SL-Class (R129) 1990-2002: SL 280, SL 300, SL 320, SL 500, SL 600, SL 60 AMG

SL/R129: 1991 300 SL: Is this rotor/cap bad?

Old Sep 8, 2014 | 01:36 PM
  #1  
Wulmserine's Avatar
Thread Starter
Newbie
 
Joined: Aug 2010
Posts: 9
Likes: 0
From: Baltimore, MD
1991 Mercedes 300SL
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?






Reply
Old Oct 6, 2014 | 08:12 AM
  #2  
sutliffe's Avatar
Junior Member
 
Joined: Oct 2014
Posts: 68
Likes: 6
From: Epping,NH
1998 SL500
Change those parts out!
Reply
Old Oct 6, 2014 | 08:17 AM
  #3  
Wulmserine's Avatar
Thread Starter
Newbie
 
Joined: Aug 2010
Posts: 9
Likes: 0
From: Baltimore, MD
1991 Mercedes 300SL
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....
Reply
Old Oct 7, 2014 | 12:07 AM
  #4  
sutliffe's Avatar
Junior Member
 
Joined: Oct 2014
Posts: 68
Likes: 6
From: Epping,NH
1998 SL500
Faulty crankshaft position sensor highly probable, about $60 right? Let me know how you make out.
Reply
Old Oct 7, 2014 | 12:18 AM
  #5  
sutliffe's Avatar
Junior Member
 
Joined: Oct 2014
Posts: 68
Likes: 6
From: Epping,NH
1998 SL500
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.
Reply
Old Oct 7, 2014 | 07:23 AM
  #6  
Wulmserine's Avatar
Thread Starter
Newbie
 
Joined: Aug 2010
Posts: 9
Likes: 0
From: Baltimore, MD
1991 Mercedes 300SL
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...
Reply
Old Dec 11, 2014 | 05:43 PM
  #7  
Wulmserine's Avatar
Thread Starter
Newbie
 
Joined: Aug 2010
Posts: 9
Likes: 0
From: Baltimore, MD
1991 Mercedes 300SL
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
Reply
Old Dec 11, 2014 | 10:00 PM
  #8  
sutliffe's Avatar
Junior Member
 
Joined: Oct 2014
Posts: 68
Likes: 6
From: Epping,NH
1998 SL500
CPS Problem

How did you make out with the CPS?
Reply
MB World Stories

The Best of Mercedes & AMG

story-0

6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)

 Verdad Gallardo
story-1

Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun

 Verdad Gallardo
story-2

Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren

 Verdad Gallardo
story-3

8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine

 Verdad Gallardo
story-4

Flawlessly Restored Mercedes 190E Evo II Heads to Auction

 Verdad Gallardo
story-5

Electric Mercedes C-Class Unveiled: 11 Things You Need to Know

 Verdad Gallardo
story-6

Mercedes EQS Gets A Major Update: Everything You Need to Know

 Verdad Gallardo
story-7

5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve

 Verdad Gallardo
story-8

Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping

 Verdad Gallardo
story-9

10 Most Reliable Mercedes-Benz Models You Can Buy Used

 Verdad Gallardo
Old Dec 12, 2014 | 06:39 AM
  #9  
Wulmserine's Avatar
Thread Starter
Newbie
 
Joined: Aug 2010
Posts: 9
Likes: 0
From: Baltimore, MD
1991 Mercedes 300SL
Sorry...I don't understand the question. Not a native speaker here.
Reply

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 

Thread Tools
Search this Thread
Rate This Thread
Rate This Thread:
You have already rated this thread Rating: Thread Rating: 0 votes,  average.


All times are GMT -4. The time now is 01:00 AM.

story-0
6 Mercedes Models That Did NOT Age Well (But Are Somehow Still Cool)

Slideshow: Not every Mercedes design becomes timeless, some feel stuck in the era they came from.

By Verdad Gallardo | 2026-05-12 18:09:07


VIEW MORE
story-1
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun

Slideshow: Yes, Mercedes built manual cars, and some of them are far more interesting than you'd expect.

By Verdad Gallardo | 2026-05-02 12:36:58


VIEW MORE
story-2
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren

Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.

By Verdad Gallardo | 2026-04-29 11:19:28


VIEW MORE
story-3
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine

Slideshow: Before curves took over, Mercedes mastered the art of the straight line, and some of those shapes still look right today.

By Verdad Gallardo | 2026-04-25 12:05:49


VIEW MORE
story-4
Flawlessly Restored Mercedes 190E Evo II Heads to Auction

Slideshow: The 190E Evolution II shows how a homologation necessity became a six-figure collector icon.

By Verdad Gallardo | 2026-04-22 17:53:47


VIEW MORE
story-5
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know

Slideshow: Mercedes is turning one of its core nameplates electric, and the details show just how serious this shift is.

By Verdad Gallardo | 2026-04-21 13:58:06


VIEW MORE
story-6
Mercedes EQS Gets A Major Update: Everything You Need to Know

Slideshow: Faster charging, longer range, and a controversial steer-by-wire system define the latest evolution of Mercedes-Benz EQS.

By Verdad Gallardo | 2026-04-15 10:35:34


VIEW MORE
story-7
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve

Slideshow: These overlooked Mercedes-Benz models never got the spotlight, but they quietly delivered more than most remember.

By Verdad Gallardo | 2026-04-13 19:35:45


VIEW MORE
story-8
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping

Slideshow: A well-used 1991 Mercedes-Benz 300D with more than one million miles is now looking for a new owner, and it still appears ready for more.

By Verdad Gallardo | 2026-04-10 10:05:15


VIEW MORE
story-9
10 Most Reliable Mercedes-Benz Models You Can Buy Used

Slideshow: From bulletproof sedans to surprisingly tough SUVs, these Mercedes models proved that the three-pointed star can go the distance.

By Verdad Gallardo | 2026-04-08 09:55:49


VIEW MORE