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Discussion Starter #1
1994 E 320, body w124, engine M104.I've had this car since 97, purchased nearly new from MB dealer. Over the last year I've had intermittent stalling issues. At highway speeds >50mph the engine hesitates (rpm to 0) and then starts up again with the ASR light on. At city speeds the engine will not immediately restart. Have to stop and restart. Sometimes it restarts immediately, sometimes only after a couple of tries. Sometimes only after it's been towed to the garage!! Each time the ASR light comes on, but has no effect on the engine performance (no limp mode).
Have changed:
NNS
CPS
Fuel pump relay
Fuel pump
Note: the upper wiring harness is dated 1994. I cannot see any degraded insulation.
I would appreciate any info as would my mechanic.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,373 Posts
Your symptoms describe a defective ETA (electronic throttle actuator), usually caused by defective bio wiring. Only solution is replacement with newer generation that has been relieved from treehugger wiring.

The ETA is version specific. In other words, if your vehicle has ASR, you must get a ETA that is made for ASR. Using a ETA from another W124 w/o ASR will NOT work. Best to get a replacement unit matched to your vin#.

Also, still consider the main engine wiring harness to be throwing monkey wrenches in this game. You still have the original harness as it is dated 1994 and no original wiring has made it this far out without showing signs of degrading. There were a few running changes in the last couple of years of W124 production, so getting a new harness matched to your VIN# is highly recommended. Otherwise, you could end up with some different connectors on the new harness.

Also replace the OVP relay as it is responsible for a whole bunch of engine electrical systems and is tied into the main engine harness.

Replacing the harness and ETA are the only solutions to permanently curing the electrical gremlins on the early-mid 90s generations MBs. Not a cheap solution, but it is the only real solution and is still cheaper than letting the wiring short out the ECU.

I have a spare ASR ETA unit if you're interested. PM me if you want.
 

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Discussion Starter #3
Thanks for your info and your offer, I will get back to you after sharing this with my mechanic. Also found my OVP has only one fuse (15A) on it, was thought to have two?
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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I can't recall exactly, but I think my original E320 OVP relay (as installed @ the factory) only had 1 fuse. I believe the design of the OVP was updated in subsequent years and grew a fuse. My current OVP on the E320 has 2 fuses, but the E300 diesel still has 1 fuse as it uses a different P/n# OVP even though it also has been replaced with a much newer version.
 

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W-1-2-3 Go!
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I can't recall exactly, but I think my original E320 OVP relay (as installed @ the factory) only had 1 fuse. I believe the design of the OVP was updated in subsequent years and grew a fuse. My current OVP on the E320 has 2 fuses, but the E300 diesel still has 1 fuse as it uses a different P/n# OVP even though it also has been replaced with a much newer version.
Isn't there also an updated OVP with 2 fuses and one (or two) extra pins? Or was the update only for the extra fuse (and possibly better internals)?
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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I think the OVP on the E320 was W124 specific, but the OVP on my '95 E300 DIESEL is actually a W201 part (as supplied by MB).

Since the diesel is much simpler in design (electrically), no real ECU other than some very basic idle control, no ASR, no ETA, etc, etc. As long as the glow plugs & relay work, it's gonna run. The nav radio is the most sophisticated electronic component in the whole car.

Patrick, still got the beige W123 I see. When is the next meet in SoCal? You should drive my OM606 now that it has been fully restored and has got a Euro spec OM603 injection pump.
 

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W-1-2-3 Go!
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16,161 Posts
I think the OVP on the E320 was W124 specific, but the OVP on my '95 E300 DIESEL is actually a W201 part (as supplied by MB).

Since the diesel is much simpler in design (electrically), no real ECU other than some very basic idle control, no ASR, no ETA, etc, etc. As long as the glow plugs & relay work, it's gonna run. The nav radio is the most sophisticated electronic component in the whole car.

Patrick, still got the beige W123 I see. When is the next meet in SoCal? You should drive my OM606 now that it has been fully restored and has got a Euro spec OM603 injection pump.
Steve,

Good to see you around here too. Not sure when the next meet is, or if I could join. Been real busy lately. You're tempting me! :D

Going back on topic, this is a good read on the OVP relay:

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1521289-what-actually-fails-ovp-relay.html
 

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1989 Mercedes-Benz 300E
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91-96 it was usually bio wiring harness. OVP was early w124 along with fuel pump relay since then changed and never recalled lol. But a number of things it could be try unplugging your cpu. If it still stalls then its simpler then it looks other wise it a sensor of some-sort, etc.
 

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Discussion Starter #9
Stalling issues

Continuing on my original post. The intermittent stalling was occurring with increased frequency. Finally the check engine light came on last week which allowed us to check 3 codes. Can't remember exactly but they directed the search to the throttle actuator (low signal or voltage?). Before getting into that part $$$$, opted to replace the OVP relay $$. After 5 days of running, no stalling. I will give it a month before I rejoice.
The replaced OVP had blueing on 2 of pins. If I can get it opened I will check for any burning inside.
The replacement MB part (different manufacturer) was similar to the original in appearance, 9 pin and only one fuse!
I am keeping note of your comments on the wiring harness and will have it evaluated at the next mechanical checkup.
Thanks to all for your direction. :bowdown:
 
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