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1

Engine management / M42 cold running problem

« on: November 11, 2023, 01:02:38 PM »

I am struggling to diagnose a '91 318i M42 cold running problem.  At start up, it idles fine, but backfires out the exhaust if I give it throttle.  After warming up, it runs great. 
1. I have checked the coolant and intake air temperature sensors, the resistance of those both look fine.
2. I get no CEL, but I and am seeing an occasional cam position sensor fault when I pull the fault codes.  I cannot find a new genuine part, so I have tried replacing the sensor with a new Facet aftermarket replacement, and also tried a good (I think) used genuine BMW sensor and still get the occasional code.  I checked the cam timing relative to the crank position and it looks fine (with cam holder tool on back of cams and a 5/16" pin in the flywheel recess).
3. Checked for vacuum leaks and un-metered air entry multiple times.  (The idle air and crankcase vent heaters were bypassed long ago.)
4. Compression and ignition system test good.
5. Fuel pressure and delivery rate test good.
6. Replaced O2 sensor with new Bosch part for good measure.
7. Replaced spark plugs and air filter for good measure.
8. Swapped ECU with a good used one.


I have two other good running 1991 318i's and can swap parts as needed.

Suggestions? 
Any subtleties in the cam position sensing or timing that I need to better check?
Should I buy a scanner with live data capability?  If yes, which one?

Thanks in advance.

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Member Profiles / M42-Matt

« on: November 12, 2008, 04:38:08 AM »

So my first post is supposed to be about me and my cars, right?
**Divorced white male, seeking interesting restoration projects.**
I had read that the M42 engine was BMW’s best kept secret, but was skeptical until owning one, now I am true believer.  While restoring a ’73 2002tii, a buddy at work offered to sell me his ’91 318i as a parts car.  I told him that not much would fit the 2002, but I would be happy come by his house and take a look.  He said no need to go to his house, he was still driving it to work and it was out in the parking lot.  I was surprised he was junking a drivable car, but soon realized he was mostly just mad at the car and his son who had completely trashed the car and crunched several of the body panels.  I looked over the car and found it was not too bad, but what really sold me was the discovery that it had a twin cam engine.  $400 changed hands and the 200K mile beater 318i was mine.  About $200 at the junk yard, $500 in routine maintenance parts, and a $500 paint job landed me a nice daily driver that was head and shoulders above the Volkswagen I was previously driving.  The valve tap is a little annoying, but the peaky power band is a blast to drive.  I put ‘is wheels on it eventually to dress it up, but wanted a real 318is and soon found one with a good body and bad engine for $400 with 285K miles on it.  With my youngest son lusting after the “new” 318is, I bought yet another one with engine problems for me.  The 318i and both 318is’ are now all running well and are in various states of restoration.  I get tremendous enjoyment out of reviving cars that are otherwise headed to the junkyard, and restoring them to "nice driver" condition, generally with very few modifications.  Lately I have been having a hard time parting with my cars and have accumulated a few too many.  I am certainly one of the E30 M42 faithful, but I do have a couple of other cars to play with.  My current fleet includes:
’91 318i, metallic black, now 311K miles, daily driver and still hanging in there
’91 318is, white, 285K miles, just rebuilt engine, son is driving it
’91 318is, metallic black with peeling clear coat, 220K miles, backup to the 318i
’89 325is, red, a little disappointing in power but a classic E30
’92 325is, green with peeling clear coat, too much flaky electronics
’73 Porsche 911S, sorry about the non-BMW

My dream garage would include the following:
’91 318is (probably would want two)
’65 Chevy II Nova
’63 Corvette split window coupe
’73 Porsche 911 RS Carrera
’73 Fiat Dino spider
’73 Ferrari Daytona coupe (my all time favorite car)

This forum rocks!  It is awesome having so many like-minded enthusiasts communicating freely.