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MAF diagnosis

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Old Jun 7th, 2019, 13:59   #1
Devonsteve
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Default MAF diagnosis

Hi guys, further to my massive power loss problem on my 2011 Xc90, I'm checking out the MAF now. Have a few questions if anyone about....
If you unplug the electrical connector to the MAF sensor, the engine should stop shouldn't it?
Is the sensor actually part of the plastic body?
There are ECMS bolted to the top of the air filter housing, are these OK to unplug to remove airbox, and should I disconnect battery first?
Hope someone about as just come in for a quick cuppa 😊👍
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Old Jun 7th, 2019, 14:29   #2
XJSDriver
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If you unplug the MAF the engine should still run as it will default to preset value. You can unplug the ECU on top of the filter but I leave well alone as able to move the airbox enough to remove the air filter.

If you do need to unplug connectors suggest you disconnect the battery and wait 15 minutes for everything to shutdown so you do not risk upsetting anything.
Loads of post on this in the forum.

These things can be difficult to diagnose so suggest you plug in Vida to see what fault codes there are. Good luck.
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Old Jun 7th, 2019, 14:35   #3
Devonsteve
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Default Maf

Quote:
Originally Posted by XJSDriver View Post
If you unplug the MAF the engine should still run as it will default to preset value. You can unplug the ECU on top of the filter but I leave well alone as able to move the airbox enough to remove the air filter.

If you do need to unplug connectors suggest you disconnect the battery and wait 15 minutes for everything to shutdown so you do not risk upsetting anything.
Loads of post on this in the forum.

These things can be difficult to diagnose so suggest you plug in Vida to see what fault codes there are. Good luck.
Unplugged the MAF while running and it runs but surges on tickover. Haven't disconnected it while engine off mebbe that be different. My plan was to put it on vida but can't get it to install. I had it at the dealers for an oil service 2 weeks ago and asked them to diagnose it. They said my swirl flap sustem all needs replacing? Pretty sure this won't cause the massive drop of power I'm getting. Not sure they know what they doing hence the diagnosing from home.
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Old Jun 7th, 2019, 15:00   #4
XJSDriver
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These engines are complex so proper diagnosis essential hence Vida, however there are some basic checks you can do e.g. ensure all vacuum pipes are attached and no obvious leaks, but more importantly is the bottom turbo hose intact - can you hear any hissing when revving and getting the turbo to kick in . - many posts on this fault which causes massive power loss.

As you suspect, swirl flaps cause some small issues but not a massive power loss; you might be in limp mode which I think can only be reset using Vida as happened to me when car in accident and garage disconnected ECUs at some point and car then went into limp mode when I got it back.
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Old Jun 7th, 2019, 21:27   #5
cheshired5
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You don't need Vida to at least view the swirl arm operation so look at it from start up and at various revs to check its operation.

A cheap ELM327 paired to your phone will show live MAF data so you don't need Vida for that either.
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Old Jun 7th, 2019, 23:11   #6
Devonsteve
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Quote:
Originally Posted by cheshired5 View Post
You don't need Vida to at least view the swirl arm operation so look at it from start up and at various revs to check its operation.

A cheap ELM327 paired to your phone will show live MAF data so you don't need Vida for that either.
Another possibility is the stepper motor for the flaps. After coming back from the main dealers diagnosis I saw the arm was off and had been for some time. Not sure the motor is ok as when I rev gently the arm moves but doesn't hold position but goes back to its start position regardless of the revs.
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