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BMW E36 1.8i S 1994 - Misfire on cylinders 2 & 4 - Fixed #

Posted by Jim Power on May 15, 2012, 1:42 pm

Year of Manufacture *: 1994
Engine Size and Code *: 1.8 Eng code 18 4S 1
( Optional ) ECU Type: Bosch M1. 7.2
( Optional ) Scanner Used: Snap on, Pico
( Optional) Fault Codes: Misfire

Hi all
Any suggestions appreciated on this 1994 318.
It has a complete misfire on cylinders 2&4 No injector firing signal from the ecu on pin no 3.

I have good fuel pressure, good spark, injectors resistance check out ok, have swapped them around anyway, cam and crank signals good. Have eliminated the plugs and HT leads. Triggers to coil pack all look ok to my not so experienced eye as does secondary.
So I am thinking ecu as the owner says this problem started after he power washed the car, recovered for a while but then misfiring again.
I did open the ecu and it dosent look too good.
What is making me a little hesitant is, on start up, there is one or two firing events on pin 3 before it goes dead and I can force an output with the scanner.
So, have I missed something that is causing the ecu to shut off this pin
Any thoughts appreciated
Jim
PS apologies for the long story.

Re: BMW E36 1.8iS Misfire 2&4

Posted by Fiachra Purcell <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3006' width='330' height='300' border=0 style='border:none;'> on May 15, 2012, 1:59 pm, in reply to "BMW E36 1.8iS Misfire 2&4"
Fiachra Purcell

Hi.
If you post your captures some of the more experienced Pico users might help you.
Can you see what kind of current the affected injector is pulling.
There was a recall on the 318is regarding lucas injectors (orange band on injector). They were drawing too much current and the ECU was shutting down the injectors. The resistance was always within spec.
I know it's a long shot but you never know.
Regards.
Fiachra.

Re: BMW E36 1.8iS Misfire 2&4

Posted by James Eardley <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3143' width='330' height='300' border=0 style='border:none;'> on May 15, 2012, 9:28 pm, in reply to "Re: BMW E36 1.8iS Misfire 2&4"
James Eardley

Hi Jim

What about the wiring?
I have found resistance testing is mostly pointless unless open circuit.

Voltage drop testing (under load) is the most accurate.

Post some scope captures. Pico will easily capture the whole event, making sure you measure voltage and current.

When you say the ECU dosent look good do you mean there is corrosion, I believe this sort of year BMW suffered with damp in the ecu. If the circuit board is corroded I think you may have found your problem if not lets see some scope captures

Regards
James

Fixed #

Posted by Jim Power on May 16, 2012, 11:29 pm, in reply to "Re: BMW E36 1.8iS Misfire 2&4"
Message modified by board administrator May 23, 2012, 3:19 pm

Hi
Thanks to Fiachra and James for the replies.
ECU was the problem. replaced and all fine.
Thanks again, Jim.

Re: Fixed #

Posted by mike howdle on May 20, 2012, 3:56 pm, in reply to "Re: BMW E36 1.8iS Misfire 2&4 Fixed"
Message modified by board administrator May 23, 2012, 3:23 pm

Yes I had a similar ecu go while I was testing the car!! Imagine the repercussions.
It took a long time to convince that customer that I had not caused it with the scan tool!!
Mike
It also took the same 2 cylinders

Re: Fixed #

Posted by jim power on May 21, 2012, 8:12 am, in reply to "Re: BMW E36 1.8iS Misfire 2&4 Fixed"
Message modified by board administrator May 23, 2012, 3:23 pm

Yes Mike,I know the feeling. This one had missfiring issues about 4 months due to low fuel pressure. New fuel filter and pressure regulator sorted it that time but of course the owner was convinced it was the same problem again.

I think it had probably been runing on low pressure for a while and the higher pressure after the repair probably showed up the weakness on the ecu circuitary.

It does have the orange band on the injectors as said by Fiachra but current draw is just under 9A, uniform across all 4 injectors. All well now anyway.
Jim

Re: Fixed #

Posted by Fiachra Purcell <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3006' width='330' height='300' border=0 style='border:none;'> on May 28, 2012, 9:12 pm, in reply to "Re: Fixed #"
Fiachra Purcell

Hi.
From memory (don't forget it was a long time ago 1995) what was happening was that the injectors were drawing slightly too much current causing a bigger inductive kick spiking the ECU which would falter and struggle to control the idle control valve. It would only happen once in a blue moon.
The only reason I remember is because it nearly drove me over the edge.
I wondered for years how BMW figured it out (the fix was a TSB I did not find the problem).
The power of a scope and somebody who knew how to use it.
I'm glad you got it sorted.
Fiachra.

Re: Fixed #

Posted by jim power <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3202' width='330' height='300' border=0 style='border:none;'> on May 28, 2012, 11:07 pm, in reply to "Re: Fixed #"
James Power

Hi Fiachra
Yes, I can see why you remember that one.
This one would have three, four, maybe five firing events before it would go flat line which made me wonder if the ecu was seeing something it didnt like, put the seed of doubt in my mind. Would not have seen this without the scope.
A brilliant tool no doubt, but it takes a good bit of practice and a sharp eye before you could say you had a good hand on it. Its like everything, the more I use it the more is learned.
Thanks again
regards Jim.

jim power

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