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Intermittent...Backfire, Pinging, Won't start

8K views 8 replies 7 participants last post by  Black Forest 
#1 ·
Hello Team

Re: 1991 500SL, Japan delivery, no cats, no oxygen sensors, no emission controls worth noting...

She starts and runs quite well, (gotta start 2ice when cold), has great power and is an absolute pleasure to drive, especially fast, as she should be...
However on the odd occasion, after driven a short trip (10-20 mins) and stop for a short time (10-20 mins), then try to start again you can hear pinging under the bonnet while turning over, absolutely refuses to fireup and backfires very loudly out the exhaust... Try again and again, 5 - 6 times, same same, sometimes she will start, idle rough for a few seconds and stall...
The beauty of this, is that I leave her alone for around 30 minutes, go back and try, starts and runs as good as always and as if nothing has happened...

Very rarely, while driving, she will idle rough, miss and splutter on the 1st part of acceleration (irons out as the revs get up above 2500 or so) but idle down rough and eventually stall. Try to start and the above repeats itself...

*The strangest of all, this happens on average once every 4 weeks ... Seriously... 4 weeks...

**Aside from a "divorce, does anyone have any ideas ???
 
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#2 ·
The weakest link with the early CIS models is the Distributor caps and parts. They can also suffer with condensation in them. I made a point of making them a regular service item.

This is one of mine not long after I purchased the car and only a short time after the Previous owner had had them serviced and changed by MB.

Even though it looks real bad it only had signs of a slight misfire and stalling occasionally at traffic lights :) Bullet Proof lol!
 

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#3 ·
Inspect dist cap and rotor, I have original ones on my 91, it can be a bitch starting if I let it sit for a week or more, once started and warmed it runs great, I know its getting plenty of fuel because once it starts its like a flooded condition,uneven idle till excess fuel burns off, and not enough spark in the beginning due to dirty contact points in dist caps, if I clean them up with emery cloth, issue go's away for a while.
 
#4 ·
Peter,

Aside from everything mentioned above - your car's symptoms describe 100% exactly what my W202 was doing, exactly!!! Same after warm up, non-restarting for 20-30 min, one time actually called the tow truck after a fill-up at the gas station. Just won' start, pinging... So I let it rest... Tried cranking again after 30 min - started like nothing happened! It was Crank Position Sensor in my case. Replaced that last year (10 min job) perfect ever since.

This past Friday, my 4L Jeep GC started to do exact same thing, again, same symptoms. Spend 1 hour yesterday replacing that Crank Position Sensor, good as new again!

Good luck!

Regards,
D
 
#8 ·
I had the exact same symptoms with an old 911 that I have and it was indeed due to moisture inside the dist. cap. It's a very annoying problem and quite an awkward and embarrassing situation when the car just decides not to start up after a refill at a gas station... :grin
 
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