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land sea air 05-14-2009 03:17 PM

500SE stumbles/misses heavily at 1500-2000 RPM
Hello all, 86 500SE euro. I have had this problem since I bought the car, between 1500 and 2000 RPM under light to moderate load the car misses heavily with popping from the exhaust. Under heavier loads (not necessarily full acceleration) it runs great but unfortunately 2k rpm is where the car wants to run at highway speeds (55-65mph) so often times I have to leave the car in 3rd gear to alleviate the problem or speed more than I'm comfortable. This is one of the only things keeping me from fully enjoying the car so any help would be much appreciated!

cap and rotor are not new (I have ordered them in the hope that that was the problem) but they look perfectly fine.
replaced plugs and wires last year which didn't fix the problem.
the car has EZL ECE for adjusting timing for different fuel types, I run 93 in the car but having the resistor set for 89 or 87 seems to lessen the problem which makes me think it's ignition related rather than fuel.

tinypanzer 05-14-2009 07:02 PM

Hmmm...... Are you saying that it runs rough between 1500-2000, but it runs ok when above 2K?

land sea air 05-14-2009 08:50 PM

basically, maybe a little higher than 2k and a little lower than 1500 but that's the general range

tinypanzer 05-15-2009 09:24 PM

How many miles? Any work done to the exhaust system? My initial thought is cat converter or precats plugging up, but I could be way off. Just a hunch.

I could also see a flaky crank position sensor doing things like that.... Especially if tweaking the timing resistor seems to help.

Make sure you are using the correct non-resistor type plugs and not platinums...

Other than that, without more info I'm kinda lost...

Johnhef 05-15-2009 10:54 PM

I believe it has the correct plugs- right?
It has the tri-y manifolds with precats in the down pipes and no main cats.

may want to try loosening the down pipes from the headers and see if it still does it.

I was thinking about the crank sensor as well...
Swapped coils, same thing, swapped EZL's (with a 560) same thing.

land sea air 05-15-2009 11:00 PM

Car has 250k

I don't think it's exhaust related since it all looks to be in pretty good shape. Also fairly certain the car doesn't have cats but perhaps Johnhef could shed some more light on the topic (forwards thread).

Where is the crank sensor located on M117? How would I test this?

When I replaced the plugs I used non-resistors so I doubt that's the problem.

tinypanzer 05-16-2009 12:04 AM

Man, I'm all out of guesses. I'd have to see the car to have any chance of getting this one.....

I'll leave this to the more experienced contributers here.....

My only remaining guess is a slopped out timing chain...... Ever had it replaced?

land sea air 05-16-2009 12:16 AM

hasn't been replaced but timing is correct if I remember from John hitting it with the light.

Johnhef 05-16-2009 01:29 AM

no the exhaust could still be a problem, its a halfassed attempt at federalizing with precats welded in, and cramped at that. iirc one of the cats is laying against the block or p/s box or something.

pawoSD 05-16-2009 09:44 AM

Yikes, does it have original chain guides as well? If so I'd be replacing all of that ASAP....thats an every 100k job!

land sea air 05-16-2009 06:32 PM


Originally Posted by pawoSD (Post 2201713)
Yikes, does it have original chain guides as well? If so I'd be replacing all of that ASAP....thats an every 100k job!

can that cause the miss?

Johnhef 05-16-2009 08:10 PM


land sea air 05-16-2009 10:30 PM

well understandably it's now on my to do list.

land sea air 05-21-2009 09:22 AM


I installed a new cap and rotor to no avail.

how can I check the crank position sensor and where does it plug in? (at both ends)

Johnhef 05-21-2009 08:57 PM

left rear of the engine at the bellhousing, other end is the green wire into the EZL.

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