Maf 101

Sockets said:

Great thread!! Learned much!
Being new here I have a couple of questions. I am dealing with a '06 Jetta.
1) Does MAF sensor have anything to do with EGR valve?

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No. The MAF sensor measures clean fresh air being pulled into the engine. The EGR valve regulates exhaust gases.

2) what is a VAG-COM? Does it read engines codes on a TDI? If so how much do they cost and where can I get one? Are they worth having one?

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Many questions about VAG-COM (aka VCDS) will be answered here: http://www.ross-tech.com/vag-com/vag-com-faq.php

The hardware is cheap -- a cable from the OBD port to your laptop or tablet computer. The software is proprietary, so is the major expense. Whether you need VCDS depends on your circumstances and how convenient it is for you to have someone else check out error codes for you.

3) Does chipping have any effect on the MAF sensor?
I am having no power until 2000 RPM and the boost does kick you back into the seat with heavy black smoke through 3rd gear. Would MAF sensor have anything to do with this.

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Probably not. With a bad MAF sensor you would likely experience reduced power at all RPMs. But the engine computer could be receiving bad data from other sensors -- check all vacuum hoses. And check the N75 turbo boost controller for cracks. They are relatively cheap to replace.

VWjimmy said:

I posted earlier with a bad MAF, bought a new one, and replaced the old one.

With the new MAF, the engine is overall smoother and more powerful than before with the old MAF. That said, I'm still getting MAF codes, the engine is still somewhat jerky and prone to throwing tons of smoke and be gutless when I'm in higher gears--conditions that don't change whether MAF is plugged in or not. (For instance, when driving above 40 MPH, if I want to accelerate and push the accelerator halfway down, the car belches smoke--like, people change lanes and drive by and give me the finger, etc.)

Since the new MAF is better but still problematic, does this suggest a vacuum problem? Or could bad injectors be an issue? Or...?

Thanks, y'all.

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I'm working on the same issue. New injectors and tune has been double checked. Got a 3bar map coming Monday so once I get chips for the ecu I'm going to get it installed. If you wanna keep me in mind and message me in about 2 weeks I can let you know if it helped.

What fuel economy are you getting with it that way?


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TornadoRed said:

No. The MAF sensor measures clean fresh air being pulled into the engine. The EGR valve regulates exhaust gases.

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On PD engines they are indirectly related.
1. The ECM has no way of measuring the EGR flow directly.
2.- the ECM uses the MAF reading drop to be within an expected value when the EGR is operating. There is a drop in fresh air flow because recirculated exhaust is fed to the engine. This drop in flow is proportional to EGR duty cycle, rpms, load, etc
3.- the oxygen sensor located downstream also helps the ECM trim EGR operation.

So when you block your EGR off without a tune uour ECM throws a CEL because the ecm is no reading the drop in MAF readings it is expecting.

So it is possible for a stuck open egr to mess with the maf readings.

Carlos_TJ said:

On PD engines they are indirectly related.
1. The ECM has no way of measuring the EGR flow directly.
2.- the ECM uses the MAF reading drop to be within an expected value when the EGR is operating. There is a drop in fresh air flow because recirculated exhaust is fed to the engine. This drop in flow is proportional to EGR duty cycle, rpms, load, etc
3.- the oxygen sensor located downstream also helps the ECM trim EGR operation.
So when you block your EGR off without a tune uour ECM throws a CEL because the ecm is no reading the drop in MAF readings it is expecting.
So it is possible for a stuck open egr to mess with the maf readings.

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Okay, that makes sense.

Thanks for the tips. initially the symptoms seemed to point to the MAF. loss of power and periodic idle issues. I tested the MAF and attempted to start unplugged and no change. I looked at the timming belt and the notch marks for the injection pump is 9 teeth off from the gear and the crank is 8 off the marks from gear to belt. I presume that I loss timing and thus it turns over but wont start. I have a strong battery and white smoke coming out of the pipe but no start up attempts, just chugs. I interpret this to mean that I have fuel and battery power. Any tips or suggestions?
Hector 262-215-3915

Suspected bad MAF. Replaced with new one, and all is well. I noticed a slight oil film in the one that I removed. Where would the oil come from? I'm worried about this since I don't want my new one to die early due to oil being introduced. It's a very light film, and only see it when I wipe my finger around the inside of the housing. I do have 330k on the car, and just recently had the TB changed and the intake cleaned. For about a week, the car ran like it did 10 years ago. I had no idea that I had lost so much power. Today, the CEL came on, and the power was gone.(not limp mode)

You have a stock air filter right?
Nothing of those washable re-usable ones?

spanky, you even have an air filter? Like you're running on oil-sprayed [dusty/dirt] roads w/o one!

Yep, just the standard dry air filter. Might actually be branded by STP, probably from Auto Zone.

No oil sprayed roads at all.

One possible source of tainted air that can reach the MAF is the vent for the
vacuum system that connects to the airbox. This can be left off when removing
and replacing the airbox and let unfiltered air in. Don't know about oily, though.

Hello MAF Gurus,

I'm looking for some help from you.

I have a Audi 80 1.9 TDI, franken 1z, with vnt17, AFN ecu - 68 pin, 150 pd intake, afn injectors, ahu ip.

Few days ago I had some MAF problems, and now MAF needs replacemant.
From what I understand there is a difference between 90 HP MAF (7.18221.01) and 110 HP MAF (7.18221.51.0).1z/AHU maf reads until 850 mg/st...and AFN should read until 1250 mg/st, or something similar.
I think it's a must to hook up VCDS and see how much it reads.
Is this correct? there are different PN and 1z one is 6 pin, the other one is 5 pin.
Did someone do the conversion from 6 pin maf to 5 pin? Is it even possible?