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Old 03-13-2006, 10:43 AM
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Couple of easy/dumb m104 questions

Hi All -

If you own an m104 engined vehicle, your time will come to troubleshoot it. My day is here. My wife drives an exceptionally clean 1993 300E (124.028) with the 2.8 liter m104 engine (104.942).

It had been having the oh-so-common misfire problem, so I finally got around to changing out the plugs, coil connecters, and wires. Proper Bosch plugs used, ignition parts were Bosch wires and Beru connecters. Engine is now smooth as silk again. This leads us to stupid question #1. The valley housing the coils/plugs/wires on the m104 has a cover held in place by six allen head bolts. When I put it all back together, I cannot get any one of the bolts started - it's as if they are too short to reach the threads - they just spin. The cover is sitting a few millimeters above the valve cover gasket. I'm open to suggestions. Not an urgent problem, but I'm sure the engine will be much happier in wet weather if the ignition system remains dry.

Moving on. The engine now has a wandering idle and occasional hesitation at low RPM/part throttle operation. I'm going to pull the codes using Arthur's reader, which leads us to question #2. I know where the 16-pin diagnostic connector is located, but into which slots do I plug the three banana plugs on the code reader? I've scanned through about a million m104 posts and everybody is reading codes like crazy, but I've never seen a description of how to use the code reader?

This car had the wiring harness replaced under Starmark 4-5 years ago, so at least that should be OK.

Thanks in advance for any help,

- JimY

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Old 03-13-2006, 11:07 AM
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I've always connected to battery for the +, - connections and read codes that way. But I remember I once read (then forgot) which slots they should go to. I imagine the slots would make a cleaner connection.

Didi you check the holes for the six allen bolts?... they may be stripped. Try threading them in without the cover. Working from memory, are they all the same length? You may have jumbled them.
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Old 03-13-2006, 11:14 AM
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basically you want to attach black to pin 1, red to pin 16, and the other one to:

pin 3 - emissions
pin 6 - air bag (SRS)
pin 8 - ECU
pin 14 - electronic accelerator, cruise control, idle speed control
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Old 03-13-2006, 11:47 AM
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I have found the female threads in the engine relatively easy to strip if you are not careful to stop tightening when they are snug. I have always though the bolts are plenty long enough to reach the threads, so it may be possible that a previous owner or mechanic may have stripped them.
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Old 03-13-2006, 11:48 AM
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Quote:
Originally Posted by Kestas
Did you check the holes for the six allen bolts?... they may be stripped. Try threading them in without the cover. Working from memory, are they all the same length? You may have jumbled them.
Yup, BTDT. All six bolts are exactly the same length. The three coils each have four holes at their corners. Each coil is located by two studs at diagonal corners. Two of the bolts then go through the remaining two openings, in theory threading into the head and holding the cover in place.

Perhaps some previous "mechanic" stripped the first few threads? Never thought of that. Maybe I'll get some 5mm longer bolts and try that. Good excuse to go browse at Elliots - great place for true hardware geeks in Dallas.

Thanks for the input on using the code reader, I do appreciate it.

- JimY
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Old 03-13-2006, 09:47 PM
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OK, I built the code reader and spent some quality time under the hood this evening. Oh, also verified that OVP relay is current part number. No Joplin needed here.

Pin 8: codes 4, 13
Pin 14: code 11

This car is a 1993 49 state model. It does not have a CE/MIL light, does not have a built in DM LED/pushbutton, and pin 3 of the 16 pin connector is empty. So I'm assuming it doesn't have the diagnostic module functionality...

I cleared codes and reset adaptation values. Took car for a 10 minute spin. Ran great for the first 9 minutes . Then all the same symptoms returned: intermittent wandering idle (500 - 1100 RPM), surging at cruise, and a hesitation when first tipping into the throttle. Pulled codes again after drive testing and got:

Pin 8: codes 4, 13
Pin 14: clean

Not quite sure how to proceed from here. Thinking my best bet is to go hunting for vacuum leaks and fuel pressure problems.

This car has a newish wiring harness. No record of O2 or MAF replacement. If I cannot find a vacuum leak perhaps a fresh O2 sensor is the next step? I'm open to suggestions.

- JimY

ps: Just thought of this tidbit. The car always run fine for the first minute when started cold. I assume this means it's OK while in open loop mode, and it only misbehaves after switching to closed loop. But does this indight the O2 sensor, MAF, neither, or both?


Last edited by jcyuhn; 03-13-2006 at 10:41 PM.
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