One for the technical guys..

[bmw_e30_2011]

• Hi all
  I have an e30 m30 with a irritating misfire.
  Iv done the obvious cap/arm/leads/maf/fuel pump/leads/coil/i also re-adjusted my valves which cleared it sum how for 2days and now its back...
  When i wiggle the crank sensor the misfire calms down but i tryd changin it but with now joy..
  The only thing that baffles me, when im
  Driving and it starts to miss quite bad the speedo drops off???
  Just relised it today..
  Any help would be gratefully appreciat as this i do love is geting
  On my last nerve...
  PLEASEEEE
  Thanks
  J

[rich318i]

burn it!!! unless u want to pay the money. ECU might be fooked

[bmw_e30_2011]

Not the ansa i was looking for mate...The help needed is in the title

[rich318i]

Not the ansa i was looking for mate...The help needed is in the title

if you done everything that can be done id get the ECU checked or pay the money and get a cash in hand bmw man to run it on the bmw computer. give them £40 if fault found if not £10

[poolnoodle]

Send for Dr Brian

[Grrrmachine]

Ignore rich318i; he seems to think E30s somehow developed OBDII.

If your gauges act up (esp. the tacho) when it misfires, this usually indicates a power drop to the ECU. To give willnz his credit:

This means the power to the ecu is dropping off, normally caused by the main relay. Check the contacts on the main relay are clean. If it still does it, try bridging the 30-87-87 contacts on the relay mounting socket. If this cures the problem, replace the main relay. If not, let us know and we will have to go through a process of elimination to determine where the fault lies.

[bmw_e30_2011]

Mate ur a legend...il try that and see what happens....

[bmw_e30_2011]

Do i bridge with the relay back back in or just bridge where the pins should go

[Grrrmachine]

Just where the pins would go

[fowler]

DME relay could be the culprit here

[Grrrmachine]

DME relay IS the main relay

[bmw_e30_2011]

Brigde the relay idles better but still miss..

[Grrrmachine]

Next thing is to clarify what else you've "done". If this means "replace" then be careful; you mention "maf" but AFAIK M30s use AMF, not MAF, so hopefully you've replaced like for like from a known working donor. Regarding leads, you HAVE to use genuine BMW ones, even if they're 20 years old. Aftermarket ones just aren't up to the job. A new rotor and coil are good though.

Have you pulled out the spark plugs and checked their condition? They should all be a uniform coffee colour, so if one is lighter or smokey then you're getting a bad burn (lean/rich) on that cylinder. You may have a lean or rich running issue, caused either by the blue temp sensor (TEST, don't replace), or by an air leak in the intake system.

[bmw_e30_2011]

Excuse my dumbness how do i test the blue temp sensor..yes sorry afm
Was of a running m30 engine it was a like for like swap..its defenatly running rich..its now idle ok but under load its over/under fueling....it majorly misses at a certain rpm??when i rev the car at standstill you dont hear the stutter as obvious but as soon as you pull away it cloggs n stutters??

[Grrrmachine]

I don't have any direct experience with M30 engines, but their overall principle is the same as the M20. Fuelling is based on a number of sensors, and two of them can go duff; the blue temp sensor is the main one, so read about how to test it here:

http://www.e30zone.net/e30zonewiki/inde ... emp_Sensor

You NEED to test it at the ECU plug too, to make sure your wiring is sound. I've no idea what pins that is for an M30 ecu, but you should be able to find them with a search.

Other thing to check would be the throttle position switch (TPS), just in case.

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch