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Mass Air Flow (MAF) question for replacing

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Old 10-04-2013, 03:20 PM   #1
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Default Mass Air Flow (MAF) question for replacing

So I replaced my MAF on my 2002 Audi A6 2.7t. And it did not fix the problem of hesitation and jerking and bouncing within a range of RPMs.

When I had it unplugged it worked fine. Is there anything special I must do when replacing with a new MAF? I did disconnect both battery terminals is there anything I must do when putting a new MAF on my car?

Keep in mind the old MAF was doing the same thing. If I unplug the MAF it works a lot better and smoother almost normal.

Thanks
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Old 10-04-2013, 03:47 PM   #2
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Definitely check for vacuum leaks and I don't think you can completely rule out that the new one was good (I'm assuming it was used?). Or who knows maybe the connector/cable is bad? Make sure to clean all the contacts and look for bare wires.
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Old 10-04-2013, 05:59 PM   #3
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Boost leak.
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Old 10-05-2013, 04:35 AM   #4
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Boost leak.
Do you mean a leak by the turbo boost?
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Old 10-05-2013, 09:41 AM   #5
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You have a large intake leak after the MAF, so any of the intake plumbing, intercoolers, crankcase ventilation system, or intake manifold leaks will cause big problems. Disconnecting the MAF makes the engine run on preset values and leads me to believe its something between the MAF and throttle plate and not a manifold vacuum leak.
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Old 10-05-2013, 04:05 PM   #6
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You have a large intake leak after the MAF, so any of the intake plumbing, intercoolers, crankcase ventilation system, or intake manifold leaks will cause big problems. Disconnecting the MAF makes the engine run on preset values and leads me to believe its something between the MAF and throttle plate and not a manifold vacuum leak.
Ok, got some of that. I disconnected it again and runs 10 times better.

Possible places I could check for leaks? I do not have pressure test system. Could I use smoke from a cigar? Any suggestions?

Trying to get my hands around what you said. So with preset values even with leaks how does that happen to still run smoother with MAF disconnected? Should I try cleaning the new MAF I received? Or return it for another new one from where I got it? The error codes I am getting are P0103 and P0175. MAF error and system 2 rich bank 2.

Now my car has 155k miles, should I be concerned about the Diverter valves and N75 valve? Change those at this mileage? are they known to go?

Thanks for the help.
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Old 10-05-2013, 06:48 PM   #7
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So the MAF reads air coming through the intake to the engine. If the engine pulls air through a different location, like a boost hose blew off under the car, then there will be no/lower MAF signal, no MAF signal, you get codes and poor running. You unplug it, then its running on preset values, not being fooled by the lack of MAF signal.

Actual engine vacuum leaks really affect mixture directly, so even on preset values it may run too lean and run poorly. Doesnt mean thats its impossible though
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Old 10-05-2013, 06:59 PM   #8
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So the MAF reads air coming through the intake to the engine. If the engine pulls air through a different location, like a boost hose blew off under the car, then there will be no/lower MAF signal, no MAF signal, you get codes and poor running. You unplug it, then its running on preset values, not being fooled by the lack of MAF signal.

Actual engine vacuum leaks really affect mixture directly, so even on preset values it may run too lean and run poorly. Doesnt mean thats its impossible though
Ok that makes sense.

Being I don't own a pressure test system. What "DIY" could I use to help determine where leak is? Also do you think at a 155k the Diverter Valves and N75 should be replaced regardless? DO they last a long time?

Thanks for the help and understanding.
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Old 10-05-2013, 07:52 PM   #9
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Ok that makes sense.

Being I don't own a pressure test system. What "DIY" could I use to help determine where leak is? Also do you think at a 155k the Diverter Valves and N75 should be replaced regardless? DO they last a long time?

Thanks for the help and understanding.
Agreed...check for leaks and codes with VCDS. Had the exact same symptom so I purchased a new hitachi maf (now I have two because I went to a larger MAF so I have the original MAF, and a brand new Hitachi). Found it was a simple boost leak. The intercooler hose blew completely free.

