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Author: Subject: MAF knackered
craigdiver

posted on 13/7/18 at 04:46 PM Reply With Quote
MAF knackered

Hi all, after spending ages diagnosing idling issues on my BMW powered haynes roadster it turns out that I think the MAF is knackered. Plugged in it idles really rough and stalls if you try to rev it. unplugged the engine runs ok and revs (but quite rich).

Does this point to a faulty MAF and do I replace it with a £22 ebay special, the £160 siemens oem one or some other reputable manufacturer of MAFS (Its a Siemens 5WK9605, BMW part no 1432356).





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craigdiver

posted on 13/7/18 at 04:48 PM Reply With Quote
I have tried carefully cleaning it with MAF cleaner but no change





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mcramsay

posted on 13/7/18 at 06:32 PM Reply With Quote
Got exactly the same issue on my m3 marlin, suspected the MAF was bad and bought the 40 quid eBay special from Latvia... absolute rubbish, just made the car run extremely rich.

Waiting for payday to buy the 160 quid Bosch one

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craigdiver

posted on 13/7/18 at 06:42 PM Reply With Quote
quote:
Originally posted by mcramsay
Got exactly the same issue on my m3 marlin, suspected the MAF was bad and bought the 40 quid eBay special from Latvia... absolute rubbish, just made the car run extremely rich.

Waiting for payday to buy the 160 quid Bosch one


Iím far from a car mechanic and have limited experience with engines. Iím concerned that unplugging the MAF which seems to make it run rich. Could this be masking a different issue and not actually the MAF thats faulty? Any mechanics out there that would confirm that they would swsp out the MAF with these symptoms?





If it ain't broken, fix it anyway (just because).

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steve m

posted on 13/7/18 at 07:05 PM Reply With Quote
I bought a cheap Maf sensor for my Mondeo tdci, and wish I had bought a genuine one, as ive had no end of problems, with engine lights and limp modes, all going back to the maf obd codes,

I will be buing a genuine Ford item soon

steve





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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mcramsay

posted on 13/7/18 at 07:11 PM Reply With Quote
Unplugging the MAF will make the car run rich as the ecu will default to a base Alpha-n map which ignores the input from the MAF. Instead of determining the best fueling mix for the amount of air going in. So running rich with it unplugged is normal. But if you had an air leak on the intake this rich condition may mask it

I would check for intake leaks and make sure the IACV is clean and working and that the throttle position sensor is working correctly. A simple resistance check of the TPS will tell you this. The values will be on the net somewhere

If that fails swap the MAF

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craigdiver

posted on 13/7/18 at 07:58 PM Reply With Quote
quote:
Originally posted by mcramsay
Unplugging the MAF will make the car run rich as the ecu will default to a base Alpha-n map which ignores the input from the MAF. Instead of determining the best fueling mix for the amount of air going in. So running rich with it unplugged is normal. But if you had an air leak on the intake this rich condition may mask it

I would check for intake leaks and make sure the IACV is clean and working and that the throttle position sensor is working correctly. A simple resistance check of the TPS will tell you this. The values will be on the net somewhere

If that fails swap the MAF


That was my concern that unplugging the MAF would also mask any air leaks. Iíve had the ICV off this evening and gave it a good clean with carburettor cleaner - need to see if I can cycle the valve with the BMW diagnostic software INPA. The TPS is on the throttle body and I should be able to read the analog value with INPA.

Iíve already replaced one split vacuum tube and done a smoke test but still canít help thinking there is something else causing the rough running. Ill check to see what I can read off the MAF on the diagnostic software.

Thanks for your help, going to hold off buying a new MAF until I can do some more checks.





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tims31

posted on 13/7/18 at 07:59 PM Reply With Quote
Could you not get one from a scrappy as that would be cheaper?

Also, have you tried seeing if there are any fault codes using a OBDII reader and the Torque app? Also with Torque you can see what airflow the MAF meter is reading.





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craigdiver

posted on 13/7/18 at 08:10 PM Reply With Quote
quote:
Originally posted by tims31
Could you not get one from a scrappy as that would be cheaper?

Also, have you tried seeing if there are any fault codes using a OBDII reader and the Torque app? Also with Torque you can see what airflow the MAF meter is reading.


Iíve got INPA BMW diagnostics on my laptop - tells you everything and lets you manually operate valves, actuators, electronic thermostst etc., ill take a look tomorrow.





