It wasn't the EACM
 

Sorry this post has been delayed. Some of you have been e-mailing me for a progress report. It hasn’t been positive! The new fuses and connector-cleaning held off the gremlins for five days. That was pretty good, I thought - just long enough to get my hopes up. After the symptoms came back (on light acceleration from a stoplight, level road, heavy traffic), I decided to buy-and-try the EACM. The EACM that was in my car is an original part number 124-545-07-32, version K9, manufacture date 10th week of 1991. The new one is a superseding part number, 124-545-45-32 originally specific to chassis numbers from 840529 (mine is 766858). It is software version K13. I installed it myself. I planned to bring the car in to my interested independent tech to have the remaining diagnostic codes read and the ‘check engine’ light reset. As it turns out, the EACM didn't do the trick; on the 5 mile trip to the shop, the ASR/ limp home symptoms recurred. This may have been because I didn’t know about the reprogramming time required upon reinstallation of the module - 90 seconds with ignition on before starting the engine. But after my tech reset the system, it still goes into ‘limp home’ mode.

I feel like I took some chances, to save some money, by turning to an independent after I got sick of spending dealer-dollars. The dealer was going down the same path I saw others on this forum followed (first the harness, then the idle speed control, then the throttle actuator), so I thought I could see where it was headed. By following the threads here and making my own diagnosis, I gambled that I could spend less installing the parts myself, or having an indy install the parts, but that meant committing to the cost of the throttle actuator and then the EACM, which was purchased at a discount but nonreturnable. I might have done better to stick it out with the dealer, who had offered to do a trial with a new EACM after MBNA refused to warranty it. So with a new harness, new throttle actuator, new idle control, and now a new EACM, nothing has solved the problem yet. The car goes into ‘limp home’ mode just about every day. This morning the car is headed back to the indy, who has been doing his own research. Looks like the next suspects are faults in the CAN bus or the other modules. Any advice out there?

Have you tried the alternator. My E320 went into "limp home" mode when the alternator was on it's way out. Only did it in stop and go traffic - never had problems with it on the open road.

DTC codes. . .
 

where were they read? From the Diag Module or from the EA?

Model: 124.036 1992-93 EA Module (Pin 7 on 38 pin)
7: CAN data bus signal from EA/CC/ISC, ABS/ASR, HFM-SFI or LH-SFI (right or left)
control module faulty.
6: Starter lock-out/backup lamp switch.
2: EA/CC/ISC control module (N4/1) or Safety contact switch (M16/1s1) or Stop lamp
switch or Cruise control switch or Actual value potentiometer or Starter lock-out/back-up
lamp switch or engine speed signal or vehicle speed signal or closed throttle position
switch or safety relay in EA/CC/ISC control module.
96: ???
224: ???

Model: 124.036 1992-93 DIAG Module (Pin 19 on 38 pin)
2:Oxygen sensor faulty
6:Idle speed control faulty
7:Ignition system faulty
17: Data exchange fault between individual control module
96:???
224:???

DTC 7 would cause the problem since the EA must communicate with the LH-SFI directly and others indirectly. Check my page, menu #2 for EA and #1 for overall engine management block diagram.

Hope you can get it fixed soon!

Check Alternator!
 

Mark: I'd like to endorse ENGATWORK's suggestion that you have the alternator checked. Last summer I spent a week stranded in Las Vegas while the dealer puzzled over random fault codes in my E500. The car was in "limp home" mode and going nowhere...

The "technicians" couldn't figure out the problem 'cause the fault codes were wonky. They kept swapping parts in and out with no effect. Finally the service manager noticed voltage spikes and had the alternator checked. New part - problem gone!

BTW - kudos to M-B Roadside Assistance for giving us a Jaguar rental car and putting us up at the Sahara for the week ;)

Thanks, Jim, Jim, and Dean. The tech who is looking after my car had similar codes read, and is currently just clearing, recreating the fault, and re-reading to try to find a pattern. I called him about the alternator spikes, and he is aware of that unit being on the list of suspects. He has been looking at the alternator readouts when the diagnostic unit is plugged in, as I understand it. So far no problem there.

Forget the diagnostic readout on the alternator, have the alternator hooked-up to a scope and measure the amps and voltage under load.

If the power is not clean to the diagnostic module, how can you trust it?

:-) neil
1988 360TE AMG
1993 500E

Mark,

Not trying to encourage you to continue your parts trial and error nightmare, but an Alternator is almost a maintenance item @100k (emphasis on "almost"). What you could do alternately to ensure the alternator is not the culprit, is spray some electrically conductive grease in there (I know there are such products out there) to make sure it's giving you the best, most consistent voltage.

Our hopes & prayers are with you, brutha:)

Limp Home
 

Mark,
My car is in winter storage so I cant speak to the problem currently, but this only happens to my car on full- bore acceleration. There might be a clue in there somewhere.
Best wishes

I'll second Michael on the alternator note. Mine, on the 500E , went out right at 108K... My wife was stranded and we had to tow to the mech.

I'll suggest, for the reasons related to your problem, AND to save yourself a major inconvenience, to replace... ( it is SOOO easy to spend someone elses money :D )

Thanks guys. I'll bring up the alternator issue again with my tech. I think he's reading this thread too. Right now, the current suspect is a faulty shift indicator sending intermittent info. I'll post an update after I get my car back after the latest round.

Dare I say it?
 

Three days and counting, I think my tech found the problem. It was the S16/3 starter lockout and reversing lamp switch (with selector lever position recognition), also called the safety neutral switch. It is an electro-mechanical switch that is actuated by the shifter and sends gear selection information to the EACM, more properly called the EA/CC/ISC module, as I have learned. Part no. M000-545-62-06, $69.00. It showed up on the diagnostic unit as a misread on the shift lever position, that would not represent actual gearshift selector changes. Apparently that was enough to kick it into 'limp home' mode. I got my car back Friday and drove it 45 miles - no problems. I drove it 20 miles Saturday - no problems. I gave it the dreaded car wash test Sunday - no problems. I just might start enjoying this thing again! Wish me luck!

Hey Mark that sound like good news. If it showed it up on a scan, how come not before? Did they have to SCAN a different electronic UNIT?

:-) neil

Knocking on burl...

Neil, Three reasons it didn't show up before:
1 - So many error codes it got lost in the clutter. That's why I needed to replace the harness, etc.
2 - My tech brought in a consultant to review the problem - a guy named Marty from Luxury Motor Vehicle Information Systems (LMV Info). Marty put a different diagnostic unit on it. Marty's unit was laptop PC based. It could read more inputs live than the error memory stored, so the generalized error codes could be broken down into specifics.
3 - The shift selector error only showed up as a live error, while the car was running.

This, of course, is as I understand it as a layman.

And Michael, yes, I knock the burl every time I start it!

Mark,

Great to here your car is back to normal. Isn't it the most rewarding experience when you have worked out a problem. The best part is that you have checked so many electrical components you shouldn't have to worry about this for a long long time....Have Fun!!

Placo1