Car running lean but no vacuum leak?
#1
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Car running lean but no vacuum leak?
So basically a month ago i got a CEL. Pulled the code and P0101 (MAF), P0171 (lean bank 1), P0174 (lean bank 2) were showing up. Plus my car was having rough idling. All the symptoms of a vacuum leak.
I brought the car to the dealer and tell them i have a leak so please check and replace if necessary the intake manifold gasket. Few hours later i was right as the SA came back to me saying they had to replace PCV hose and the gasket/bolts all under warranty. I was happy. Took my car home.
Next morning on my way to the office CEL came on while entering the highway under acceleration! Same lean OBDII codes! Damn! Brought the car back to MB and asked them to have a second look. They kept the car a whole week without figuring out what the issue was!
That's where i need your help pinpoint the problem. They said they check the MAFs, they changed the fuel pressure pump, there is no more vacuum leak/no cracks, the purge valve is ok. What else should I investigate?
The MB tech said he tried to reset the self adaptation values but couldn't. Like the ECU won't allow him to do so. I don't know if it's true but could the tune be the issue? I doubt it since it has been on the car from day 1. So why all of a sudden? I will call Renntech and ask them if there is something they can do like an update or else
I'm thinking of putting my OEM filters and airboxes back to see if the CEL clears. As well I'm doubting about this being the root cause since when i installed the AFE filters and ROW airboxes i never had any CEL.
I'm running out of ideas....O2 sensors would unlikely be the problem as both would have to be at fault at the same time....
Any suggestions will be much appreciated.
I brought the car to the dealer and tell them i have a leak so please check and replace if necessary the intake manifold gasket. Few hours later i was right as the SA came back to me saying they had to replace PCV hose and the gasket/bolts all under warranty. I was happy. Took my car home.
Next morning on my way to the office CEL came on while entering the highway under acceleration! Same lean OBDII codes! Damn! Brought the car back to MB and asked them to have a second look. They kept the car a whole week without figuring out what the issue was!
That's where i need your help pinpoint the problem. They said they check the MAFs, they changed the fuel pressure pump, there is no more vacuum leak/no cracks, the purge valve is ok. What else should I investigate?
The MB tech said he tried to reset the self adaptation values but couldn't. Like the ECU won't allow him to do so. I don't know if it's true but could the tune be the issue? I doubt it since it has been on the car from day 1. So why all of a sudden? I will call Renntech and ask them if there is something they can do like an update or else
I'm thinking of putting my OEM filters and airboxes back to see if the CEL clears. As well I'm doubting about this being the root cause since when i installed the AFE filters and ROW airboxes i never had any CEL.
I'm running out of ideas....O2 sensors would unlikely be the problem as both would have to be at fault at the same time....
Any suggestions will be much appreciated.
#2
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I think you have a decent approach set up in that post...
Call Renntech and see what they have to say and maybe can update or reflash.
Then, I'd put the stock boxes back on just to see if that did the trick.
Then, address the issue with it possibly being the O2 sensors.
In other words, go from the less expensive option up to the most. But it seems like you know what you're doing. I'm not really sure of any other gremlins that have thrown those codes but hopefully someone who has been around longer will know of little things that could throw those codes.
Good luck
Call Renntech and see what they have to say and maybe can update or reflash.
Then, I'd put the stock boxes back on just to see if that did the trick.
Then, address the issue with it possibly being the O2 sensors.
In other words, go from the less expensive option up to the most. But it seems like you know what you're doing. I'm not really sure of any other gremlins that have thrown those codes but hopefully someone who has been around longer will know of little things that could throw those codes.
Good luck
#3
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So i did a few tests today in order to rule out all air system parts one by one.
The outcome of this is i had to revert to my OEM airboxes + charcoal delete + AFE dry filters. I did a few drive cycles (15+ mls each) and so far CEL hasn't come back!
I really have no idea why should the ROW airboxes trigger the CEL. It never did it in the first place. Why some thousands miles later?
Now the next step is to see if I'll be CEL free for a while and at the same time I'll contact Renntech to see if any tune update is needed.
The outcome of this is i had to revert to my OEM airboxes + charcoal delete + AFE dry filters. I did a few drive cycles (15+ mls each) and so far CEL hasn't come back!
I really have no idea why should the ROW airboxes trigger the CEL. It never did it in the first place. Why some thousands miles later?
Now the next step is to see if I'll be CEL free for a while and at the same time I'll contact Renntech to see if any tune update is needed.
#4
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07 E63 + 07 CLK63CAB
Possible the dealer removed the air boxes for access and then did not reseal them properly. Were the intake connector clamps displaced allowing air on the back side of the MAF ?
#5
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No everything was fine. Dealer ran several smoke tests to find any leaks but couldn't get none.
One thing weird (which is actually the root cause of the CEL) is when i checked my fuel trims SFT/LFT values (ROW airboxes + AFE filters) with my OBDII reader my short term values were lower than my long term values that would increase continuously until the max adjustement (>+25%) which triggered the lean condition CEL. In contrary with OEM airboxes + AFE filters my SFT and particularly LFT were as expected very close to 0.
