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Old 04-25-2019, 05:11 AM
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Join Date: Apr 2019
Location: SoCal
Posts: 13
Testing MAF values, M113 engine

It is my understanding that Air Mass (with no vacuum leaks) at idle should be 14-18 Kg/h, at 2000 rpm (in P/N) 30-45 Kg/h… driving 40mph, flooring accelerator should go to 480 Kg/h or above… and it does

In MB Star Diagnostic… set values are 10-20 Kg/h at idle… 480-580 Kg/h at 4000 rpm in 3-rd gear

When I drive the car in 3-rd gear, at 4000 rpm (80mph), steady throttle…. Air Mass is nowhere near 480-580… 250-260 Kg/h is what I see on the scanner.

The reason I ask how to test MAF… I got a new one and I'm not convinced it is working as it should.

After replacing MAF, getting rid of vacuum leaks… new O2 sensors… injectors, spark plugs… etc.

This is what I get when I accelerate in P/N… very rough when reaching rev limiter.


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Old 04-25-2019, 07:26 PM
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Join Date: Jan 2012
Posts: 7,515
What kind of root problem are you trying to solve?

Revving an engine in neutral doesn't prove much, many cars have a lower rev limit in P / N .
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Old 04-25-2019, 11:55 PM
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Join Date: Apr 2019
Location: SoCal
Posts: 13
The issue I have is that idle speed adaptation values are higher than they should be and that new MAF I just bought (from the dealer) drives them even higher than my old MAF. Too close to CEL threshold (+1.00 ms).

I'm not sure if this is causing rough running at rev limit in P / N but I suspect it might. Unless there is something else going on…
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