4.3 MAF is slightly smaller diameter. After putting the 4.3 MAF on (had it on for approx 400 miles) the codes never came back on. That lead me to believe that my LS1 MAF was bad. No problem, ordered a new Delphi MAF for an LS1 (the new plastic variation), now I am getting the same lean codes every time I drive it again. Have put approx 100 miles on it since new MAF.
I am at a loss. I am lead to believe it is not a vacuum leak because no codes were shown while using the 4.3 MAF. Maybe the new LS1 MAF I bought is faulty? Possibly, but seems unlikely.
Does anyone have any suggested remedies or tests?
I have had a codes PO171 and PO174 (I know, a lot of threads on those and I have read most). I've done a lot of research on this subject and have not found a solution. All intake gaskets have been replaced, and I have visually inspected all PCV hoses and they do not appear to be leaking.
I was using the stock aluminum LS1 MAF, and after reading that it could be the MAF causing the codes, I swapped it out with the MAF from the 4.3L V6 from the motor I pulled out of the truck. The MAFs look identical except the 4.3 MAF is slightly smaller diameter. After putting the 4.3 MAF on (had it on for approx 400 miles) the codes never came back on. That lead me to believe that my LS1 MAF was bad. No problem, ordered a new Delphi MAF for an LS1 (the new plastic variation), now I am getting the same lean codes every time I drive it again. Have put approx 100 miles on it since new MAF.
I am at a loss. I am lead to believe it is not a vacuum leak because no codes were shown while using the 4.3 MAF. Maybe the new LS1 MAF I bought is faulty? Possibly, but seems unlikely.
Does anyone have any suggested remedies or tests?
If you have long tube headers in the mix, those often
make the O2 sensors go sleepy at idle. Start with a
scan (after resetting all codes) and look for normal
sensor waveforms, just to be sure something isn't bad
about the swap wiring or a fuse blown etc.
Sleepy or dead O2 sensors cause false trimming that
the PCM interprets as lean, even though actual mixture
is not.
Your MAF would have to be a real turd to bend the
trims 25%. Only time I've seen this from a MAF was with
swapping an 85mm onto an untuned car and this gave a
rich code, not lean.
make the O2 sensors go sleepy at idle. Start with a
scan (after resetting all codes) and look for normal
sensor waveforms, just to be sure something isn't bad
about the swap wiring or a fuse blown etc.
Sleepy or dead O2 sensors cause false trimming that
the PCM interprets as lean, even though actual mixture
is not.
Your MAF would have to be a real turd to bend the
trims 25%. Only time I've seen this from a MAF was with
swapping an 85mm onto an untuned car and this gave a
rich code, not lean.
What is the fuel pressure measured at the rail? I see more fuel pressure issues on swaps than any other problem. Also is it still using a return system like the S10 4.3 would of had? Is the LS1 fuel rail return or returnless. Most were returnless but early Vette LS1s used return fuel rails. What year LS1 injectors are being used and with what year LS1 pcm? Lots of differences. Give more details on all the parts used including vehicle type and year the parts came from. Do you have tuning ability? And don't try and use the 4.3L MAF any more. Find and fix the real problem.
Thread Starter
Teching In
Joined: Jan 2013
Posts: 27
Likes: 0
From: Dallas, TX
If you have long tube headers in the mix, those often
make the O2 sensors go sleepy at idle. Start with a
scan (after resetting all codes) and look for normal
sensor waveforms, just to be sure something isn't bad
about the swap wiring or a fuse blown etc.
Sleepy or dead O2 sensors cause false trimming that
the PCM interprets as lean, even though actual mixture
is not.
Your MAF would have to be a real turd to bend the
trims 25%. Only time I've seen this from a MAF was with
swapping an 85mm onto an untuned car and this gave a
rich code, not lean.
make the O2 sensors go sleepy at idle. Start with a
scan (after resetting all codes) and look for normal
sensor waveforms, just to be sure something isn't bad
about the swap wiring or a fuse blown etc.
Sleepy or dead O2 sensors cause false trimming that
the PCM interprets as lean, even though actual mixture
is not.
Your MAF would have to be a real turd to bend the
trims 25%. Only time I've seen this from a MAF was with
swapping an 85mm onto an untuned car and this gave a
rich code, not lean.
What is the fuel pressure measured at the rail? I see more fuel pressure issues on swaps than any other problem. Also is it still using a return system like the S10 4.3 would of had? Is the LS1 fuel rail return or returnless. Most were returnless but early Vette LS1s used return fuel rails. What year LS1 injectors are being used and with what year LS1 pcm? Lots of differences. Give more details on all the parts used including vehicle type and year the parts came from. Do you have tuning ability? And don't try and use the 4.3L MAF any more. Find and fix the real problem.
Thanks for the input guys!