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mcramsay

posted on 13/7/18 at 08:13 PM Reply With Quote
You can see TPS and MAF values on INPA. I would have a look at what the short and long term fuel trims are doing on INPA aswell that will give you an idea of how far out your fueling is. Normally if you have an air leak you will see a high +number as the ecu tries to compensate for the unmetered air. It should drop back to normal values when you apply throttle as the the leak will be masked, unless itís a big leak.


Been messing around with the exact same things on my car this week with INPA and DIS GT1. These are used by bmw dealers and can read many more codes and values than the generic Obd readers/torque app Iíve got quite good with them both so if you need a hand let me know. I was reading up on this last night and may be some help

http://wiki.bavariantechnic.com/index.php?title=Engine_Mixture_Adaptations

MAFs seem to be almost a service item on BMWís so I wouldnít be surprised if it needed done

[Edited on 13/7/18 by mcramsay]

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craigdiver

posted on 13/7/18 at 09:09 PM Reply With Quote
quote:
Originally posted by mcramsay
You can see TPS and MAF values on INPA. I would have a look at what the short and long term fuel trims are doing on INPA aswell that will give you an idea of how far out your fueling is. Normally if you have an air leak you will see a high +number as the ecu tries to compensate for the unmetered air. It should drop back to normal values when you apply throttle as the the leak will be masked, unless itís a big leak.


Been messing around with the exact same things on my car this week with INPA and DIS GT1. These are used by bmw dealers and can read many more codes and values than the generic Obd readers/torque app Iíve got quite good with them both so if you need a hand let me know. I was reading up on this last night and may be some help

http://wiki.bavariantechnic.com/index.php?title=Engine_Mixture_Adaptations

MAFs seem to be almost a service item on BMWís so I wouldnít be surprised if it needed done

[Edited on 13/7/18 by mcramsay]


What is DIS GT1 used for?





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mcramsay

posted on 13/7/18 at 09:24 PM Reply With Quote
Itís the dealer software. It allows tests to be performed on different things on the car, and can run test procedures based on fault codes. Ie you can test the MAF by performing the MAF sensor check and it will give live voltage readings of the MAF at different rpms and tell you if itís within spec

The level of testing depends on the age of your car. On my m3 I can perform a vanos test procedure where it leak checks the vanos and checks the required angles are achieved in the correct time. It also links with the bmw TIS (technical documents) so you can read up on fault codes and how things are supposed to work.

Great tool, I bought my version from B cables on eBay which with INPA, GT1 and the workshop manuals / TIS documents. Must have if you own a bmw!

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craigdiver

posted on 13/7/18 at 09:26 PM Reply With Quote
quote:
Originally posted by mcramsay
Itís the dealer software. It allows tests to be performed on different things on the car, and can run test procedures based on fault codes. Ie you can test the MAF by performing the MAF sensor check and it will give live voltage readings of the MAF at different rpms and tell you if itís within spec

The level of testing depends on the age of your car. On my m3 I can perform a vanos test procedure where it leak checks the vanos and checks the required angles are achieved in the correct time. It also links with the bmw TIS (technical documents) so you can read up on fault codes and how things are supposed to work.

Great tool, I bought my version from B cables on eBay which with INPA, GT1 and the workshop manuals / TIS documents. Must have if you own a bmw!


I have the b cables software but only installed INPA, will give it a go tomorrow





If it ain't broken, fix it anyway (just because).

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mcramsay

posted on 13/7/18 at 09:41 PM Reply With Quote
Itís not very user friendly! Pm me if you need some help
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craigdiver

posted on 13/7/18 at 10:04 PM Reply With Quote
quote:
Originally posted by mcramsay
Itís not very user friendly! Pm me if you need some help


Tried running it, opened ok in a virtual window. Will hook it up to my car tomorrow and see what happens!





If it ain't broken, fix it anyway (just because).

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Irony

posted on 16/7/18 at 07:43 AM Reply With Quote
My Ford C-Max for some unknown reason used to chomp through MAF sensors. It had a new one every six months. I bought new at well over £100 and then got fed up and bought used but genuine of eBay from a breaker (£25). Always performed reasonably well.
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craigdiver

posted on 16/7/18 at 08:33 AM Reply With Quote
quote:
Originally posted by Irony
My Ford C-Max for some unknown reason used to chomp through MAF sensors. It had a new one every six months. I bought new at well over £100 and then got fed up and bought used but genuine of eBay from a breaker (£25). Always performed reasonably well.


Good advice, took your advice and just bought a used genuine siemens OEM one off of ebay. I also have a new crankcase breather valve on order to rule that out too as a common failure item along with its associated vacuum pipework.





If it ain't broken, fix it anyway (just because).

Building - BMW powered Haynes Roadster/442E hybrid.

Abarth 595
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