Won't start.. Maybe a brain teaser. I'm stumped. 300SEL
 

I've been battling a condition wher this car will just be driving down the road, and cutt off. It would start right back, and may be a month before it does it again. One MB mechanic has looked at it, and come back empty..

It has sat without driving for a couple of weeks, and the other day it took a while to start, but ran fine when it did. It usually starts immediately. I drove it down the road, and it cutt off frequently, but ran with great power when it did run. I parked it for several days while I was out of town.. Today, it will not start. I'm assuming the two problems are related.

Engine turns over fine. Has fire at the plug wires (will jump 1/4 inch gap) that are new ( so is cap, and rotor). Cap and rotor look fine inside. Plugs look fine. I jumpered the fuel pump relay. Tried a different OVP even though I know it will start without it. Sprayed ether in the air flow meter. Made sure the engine was grounded with a meter. It never made any attempt to even sputter.

I don't have a way to verify fuel pressure, but the bosch pump is quite new, and this cutting off problem existed before it was replaced. What has me baffled is that I seem to have a good spark, but spraying ether in the AFM will not make it run..

I'm stumped.. What else am I missing? I doubt the engine has jumped time. It was running smooth when I parked it. HELP.. Somebody throw me a bone.

I would lean towards no or improperly timed spark. Reason being that it won't try even sputtering on the ether bunny (or "summer aire" as we call it. Also heard it called "turbo-in-a-can"). If there is a spark, and it's even close to being correctly timed, it should "try" to start at least briefly, assuming the ether doesn't actually explode and ruinate something.
SO, what the bone is that I'm going to throw is this, and YES I have seen this:
The rotor bracket (the part the rotor screws to) can crack and change the direction the rotor is pointing. Remove the cap again and see if the rotor is staying in a fixed position or if you can rotate it, it should stay in a fixed position (rotates only with the camshaft). i had one like this, very frustrating, somethimes it would catch onto the rest of the rotor bracket and run, other times it would be turning too far out of time for the ignition system to work properly.

Gilly

Thanks Gilly..
I'll pull the rotor off AGAIN, and check the bracket it attaches to for loosenes or if I can rotate it..

Here's the part that makes it even more frustrating.. When my wife got home, I had her get in the car.. I pulled a plug out, and attached it to the plug wire, grounded it to the engine to be absolutely sure the plug was firing.. It fired twice, and started right up on 5 cylinders. Put the plug back in, and the car runs perfectly.. Actually, it runs exceptionally good..

Before, I had checked spark by using a 10 Ft. piece of wire I could pull around to the drivers seat.. But it was making a big spark.. I checked from the coil, and from several plug wires..

Beats me.. I'm sure it will be back though. It's a beautiful car, but I'm tired of it, and I wish it would go away..

Don't remove the rotor, just the cap, then just try yanking on the rotor and see if it doesn't pull right out with the front half of the rotor bracket still attached to it. Boy, sure sounds alot like this car I worked on. Tough part is you'll ALWAYS have the spark, but maybe not at the right time. I'd still stand by my assertion that it's spark related though.

Gilly

Check your coil wire. Mine is fried where it clips to the plastic bracket beside the distributor, under the cover. I need a new one. Mine does not cut out though.

Check all your fuses for corrosion.

Coils on those cars can cause considerable problems. I have had ones that would just make enough voltage to idle the car. I have had plenty that wouldn't do that. I have had at least one lead us astray by looking like it made usable spark. One needs to know that a 6-8000 volt spark won't get it, in the cylinder. I have a scope pattern of one of these at work. It took 10kv to idle once fixed. It was only getting 8kv cranking and the needs cranking were probably higher than idling.

Coil wire is good (new). Both ends look new, and it tests good with a meter. Any way to test the coil??? The car starts perfectly now. Just bump the starter, and it purrs like a kitten. I'll pull the cap, and check the rotor bracket. If anything is noteable there I'll post back.

Thanks again for your help.

There are testing techniques for most everything. The test needed here for the coil will look at available voltage. With your scondary ignition scope hooked up pull a plug wire and evaluate the open circuit voltage. It should see 25-30kv. If it only makes 10-15kv one needs to see if the reason is lack of capability or a high voltage short. The common hi voltage short is the rotor. To separate the posibilities one then takes the coil wire to ground and then opens the circuit to ground increasing the spark length while monitoring the voltage.

Without tools one tests by substitution.