johnathan1

I have a 1991 560sel that was running OK for a long time, then developed a misfire. I traced it down to several vacuum leaks, and one or more bad spark plug wires. Replaced all of these things, and it ran PERFECTLY. Well, for one or two drives. Then after a couple days passed, it would start up perfectly, but then the idle would get lower and lower until the engine would die. No amount of throttle would keep it running. It would only run for about a MINUTE each time. Pretty consistently. After it would die though, it would always start RIGHT back up (no cooling-off or anything needed). It did this for about a month, while I tried various things in the way of diagnosing it. Then one morning when I went to start it, nothing. It would crank but never start up and run.

So since then, I have done the following: Replaced the crank position sensor (rear of engine, NEW MB Genuine part), Tried 4 different EZL's (all had four pins, all different part numbers) but no improvement at all. I have tried all kinds of things. Before the crank sensor was replaced, I was getting NO bouncing of the tach needle during cranking, after replacement, it now bounces. Tested AC Voltage output of crank sensor (new one) and it shows about 0.49 V Max. I also replaced the Coil (before problems started, as preventative maintenance) with an aftermarket one, and it seemed OK. Tried swapping back to the original one that worked fine before once problem started, but it doesn't seem to make any difference.

What the heck am I missing here?? The only issue that I can KIND of pick out is that the pins in the EZL connectors do NOT seem to read correctly as per the MB WIS pinout. It seems like I have 12V just about everywhere, and no ground. Does the EZL ground itself through its mount to the drivers side fender, or?? Can anyone offer any insight??

I have done much reading about this seemingly common problem, and usually people don't come back and follow up with what the solution was (so incredibly frustrating). This is a very nice, well maintained car that I have owned for the last five years or so, always ran quite well. Thank you for reading.

Mr. A Kaufman

Three Words:

Fuel Pump Relay

johnathan1

Ok. Well I bought a Brand New (Genuine, NOS) that I actually found by accident. Popped it in, and NOTHING. No start still just sits there and cranks.

johnathan1

Seems like a break in the wiring, when I move the (brand new) Fuel Pump Relay around while its plugged in, but out of its holder, I can get the fuel pumps to cycle on and off (the same as when the ignition key is cycled on and off). If I hold it in JUST the right position and crank the engine, it will run then stall when I slightly move the FPR.

So is this something anyone has encountered before on the W126? The only thing I can see the wiring chafing on is the throttle linkage, which is VERY close to the routing of the wiring harness.