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Discussion Starter #1
Hi Everyone

I hope someone can help. My 1997 328i Manual has a weird issue: Every now and then the car has a random, single, momentary, violent jerk when accelerating (hard or not), and also when idling. She idles sweetly, then suddenly the rev counter drops for a split second before the electronics sort themselves out and she continues to idle sweetly. Similarly, when accelerating, the car pulls smoothly and then for an instant it jerks violently (one jerk) and then continues to accelerate sweetly, as powerfully as I expect and as if nothing happened. I haven't experienced it during constant speed running, but I cannot discount it happening then as well. It’s not the aircon compressor kicking in – what I’m experiencing is more violent, like there is a momentary complete cut-off of spark or fuel. Also, it’s not cyclic, it just happens randomly every now and then. It does seem to be happening more regularly nowadays though…Say once or twice a day.

I service the car regularly and I’m very particular about the car. It’s in very good condition, with around 220 000km on the clock. It drives daily and mostly in town, but I rev it out to around 6000 say every 2nd day. I take it on the open road say once every two weeks. I changed the coil packs around 8 months ago – all 6 – after experiencing a misfire. OEM spec Bosch units. All was well after the change and the misfire gone. The plugs I also changed about a year ago (prob around 12000km ago) during a service. As mentioned, the car pulls fine – yesterday I chirped the tyres shifting from 1st to 2nd, for instance, so no power loss in general and she idles beautifully. Fuel consumption is also spot on. Just this random violent jerk every now and then. The car is stock standard, all I did was disconnect the little vacuum pipe running to the exhaust flap and blanked it off with a screw.

Any ideas? Any help will be much appreciated!

Johan
 

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Screamin demon
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883 Posts
Read live data. It could be loss of battery connection, failing altinator, bad dme, failing crank sensor, bad wireing to the injector or coil pack, bad knock sensor, or just a bad ground. Without seeing live data theres no telling.
 

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Discussion Starter #3
Thanks Spyderg0d. I'll do that. Much appreciated!
 

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Discussion Starter #4
Hi Everyone

So I took spyderg0d's advice and ran diagnostics on the car. Turns out the crank position sensor was faulty. Thanks for pointing me in the right direction, spyderg0d. Much appreciated.

The car now runs more smoothly, and pulls better as well. Seems to sound a bit more meaty as well, but that might just be me.

Anyhow, problem solved, for those who are interested.

Johan
 
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