Another "Rich at Idle" thread
Thread Starter
Staging Lane
Joined: Feb 2014
Posts: 68
Likes: 1
Another "Rich at Idle" thread The car in question is a '96 Z28 M6. The exhaust is essentially stock with BBK shorty headers and the magnaflow replacement y-pipe with stock location catalytic convertors.
The car starts, runs and drives fine. It idles at 800 RPM
A month ago the element in the passenger side cat broke apart. It turns out my EGR has been non functional for who knows how long. So, I'm guessing the resulting increase in exhaust gas temperature is the culprit as the cat was only one season old and the pieces of the element were perfectly clean.
Not wanting to side line the car I gutted the driver's side cat as well. I was expecting a change in the smell of the exhaust but the car has been running rich according to the AEM wideband. Prior to this while stopped at a light the car would idle between 14.6 and 14.9:1. Now it runs between 13.7 and 14.2: Expecting that I had introduced an exhaust leak ahead of the upstream O2s I pulled the Y-pipe off. There was no audible sound of a leak and I could not feel anything coming out of the joint but the driver's side Y-pipe-to-header gasket did show black soot going towards one edge. I replaced the gasket with a Remflex one and subsequent removals of the Y-pipe show that it is sealing correctly.
Scanning the car showed no misfires (and no EGR codes, even though one of the hoses from the solenoid was torn) but it did show low activity on the bank2 downstream O2. My understanding is that downstream O2s do not affect fueling but |I changed it anyway.
I could not find any obvious vacuum leaks. I did try running a propane torch attached to a hose around the intake while running to see if the engine ingested any but without result.
The CAI is all straight and tight. So, there does not appear to be any un-metered air being drawn into the intake.
Wondering about the state of the FPR I put a gauge on the fuel line.
The fuel line primes to 45PSI, settles to 42PSI with the key off, idles at 37.5PSI and 36 PSI at 5000RPM (No load - car stationary).
It held 40PSI for two and a half hours before I went home for the night. By morning it was down to 3PSI. I haven't removed the fuel rail from the intake to see that the injectors hold pressure but I would think that even if the pressure regulator or an injector had a slight leak the fact that the system held pressure for a least two and a half hours would indicate that this is not the problem?
Both upstream O2s are relatively recent (NTK) with less than 4000 miles of run time.
I haven't properly vacuum tested the EGR valve but the diaphram does move and the car wants to stall when the diaphram is manually manipulated.
Other parameters from the last scan in case something pops out to anyone:
Car idling at 800PM
MAF = 7.6GPM
MAP = 31KPA
IAC position = 31
Knock retard = 0
KS Counter = 709
Spark advance fluctuating between 17*-20*
STFT B1average =127
LTFT B1 average = 123
STFT B2average =129
LTFT B2 average = 131
Am I overlooking something obvious?
Any and all help is appreciated.
Jon
The car starts, runs and drives fine. It idles at 800 RPM
A month ago the element in the passenger side cat broke apart. It turns out my EGR has been non functional for who knows how long. So, I'm guessing the resulting increase in exhaust gas temperature is the culprit as the cat was only one season old and the pieces of the element were perfectly clean.
Not wanting to side line the car I gutted the driver's side cat as well. I was expecting a change in the smell of the exhaust but the car has been running rich according to the AEM wideband. Prior to this while stopped at a light the car would idle between 14.6 and 14.9:1. Now it runs between 13.7 and 14.2: Expecting that I had introduced an exhaust leak ahead of the upstream O2s I pulled the Y-pipe off. There was no audible sound of a leak and I could not feel anything coming out of the joint but the driver's side Y-pipe-to-header gasket did show black soot going towards one edge. I replaced the gasket with a Remflex one and subsequent removals of the Y-pipe show that it is sealing correctly.
Scanning the car showed no misfires (and no EGR codes, even though one of the hoses from the solenoid was torn) but it did show low activity on the bank2 downstream O2. My understanding is that downstream O2s do not affect fueling but |I changed it anyway.
I could not find any obvious vacuum leaks. I did try running a propane torch attached to a hose around the intake while running to see if the engine ingested any but without result.
The CAI is all straight and tight. So, there does not appear to be any un-metered air being drawn into the intake.
Wondering about the state of the FPR I put a gauge on the fuel line.
The fuel line primes to 45PSI, settles to 42PSI with the key off, idles at 37.5PSI and 36 PSI at 5000RPM (No load - car stationary).
It held 40PSI for two and a half hours before I went home for the night. By morning it was down to 3PSI. I haven't removed the fuel rail from the intake to see that the injectors hold pressure but I would think that even if the pressure regulator or an injector had a slight leak the fact that the system held pressure for a least two and a half hours would indicate that this is not the problem?
Both upstream O2s are relatively recent (NTK) with less than 4000 miles of run time.
I haven't properly vacuum tested the EGR valve but the diaphram does move and the car wants to stall when the diaphram is manually manipulated.
Other parameters from the last scan in case something pops out to anyone:
Car idling at 800PM
MAF = 7.6GPM
MAP = 31KPA
IAC position = 31
Knock retard = 0
KS Counter = 709
Spark advance fluctuating between 17*-20*
STFT B1average =127
LTFT B1 average = 123
STFT B2average =129
LTFT B2 average = 131
Am I overlooking something obvious?
Any and all help is appreciated.
Jon
Last edited by Jonathan Dyer; Sep 1, 2019 at 09:46 AM.
Thread Starter
Staging Lane
Joined: Feb 2014
Posts: 68
Likes: 1
Update: despite not having properly tested the EGR valve (I don’t have a vacuum pump) I swapped it out this morning. No change in the AFR...
A little silly to randomly change parts but it didn’t cost anything since I had a spare Delco EGR valve in a box of parts.
My next step is to just start back at square one and hunt for possible vacuum/exhaust leaks.
The previously posted fuel trims are positive. So, the ECM is adding fuel correct? So, it is not trying to lean it out. Would that not point to incorrect O2 feedback being passed to the ECM? So, faulty O2 sensor(s) or an exhaust leak, no?
Thanks,
Jon
A little silly to randomly change parts but it didn’t cost anything since I had a spare Delco EGR valve in a box of parts.
My next step is to just start back at square one and hunt for possible vacuum/exhaust leaks.
The previously posted fuel trims are positive. So, the ECM is adding fuel correct? So, it is not trying to lean it out. Would that not point to incorrect O2 feedback being passed to the ECM? So, faulty O2 sensor(s) or an exhaust leak, no?
Thanks,
Jon
Thread Starter
Staging Lane
Joined: Feb 2014
Posts: 68
Likes: 1
Tying up a loose end on this old thread.
I eventually changed the drivers side header gasket and replaced the header bolt for the #8 cylinder that possibly wasn't sealing well.
The closed loop rich condition went away. However, since then it idles lean in closed loop.
I've started a new thread on this here:
https://ls1tech.com/forums/lt1-lt4-m...l#post20337912
I eventually changed the drivers side header gasket and replaced the header bolt for the #8 cylinder that possibly wasn't sealing well.
The closed loop rich condition went away. However, since then it idles lean in closed loop.
I've started a new thread on this here:
https://ls1tech.com/forums/lt1-lt4-m...l#post20337912