MAF= 25% lean...possition issue?
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From: Phoenix, AZ USA
MAF= 25% lean...possition issue? For a few months now I had been running my truck with the MAF directly on/in front of the TB and an cone filter on the end of the MAF. Everything was working fine.
Last weekend I swapped from the truck manifold to an LS6 manifold which required installing a 90degree bend between the MAF and the TB. Now I'm showing massive lean (15-25%...pegs LTrims) condition with the MAF. I can unplug the MAF, drive (not very well.....stumbles at idle but does ok off idle), and see almost 0-LTrims (I'm forcing the system into closed loop and into learn mode). When I plug the MAF back in, LTrims quickly move back to 15%+. This isn't localized to just low throttle/idle either. It seems to be across the entire range.
Could the location (being so close to the 90) be causing the MAF to read poorly? I'm rather shocked since I see people mount MAFs right off of 90s on supercharger/turbocharger setups.
When I skew the MAF table (mult by 1.25), the LTrims come down (actually slightly rich in some places) yet I also get some areas (I think in deceleration areas) that still show lean (at locations <35kPa MAP readings).
Thanks,
Chris
Last weekend I swapped from the truck manifold to an LS6 manifold which required installing a 90degree bend between the MAF and the TB. Now I'm showing massive lean (15-25%...pegs LTrims) condition with the MAF. I can unplug the MAF, drive (not very well.....stumbles at idle but does ok off idle), and see almost 0-LTrims (I'm forcing the system into closed loop and into learn mode). When I plug the MAF back in, LTrims quickly move back to 15%+. This isn't localized to just low throttle/idle either. It seems to be across the entire range.
Could the location (being so close to the 90) be causing the MAF to read poorly? I'm rather shocked since I see people mount MAFs right off of 90s on supercharger/turbocharger setups.
When I skew the MAF table (mult by 1.25), the LTrims come down (actually slightly rich in some places) yet I also get some areas (I think in deceleration areas) that still show lean (at locations <35kPa MAP readings).
Thanks,
Chris
There is a possibility that airflow bias from the 90
bend, is skewing the MAF reading - particularly if
descreened.
But if this is the case, then rotating the MAF in
place should vary the airflow distribution vs the
sense bridge elements, and change things. Maybe
there is a "magic orientation" that is closer to the
original airflow:frequency relation. Might give it
a try and see (try 90 degree increments?).
bend, is skewing the MAF reading - particularly if
descreened.
But if this is the case, then rotating the MAF in
place should vary the airflow distribution vs the
sense bridge elements, and change things. Maybe
there is a "magic orientation" that is closer to the
original airflow:frequency relation. Might give it
a try and see (try 90 degree increments?).
Launching!
Joined: Jan 2002
Posts: 299
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From: Detroit, Murder City
Any change to the intake plumbing upstream of the MAF sensor element will likely change the correlation between output Hz and actual g/s airflow. this means that you will need to recalibrate the MAF curve in the PCM whenever you change airboxes, ducting, elbows, whatever so that the PCM knows the actual airflow even when the input Hz has changed.
The best way to do this is in forced open loop on a dyno, using a good quality wideband and steady state measurements at each Hz breakpoint.
The best way to do this is in forced open loop on a dyno, using a good quality wideband and steady state measurements at each Hz breakpoint.
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From: Phoenix, AZ USA
Bad Intake Gaskets.....
I removed the intake last night and on comparison of the old vs. new gaskets, the old ones were about half as thick and rather stiff. Installed new gaskets and the LTrims are back where they should be (mostly).
I did still have to add 10% to the MAF table (just did a blanket multiply by 1.10) to see consistent negative Trims. I will check everything again in a week or so after the computer has time to get a good history in it. At current I'm seeing 0.0 to -1.5 without MAF and 0.0 to -3.5 with MAF. Only positive Trims are during deceleration which I'm attributing to DECO being on.
Thanks guys.
I removed the intake last night and on comparison of the old vs. new gaskets, the old ones were about half as thick and rather stiff. Installed new gaskets and the LTrims are back where they should be (mostly).
I did still have to add 10% to the MAF table (just did a blanket multiply by 1.10) to see consistent negative Trims. I will check everything again in a week or so after the computer has time to get a good history in it. At current I'm seeing 0.0 to -1.5 without MAF and 0.0 to -3.5 with MAF. Only positive Trims are during deceleration which I'm attributing to DECO being on.
Thanks guys.
Thread Starter
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From: Phoenix, AZ USA
Update: I have been having some "funny spots" that go lean now and then. Tonight I was hit with a MAF error saying it was Lean. Just the rule out a dirty MAF sensor, I decided to remove the air filter and spray the resistors with some electrical parts cleaner.
The engine was idling and LTrims were ~ -0.8%. The moment I removed the conical filter off the MAF, the engine stumbled and the LTrims pegged at 25%. I sprayed the resistors off and reinstalled the filter on the MAF. As soon as the filter was on, the LTrims came back to -1%.
So, it looks like a MAFs proximity to either bends in the tube, or more importantly the location of the filter element can have a significant impact on the MAFs ability to read correctly.
The MAF I'm using is the Z06 MAF that comes from the factory "de-screened". There might (would guess there is) be less of an issue with a "screened" MAF but I can't say for sure.
The engine was idling and LTrims were ~ -0.8%. The moment I removed the conical filter off the MAF, the engine stumbled and the LTrims pegged at 25%. I sprayed the resistors off and reinstalled the filter on the MAF. As soon as the filter was on, the LTrims came back to -1%.
So, it looks like a MAFs proximity to either bends in the tube, or more importantly the location of the filter element can have a significant impact on the MAFs ability to read correctly.
The MAF I'm using is the Z06 MAF that comes from the factory "de-screened". There might (would guess there is) be less of an issue with a "screened" MAF but I can't say for sure.
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You could relocate the MAF forward in the pipe, if your
lineup has that kind of room. Right up in the air filter box
even, anywhere it looks like diffuse and straight. Might
even get a better IAT behavior if it were out of the
engine bay heat.
lineup has that kind of room. Right up in the air filter box
even, anywhere it looks like diffuse and straight. Might
even get a better IAT behavior if it were out of the
engine bay heat.
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