Unusual rough running problem - BMW M5 Forum and M6 Forums
E34 M5 Discussion 1988-1995 Sedan and Touring

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post #1 of 20 Old 19th January 2013, 02:25 PM Thread Starter
AseanAero
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Unusual rough running problem

I have a short 4 km drive to the office each day.

This morning while closing the gate I noticed the idle rpm surging from 600 to 1000rpm , I turned the engine off and restarted and it was back to normal at 950rpm.

About 1km from home I was getting a hestitation on normal acceleration up to 2,500rpm , if I backed off the throttle slightly it would clear up and I continued on my way.

About 2.5km into the trip the engine rpm dropped to 400rpm at idle and then the engine cut out, it restarted on the 2nd attempt and I drove about another 300 metres before the engine stopped again this time accompanied by the smell of raw fuel.

The next attempt to restart resulted in a 3 ft long flame coming out of the exhaust (according to a startled observer) and the backfire blew 4 of the 6 ITB rubber caps off the ITB ports.

I managed to find 2 of the 4 missing caps , put them back on and tried again , the caps flew about 10 metres landing on the other side of the 2 lane road.

The next few start attempts the engine didn't want to fire at all so I decided to let the M5 sit for 10 mins while I arranged for a tow from my office with the office delivery truck.

I decided to give it one last try before towing and the engine kicked and died , 3 more start attempts and it slowly came up to normal idle speed. I then drove the M5 to the office, the hestitation was there but getting better and now smell of raw fuel.

After arriving at the office I had a meeting for an hour and I went out and started the M5 and the start and idle was totally normal.

I then disconnected the battery for 20 mins and it started straight up with a smooth idle.

What would be causing this backfire ?

To me it looks like the computer is either advancing or retarding the ignition to a point when the engine won't run.

DME fault or bad connection ? Intermittent fault with the crank sensor ? TPS ?

Anyone seen the HAL-like (2001) behaviour before ?



Tony, Aussie expat in Jakarta Indonesia

1990 E34 M5 S38B36 GA25324
GA25324
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post #2 of 20 Old 19th January 2013, 02:27 PM Thread Starter
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PS , this is the second time this has happened , the car stopped dead 20 metres from where it stopped today about 4 months ago, it took a similar time to restart but without blowing the ITB caps off the engine like today.



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1990 E34 M5 S38B36 GA25324
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post #3 of 20 Old 19th January 2013, 03:59 PM
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When we were doing compression test on Your car the fuel smell is really strong.
On my engine there was no fuel smell at all

It is said that if you line up all the cars in the world end to end, someone would be stupid enough to try and pass them.
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post #4 of 20 Old 19th January 2013, 04:01 PM Thread Starter
AseanAero
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Shhh , where supposed to disable the injection system when doing the test , in today's heat I couldn't be stuffed.

Must have been over 90% humidity today.



Tony, Aussie expat in Jakarta Indonesia

1990 E34 M5 S38B36 GA25324
GA25324

Last edited by AseanAero; 19th January 2013 at 04:02 PM.
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post #5 of 20 Old 19th January 2013, 04:17 PM
BlueBiturbo
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Hahahaha

It is said that if you line up all the cars in the world end to end, someone would be stupid enough to try and pass them.
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post #6 of 20 Old 19th January 2013, 08:20 PM
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Unusual rough running problem

You shouldn't drive at all without those caps for the ITBs in place. You will have a tremendous vacuum leak on that cylinder otherwise.
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post #7 of 20 Old 19th January 2013, 10:35 PM
Sub8
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Check the crank damper nut is tight.

Check that the rubber in the damper is not split.

check that the woodruff key is still locating the damper correctly.
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post #8 of 20 Old 20th January 2013, 08:13 AM
BlueBiturbo
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Throw away Your Throwing Strars wheel, install turbine wheels. Idle problems will disappear.

It is said that if you line up all the cars in the world end to end, someone would be stupid enough to try and pass them.
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post #9 of 20 Old 20th January 2013, 12:51 PM
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Possible issues around Crank sensor, as Sub8 is alluding to... Hopefully sensor rather than the mechanical stuff, if that is the area of concern.
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post #10 of 20 Old 20th January 2013, 05:53 PM Thread Starter
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Quote:
Originally Posted by Nikosx View Post
You shouldn't drive at all without those caps for the ITBs in place. You will have a tremendous vacuum leak on that cylinder otherwise.
I realise that , however the person that turned up to tow me from the office is a bit of a dill so I weighed up the pros of driving 1km with 2 ITB caps off (I found the other 2) or getting the front of the M5 pulled off with the office pick up, I drove it the 1km



Tony, Aussie expat in Jakarta Indonesia

1990 E34 M5 S38B36 GA25324
GA25324
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