SL/R129: 1991 300 SL Starter issues
08-21-2013, 02:59 PM
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1991 Mercedes 300 SL
1991 300 SL Starter issues
See update below first
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Hi, my 1991 300 SL is only driven in summer and this year for some reason it has decided to periodically (say once every ten times but completely at random) crank but not turn over.
I’ve replace batteries, checked plugs (no spark seen when shorting plug to chassis when this occurs) and had “deduced” this to be an issue only when it was too hot (ie outside plus having run for awhile) and therefore according to web search likely due to a fuel filter issue. However, yesterday it did this again when completely cold. Specifically I started it in my driveway no problem. Drove 10 miles, parked and then restarted no problem and drove another mile. Then had dinner (3+ hours) and upon returning to the vehicle it would not “catch” (ie crank but no engine) despite trying at least 10 times with various “web sourced diagnostic solutions” (such as putting car in Neutral and trying to start, moving the steering wheel up/in/out, feathering the gas, letting the starter crank for 20 seconds etc)
NOTABLY, when this happens the instrument cluster DOES NOT LIGHT UP (ie normally when the key is inserted and turned a notch or two the instrument panel idiot lights turn on and then disengage when the engine has started) and no electrical services are available (specifically when this situation occurs and say I am stranded somewhere so decide to put the soft top up, the soft top nor any of the climate controls operate even when I stop trying to “start” the car and simply put the key in and turn it one notch as would normally provide electrical services).
HOWEVER, last night for example I disconnected the battery and went back into the restaurant, had a cola and then 15 mins later went out, connected the battery and . . . turned the key and had it both crank (with power to the instrument panel lights) and turn over no problem whatsoever.
Thus there is no rhyme nor reason I can suggest -- and when this has happened previously I have tried disconnecting the battery, letting it sit and then reconnecting the battery but this did not then help the problem as it still -- for about three hours duration -- everytime I tried would not turn over the engine. Yet at some random point a few hours later, whether I disconnected the battery or not it started right up.
Any suggestions???
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Hi, my 1991 300 SL is only driven in summer and this year for some reason it has decided to periodically (say once every ten times but completely at random) crank but not turn over.
I’ve replace batteries, checked plugs (no spark seen when shorting plug to chassis when this occurs) and had “deduced” this to be an issue only when it was too hot (ie outside plus having run for awhile) and therefore according to web search likely due to a fuel filter issue. However, yesterday it did this again when completely cold. Specifically I started it in my driveway no problem. Drove 10 miles, parked and then restarted no problem and drove another mile. Then had dinner (3+ hours) and upon returning to the vehicle it would not “catch” (ie crank but no engine) despite trying at least 10 times with various “web sourced diagnostic solutions” (such as putting car in Neutral and trying to start, moving the steering wheel up/in/out, feathering the gas, letting the starter crank for 20 seconds etc)
NOTABLY, when this happens the instrument cluster DOES NOT LIGHT UP (ie normally when the key is inserted and turned a notch or two the instrument panel idiot lights turn on and then disengage when the engine has started) and no electrical services are available (specifically when this situation occurs and say I am stranded somewhere so decide to put the soft top up, the soft top nor any of the climate controls operate even when I stop trying to “start” the car and simply put the key in and turn it one notch as would normally provide electrical services).
HOWEVER, last night for example I disconnected the battery and went back into the restaurant, had a cola and then 15 mins later went out, connected the battery and . . . turned the key and had it both crank (with power to the instrument panel lights) and turn over no problem whatsoever.
Thus there is no rhyme nor reason I can suggest -- and when this has happened previously I have tried disconnecting the battery, letting it sit and then reconnecting the battery but this did not then help the problem as it still -- for about three hours duration -- everytime I tried would not turn over the engine. Yet at some random point a few hours later, whether I disconnected the battery or not it started right up.
Any suggestions???
Last edited by MikeShields; 05-13-2014 at 03:58 PM.
05-13-2014, 03:57 PM
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1991 Mercedes 300 SL
No start when hot 1991 300 SL
As an update to the above:
I have a 1991 Mercedes Benz 300SL which SOMETIMES will not start (to my recollection only when it gets hot but not always when hot). Specifically when cold, I can turn the ignition key one notch and all the lights on the instrument panel come on. Turning the key to the second notch then starts the car as normal.
However (for example yesterday after driving it a mere 15 minutes to a gas station) sometimes (and only when hot) upon turning the key to the first notch no instrument panel lights come on except for the SRS. Turning the key to the second notch then yields the starter cranking but the engine refusing to catch. Continued attempts to start the car meet the same result regardless of battery charge or boost (yesterday for three hours though obviously not constantly).
Notably when it refuses to start is that in addition to the aforementioned instrument panel not lighting up (or gauges operating) the windows, power soft top and temperature control panel do NOT work, however with the key turned one notch the power mirror and seat heater (button lights at least) still do work. (After failed start attempts there is also a faint clicking noise from what seems to be the dash in front of the passenger seat when the key is left at notch 1.)
