1992 sl 300 24 [r129]

[mick benz 320sl]

Hi, I hope someone can help. My son has a 1992 SL 300 24 that has started to breakdown once it reaches running temperature. It drives great until it warms up then it seems to lose spark. The coil has been changed but has made no difference. Starts and drives fine once it has cooled down until it warms up.

 

[Hawkwind]

Don't know, but I've read that the SL's can have wiring loom problems

 

[jonnyboy]

Dont think the 24v engine suffers loom-wise as it is a std dizzy cap not coil packs.
This sounds to me like the ignition module on the inner wing breaking down - they have some weird white paste on the back (heatsink paste?) that breaks down over time.....


He bought the best engined-one !

 

[neilrr]

I think the heat sink paste problem on the bottom is just an urban myth.

IME they die because after 20 years or more the 'O' rings on the 8 pin plugs don't do their job any more & allow moisture in, which kills the EZL.

 

[GAV105N]

Distributor cap

 

[Mercedes man]

Misfire

Hi defiantly distributor cap and Roger arm these engines eat them very expensive

 

[Mercedes man]

Meant rotor arm

 

[mick benz 320sl]

Why would it only break down once warmed up . I would have assumed that if the rotor arm and cap were no good it wouldn't run at all.

 

[Druk]

Why would it only break down once warmed up . I would have assumed that if the rotor arm and cap were no good it wouldn't run at all.

Because they get moisture in them which condenses out when cold but when hot goes back to vapour which buggers the spark. New cap is best solution.

 

[E55BOF]

The SLs definitely DO suffer from the engine wiring harness problems, but it depends when they were made - only certain years develop the problem. I'd go with the opinion of the guys who know on here to look for a cure of the OP's car.

Druk, is it not possible to stop moisture getting into the cap in the first place, thereby avoiding the need for a replacement? I ask because I pick up my R129 SL500 - new engine wiring harness just fitted - quite soon.

I can't recall the last time I had a car with a rotor arm, but it was a long time ago; a VERY long time ago...

 

[ray_hennig]

Hi, I hope someone can help. My son has a 1992 SL 300 24 that has started to breakdown once it reaches running temperature. It drives great until it warms up then it seems to lose spark. The coil has been changed but has made no difference. Starts and drives fine once it has cooled down until it warms up.

1992 sl 300 24 [r129] is much the same as mine. Start by replacing the rotor arm. Then make sure all HT is in best possible condition with MB original or Beru/Bosch parts. Only non-resistor plugs, too.

It's unlikely to be the ignition module but do make sure the module is well seated on a thin layer of heatsink compound.

Then try it again.

Best of luck.

That car does not have the eco-junk wiring.

RayH

 

[ivan1983]

Do these have the crank position sensor? If so then could be a possible candidate as failing ones have symptoms similar to what is described

 

[ray_hennig]

Do these have the crank position sensor? If so then could be a possible candidate as failing ones have symptoms similar to what is described

Yes, they do, but start with the HT.

The CPS is pretty reliable and never gave a problem for me.

HT.

RayH

 

[mick benz 320sl]

Thanks everyone for your input. Changed the rotor arm and distributor cap, problem solved.

 

[Vlad]

Just as a heads up the 300-24 does not suffer from wiring harness issues....its only the later 320's and 500's from late 1992-1995 that suffer

 

[Druk]

Druk, is it not possible to stop moisture getting into the cap in the first place, thereby avoiding the need for a replacement? I ask because I pick up my R129 SL500 - new engine wiring harness just fitted - quite soon.

This question has long interested me. This cap is sealed to the engine with an O-ring and my theory is that as the engine heats up the air inside the cap expands and is forced out past said O-ring. As it cools, air + any moisture present is sucked back in which then condenses out and is trapped. (Applying the theory that water molecules are larger than air)
I often wonder what would be the result if permanent ventilation were incorporated into the design so that any airborne moisture was free to come and go as it pleased rather than be trapped inside the cap by the O-ring.


Just a thought......




.

 

[E55BOF]

An interesting thought. SAAB 9-5 headlight units, to name one I know about, have a little rubber drain tube on the underside to let out any water that gets in. It wouldn't be too difficult to fit something similar to the distributor caps, I would think. I'll start by greasing the O-ring liberally with high-temperature grease, though, and see how it goes.