bchogan

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

Miked56

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.

Lee Wireless

Take it to the dealer or have it flat-bedded there. They will be able to pull codes easily enough and are very familiar with these types of issues.

BJonesFL

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

Sir_Pierre

Did you solve it? I have the same problem.

Mbouboulis

I’m having this same issue in my 90 500sl. Changed the crankshaft sensor and did not fix the problem. Would appreciate any ideas. Thanks

E55Greasemonkey

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....

Mbouboulis

Thanks - I’ll check that next weekend. Fingers crossed

Mbouboulis

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!