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Strange Misfire On Mpi Mini


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#1 badnap

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Posted 14 September 2017 - 06:38 PM

Hello everyone,
I've got a strange misfire that I can not figure out, and I thought it would see if anyone has some ideas.
It is a 98 Mini with the MPI fuel injection.
The car has dead miss on cylinders 3 & 4.
Here is what I know:
I first replaced the plugs and wires because they were blasted out anyhow
Then I checked to verify that I had spark - I do on all 4
Then I checked my fuel injectors for power and ground - Noid light flashes the same for both injectors. So, I then switched the injectors to see if the misfire would follow, and it doesn't.
After that I did a compression and leakdown test, both passed perfectly.
So still baffled, I then removed the coolant temperature sensor and tested it - passes fine. Check IAT sensor - passes test. Checked TPS sensor - passes test.
What I found out then is that cylinders 3 & 4 are being heavily washed out with fuel. Both pistons are very much cleaner than 1 & 2, and when I unplug cylinder 3&4 injector the idle smooths out instantly, just for a few seconds until all the fuel is burnt up and then it resumes its misfire.
Any thoughts would be greatly appreciated. Thanks!

 

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#2 FlyingScot

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Posted 14 September 2017 - 06:43 PM

Unscrew and swap the physical injectors in the inlet. This is in case you have an injector fault for 3 and 4.

FS

#3 badnap

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Posted 14 September 2017 - 08:43 PM

I have done that... no change :goaway:



#4 FlyingScot

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Posted 14 September 2017 - 09:06 PM

I have done that... no change :goaway:

Okay missed that sorry

Mechanically are all settings correct- valve clearances etc?
Otherwise if problem remains despite changes you need to have ECU checked as injector driver circuit sounds suspect.

FS

#5 AeroNotix

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Posted 15 September 2017 - 12:39 PM

Not got an answer but isn't unplugging injectors while the car is running quite dangerous as the compression may continually heat up the cylinders/pistons to the point of breakage?



#6 bigchief3679

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Posted 10 November 2017 - 01:17 AM

Has this been resolved?

Had a similar problem with an Spi with loose Vacuum servo banjo bolt, both cylinders 3 and 4 would lean out though.......worth a check as the MPI vacuum take-off is on the same runner with a quick release fitting whose ring easily cracks with heat.






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