92 MBZ E300 having strange engine trouble!

Hi all, I need some help diagnosing a car problem, then figuring out if I can do it myself or if I need help! Thanks in advance.

This 92 MB E300 has been sitting around for the better part of the last two years for various reasons (have another car with better mileage, don’t drive much anyways, no insurance on it, etc), and we’ve been trying to get it going again with some mixed luck. I just replaced one of the window regulators (cable busted) and the battery (alarm drained it dry), but now we’re having trouble starting it. It doesn’t happen every time, but when we try to start it, the starter motor seems to get going no problem and it turns pretty good, but it just won’t catch consistently. Its almost like there’s no fuel in there, or maybe no sparks or something? Sometimes it will catch for a second, but it takes a while. Usually once its going its good, but if we have to stop and wait at a red light, it will sometimes just die when shifting to drive (I usually put it in neutral and give some gas while waiting). Also sometimes just when its in a low gear and shifts up it will die too. Then, we have trouble starting it up again!

So whats going on, do you think? I was thinking maybe something along hte lines of fuel pump, spark plug, or injectors, but what do I know? (not much). Thanks for your help everyone!


I had similar problems in my 89 Mercedes. It’s pretty common for the Over-voltage protection relay to go bad. It temporarily takes out electrical current from the circuit and makes the car run as if the alternator isn’t working. A new relay fixed my problem. It’s pretty common in this era Mercedes. May or may not be your problem though.

Here it’s pretty cheap at rockauto.com. http://www.rockauto.com/catalog/x,carcode,1193914,parttype,13101

First off, I’m not a Benz expert by any means but an uneasy feeling led me to check and see that both engine options on this car use CIS fuel injection; a.k.a. pain in the neck in family friendly terms.

These systems are very touchy about any vacuum leaks which can cause hard starting, erratic idle, and so on.
A fault with the cold start injector can also cause difficult, or near impossible, starting.
CIS injectors are also prone to developing faulty spray patterns and leaking off and this can also cause a poor idle and difficult starts.
Aged Bosch fuel pumps can also be problematic.

I’m familiar with CIS, CISe, etc but there’s no way I can pinpoint this problem for you without car in hand. If no vacuum leaks can be found the next step is a fuel pressure check and this requires a special fuel pressure tester, a manual, and the ability to sort it all out.