How come this is happening? My understanding of fuel trims is LFT are basically based out of SFT trends and is a learn value where SFT are more instantaneous fuel trim corrections based on O2 sensors measurements. So if your SFT are low or equal to zero during drive cycles how come the LFT is high?
Again i have no more vacuum leak, the MAFs are OK. The only difference in this test is different airboxes.... Any ideas ?
One thing weird (which is actually the root cause of the CEL) is when i checked my fuel trims SFT/LFT values (ROW airboxes + AFE filters) with my OBDII reader my short term values were lower than my long term values that would increase continuously until the max adjustement (>+25%) which triggered the lean condition CEL. In contrary with OEM airboxes + AFE filters my SFT and particularly LFT were as expected very close to 0.
How come this is happening? My understanding of fuel trims is LFT are basically based out of SFT trends and is a learn value where SFT are more instantaneous fuel trim corrections based on O2 sensors measurements. So if your SFT are low or equal to zero during drive cycles how come the LFT is high?
Again i have no more vacuum leak, the MAFs are OK. The only difference in this test is different airboxes.... Any ideas ?
#6
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2010 C63 P31 AMG
No everything was fine. Dealer ran several smoke tests to find any leaks but couldn't get none.
One thing weird (which is actually the root cause of the CEL) is when i checked my fuel trims SFT/LFT values (ROW airboxes + AFE filters) with my OBDII reader my short term values were lower than my long term values that would increase continuously until the max adjustement (>+25%) which triggered the lean condition CEL. In contrary with OEM airboxes + AFE filters my SFT and particularly LFT were as expected very close to 0.
How come this is happening? My understanding of fuel trims is LFT are basically based out of SFT trends and is a learn value where SFT are more instantaneous fuel trim corrections based on O2 sensors measurements. So if your SFT are low or equal to zero during drive cycles how come the LFT is high?
Again i have no more vacuum leak, the MAFs are OK. The only difference in this test is different airboxes.... Any ideas ?
One thing weird (which is actually the root cause of the CEL) is when i checked my fuel trims SFT/LFT values (ROW airboxes + AFE filters) with my OBDII reader my short term values were lower than my long term values that would increase continuously until the max adjustement (>+25%) which triggered the lean condition CEL. In contrary with OEM airboxes + AFE filters my SFT and particularly LFT were as expected very close to 0.
How come this is happening? My understanding of fuel trims is LFT are basically based out of SFT trends and is a learn value where SFT are more instantaneous fuel trim corrections based on O2 sensors measurements. So if your SFT are low or equal to zero during drive cycles how come the LFT is high?
Again i have no more vacuum leak, the MAFs are OK. The only difference in this test is different airboxes.... Any ideas ?
Let me know
#7
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Actually i fixed my problem. It wasn't a ECU tune problem nor a new vacuum leak. It was just my airboxes. I had unmeasured air passing the MAFs.
So that is why i recommended you to put your stock airboxes back on. If you stay CEL free for a while this would indicate the carbonio are the culprit.
So that is why i recommended you to put your stock airboxes back on. If you stay CEL free for a while this would indicate the carbonio are the culprit.
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#8
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2010 C63 P31 AMG
Actually i fixed my problem. It wasn't a ECU tune problem nor a new vacuum leak. It was just my airboxes. I had unmeasured air passing the MAFs.
So that is why i recommended you to put your stock airboxes back on. If you stay CEL free for a while this would indicate the carbonio are the culprit.
So that is why i recommended you to put your stock airboxes back on. If you stay CEL free for a while this would indicate the carbonio are the culprit.
#11
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I had modified ROW airboxes. I thought it would be cool to have the boxes completely stripped like no duct to direct the airflow through the MAFs. So i removed the black plastic tube. Well I was wrong .
Air was flowing under the MAFs. Took me time to figure out I had to put the ducting back on.Et voila! It was fixed! no more CEL.
Air was flowing under the MAFs. Took me time to figure out I had to put the ducting back on.Et voila! It was fixed! no more CEL.
#12
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2010 C63 P31 AMG
I had modified ROW airboxes. I thought it would be cool to have the boxes completely stripped like no duct to direct the airflow through the MAFs. So i removed the black plastic tube. Well I was wrong .
Air was flowing under the MAFs. Took me time to figure out I had to put the ducting back on.Et voila! It was fixed! no more CEL.
Air was flowing under the MAFs. Took me time to figure out I had to put the ducting back on.Et voila! It was fixed! no more CEL.
#13
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Well I had the boxes for a while but the mod i did was at the same time as I had the vacuum leak. And actually i was running the normal ROW airboxes for a while not the modified ones.
I hope you'll fix your issue as well.
I hope you'll fix your issue as well.
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2010 C63 P31 AMG
Ok great to know....points me in the right direction. The good thing is that through all this, they discovered an intake manifold leak and a bad 02, all covered work under warranty....a definite blessing if carbonio acted up on time. Warranty out in a few months.