1991 300 SL: Is this rotor/cap bad?
 

Hi everyone,

I'm having the misfiring issues with my 1991 300SL. I guess this problem has been discussed in detail. Lots of 90s engines had these problems. While I haven't tried out everything yet (I'm going step by step):

Planing to replace the following in this order and see when I solve the problem. I'm hoping for this easy fix.

1. spark plugs
2. dust shield
3. rotor/cap

My spark plugs are kind of old, so this is a no-brainer. After some research the culprit seems to be the dust shield very often. It appears OK from the front, but might be cracked in the back.

I need some help/advice on the rotor/cap though and attached some pictures. Booth look pretty worn to me, but I'm not an expert. Any thoughts?


https://cimg7.ibsrv.net/gimg/www.mbw...c1eb1e0e00.jpg



https://cimg8.ibsrv.net/gimg/www.mbw...14f1c7fb5e.jpg

Change those parts out!

Thanks for the advice sutliffe. I will go ahead and do this asap.

Apparently, the common misfire issues can have many causes. I put in new spark plugs and put in a new dust cap (behind the rotor, mine fell apart after deinstallation).

The car drove perfectly fine for about two weeks and then the misfires came back. After reading out fault codes it turned out that I have a faulty crankshaft position sensor. I will swap this one and also put in a new distributor/rotor.

Thanks....

Faulty crankshaft position sensor highly probable, about $60 right? Let me know how you make out.

Starts and runs fine for about 10 mins. Afterward - begins to hesitate and idles roughly. After cutoff - restarting results in choking, coughing, sputtering engine. Sometimes doesn't restart. And stalls at idle when this condition occurs. This an example faulty crankshaft sensor. Replace the other items first before you get the Crankshaft sensor, unless you have a definite fault code calling out the sensor.

These are exactly the symptoms. I got a fault code for the CPS, ordered it and will replace it on the weekend. Will keep you posted.

Thanks mate...

Soooo.....it's been a while.

As I said before, I had a fault code for the CPS. Started to work on it....what a b**ch. After about an hour I finally broke it off. Super! Had to wait a few days to get the right tools and drill it out. Basically, destroying it. I put in the new one last weekend, I have to admit I forgot to reset the fault code if that makes a difference, and a few days later....I had the same issues again.

I did not swap the rotor/cap yet, since I had a fault code....and was a little tight. The CPS was the cheaper option for now.

Another thing that was kind of interesting is that the bogging/sputtering mostly appear when in gear, not when I'm in neutral.

- I know I need to swap the rotor/cap.
- Does it make a difference if I reset the fault code? Will do so on the weekend.

Thx

CPS Problem
 

How did you make out with the CPS?

Sorry...I don't understand the question. Not a native speaker here.