SL/R129: 95 500SL with possible ignition problem
Thread Starter
Newbie
Joined: Jun 2008
Posts: 1
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1995 SL500
95 500SL with possible ignition problem
I have recently purchased a 95 500SL with 72K on the dial. This is a really nice car but, unfortunately for me, has decided to lay down every once in a while. Here is the problem and I really would appreciate your thoughts on a solution.
Sometimes the Benz runs great. Then again, sometimes it will backfire while cranking and will never start. Once it backfires, it will not start, however, I can go back and try again in several hours or overnight and it will start right up.
Then again, there are times when I will be driving and will pull up to a stop sign or a red light and the car will die in place. In this case, I am forced to push the car off of the road because it will not start again. However, I can go back several hours later or overnight and it starts right up.
I have taken the car to a local shop (the closest MB dealer is 65 miles) with a great reputation. They told me that the cats were poisoned and needed to be replaced. They did not do a computer scan of the engine because they said their equipment would not read the 95 or 96 models? They made the recommendation based on the sweet/gas smell in the car after running it. So I purchased two cats on the internet and had them installed.....and the car wouldn't start at all. That was yesterday and I went back today and the car started right up.....go figure.
What am I missing here? Does anybody have any experience with this kind of behavior? What else can I try? I am a new MB owner and I sure would appreciate you folks sharing some of your experiences with me.
Thanks for your consideration.
Boyd Hogan
95 500SL
63 TBird
Suffolk, VA
Sometimes the Benz runs great. Then again, sometimes it will backfire while cranking and will never start. Once it backfires, it will not start, however, I can go back and try again in several hours or overnight and it will start right up.
Then again, there are times when I will be driving and will pull up to a stop sign or a red light and the car will die in place. In this case, I am forced to push the car off of the road because it will not start again. However, I can go back several hours later or overnight and it starts right up.
I have taken the car to a local shop (the closest MB dealer is 65 miles) with a great reputation. They told me that the cats were poisoned and needed to be replaced. They did not do a computer scan of the engine because they said their equipment would not read the 95 or 96 models? They made the recommendation based on the sweet/gas smell in the car after running it. So I purchased two cats on the internet and had them installed.....and the car wouldn't start at all. That was yesterday and I went back today and the car started right up.....go figure.
What am I missing here? Does anybody have any experience with this kind of behavior? What else can I try? I am a new MB owner and I sure would appreciate you folks sharing some of your experiences with me.
Thanks for your consideration.
Boyd Hogan
95 500SL
63 TBird
Suffolk, VA
Newbie
Joined: Sep 2007
Posts: 2
Likes: 0
70 280SL, 71 280SE 3.5, 86 560SL
Seems very similar to the problem I'm having with my 86 560SL. When mine wont start I seem to be getting a clattering from the metering plate/air flow sensor under the air cleaner. I've been chasing this down for several weeks now. It appears to be something to do with the stereo amps that were installed a couple of months ago. See this tread
http://www.benzworld.org/forums/r-c1...roblems-2.html
We'll see what I can find.
http://www.benzworld.org/forums/r-c1...roblems-2.html
We'll see what I can find.
Senior Member
Joined: Nov 2004
Posts: 282
Likes: 3
From: Bradenton, FL
'87 560SL Sold, '99 SL500 For Keeps
Boyd,
I think Lee is quite correct about having the codes read either at a dealer or better independent tech that invested in the MB Star Diagnostics system. Having said that, from what you're describing and the MY of the car, my inclination would be to inspect the engine wiring harness as the mid 90's MY's had known difficulties with wiring/insulation degradation. The start/stall/no start/cool down/start symptom sounds to me like the crankshaft position sensor at the rear of the engine. When these fail, the fuel pump is shut down, fuel pressure is lost and the car stalls. When the engines cool somewhat, they will often start again, but you're on borrowed time.
Last, find a new indy who has a better sense of smell. This is the first I've heard that clogged cats smell sweet. It could be true, I've just never heard that 'diagnostic'.
Bob
I think Lee is quite correct about having the codes read either at a dealer or better independent tech that invested in the MB Star Diagnostics system. Having said that, from what you're describing and the MY of the car, my inclination would be to inspect the engine wiring harness as the mid 90's MY's had known difficulties with wiring/insulation degradation. The start/stall/no start/cool down/start symptom sounds to me like the crankshaft position sensor at the rear of the engine. When these fail, the fuel pump is shut down, fuel pressure is lost and the car stalls. When the engines cool somewhat, they will often start again, but you're on borrowed time.
Last, find a new indy who has a better sense of smell. This is the first I've heard that clogged cats smell sweet. It could be true, I've just never heard that 'diagnostic'.
Bob
MBWorld Fanatic!
Joined: Jul 2012
Posts: 4,509
Likes: 1,513
From: Orbiting the planet
This place is a joke.
Look into something called the "overvoltage protection relay" or as mechanics call it- the breakdown relay- because that's what it causes while preventing nothing. Gotta love German engineering....
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Joined: Jan 2020
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1990 Mercedes 500sl
Fixed!
Thanks for the info. I previously replaced the crankshaft sensor (very easy and from the routing, appeared to have been replaced before) = same problem. Checked the distributors (worn but ok - cleaned them up) = same problem. Check the over voltage protection relay as suggested. Appeared the case had been opened before and found light corrosion on pins and circuit board. Cleaned it up with a copper brush = car now runs fine!! Next issue is uncontrollable hot air coming from side vents with cold AC air from center vents. Thanks all!