Search and you will find a cheap DIY on how to test for boost leaks. You used a 3" rubber plumbing coupling, a 3" pvc cap, and a compressed air hose fitting. Very easy and cheap.
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Old 10-06-2013, 07:50 AM   #10
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Just check all the boost hoses. There are ones from the turbos to the intercoolers that blow off and loosen up the clamps. Theres hoses from the top of the intercooler to the throttle body, theres the big Y intake on top of the engine with the DVs plumbed in. Dont just look, grab and try to pull on the rubber pipes.
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Old 10-06-2013, 01:11 PM   #11
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Just check all the boost hoses. There are ones from the turbos to the intercoolers that blow off and loosen up the clamps. Theres hoses from the top of the intercooler to the throttle body, theres the big Y intake on top of the engine with the DVs plumbed in. Dont just look, grab and try to pull on the rubber pipes.
Yes I will check that out. thanks
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Old 10-07-2013, 07:55 AM   #12
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Default Propane trick to find vacuum leak

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Yes I will check that out. thanks
Get a propane torch and turn on the gas but don't light! Let the engine idle and direct the flow around the whole intake and vacuum line circuits. When the idle speed increases, you've identified the vicinity of the leak.
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Old 10-07-2013, 01:50 PM   #13
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Get a propane torch and turn on the gas but don't light! Let the engine idle and direct the flow around the whole intake and vacuum line circuits. When the idle speed increases, you've identified the vicinity of the leak.
Saw this trick being mentioned in many forums and repair advices online and can't speak for others but I didn't have any success with it whatsoever. I opened the propane valve completely and even put it directly to air intake -still no increase in rpms!

What did work is with engine off, slowly pressurize (no more than 10 psi) with compressed air each of vacuum / intake sections (i.e. breather hoses etc.) and listen for "hiss"; found a leak by camshaft adjuster gasket and half-moon seals on both sides.

Another method IMO is far more effective is to build a simple smoke machine from a glow plug in a sealed metal can (you can use cheap metal water bottles for example) filled above the plug with pure mineral oil, couple hose fittings from home depot, one for compressed air input and another for smoke output. You can buy hoses of different sizes from auto parts store. Connect the glow-plug to a 12v battery charger (external) and when smoke is being generated, slowly introduce compressed air. The output smoke can be then connected via another hose to section/area(s) in question and you will definitely see the smoke come out if there is a leak.

Just be careful, the metal bottle will get very hot

I built this all under $25 with most parts from home depot and in less than 1 hour. (see my rudimentary pic)

Just sharing my thoughts...
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Old 10-08-2013, 04:15 AM   #14
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Where on a 2002 Audi A6 2.7 are the breather hoses located?

What are they anyway? Is it the intake?

There are so many hoses, I get lost.
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Old 10-08-2013, 04:26 AM   #15
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Where on a 2002 Audi A6 2.7 are the breather hoses located?

What are they anyway? Is it the intake?

There are so many hoses, I get lost.
This is what I replaced recently, is this the breather hose your talking about? If it is where do I place air pressure or smoke?

Click the image to open in full size.
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Old 10-08-2013, 06:03 AM   #16
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Saw this trick being mentioned in many forums and repair advices online and can't speak for others but I didn't have any success with it whatsoever. I opened the propane valve completely and even put it directly to air intake -still no increase in rpms!

What did work is with engine off, slowly pressurize (no more than 10 psi) with compressed air each of vacuum / intake sections (i.e. breather hoses etc.) and listen for "hiss"; found a leak by camshaft adjuster gasket and half-moon seals on both sides.

Another method IMO is far more effective is to build a simple smoke machine from a glow plug in a sealed metal can (you can use cheap metal water bottles for example) filled above the plug with pure mineral oil, couple hose fittings from home depot, one for compressed air input and another for smoke output. You can buy hoses of different sizes from auto parts store. Connect the glow-plug to a 12v battery charger (external) and when smoke is being generated, slowly introduce compressed air. The output smoke can be then connected via another hose to section/area(s) in question and you will definitely see the smoke come out if there is a leak.

Just be careful, the metal bottle will get very hot

I built this all under $25 with most parts from home depot and in less than 1 hour. (see my rudimentary pic)

Just sharing my thoughts...
The propane won't work in the intake because at idle the butterfly is closed. The propane works fine for vacuum leaks at assorted hoses and connections after the intake butterfly.
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Old 10-08-2013, 09:55 AM   #17
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The propane won't work in the intake because at idle the butterfly is closed. The propane works fine for vacuum leaks at assorted hoses and connections after the intake butterfly.
Thank you, I learned something today. When I was troubleshooting possible vacuum leaks, I tried that trick and was not successful hence, the concoction of smoke through glow plug. But, I'll keep in mind what you mentioned here.
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Old 10-08-2013, 11:53 AM   #18
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I found alot these newer cars do not react the same when trying to use a fuel source to find the air leak. I use brake cleaner, and watch the scan tool on live data at short term fuel trim. As soon as i spray where the leak is, it will go from Adding tons of fuel (lean condition) to subtracting fuel (rich condition you created) There usually is no change in how the engine runs, thats how seamless the management systems in these are.
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Old 10-10-2013, 10:40 AM   #19
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Would all the little hoses at the back of the engine around the egr valves, sai and such like also affect the idle / vac leak issues?
You know, all the little pipes that are almost impossible to get to........
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Old 10-10-2013, 10:40 AM
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