spicyguy2005

I live in Ames, Iowa. My 1989 420sel with 230,000 miles being irritating lately. It had one fuel pump, fuel filter, fuel pump relay, and ignition control unit replaced recently because the car occasionally losing power, suddenly stop, or has trouble started. They were replaced with used mercedes pieces because those parts that came with the car are all after market units.
Right now it still has problem with losing power, sudden stop or difficult to get started. When it is running, everything is fine with no noticeable problem. Yesterday, it lost power and then stopped on the road. After about 1 min., I tried starting it and it came back. This morning I went to my mechanic. After I turned off the car, went into his office and came back, the car would not start. I have tried starting it about 10 time within 15-20 min. with no success. My mechanic put meter on while I tried starting it. It appeared that the ignition is fine. He felt that fuel pump is working OK. After ruling out the ignition and fuel pump, he kind of believed that it has something to do with fuel distributing system which he is not capable of checking it. What else can I do to identify what is the actual problem? It is very annoying that I don't know when it gonna die again and without getting it to that point, the other mechanic also said that he could not tell what is wrong.
Can anybody help me with this issue?

spicyguy2005

I forgot to tell that after about 20 min. I can get it to start with no problem and it is fine since then. I don't know when it gonna happen again.

BENZITCH

I know you changed it out, but it does sound like the fuel pump relay. Maybe it has a bad cold solder joint and when heated up a tad expands and after cooling down contracts.
Bruce

Untertürkheim

Have you checked the temp sensor (not the one for the instrument cluster), and the EHA?

stormtroopers4

SAME PROBLEM! Can you please help out both of us. My car is having exact same issue. Its sitting at 7-11 as we speak. I have a video on what its doing and was hopping somebody could help.

stormtroopers4

I have been doing some research guy2005, maybe its the cps sensor I guess it somewhat common. Sounds like the same issues. I just dont want to start the car again what if its the engine?? Did yours loose power on the roads?

spicyguy2005

Yes, one time on highway, but the power came back in about 20-30 sec. That is very scary. The other time it happened in town before it stopped completely.

I had my car with my mechanic for about a week now. He checked CPS and found the resistant is within the range with no fluctuation. We kind of think that if the CPS is not totally bad, we may not be able to detect the problme. After some discussion and because I am so desperated, I decided to order a new CPS for replacement. I should get a new part early next week. I will let you know if the problem solved after I put the new CPS in.

Keep my finger crossed that the problem will be solved.

whoover

There's a good chance it will work. Bad CPSs are heat-sensitive. You won't see any problem until the engine heats up. That's why it checks out good but causes intermittent problems at operating temperature. Good luck with it.

hineywineries

My money is on you with this one. It sounds exactly like a crank sensor. It could be an EZL, but my first bet would be as you suggest.

spicyguy2005

Just got my car back today with Crankshaft position sensor replaced. Car started right away and so far never had the same symptom again. Keep fingers crossed. Will keep you informed whether the problem is solved.

hineywineries

The crank sensor has a high failure rate on MBs and difficult to diagnose, because it's always fine when you check it. I'm going to have to change it on my roadster although it doesn't have the common symptom of failing while driving and starting later. Three times in the past 6 months it wouldn't start cold. It's got 110k on the clock, so if that isn't the problem now, it will be someday. Good luck and thanks for the feed back. Most get their problem solved and don't post again til they have another problem.

spicyguy2005

After Crankshaft position sensor replaced, car seemed to start stronger than before. However, problem with stop running and hard to start were not corrected as I thought they were. I called one MB mechanic in Des Moines and told him the story. He mentioned that it sounded like Fuel Pump Relay to him, even though I just had it replaced. He said that with the used unit, it may be bad too.

I decided to order brand new Fuel Pump relay from MB dealer last week. It costs me about $100 delivered. I got it last Thursday, so I replaced it right away. Up until now, 5 days, everything seems to be OK. Car is running fine with no sudden stop and start strong everytime.

Hope that the problem is solved. Even though replacing CPS didn't solve the problem, I don't feel bad. With 230,000 miles on it, a new CPS will give peace of mind that it will most likely not going to go wrong within its usable life.

Thanks for all the opinion and suggestion.

hineywineries

I consider myself to very observant and usually pick up on things, but I guess I missed the part where you installed used components. You may have stumbled onto the solution, but it may be short lived. It could be that the relay was tired and failing on its own or it could be that you have a fuel pump drawing excessive current. If that is the case the new relay is tougher and will last for awhile, but will also eventually fail. You need to have a current draw test done on both pumps. One tip off of a failing pump is it will become noisy while running. Also what makes diagnosis difficult is that the pumps may draw excessive current intermittently.

I agree that changing the CPS was a good idea. I'm going to change the one on my roadster before taking a trip down the coast to San Diego the end of May. because I have 100k on the clock. Good luck.