R129 ASR and ABS lights with stalling

[Mike in Vancouver]

Hi. I have a 1991 300 SL with 300K kilometers. Unfortunately it only has an OBD-1 diagnostic (16 port with led flashes referencing a pdf table).

It ran great all summer but when the engine was hot I had to give the engine gas for it to catch. All summer the rollbar dash and switch lights regularly went on for awhile then off and back again. A couple times the ASR and ABS lights came on together whilst driving but then would go out in a few minutes or upon restart.

Last week the ASR and ABS lights came on when starting car and accelerating from a stop caused staggering as if starved for gas before stalling out completely as gas is applied. However it did start and idle and even rev in park immediately after stall. To get home I found I could feather the acceleration and slowly get to speed. Diagnosing the next day the problem went away while driving but the ASR/ABS lights remain on at start and constantly thereafter. Over the past week the stalling problem has returned sporadically and now sometimes when starting I must rev engine for a while or it stalls by itself.

The LED codes report errors as follows:

7-7 Left or Right Axle switch rollbar short circuit to 30 or 31

8-17 Crankshaft position sensor faulty

10-23 Rollbar control module

10-29 No axle vehicle speed sensor signal

13-9 Control valve

Fwiw when last returned from a mechanic the odometer had stopped working. And at the start of this past week error code 10-28 “No speedometer signal” and 10-27 “Insufficient voltage” displayed but they have not returned after being cleared. I checked both axle switches setting either one to “Arrete” and braking sharply deployed the rollbar but setting them to “Funktion” and manually pulling down (with car running) did not. I’ve checked all fuses and replaced #4 fuse in trunk without change. The softtop operates without problem.

I’ve ordered a new Crankshaft position sensor (before reading and confirming that the error code 8-17 disappears when engine is running) PART NUMBER 0021539228.

I am contemplating buying a replacement Rollbar Control Module PART NUMBER 0285001016.

I am unsure about the wheel speed sensors – there seems to be a Front Right (1295402717) and Front Left (1295400817 ) plus Rear Right (1295402117) and Rear Left (can’t find part # suggestions welcomed)

I’ve read extensively in forums with suggestions including (please correct any errors in the cut and pastes below):

1. Throttle body rebuild (where is this and how can I test?)
2. OVP fuse (It is located in the module coffin/ compartment, right side of the fire wall. Remove the six screws and it is the aluminum one with a red top that has one or two fuses on it)
3. Fuel filter check and base fuel mixture adjustment
4. Remove iron filings on front sensor tips (Turn the steering to get access behind the wheel, remove the bolt holding the sensor in place and then gently remove the sensor. If there is a hair ball of iron filings on its tip then this could be your problem, use a vacuum to remove the filings. Replace sensor and bolt and then do the same on the other front wheel.)
5. Distributor cap/rotor problems (a common fault with older R129's and also worth checking is H.T lead (plug wire) resistance and spark plugs)
6. Battery (If the battery is disconnected the ABS light will come on when the vehicle is restarted. The steering wheel turned full in both directions will reset that issue).
7. A faulty Brake Light Switch????

I realize I may be dealing with two or more separate issues but suggestions on what to try next would be much appreciated.

Thanks in advance.

 

[rayhennig]

As said in another place:

The mechanical ignition system requires new caps and rotors roughly every 30k miles.

My original cap and rotor were changed at 250k Km. The Bosch (not MB) cap installed about 20k Km ago is showing signs of distress. Stump up for MB cap, coil, rotor and plugs. And leads if you can find someone to make them up. Mine were made up by MB in Bochum.

Have you changed your OVP relay? Being lazy, I'd do that first. Not a cheapo one.

8-17 Crankshaft position sensor faulty

I've had that for 15+ years. I assume it to be a red herring and has always returned after being cleared. The CPS on these rarely fails, unlike, so I hear, that on later cars.

Of course, ensure all aspects of the fuel system are top notch. O2 sensor, EHV etc.

And clean every electrical contact you can with high grade contact cleaner.

And ensure your EZL is thermally connected to the bulkhead with high grade heatsink compound.

Much of what I rant about is general and not specific to your symptoms. Just good practice based on 25 years of ownership.

It's easy for me to spend your cash but you have a potentially stunning car.

Good hunting.

RayH

 

[Mike in Vancouver]

Thanks for the reply. I replaced the OVP relay . . . . and the ASR/ABS warning lights in the instrument cluster went OFF!!!

The car then started and idled great but when I went to drive it the stalling on acceleration was still there. I staggered around a few blocks and was just about to return home and have it towed to a mechanic . . . when the stalling problem went away and the car has driven perfectly for the past week or so.

The ASR/ABS lights have remained off the whole time and if the problem returns (sans lights) my next move will be to clean the distributor cap and rotors which were replaced in 2018. I will post any updates as appropriate but hope my lesson (OVP REPLACEMENT) can help others.

As a side note the auto parts place only had a URO available though I subsequently have read KAE/Kaehler, Stribel and MB OEM part # is 201-540-37-45 are better (in that order).

 

[rayhennig]

auto parts place only had a URO available

I would only want genuine MB for this vital part. But they are quoting delivery into 2022. I found one on eBay from Lithuania and it's istalled.

As you say, Kaehler or Stribel may be better alternatives.

I keep the old (2017) working unit in the boot for emergencies.

RayH

 

[Mike in Vancouver]

Bad news -- sort of. It's been running like a top for a week but yesterday (a rainy day fwiw) the stalling out returned though only for a few minutes. The car was warm and after four or five attempts to start and feather the revs past stalling it forgot the problem and has driven great for two days. But obviously worrying. Here is video of the failed startup attempts: https://share.icloud.com/photos/0YQzTYa6tOJqDPG4qHqOFzpEw

 

[Garista]

Bad news -- sort of. It's been running like a top for a week but yesterday (a rainy day fwiw) the stalling out returned though only for a few minutes. The car was warm and after four or five attempts to start and feather the revs past stalling it forgot the problem and has driven great for two days. But obviously worrying. Here is video of the failed startup attempts: https://share.icloud.com/photos/0YQzTYa6tOJqDPG4qHqOFzpEw

I had this symptom and I cleaned the throttle plate, which seemed to have a sort of old varnishy film on it, after this it was fine. I also cleaned the rest of it.

 

[alexanderfoti]

Did you check the distributor cap, rotor and leads?

Wet weather usually brings failures in these out