1987 300E Will Not Run

About 2 months ago my wife took the car to exercise class and when she came out to come home and started the car it backfired and would not re-start. I checked it out the following day and though it didn't backfire it would not run for more than 1/2 a second. I had the vehicle towed to my house and have periodically tried to start it with the same result. It will fire, run for about 1/2 a second than shut off. It will continue to do that until I depress the accelerator pedal then it won't start at all.
Before I get into replacing the part game, do you have an idea where to start?

Forums

Gas Engine Specific Aid

Chassis Model Number

W124

Becoming more common

As the cars with the 102 103 and 104 gas engines continue to age, the problem you describe is becoming more common and it can be very frustrating to troubleshoot, especially if it does not happen all the time. I am planning on doing a series of videos on these engines next spring.

Your first challenge is to find out the root cause. It could be any one of or a combination of the following:

1. Loss of fuel pressure/fuel flow

2. Loss of ignition spark

3. Mechanical failure.

I can't go into everything in this post, but here are a few tips

Check if the fuel pump is running (you should here it run a few seconds right after you turn the key on
Loosen the fuel line going into the fuel injection distributor (caution very high pressure) do you see fuel squirt out
Pull the ends of the distributor wires out of distributor cap - see any burnt or corroded - especially coil wire
Pull the distributor cap and have someone turn engine over to make sure the distributor rotor is spinning
Pull and inspect your spark plugs (yes these can cause a no start situation) replace if worn and dirty

You are smart diagnosing before throwing parts at it... :-) Report back your findings and we will go from there.

Kent Bergsma

1987 300E will not run

Ravenwolf, I have been in the same place with my 1988 300TE. They share the same great 103 in-line six. All I can suggest from my experience is that you seek the solution to the problem in a methodical manner. Some of what you need to do may fall into the category of taking care of neglected maintenance. First, check to see if you have a continuing spark. Pull a wire off one of your spark plugs and have someone crank the engine while you hold the wire close to the top of the plug. If there is a strong consistent spark that leads you toward fuel supply problems. While you are looking at the spark plugs consider how long has it has it been since you replaced the spark plugs, wires and distributor cap. If they are old, it won't hurt to replace them.
Next comes the fuel supply. There are two fuel pumps under the car along with a filter and a pressure accumulator. Under the hood, there is a fuel pump relay that runs the fuel pumps. I replaced the pumps and the filter and the car ran better, but it would still quit and not start again.
Going back to the spark that runs the engine there are three major components to examine, the ignition control unit, the spark coil, and the crankshaft position sensor. Replaced the ICU, not much change. replaced the coil and crank position sensor at the same time. The old coil looked fine, the crank sensor was obviously old and beat up. after that the car has run perfectly! It is amazing how much power that little six will pump out!!

I replaced all of these components one at a time before my basic stall and no restart problem was solved. (most likely it was the crankshaft position sensor). That being said, I noticed better driveability and performance improvements with each part I replaced.

I know that Kent is working on a manual that will help solve your specific problems, and I know that they supply many of the parts required to get your car running perfectly.

There are methods to test all the components that I replaced but special equipment is needed for many of the tests. All in all I spent close to $1,000 on parts and 4 to 6 hours a day four three days to do this. I am 63 and I don't work very fast. In the past I may have been able to do this in a day. Had I gone to a mechanic I would have spent two or three times as much because of the labor costs.

Good luck, Michael

1987 300E Will not Run

Thank You Gentlemen, this gives me a great place to start and as I progress through the procedure I will let you know the outcome.

1987 300E - Success - KINDA

Well I didnt do anything either of you guys said - basically I turned the fuel adjustment 10 to 20 turns back and forth. And it actually finaly started and is running now. Problem is when you give it gas, running down the road, it feels like I am applying the brake, then it goes, and then when you let off the gas, it again feels like the brakes are being applied.

Hmmm, no response to my last

Hmmm, no response to my last post, I hope I didnt irritate anyone. Anyway the car is running better every day, but I have put in Lucas Gas treatment and Heet - and I am starting to think that there was water in then tank. I will keep you up to date on my progress, and if you have any other suggestions I would appreciate it.

Check the electronics

Hi Ravenwolf,

I believe you car has the same CIS-E injection control system as my 87 420SEL. I've had similar symptoms as you, especially when giving it more than ~1/4 throttle. I am still trying to figure out which component is bad on mine, but I know the problem is with one of the electronic modules because it goes away when I disconnect the electrohydraulic actuator. It's a small black part right near the throttle body with a two- prong connector. If I take off that connector and drive it, the throttle problem goes away but my fuel economy gets even worse. It makes sense because, while the electronics are not necessary for the car to run, they do make it more efficient. If only they weren't so difficult to troubleshoot!

Broken Bowden Cable was the

Broken Bowden Cable
was the culprit - it was broken at adjustment 29(from MB manual) thus causing about a 1 inch slop in the cable. Now I just have to fine tune the transmission cable and the throttle cable and hopefully I will be back on the road.

Electrical???

In the continuing Saga of MB problems - it seems the cable was only part of the problem. The engine runs smooth once running for 10-15 minutes. Before that it's a bit rough and occasionally stalls.
I have noticed that occasionally, and I can't figure out what I'm doing to have this happen, the engine suddenly looses power (tach drops to around 700 and oil pressure drops down to 1) and then if I give it gas it goes back to normal. In addition this will happen with the cruise on, and sometimes the cruise starts again and sometimes it doesn't. When it doesn't come back on there is no way to get to work, until I shut off the car and restart it.
In addition, when trying to drive "softly" - just lightly depressing the accelerator, the engine bogs down and sometimes stalls. And if it's at a stop and I press the accelerator all the way to the floor abruptly, there is a 1/2 second hesitation while the car tries to figure out what I have done.

I unplugged electrohydraulic actuator and that had no effect at all on the engine.

(By the way in the original answer to my first post, I was asked to check fuel pump,accumulator, fuel filter coil and spark plugs, plug wires, and rotor. All of those items were replaced when I originally purchased the car 2 years ago.)

New Problem!!

Yesterday I noted if I hold the accelerator pedal in one particular spot and not move it, the engine revs up to 3000 then immediatley back down to 1000 and will continue to do this non stop until I move the pedal.

I'd appreciate any help or suggestions as this is getting to be a lot more hassle than I have time to deal with.