1989 300e wont start

Guys,
I have a 1989 300e with 133K miles. I drove the car down the street the othe day, parked and the car would not start again. I have tried several times and it still wont start. The car cranks and sometimes ALMOST catches but never starts.
Recently we had the same problem and took it into the service center. They replaced BOTH fuel pumps and the symptoms went away for a week or so until my latest adventure.

The car is LOW on gas but not out. Could this be the problem? I AM SURE IT HAS GAS IN IT, I am not dumb.
Could it be the coil?

Any suggestions would be very helpful.

Thanks,

Reed

[suginami]

Fuel pressure regulator?
Fuel accumulator?
OVP?

[Ron Johnstone]

Same thing happened to my '88. Don't throw parts at it until you know exactly what is wrong. Buckle the seat belt, open the R window and turn the key. If you hear the fuel pumps running, you are o.k. there. If you don't, you may have a bad fuel pump relay. Lots of threads on that subject.
To isolate quickly the ignition system, add an ounce or so of fuel to the air intake (remove the air cleaner) and crank it over. If it starts and runs momentarily, the ignition is o.k. and you are probably not getting any fuel to the cylinders from the fuel distributor. Diagnosis of this problem really should be done with a pressure tester, which usually is only available at a MBZ shop.
We never really found what caused my problem as my mechanic ran all the tests and couldn't figure out what was causing my no fuel problem. He finally was pouring raw gas into the air intake while his helper was pushing on the accelerator. The car let out a huge backfire and has run just fine ever since??????? Good luck with yours.

[haasman]

If it were my car I would do 3 things that are easy ways to check two basics-

First, if you can find someone to help, pull a spark plug connector at the plug and out say a screw driver or something in the end of it and position it close to the plug. What you are trying to do is to see if there is a spark. Do Not Hold the wire while you do this as the spark system has a lot of volts!

Second, while the right-rear door is open so you can hear it, turn the key on and then off again. Do you hear the fuel pump? You should be ideally in a quiet location maybe next to another car or a wall, or have someone listen near the right-rear wheel.

Third, take off the air cleaner cover. Turn the key on and gently move the air mass sensor plate. You should feel a resistance from fuel pressure and most likely hear it as the key goes on and off, pressurizing the fuel distributor.

The OPC could be the problem as well - or the MAS relay. Both are located on your car, I believe like my '91 behind the battery, behind a vertical black plastic splash shield. Push down on the top of it and then pull out. Revealed are the two relays.

The OPC has a fuse at the top of it. Remove the fuse (under a clear little plastic cap) and make sure it is good.

The MAS relay is the tall silver device that can only be removed by twisting its black knob at the top counter-clockwise. I have no way of testing it. I went to a junkyard, paid for a used one, had them put their mark on it in case I needed to return it. They agreed. Never returned it. It was the problem.

Finally, are you sure there is enough fuel in it. I have been down this road before and what started one car was a couple of gallons of fuel. You could have crap at the bottom of your tank or even a bad sending unit.

Keep us posted.

Haasman

[Mick J]

Fuel pump relay is the most likely cause judging from previous posts, may also fit in with your previous problem. You can check it out by either listening for the pumps running when you turn on the ignition (but they only run for about a second unless the engine is being started or is running) or by temporarily jumping the relevant terminals on the relay base/connector. Terminal 30 is incoming live from battery, 87 goes to pumps, 87V to cold start relay.

Thumping it with the handle of a large screwdriver often effects a short term cure.

Forget about the OVP relay, assuming you car is KE jetronic injection (round distributor with injection pipes connected around the outside) it is unlikley to prevent starting altogether.

Hi,

Check all the vacuum lines around the starter motor and for that matter, all of the vacuum lines around the air cleaner box.

My car would not start but it would crank. Turned out to be a vacuum hose somewhere in the starter area.

Good luck,

chicago124

[Mike Murrell]

I think Mick J's points are interesting.

The fuel pumps were replaced. Assuming this was the result of intelligent diagnosis, you may indeed have a faulty fuel pump relay. When fuel pumps get old, they often times produce excess amperage which can damage/destroy a fuel pump relay.

Jumpering the pins as Mick suggested could answer some questions.

There have been many write ups here regarding this process and there may even be some visual info as well in a previous post(s). Try the SEARCH facility for help in this area.

[jayhawk]

I'd put my money on the fuel pump relay. I have a 89 190e with 300k - I've replaced the relay twice both times happened just as you described. I dignosed problem by listening for the pumps to come on. When they did not, I removed the relay and jumped two of the connections (forgot which ones) and they fired right up.

[Ron Johnstone]

The fuel pump relay is frequently fixable by careful examination and a bit of re-soldering. Probably best to buy a new one and keep the fixed one as a spare though. If the fuel pumps don't run when the key is first turned, the relay is the thing to check next.

Ok guys...
The next night after I posted the inital message and without reading your followup posts (had not had the time), I went to the car and tried to start it. I figured what the heck, can't hurt. The car fired on the first try!!

Was it a fluke? Is this a sympom of the vacuum hose problem or a poorly soldered fuel relay?

For laughs, I tried it this morning as well and it starts fine. I am still very concerned as I dont want to be stranded anywhere when it decides it does not want to start.

How do I remove the relay to check it/replace it with a junker one? How much does a junker on cost about?

Thanks for all the advice. This at least makes me knowledgeable and have some idea if I NEED to take it in for service even if I cant fix the problem


Reed