Source of missfire? - The Unofficial BMW M5 Messageboard (m5board.com)

Evoman · 21st February 2009, 15:56

Folks,

Been replacing coil packs and stems one by one hoping that would cure the missfire on my M5T to no avail so far.

However, I found a loose connection that literally came off in my hand - what is this for and could it be the source of the missfire I wonder???

Obviously I will reconnect it though the wire is tight with minimal available for resoldering the connection pins.

Cheers

Rich

davidoli · 21st February 2009, 20:39

It looks to be one of the electric vacuum control valves .

See : http://www.realoem.com/bmw/showparts...68&hg=11&fg=45

Does your resonance flap actuate when you blip the throttle Richard ?

D

Evoman · 21st February 2009, 23:16

Hi David, does the resonance flap actuate when I blip the throttle? Well it did before I went messing! A^se

farrell · 22nd February 2009, 14:13

Discharge solenoid valve pictured & the wring to, faulty or otherwise can't cause mis-fires.

Where is the misfire within the rpm range ?
Can you drive through the mis-fire ?
Is it part or wide open throttle induced ?
Wether @ cold start or operating with coolant temp @ > 79 Deg C
will determine a diagnosis path.

Cheers
Farrell

Evoman · 22nd February 2009, 15:11

Hi Farrell

Thanks for the tips. The mis-fire is on part throttle low down the rev range, I would say around 2000-4000rpm and only when warm.

I would say the mis-fire can't be driven through unless you floor it and then it clears, so wide open throttle seems ok. Definitely no mis-fire higher up the rev range, or if there is, it clears much more easily.

So far I have removed and checked all plugs, re-gapped them to 0.6. One stem to one of the coil packs I replaced because the bottom 1cm was melted (?!) where it connects to the spark plug.

I was hoping once that and the coil on that cylinder were replaced that would be it, but oh no. So, 2 coilpacks and one stem replaced so far and a new throttle cable (previous one was fraying). MAF cleaned, new air filter, throttle bodies cleaned and balanced, valve clearances checked.

If you have some pointers where to go from here I would, it goes without saying really appreciate it!

Cheers
Rich

farrell · 22nd February 2009, 15:51

Ok Rich
If you want, I will send you 4 used but known to function coil packs to eliminate that side.
I will send you a used but known functional B38 MAF.
That will eliminate MAF.

Cost is postage only so probably less than £10
Send me your details via PM

If this does not work, we can explore other paths one step at a time.
You may not immediately hear from me due to big projects looming.
Phone me if I do not get back via pm.

Cheers
Farrell

davidoli · 22nd February 2009, 16:11

Wow ...... One big happy E34 M5 loving family !

You can't get better than that Rich ......Good luck with the misfire and please keep us updated .

D

nebpor · 22nd February 2009, 18:24

Agreed - excellent offer from Faz!

Rich - if you want to take car down to our garage in Greenock to help diagnose Cha would be happy to have a look!

davidoli · 22nd February 2009, 21:14

Great stuff Stephen .......

Best of luck getting this sorted Richard .

Efficient combustion is required for an efficient combustion engine .....it's not Rocket Science !

D

Evoman · 23rd February 2009, 01:18

Quote:

Originally Posted by farrell

Ok Rich
If you want, I will send you 4 used but known to function coil packs to eliminate that side.
I will send you a used but known functional B38 MAF.
That will eliminate MAF.

Cost is postage only so probably less than £10
Send me your details via PM

If this does not work, we can explore other paths one step at a time.
You may not immediately hear from me due to big projects looming.
Phone me if I do not get back via pm.

Cheers
Farrell

I know this board is full of gents and ladies of a more discerning and amicable nature than most, that is however a very generous offer that I will happily accept! PM on the way.

Cheers

Rich