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Ugh, this can't be good...

2K views 19 replies 11 participants last post by  ackvig 
#1 ·
Driving home a few days ago and just a mile from home I heard this strange sound, like something breaking. After that the car ran like crap, rattled like an old diesel, low power a faint smell of plastic burning. I parked the car at home, opened the hood and then immediately shut the engine down, it sounded like something was having all kinds of fun running loose under the valve cover. Geez, this after chasing down a series of check engine codes that I've gotten then addressed. (Yes, the wiring harness was previously replaced with a good one.) They were like a cascade, fix one then another arises days or weeks later. All told the coolant temp sensor, voltage regulator, OPV and fuel pressure regulator have now been replaced. Once I had all that resolved it was running great then boom.

I yet to pull the valve cover off to see what I might find. If it's really bad then it's decision time which is made all the more difficult given the car is in excellent shape with 88K original miles. Side note, I'm kicking myself for ignoring the ticking sound I've heard from the engine since I purchased it last fall.
 
#3 ·
Bad luck.
M104 has the reputation to be overheating, but to be also a very strong an reliable engine.
You first need to understand/see what happened inside the engine, or elsewhere.

Just to give you some courage, my 300td Turbo has had a serious damage few years ago: the hydraulic pump attachments broke suddenly, and the auxiliary belt went everywhere under the hood. I was driving back home at that moment, and all the sudden no more cooling water, no more power steering, no alternator (so, no battery), and so on.
Just parked some meters ahead, and opened the hood: I though the car was dead! But, with some help, good DIY supports, patience, the car was repaired and is running fine.

So open the hood, have a correct diagnose, and then sort out what is to be repaired and what is still ok, without emotion.
Jean-Louis
 
#4 ·
You would need to use the cars onboard diagnostic trouble code port and also use a home-made LED DTC reader to find out which component may have failed. There's plenty of resources on how to do that and build the 3 wire DTC reader on the internet.

http://www.w124performance.com/docs/mb/diagnostics/DTC_List_W124_M104.pdf

You can post the results here for guidance before you throw parts at it.




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#5 ·
Well here's the latest news. After in-depth diagnostics by a local W124 tech the #2 and 5 cylinders are firing. Coils and plugs are soaked in oil. The valve cover is a bit iffy and the ignition control module has gone bad. A new module is $2400. So, its decision time for sure.
 
#8 ·
Yep, that is step one in my plan. It'll be interesting to see if doing so resolves the rest of the issues. Along with that I am searching for a new valve cover. The shop said mine's not looking so hot which I already knew.

I also have the original ECU which the previous owner replaced with a used unit because a shop told him it was bad because of a bad fuse box, which they replaced. (Somehow that just sounds suspect.)

I have found a company in FL that rebuilds ECUs and is familiar with the M-B/Bosch unit in the W124. I'll send my unit out to them once I've completed step one.
 
#10 ·
On that motor, the ENTIRE ignition system (3 coils, 3 coil to plug boots, 3 spark plug wires, 6 plugs) is disposable and needs to be replaced about every 100-125K miles with plugs every 25K miles. The only proper plug for that engine is Bosch F8DC4, no exceptions.

However, IF eco junk wiring is still present then all bets are off.
 
#11 ·
Here's the update. I found a company that could test and repair the ECU. They found that a short in the board has caused the main processor chip to fail. Unfortunately, that chip can't be replaced. The good news, they have re-manufactured units available for $514 which come with a 1 year warranty.

Next steps, replace coils, boots, plugs and wires then install the new ECU and get to driving my E320 again. :)
 
#13 ·
Brand new ones are $2,000+. The remanufactured one does come with a warrantee at least.
 
#14 ·
Not exactly a wear item. Are junk yards not available in NC? ECU's are easy to pick and replace (I assume for the late 124) and my spare one (for W201) cost me only $50. Just find a less traveled good donor. Mine came from a 90K mile car.

I suspect a $500 refurbished one may be from a JY too, who knows?

I would not recommend this for any wear items of course.
 
#15 · (Edited)
I would save the $514 if I were you and just get an used ECM. However do you have the part number of the ECM they're trying to sell you? Because the 1990-92 M104 was a CIS unit that used a 8-pin EZL like the 560 M117 V-8 motors, and are tough to find - same engine as used in the 1990-92 300SL's. 3.0 M104-980's I think these were called, while you have the 3.2L 104.990.

In an late M104 the ECM would be a black box next to the OVP relay. Pictured below.

Don't forget to replace the rubber rings for the spark plug channel holes with the valve cover off. Heck, just get a new Victor Reinz top rubber gasket set while you're there.

Not sure what would cause a valve cover not to "be so hot" other than being simply dirty and/or corroded on the surface which is how some of these aluminum VC's are in some weather situations.

http://www.pelicanparts.com/techart.../48-ENGINE-Valve_Cover_Gasket_Replacement.htm



 
#16 ·
On my 1995 E320, eco-junk wiring had damaged the o2 sensor heater circuit pin and been driving with check engine light for couple of years. Finally, purchased an ECU for $80 on ebay and it works great. Find a seller with good return policy, so, in case you are getting a bad unit, you can return it.
 
#17 ·
For me, I'd rather have the piece of mind that I will get with a remanufactured unit and associated warranty. I've got an 88K original mile car in super condition with a good, replaced wiring harness. Prior to this current issue, it ran like a top and looked even better.

I strongly suspect that the beginnings of this issue were wiring harness related. The previous owner replaced the original ECU with a used one when the car started having starting and missfiring issues. It was some time later that the wiring harness was replaced. I also suspect that the failing valve cover gasket and the associated O rings for the spark plug channel holes only added to the fun.
 
#19 ·
Given how nice this car is and past experience with electronic parts (this isn't my first rodeo with a W124 or owning and maintaining old cars, I have and had several older Porsches), my feeling is that rather than band-aid the issue which only kicks the can down the road, making a deeper investment in this situation, is money well spent.

I greatly appreciate the insights including differences of opinions that some have brought to this thread, thank you very much. Differences of opinions on solutions help us find the best possible solution within our budget and our comfort level for our issue. However, I am a bit surprised by the criticisms and vailed insults displayed in some posts that also offer no additional thoughts, ideas, insights or experience. So, I'll be going back to just being a occasional forum reader visiting only when I need further research for an issue.

Enjoy your drives!
 
#20 ·
However, I am a bit surprised by the criticisms and vailed insults displayed in some posts that also offer no additional thoughts, ideas, insights or experience. So, I'll be going back to just being a occasional forum reader visiting only when I need further research for an issue.

Enjoy your drives!
This is the most "polite" beef I've read on a forum in a long while. Man, don't go to your town's "Topix". You are in for a helluva ride.
 
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