Duramax Diesels Forum Truck of the Week
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Old 03-25-2020, 04:16 PM
Kunz111 Kunz111 is offline
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Default Low maf reading

So I did a turbo swap on my 09 lmm and when I was done I flashed my new tune to the truck for the turbo swap. Started it and went for a test drive and it had no power, no smoke, and no codes. So I grabbed my scan tool started to look over live data. Noticed the maf was jumping all over, 0 to 75 to 15 to 170 and this was just at idle. So I figured maf was junk, got a new Delphi in and then went for a drive again. Still no power, no smoke, no codes. So put the scan tool back on and the maf at idle reads 14-17g/s, brake boost it and with the truck floored the best it will do is 37-40g/s. If I do out and floor it and keep it floored for awhile the rpms will get up to a point and then all of a sudden the truck starts to buck, the turbo starts to spool up and make some boost some smoke out the back. So I contacted my tuner he said that in very rare occasions heís see issues with mafs on lmms and the only way to get rid of the issue is to tune it out pretty much. so he sent me a mafless tune file, flash it in, and it still reads and acts the same way. Talked to the tuner again, he said that it has to be a wiring issue. I ordered up a brand new ecm harness from GM, put it in, and flashed my first tune file back on, maf still reads very low, no power, no codes. I had a new ecm laying around installed that and flashed it to factory GM programming and then flashed it with efilive and maf reading is still the same. So Iím at lost here. Just for shits and giggles I installed the first maf that was jumping around all over to see what it would read and it still jumps all over like it did before. So I have no idea what to do or look for at this point. If someone has any ideas please let me know. I do have videos of scan data if anyone wants to see those. Q
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Old 03-25-2020, 04:35 PM
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Sounds like the first sensor was junk but the maf calibration needs to be raised to match the intake you have on it since it is reading about half of what it should be at idle. That's where I would start with it.
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Old 03-25-2020, 05:00 PM
Kunz111 Kunz111 is offline
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Quote:
Originally Posted by MarkBroviak View Post
Sounds like the first sensor was junk but the maf calibration needs to be raised to match the intake you have on it since it is reading about half of what it should be at idle. That's where I would start with it.
That was the first thing the tuner asked was what intake I am running so Iím assuming that part has been taken care of, heís a very knowledgeable guy.
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Old 03-25-2020, 06:27 PM
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do you have a egr blocker plate?
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Old 03-25-2020, 06:50 PM
Kunz111 Kunz111 is offline
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Quote:
Originally Posted by Tothemax View Post
do you have a egr blocker plate?
Full hsp piping kit on the truck with a 10mm cp3, lift pump, downpipe, exhaust, and marks 63.5 stage 2 turbo
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Old 03-25-2020, 09:09 PM
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Check voltage on the 5v ref circuit at the maf connector
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Old 03-25-2020, 09:27 PM
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Quote:
Originally Posted by juddski88 View Post
Check voltage on the 5v ref circuit at the maf connector
And the low reference ref also. You have to have a steady 5v, and a good ground (low reference) in order to get an accurate MAF reading. The face that the reading is erratic tells me there is a circuit problem.
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Old 03-26-2020, 06:57 AM
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What kind of harness did you buy? I have seen a lot of problems on LMM truck with the wires to the MAF sensor breaking right at the connector. It is hard to tell though because the insulation is still intact.
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Old 03-26-2020, 07:07 AM
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See if this helps
Attached Images
File Type: jpg Screenshot_20200326-100649.jpg (94.2 KB, 26 views)
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Old 03-26-2020, 07:39 AM
Kunz111 Kunz111 is offline
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Quote:
Originally Posted by JoshH View Post
What kind of harness did you buy? I have seen a lot of problems on LMM truck with the wires to the MAF sensor breaking right at the connector. It is hard to tell though because the insulation is still intact.
Bought the harness right from the dealer.

Iíll check the 5v and ground wires tonight after work.
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Old 03-26-2020, 05:36 PM
Kunz111 Kunz111 is offline
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Just checked power and ground with my power probe. Everything checks out good.
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Old 03-26-2020, 07:09 PM
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What was the voltage on the 5v circuit?
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Old 03-26-2020, 07:16 PM
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You can also jump the 5v and reference wires and monitor what the ECM sees. Should also set an appropriate code too if the signal is steady enough
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Old 03-27-2020, 06:42 AM
Kunz111 Kunz111 is offline
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12v on the power wire and 0 on the ground. Tested by back probing the connector with T pins and KOEO
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Old 03-27-2020, 07:56 AM
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It sounds like the sensor calibration is off. What size is the pipe on your intake where the sensor is mounted? This may be a dumb question, but you don't have any open ports in the intake where it could pull in air after the MAF do you? Are you sure the MAF is facing the right direction? I know you said you got a new Delphi sensor (should be good, but is it possible you got a bad sensor out of the box? Do you have a buddy with an LMM you could trade sensors with to test it?
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