91 300e will not start
 

I know that there are a lot of threads out there addressing this problem and I have read as many as I have found in the last few days.

Here's my problem:

My 91 300e 4matic was having some problems starting, I would have to keep the starter engaged an extra second or so. The other morning my car would not start (it turns over fine) when it was 30* F, I tried it again when I got home from work (40* F) and it still did not start.

My Questions:

Could this be the water temp sensor? Would this prevent the car from not starting at all? Would an adjustment to the EHA be helpful?

Answers to these questions and any hints on diagnosing the problem will be much appreciated.

Brian

try searching the list again. There was a recent thread that started last december and went around for a couple months. Turned out to be the fuel pump. But I can't recommend throwing parts at it. The thread would be useful because there's lots of good advice for diagnosing the problem. Literally could be dozens and dozens of things.

I don't the think the EHA or the water sensor is where I'd start. You could attach a timing light to the plug wires to ensure you have spark. Then I'd shoot some ether into the throttle body while trying to start it up (depress the gas pedal a little too). If it sounds like there's combustion then you know you've got a fuel system problem. Next steps would be to verify the operation of the fuel pump, cold start valve, and the idle control valve. fuel pump is pretty easy - try to start the engine and return the key to the "on" position - if you hear a humming from the back of the car that continues for a second or two then you know the main pump is functional.

Good luck

my 88 300E did not start. I found today that the....
 

fuel pump relay was the problem.
check this post http://www.peachparts.com/shopforum/showthread.php?t=118676

Thanks for giving me some direction...
 

I'll check out the pump and relay today, that is if it stops snowing. We received about 6 inches last night.

Waiting for spring to arrive.

It's starting, but I don't know why
 

I checked for the pump relay, but this being a 91, the relay is part of the MAS. So I disconnected the battery, removed the MAS and checked out the condition of the metal connectors/pins. They all looked clean, so I replaced the MAS and reconnected the battery and attempted to start the car to listen for the fuel pump. The car started right up, no problem. I have started the car up a half dozen times in the last day and taken it for a test run. Still no problems.

However, I am hesitant to drive it any real distance, afraid that I will have the same problem again. Does anyone have any insight on what the problem may have been? And if so, what I can do about it.

Thanks,
Brian

fuel relay
 

my fule pumo relay looked like new but when I opened it inside one of the contacts was cracked. Some soldering did the job. :D
ACM

Brian,
Ryan gave you about the same advice I would have. Removing and reinstalling the MAS might have cleaned the contacts, but I'm betting one of your two fuel pumps in going South. This is a common problem on Mercedes of this era. The most dreaded word in a mechanics dictionary comes into play here. That word is INTERMITTENT. These pumps play that game. I also had an EZL module play that game a few weeks ago. It drove me nuts. The car would crap out on the road and be fine when it got to the shop. Good luck.

Peter

Intermittent is the word.
 

I drove down to town yesterday and the car stalled out at an intersection. It started right back up and I drove it home and have been driving my truck since then. I'm assuming that my fuel pump is the problem, hoping that I only have to replace one of them.

I did hear an occasional clicking sound (like a stone was stuck in the wheel) coming from the area where the pumps are located.

When I access the pumps, is there a good way of testing which pump to replace? Since the problem appears to be intermittent, I'm not sure that it will be all that obvious. Or should I bite the bullett and replace both pumps? I prefer not to take the trial and error approach, but would like to save on the $200+ that each pump costs.

Thanks,
Brian

Brian,
There is a factory test that checks fuel pressure right at the pumps, but it requires a special fitting that you will have to order. This test is really only for premature failure. If you only had say 20k on this car new, and the pumps failed, you could tell which one to replace. It is an old axiom in the business that if you have two calipers, or two shocks, or two fuel pumps, or whatever you have two of, when one fails, the other isn't far behind. Also you need to deal with it before the extra current draw takes out the fuel pump relay.

Peter