Moreover, this morning (after having it towed home yesterday) it starts (cold) without any problem whatsoever (and I did not charge the battery overnight or otherwise touch the vehicle). Perhaps relatedly these models apparently run quite hot and the engine compartment of my vehicle seems very hot though the temp gauge does not when running show red/warning etc.
Extensive searching online suggests (but doesn't seem directly on point):
1. There was a wiring harness recall on these vehicles (though my Vancouver MB service departments insist not) and that said harnesses are prone to failure when hot (specifically cracking) although the wiring harness (P/N 129 540 2605 or 129 540 4505) is apparently no longer available from MB.
2. The use of a non-MB fuel filter may be the issue (I’m pretty sure the filter is non-aftermarket but am having it replaced with an official one as my next step though the electronics issues described above seem to make this unlikely as the cause).
3. The Ignition Switching Unit maybe faulty (though there seems to be more than one?)
4. An over voltage protection relay in the engine bay right rear module box maybe faulty
My mechanic suggests that without wiring diagrams (which I will buy if avail at a suggested link) he doesn’t want to risk causing damage via random testing while MB service has no suggestion other than to bring it in for them to start poking around at $150+/hour (which fwiw I did with a previous soft top issue that their assigned most junior tech could not resolve).
Thoughts/Suggestions/Advice (& my sincere thanks for all in advance)?
I have a 1991 Mercedes Benz 300SL which SOMETIMES will not start (to my recollection only when it gets hot but not always when hot). Specifically when cold, I can turn the ignition key one notch and all the lights on the instrument panel come on. Turning the key to the second notch then starts the car as normal.
However (for example yesterday after driving it a mere 15 minutes to a gas station) sometimes (and only when hot) upon turning the key to the first notch no instrument panel lights come on except for the SRS. Turning the key to the second notch then yields the starter cranking but the engine refusing to catch. Continued attempts to start the car meet the same result regardless of battery charge or boost (yesterday for three hours though obviously not constantly).
Notably when it refuses to start is that in addition to the aforementioned instrument panel not lighting up (or gauges operating) the windows, power soft top and temperature control panel do NOT work, however with the key turned one notch the power mirror and seat heater (button lights at least) still do work. (After failed start attempts there is also a faint clicking noise from what seems to be the dash in front of the passenger seat when the key is left at notch 1.)
Moreover, this morning (after having it towed home yesterday) it starts (cold) without any problem whatsoever (and I did not charge the battery overnight or otherwise touch the vehicle). Perhaps relatedly these models apparently run quite hot and the engine compartment of my vehicle seems very hot though the temp gauge does not when running show red/warning etc.
Extensive searching online suggests (but doesn't seem directly on point):
1. There was a wiring harness recall on these vehicles (though my Vancouver MB service departments insist not) and that said harnesses are prone to failure when hot (specifically cracking) although the wiring harness (P/N 129 540 2605 or 129 540 4505) is apparently no longer available from MB.
2. The use of a non-MB fuel filter may be the issue (I’m pretty sure the filter is non-aftermarket but am having it replaced with an official one as my next step though the electronics issues described above seem to make this unlikely as the cause).
3. The Ignition Switching Unit maybe faulty (though there seems to be more than one?)
4. An over voltage protection relay in the engine bay right rear module box maybe faulty
My mechanic suggests that without wiring diagrams (which I will buy if avail at a suggested link) he doesn’t want to risk causing damage via random testing while MB service has no suggestion other than to bring it in for them to start poking around at $150+/hour (which fwiw I did with a previous soft top issue that their assigned most junior tech could not resolve).
Thoughts/Suggestions/Advice (& my sincere thanks for all in advance)?
08-16-2015, 02:40 PM
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1991 Mercedes 300 SL
So for anyone with similar issue reading through this thread, I took the car into Euro Otto Sport 1610 Langan Ave Port Coquitlam, BC Canada (604) 941-1466 -- can't recommend them highly enough fwiw.
Anyway, based on my/our research they set out to install the new ignition switch I ordered online . . . but found that it was in fact that the "Key" cylinder had at the very end of it a broken piece (which they said they had seen before in other similar cars). Thus they had to send it (or a new replacement unit, I'm not sure) out to a key shop to do something then reassemble etc.
$650 in total costs but at least it's fixed (though just today my accelerator cable snapped, oh the joy .
Also, the new ignition switch was installed as well but apparently it was not necessary as the old one was still working fine -- so I have a used ignition switch for a 1991 era 300 SL if someone wants it but obviously it would have no warranty or promises . . .
Thanks again to all who replied to help . . .
Anyway, based on my/our research they set out to install the new ignition switch I ordered online . . . but found that it was in fact that the "Key" cylinder had at the very end of it a broken piece (which they said they had seen before in other similar cars). Thus they had to send it (or a new replacement unit, I'm not sure) out to a key shop to do something then reassemble etc.
$650 in total costs but at least it's fixed (though just today my accelerator cable snapped, oh the joy .
Also, the new ignition switch was installed as well but apparently it was not necessary as the old one was still working fine -- so I have a used ignition switch for a 1991 era 300 SL if someone wants it but obviously it would have no warranty or promises . . .
Thanks again to all who replied to help . . .
