Subject: Hmmm, need some troubleshooting help (a little long) Author: geerhed : member since September, 2007 : 337 posts Posted on: 2009-09-30 21:34:50

I posted the following on justanswer.com
I had gotten some really good help from "Eurotec" earlier this year on that site, so when nobody answered my question I msged him directly to ask his opinion. What follows is the general question I posted regarding my rough idle and check engine light, and then his reply to my request for his help:
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POSTED TO JUST ANSWER.COM:
I have a 1994 BMW 740iL. 160K miles, but in very good shape.
The major problem is very rough idling, check engine light (CEL), and even stalling at intersections and such.
Faint smell of gas from exhaust during the rough idle.
If I run the car for an extended trip (40 miles or more) it goes away, idles like a champ. Then, the next morning I'll start out on my commute, get to the intersection down the road, idle fine for a minute and then the car shudders, CEL comes on, and rough idle. Sometimes it goes away immediately, other times I'm stuck with it for the day/week/month.
Earlier this year, I replaced the PCV assembly on the back of the intake - great sleuthing by Eurotec. That fixed my rough idling for about a month, and then this started again. While I had the intake off, I replaced the injectors with rebuilt 19# injectors and replaced the intake gaskets. Looking for some useful troubleshooting steps. Thanks!

Optional Information:
Year: 1994
Make: BMW
Model: 740iL
Engine: M60 4.0 V8

Already Tried:
So far I have:
Cleaned all the coils, they seem OK
Replaced all spark plugs (old plugs looked great). Checked connectors.
Borrowed a code reader: Codes are:
C9 Lambda Ctrl #1
Cb Lambda Ctrl #2
0d Oxy Sens #1
0c Oxy sens #2
d2 "CAN message" (what's that?)
29 Air Mass Sensor (I had unplugged it while the engine was running to check for a difference - the car stalled)
65 Output Stage Group 2
"Stomp Test" Code 1222 "Lambda Bank 1" (big help there - could be anything.
Monitored voltage at idle: VERY steady at ~14VDC
Air Filter isn't brand new, but reasonably clean
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MARTY'S (EUROTEC) REPLY:
Hi Geerhed, sorry to hear you're having trouble again. I spend most of my time helping out in the Mercedes section nowadays and don't get over to the BMW section as often as I used to. I'm out of the office today. I'll leave your new question open for other experts for now. Initially it sounds like some balky injectors. I see that you installed some rebuilts when you had it apart. I would try to isolate the missing cylinders if possible. If you feel like it's an overall rich running problem I would question the mass air flow sensor and recheck for vacuum leaks. The intermittent nature leads me to think it may be some sticking injectors. It would be very helpful to know what your long and short term fuel trim values are with a scan tool so you can see if your problem is too much or too little fuel. I'll keep an eye on your question.
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Anyone know how to check "fuel trim"? How can I check for a sticking injector? Wouldn't the code reader have turned up a bad injector, bad coil, or at least a mis-firing cylinder?

I need the best and the brightest here! I'm not into "shotgun troubleshooting" - replacing expensive parts "just to try it". I'm much more into procedures. Of course, any help or "gut feelings" are welcome as well.

Thanks;
Lonnie

1994 E32 Brokatrot 740iL 3/94
1989 E32 Lachssilber 735i 11/18/88
1986 E28 Bronzitbeige 535i

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  • SOLVED? $8.19 - geerhed 2009-10-26 21:31:48 (3 views)
  • Re: Hmmm, need some troubleshooting help (a little long) - maun 2009-10-15 20:43:34 (13 views)
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  • d2 'CAN message' (what's that?) - rv8flyboy 2009-10-01 10:58:39 (46 views)
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