1989 Mercedes Benz 300e Help

Donations are seriously appreciated but that has nothing to do with getting an answer of value. I read your question but didn't feel qualified to give you the best answer, so I skipped it. Once one of us posts an answer, your question goes "off the list" of questions waiting for an answer, and no one else will ever see it or have a chance to reply. That's why we leave them for the most qualified expert. Most of us work and can only be on the computer for a few hours. In my case, due to a major house fire, I have to drive 20 miles round trip once each night to sit in the library parking lot to use their wireless internet, for the benefit of people with car problems, most of which I answer for free. When your question gets answered depends on when it is seen by one of us who knows the answer or knows the best way to solve or diagnose the problem. It's rare but not uncommon for that to take a day or two, or it could take ten minutes.

Also remember that while this may not apply to you specifically, we get a lot of questions about engine running problems and the engine size is not listed. We get questions asking how to do a procedure with no history of what led up to the problem or why they want to do that procedure. How that question is answered depends on knowing that history or background details. A lot of people don't understand that "doesn't start" can mean a dozen different things, just like "I'm in pain, ... Why"? We need specific details, observations, test results, and clues. A lot of us have been yelled at for daring to ask for those details or for not being psychic, so we just skip over those questions now when there's no information provided. Experience has shown most of those people never reply back anyway, so we just waste our time. Other people are very appreciative of our help, and it's not uncommon to go through 20 to 50 replies before we come up with a solution. Most of us will stick with the problem when we think we can help.

You actually posted two separate questions. I see your original one has gone off the list so someone did answer it recently. You got an automated e-mail with a link directing you back to that reply. Be sure to post your followup replies to that same thread. If you start another new question each time, like you did here, that first expert won't know about it or get the e-mail message with the link to it to read it. It would just be by chance that he might see your new post, but there would be no way for him to go back and reread your previous comments.

There are a couple of things I can suggest. First of all, fuel pump relays on all cars will never turn on continuously with just the ignition switch turned on. To do so would create a serious fire hazard if a fuel line got ruptured in a crash. With a damaged fuel line, the engine can't run without fuel pressure. When it stalls, the Engine Computer sees the lack of rotation, so it turns the fuel pump relay off. My reason for mentioning that is you can have a problem with one of the two sensors the computer looks at to determine if it should turn the relay on. Those are the crankshaft position sensor and the camshaft position sensor, or whatever name the manufacturer gives them. If you have a distributor, the camshaft position sensor is usually inside it.

Those sensors are also what is used to determine spark timing. A failing sensor can cause erratic loss of spark and / or backfiring, and it can cause the computer to intermittently turn the fuel pump relay on and off. Replacing the relay can result in the illusion something has changed when the real cause is related to those sensors.

(Looks like you're in the Central time zone. So am I).

Since your engine uses those sensors, there is going to be an Engine Computer involved, and that usually means the ability to detect problems and set diagnostic fault codes. We have listings here for those codes and how to read them, but I don't see anything for Mercedes. For '96 and newer cars, most auto parts stores will read the codes for you for free, if you can get the car there. For '95 and older models, scanners specific to the vehicle brand are usually needed, so that means making a trip to the dealer, or buying your own scanner. I have a number of scanners that work on Chrysler vehicles, and you can find those on eBay for as little as 50 bucks.

Reading those fault codes is the place to start. They never say to replace parts though, or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a sensor is referenced in a fault code, it is actually the cause of that code about half of the time. You also have to look for cut wires, bare wires that are grounded, stretched connector terminals, corroded splices, and things like that.

Don't overlook a jumped timing chain too.