560 SEL hesitates from stop when warm
 

I've had my '90 560 SEL for about 500 miles and recently after sitting through a couple of drive-thru's (bank & fast food) it hesitated really bad when starting from a complete stop. It felt like it was going to stall out, but didn't, the fuel just seemed to cut in and out but the tach never dropped below idle. The coolant temp was probably around 90/95 (c) at the time and the outside temp was around 72 (f). Once I got going there was no problem with throttle response. At the next stoplight the car once again exhibited the hesitation, with the fuel seemingly cutting in and out. I'm running premium fuel, it wasn't a really hot day (by West Texas standards), but the car does have 202K miles on the motor. Anyone have any ideas? The car also seems to run on the rich side, especially when cold.

TIA,

MJ Miller

Sounds to me like a bad spark plug insulator, which is shorting the electicity from that plug to the head and thus not firing the cylinder.

30 seconds on a scope will tell what is happening. Take it to a shop, and have them put the car on a scope, and you will see the electrical characteristics (or lack thereof) for each cylinder on the screen. A good tech will diagnose the problem just from that.

You can get new insulators for around $25-30 each, or better yet probably best to just get a new set of plug wires.

Good luck.

CHeers,
Gerry

I had a similar experiance with my 88 560SEL.

My car out of the blue started acting up on me just after I got it back from the shop (air intake issue left over from my 1st valve-job) and at first it started gimping out at stoplights when I was running an errand. When I shifted to neutral, everything was fine. When I returned from the store to my car it wouldn't start at first. I got it half-way home and it died in the middle of the intersection. Before it died it would miss and generally act as I would have expected if the transmission had jammed or if the fuel was bad.

On my car the problem was a dying ignition coil.

I don't know if it's a spark plug insulator as gerryvz suggested, but I would initially suspect the electrical ignition system.

The more I work on my 560SEL the more I love my 300CD. Maybe I should have gotten an SDL instead?

Good luck and the car is worth the effort! I love cruising 65mph at 2k rpm (with the redline sitting at 6k!)