Help needed: CEL and lean codes (171, 174) on hot engine
09-25-2016, 06:29 PM
#1
Solved: CEL and lean codes (171, 174) on hot engine
I started getting CEL and lean codes on both banks (codes are 171, 174). The car drives normal, no hesitations, no idle issues, no power loss. The first time it happened, I reset the codes and they cam back after around 2-3 weeks. The problem gets progressively worse and now I am getting codes every day after I reset them.
The car is completely stock and has < 40,000 miles and is 2011 Grand Sport.
What I noticed about the CEL:
- after I reset it, usually it shows up on every 2nd drive (not the first)
- CEL turns on only when the car is fully warmed up (engine oil up to 190-200F) and it always happens when the car is idling and not moving
What I did:
- checked vacuum lines: nothing is disconnected or cracked
- tried to use a home-built smoke machine: could not find any leak
- cleaned up the MAF sensor (had a little oil near the place where the small hose connects) but this did not solve the issue
- removed the intake and filter, nothing wrong was found
- removed and checked EVAP solenoid, it worked fine (was in closed position, goes to open if voltage applied).
I am fully at a loss. The car goes to the dealer in one week unless I can fix it before that.
Thank you for all your input!
The car is completely stock and has < 40,000 miles and is 2011 Grand Sport.
What I noticed about the CEL:
- after I reset it, usually it shows up on every 2nd drive (not the first)
- CEL turns on only when the car is fully warmed up (engine oil up to 190-200F) and it always happens when the car is idling and not moving
What I did:
- checked vacuum lines: nothing is disconnected or cracked
- tried to use a home-built smoke machine: could not find any leak
- cleaned up the MAF sensor (had a little oil near the place where the small hose connects) but this did not solve the issue
- removed the intake and filter, nothing wrong was found
- removed and checked EVAP solenoid, it worked fine (was in closed position, goes to open if voltage applied).
I am fully at a loss. The car goes to the dealer in one week unless I can fix it before that.
Thank you for all your input!
Last edited by Denny79; 09-30-2016 at 10:58 AM.
09-27-2016, 11:02 AM
#2
Checked with OBD tester. The car is running lean at idle (+25% long-term fuel trim on both banks) and closer to normal at higher RPM (+6-8% at 1500 rpm).
Long-term fuel trim at idle is getting larger as engine warms up. I guess, this eliminates the fuel pump or any fuel lines.
Any suggestions?
Long-term fuel trim at idle is getting larger as engine warms up. I guess, this eliminates the fuel pump or any fuel lines.
Any suggestions?
Last edited by Denny79; 09-27-2016 at 11:04 AM.
09-30-2016, 11:03 AM
#3
The issue was solved. Was a little tricky to find but it was the U-shaped vacuum hose between the manifold and crankcase, under purge solenoid on the passenger side of the engine.
The smoke machine did not really show it. The crack in the hose was getting larger as engine was heating up. Smoke, lightning fluid or propane used on a cold engine did not show any issues.
To find the culprit, I wiggled around all vacuum hoses on a hot running engine. The moment I touched the u-shaped connector, I heard the noise of the air whooshing.
The smoke machine did not really show it. The crack in the hose was getting larger as engine was heating up. Smoke, lightning fluid or propane used on a cold engine did not show any issues.
To find the culprit, I wiggled around all vacuum hoses on a hot running engine. The moment I touched the u-shaped connector, I heard the noise of the air whooshing.
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C5forFun (10-16-2016)
