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Old 19th January 2013, 14:25   #1
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 ?
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1990 E34 M5 S38B36 GA25324 Schwarz II, 57,000kms, Tropical version, full Nappa leather interior, Superchip , staggered M-Par 235/40 ZR18 , 255/35 ZR18 Toyo T1-Sport. Mods : exhaust system - packing removed from centre + rear mufflers, Restoration items: Reinstall the SLS, interior tidy up, Bodywork : repair small dents and re-coat in the original color (done - February 2014)
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1991 E34 M5 S38B36 GA25388 Schwarz II. Non running 1/2 share parts car / track car project with BlueBiTurbo (Taffy)
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1995 E34 530i 5 speed Daytona Violet 170,000kms , TS staggered set up, M-Tech steering wheel mods planned: ENGINE: M60B40 (purchased), chip EXHAUST : 110mm big bore front Y pipe (done), centre muffler gutted (no packing), used M5 rear muffler (done) BRAKES: slotted + drilled discs TYRES: 235/45 ZR17 , 255/40 ZR17 Toyo T1R - my daily driver and a car that I can play with and modify. Long term dream - full E39 M5 drivetrain. Will be repainted Sebring Grey with black lower trim and full M5 bodykit.
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Old 19th January 2013, 14:27   #2
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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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Old 19th January 2013, 15:59   #3
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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
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Old 19th January 2013, 16:01   #4
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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.

Last edited by AseanAero; 19th January 2013 at 16:02.
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Old 19th January 2013, 16:17   #5
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Hahahaha
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Old 19th January 2013, 20:20   #6
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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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Old 19th January 2013, 22:35   #7
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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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Old 20th January 2013, 08:13   #8
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Throw away Your Throwing Strars wheel, install turbine wheels. Idle problems will disappear.
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Old 20th January 2013, 12:51   #9
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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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Old 20th January 2013, 17:53   #10
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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
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