Hi all
I have recently changed my timing belt, water pump and hoses on my 1988 325i following the wiki guide plus replaced my noisy alternator whose bearings chirped off load
In these crazy times not had a lot of running as it isn't my daily driver but managed a short run to local shop today for those essential items.
Car starts and idles fine but I had a misfire at 3000rpm the brief chance I had to rev it. Using light throttle it didn't happen but being an automatic it changed around 2000rpm anyway on the 30 limit roads.
Whilst I had it stripped back I relocated my C191 plug back into its bracket as it has always been connected outside of it during my ownership.
So question being where to look? Could a poor connection in the plug cause a misfire?
I was sure the timing marks lined up, turned it with spanner on crank at least 4 times but am also wondering if I'm possibly a tooth out on the belt?
Appreciate more of a test would have helped but not possible today.
M20B25 misfire
Moderator: martauto
It sounds like something is breaking down under load, ie 3krevs and above. In an ideal world you could put diagnostics on it and find which cylinder is misfiring. Then swap the plugs around on that cylinder and see if the misfiring cylinder has changed. If not then look at the ign leads. Is there any oil in the plug holes, (leaking rocker/cam gasket)
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Not really enough test data to attempt a diagnosis. Yes, there will be running problems if the cam is a tooth out, and yes, there will be running problems if there are C191 issues, but there are plenty of other possibilities.
HenryM3's suggestion is relevant on 16 valve E30s, and most modern cars, but unfortunately is not likely to be relevant on an M20, where the plug holes are short and heavily angled over.
One thing you have disturbed that is ignition related is the distributor cap, so I would recommend taking this off again, and making sure all is well with the rotor arm, and that the carbon button in the centre is present an working as it should.
The C191 carries the power for all the injectors on one wire, the signal for each bank of injectors on two more, and also the coolant temp. signal to the ECU, problems with any of which will cause issues. Note that the problem area is usually the wiring inside the rubber boot of the lower half of the C191, rather than with the plug and socket itself.
HenryM3's suggestion is relevant on 16 valve E30s, and most modern cars, but unfortunately is not likely to be relevant on an M20, where the plug holes are short and heavily angled over.
One thing you have disturbed that is ignition related is the distributor cap, so I would recommend taking this off again, and making sure all is well with the rotor arm, and that the carbon button in the centre is present an working as it should.
The C191 carries the power for all the injectors on one wire, the signal for each bank of injectors on two more, and also the coolant temp. signal to the ECU, problems with any of which will cause issues. Note that the problem area is usually the wiring inside the rubber boot of the lower half of the C191, rather than with the plug and socket itself.
Im inclined to agree it will most likely be something that has been disturbed during the work. It was laid up over winter but I purposely drove it before doing anything so as to know all was good before hand. The bottom half of the C191 isn't pretty and has had about 30 -40mm of cable added to each wire from the plug to the loom all in the same blue colour.
I'll check that plus the distributor and rotor. Both looked ok and I cleaned the surfaces with fine emery before re fitting
I'll check that plus the distributor and rotor. Both looked ok and I cleaned the surfaces with fine emery before re fitting
I would second Brians suggestion. I spend a fortune resolving a misfire on my 325 Touring. It started missing under load so I first did the distributor cap. It was slightly better but deteriorated over a short period. To cut a long story short, the new OEM distributor cap from the dealer was also faulty and when replaced with another, bingo (not before replacing rotor arm, plugs, coil, leads, MAF, injectors, fuel pump - you get the idea!).
Goes ok!
Had a quick half hour on the car.
Photos of the cap and rotor below, the carbon button is present and moving freely on the spring. I can see a clear shiny spot in the centre of the rotor arm where contact is there.
Cap not exactly new but was working beforehand.
Photos of the cap and rotor below, the carbon button is present and moving freely on the spring. I can see a clear shiny spot in the centre of the rotor arm where contact is there.
Cap not exactly new but was working beforehand.
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Mine had such a small tracking line it was almost imperceptible. In fact until I replaced it with a secnd new one that cured the problem, I would have sworn it was ok. It doesn't take much for tracking to happen. I think, from the photos, it would do no harm to change the rotor arm (worst case scenario is you have a spare if it proves not to solve it.
Goes ok!
I think it was the C191 plug. I have separated it to inspect the pins, there is some corrosion but not a huge amount. Re connected it and went for a run. The wife said we needed a few bits so that was all the reason I needed.
No more misfire WOT beyond 5k rpm, I don't do redline.
Can't help feeling that it feels a little flat or if it always feels like that coming straight out of an 8 speed modern diesel.
I'd like to swap the plug for something better but that'll wait for now. I do need a fan clutch and a radiator shroud. On that note is the tropical shroud different from the automatic radiator version with the transmission pipes on the side?
No more misfire WOT beyond 5k rpm, I don't do redline.
Can't help feeling that it feels a little flat or if it always feels like that coming straight out of an 8 speed modern diesel.
I'd like to swap the plug for something better but that'll wait for now. I do need a fan clutch and a radiator shroud. On that note is the tropical shroud different from the automatic radiator version with the transmission pipes on the side?
Funny how brand new original BMW parts go bad, when the original 30+ year old ones survived so long.Kelson wrote: ↑Mon Apr 06, 2020 2:39 pmI would second Brians suggestion. I spend a fortune resolving a misfire on my 325 Touring. It started missing under load so I first did the distributor cap. It was slightly better but deteriorated over a short period. To cut a long story short, the new OEM distributor cap from the dealer was also faulty and when replaced with another, bingo (not before replacing rotor arm, plugs, coil, leads, MAF, injectors, fuel pump - you get the idea!).
Indeed, c'est la vie as they say
Goes ok!