Stumbles/shuts off on cold starts, can't figure it out

[DesktopDave]

Yeah, I did that when I first got the car and never could find anything.  I sprayed so much the engine looked like new when I was done!

I might do that myself, the power steering is slowly mucking up my clean engine.  That and a few seals, timing case gaskets, etc. etc...these cars are never done...:mad:  But they're so much fun:D

[91 318is]

Here's another update


I hooked up my fuel pressure gauge inline with the feed line into the engine.  I'll just make a list of what I did and the pressures I got.

Return line capped, fuel relay jumped with engine off - 71 psi
cold idle at 850, regulator vacuum line connected - 40 psi
cold idle at 850, regulator vacuum line disconnected and plugged - 49 psi

I also let it warm up to NEAR operating temps, pressure dropped a tad to 38-39 psi.  I also held the RPM's at 3k and at first the psi went to about 50 something, then came back down about 40 psi.  Stomped on the gas from idle and the car stumbled a few times like it's been, pressure seemed to fluctuate a little on the pressure gauge, but didn't drop significantly.

One other thing I heard was what sounded like the ignition arching near the coils/plugs and the RPM would drop, say maybe 50 rpm, nothing major, but you could definitely hear the RPM's flucuate.  The arching didn't happen a lot, just every once in a while.  

This info help anyone?

[91 318is]

bump, anyone?

[91 318is]

Swapped out the DME today with another guys at work, DME is for a 91 318is.  Stumbled on me again coming home.


I give up:(

[keflaman]

Here's a thread I posted about using a vacuum gauge:

http://www.m42club.com/forums/showthread.php?t=7234

I agree with Dave about the usefulness of a vacuum gauge for troubleshooting. I've found most M42/M44 motors run about 17-18 hg at idle.

You can even put together a homemade vacuum gauge for just a few dollars.

http://www.komar.org/faq/manometer/
http://www.audiworld.com/tech/eng116.shtml
http://www.powerchutes.com/manometer.asp

(Disclaimer: I neither endorse or oppose the contents included in provided links)

[91 318is]

Here's a thread I posted about using a vacuum gauge:

http://www.m42club.com/forums/showthread.php?t=7234

I agree with Dave about the usefulness of a vacuum gauge for troubleshooting. I've found most M42/M44 motors run about 17-18 hg at idle.

You can even put together a homemade vacuum gauge for just a few dollars.

http://www.komar.org/faq/manometer/
http://www.audiworld.com/tech/eng116.shtml
http://www.powerchutes.com/manometer.asp

(Disclaimer: I neither endorse or oppose the contents included in provided links)

Thanks, I'll try and pick one up today and see what I come up with.

[91 318is]

Borrowed a vacuum gauge from my dad and have been checking my vacuum at different times and here's what I came up with.

Cold start, starts and idle at 600 for about 10 seconds, vacuum is at 14 psi, then idle bumps up to 850, idle come up to 17 psi.

Hot idle at 850, vacuum is between 18-19 psi.

From this, sounds like I have good vacuum right?  

So vacuum tested good, fuel pressure tested good, what's the next step now?  Either the cam or crank sensor?

Car hasn't stumbled on me in about a week.  It seems like the o2 sensor helped some, but didn't cure it.  Could it be air/fuel related?

I'd hate to take it to the dealer, bosch system seems like a pretty basic system, but I'm running out of stuff to check and things to swap.

[DesktopDave]

Yeah, vacuum sounds good.  I have to admit I'm puzzled too.  Now I'm just guessing, but could it be a bad injector?  Maybe a flat spot somewhere on the AFM?  I know you swapped that, might be worth a quick look under the AFM cover.

[keflaman]

Looks like you ruled out vacuum leaks.

Maybe it's not related, but the A/C idle bugs me.

The Electrical Manual, pg 77, Section 6452-2 discusses circuit operation of the A/C compressor controls (reference manual from this thread:  http://www.m42club.com/forums/showthread.php?t=7748 courtesy of ak96ss). There's some good troubleshooting tables in there.

Some more crazy thoughts:
  -What about the evap system? Is there something in there that could cause a problem like this?
  -It sounds like the DME is getting signals, but they're mixed up. By any chance is it possible to cross the connectors between the temp gauge sender and the coolant temp sensor:confused:

[91 318is]

Yeah, vacuum sounds good.  I have to admit I'm puzzled too.  Now I'm just guessing, but could it be a bad injector?  Maybe a flat spot somewhere on the AFM?  I know you swapped that, might be worth a quick look under the AFM cover.

Popped the cover off the AFM before and cleaned the wiper with contact cleaner, didn't see anything that looked bad either.  That was actually my first thought was the AFM was bad because of when it stumbled while rolling from a stoplight.  I thought it was hitting a deadsopt and losing signal.

