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Discussion Starter · #1 ·
Hi Everyone!
I have a major issue! Diagnosed a bad MAF last week it won't make any difference when plugging in or unplugging when engine is running, now i plugged in a brand new one and the car won't start at all!

Any ideas anyone?
 

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What was the problem that led you to replace the maf? Did you try the original again? If your intake boots are old and brittle, you could have broken one swapping out the maf.

Sent from my S61 using Tapatalk
 

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Discussion Starter · #7 ·
What was the problem that led you to replace the maf? Did you try the original again? If your intake boots are old and brittle, you could have broken one swapping out the maf.

Sent from my S61 using Tapatalk
My super low MPG led me to change it. Yes tried the original again, it fires up but MAF codes pops up on OBDII readers.

We tried the brand new one, and one from a friends perfectly running e46 and same with both, it doesn't start. It does crank up but doesn't idle, it just stalls in 2 secs.
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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It sounds like you have a large vacuum leak somewhere.
  • Car starts and runs with MAF unplugged. With the MAF unplugged the DME uses internal fuel mix tables. These are rich and can compensate for lean condition caused by vacuum leaks.
  • Car starts and runs with old MAF. If the old MAF is over reporting, then that will cause rich conditions. These rich conditions and can compensate for lean condition caused by vacuum leaks.
  • Car will start but not idle/run with new MAF. The fuel mixture is too lean due to a large vacuum leak. Try gassing the engine (holding down the accelerator) while trying to start the car. If you can get it to run, than that supports the large vacuum leak diagnosis

Also read through this excellent thread: Fuel trims, lean codes, misfires and how to diagnose
 

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Large vacuum leak or even more likely is a broken intake boot. If it's old and brittle, it's possible broke it when you disturbed it replacing the maf. A common place to fail is the small branch that goes to the idle control valve. That causes an extremely lean idle fuel mixture. A smoke test will get this figured out quickly.

Sent from my S61 using Tapatalk
 

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Discussion Starter · #10 ·
It sounds like you have a large vacuum leak somewhere.
  • Car starts and runs with MAF unplugged. With the MAF unplugged the DME uses internal fuel mix tables. These are rich and can compensate for lean condition caused by vacuum leaks.
  • Car starts and runs with old MAF. If the old MAF is over reporting, then that will cause rich conditions. These rich conditions and can compensate for lean condition caused by vacuum leaks.
  • Car will start but not idle/run with new MAF. The fuel mixture is too lean due to a large vacuum leak. Try gassing the engine (holding down the accelerator) while trying to start the car. If you can get it to run, than that supports the large vacuum leak diagnosis

Also read through this excellent thread: Fuel trims, lean codes, misfires and how to diagnose
Thanks for your replies mate!

Yes it does start while gassing it.
What should i look for with regards to the vacuum leak apart from the intake boot?
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Build a smoke test machine!
 
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