Looks like you ruled out vacuum leaks.

Maybe it's not related, but the A/C idle bugs me.

The Electrical Manual, pg 77, Section 6452-2 discusses circuit operation of the A/C compressor controls (reference manual from this thread:  http://www.m42club.com/forums/showthread.php?t=7748 courtesy of ak96ss). There's some good troubleshooting tables in there.

Some more crazy thoughts:
  -What about the evap system? Is there something in there that could cause a problem like this?
  -It sounds like the DME is getting signals, but they're mixed up. By any chance is it possible to cross the connectors between the temp gauge sender and the coolant temp sensor:confused:

Yeah the A/C idle kills to me too.  I'm wondering if the A/C switch would be casuing that?  I also thought about the connectors too, but that would mean that the temp gauge wouldn't work at all right?  Haven't thought about the EVAP system, don't know what would that would be.

The whole thing just boggles me, I just can't figure it out.  It comes down to me just throwing parts at it until the problem goes away I guess.  Sucks but I just can't figure it out.

[DesktopDave]

Yeah the A/C idle kills to me too.  I'm wondering if the A/C switch would be casuing that?  I also thought about the connectors too, but that would mean that the temp gauge wouldn't work at all right?  Haven't thought about the EVAP system, don't know what would that would be.

The whole thing just boggles me, I just can't figure it out.  It comes down to me just throwing parts at it until the problem goes away I guess.  Sucks but I just can't figure it out.

I'm still thinking that the car is running well in open-loop and having this trouble when it goes closed-loop.  The A/C high idle and cold idle is sent from the DME to the idle valve.  You checked both the coolant sensors already, so I discounted this.  Unless it's some odd wiring gremlin in the harness.

Don't throw parts at it.  We'll figure it out...these are well put-together cars.

[91 318is]

I'm still thinking that the car is running well in open-loop and having this trouble when it goes closed-loop.  The A/C high idle and cold idle is sent from the DME to the idle valve.  You checked both the coolant sensors already, so I discounted this.  Unless it's some odd wiring gremlin in the harness.

Don't throw parts at it.  We'll figure it out...these are well put-together cars.

Well it used to stumble on cold starts sometimes, but since I put the new o2 on, it hasn't done it since, maybe luck, maybe it partially fixed it.  The A/C idle isn't high, the idle drops down when I turn the A/C on, and when I turn it off, it shoots right back up.  Only coolant sensor I changed was the one for the DME.

ONLY other thing besides the AFM possibly is the cam or crank sensor maybe is losing signal.

Like I stated before, it usually stumbles and bucks below 2k if I put a load on the engine is say 2nd or 3rd gear.  I can get it stumble pretty good when the A/C's on and putting a load on it.  Almost like a timing issue.  Do the cam and crank sensor both play a role in timing?

[DesktopDave]

Both play a role in timing, but the cam sensor is the one that sets advance, along with coolant, air temp, AFM door, TPS, well pretty much all of them!

Odd that the O2 sensor helped cold idle.  It really doesn't do much until it's heated up.

I'm not sure if we went over this, but did you test for cracked spark plug wires or just worn out plugs?  Leaky wires would make lots of little gremlins for you.

[91 318is]

Both play a role in timing, but the cam sensor is the one that sets advance, along with coolant, air temp, AFM door, TPS, well pretty much all of them!

Odd that the O2 sensor helped cold idle.  It really doesn't do much until it's heated up.

I'm not sure if we went over this, but did you test for cracked spark plug wires or just worn out plugs?  Leaky wires would make lots of little gremlins for you.

Changed the spark plugs, ohmed out the wires, wires checked out good.  I could change them if I need to.

AHHHHHH, this is annoying me!:mad:

[romeomike]

No miracles promised...

BMW issued a service bulletin 13 03 91 (3290) dated July 1991 for M42s produced between 2/90 and 12/90, last seven of serial #s EE65001-72808 for the 318is and EJ00000 - EJ05097 for the 318i.

Dealer has to run a check through their Dealer Communication System to see if a particular car gets the fix or not.

The next two paragraphs are verbatim quotes:

Situation: Due to an occasional impairment of the signal between the air flow meter potentiometer and the DME control unit, the engine idle may dip below specification at times causing a possible rough idle condition.

Correction: Adapter harness (P/N 13 62 1 734 516) must be installed on all affected vehicles between the engine wiring harness and the air flow meter. The adapter harness, which incorporates and impedance converter, filters and amplifies the signal from the air flow meter to the DME control unit.

Edit: Again the correct part # is (P/N 13 62 1 734 516), my original post had 61.