1989 300TE dies then restarts

[IKE]

I poste this in the old forum but any additional input would be appreciated. This one has got me baffled. I am assuming it is electrical but what? The engine just stops. It seems to be random. Sometimes it will run fine for weeks and then it will die three or four times in a day. Over the last weekend it died at least six times. BUT if you wait a minute or 2, it starts and runs just fine. It seems to do it more when the car is decelerating but it has happened on acceleration. When the engine quits, the transmission drops out of gear. Maybe it's supposed to do that, but when it happens during acceleration it does it with a sudden loud thud. Anyway, I have checked ignition wiring, connections, fuses, any thing I could think of. Any ideas? Just as background the car has 196,000 miles. The head was just completely overhauled. The transmission is fairly new with about 30,000 miles on it. It has a completely new exhaust system. This has happened in the past (before all these repairs) but not with the frequency in the last six months or so. It happened so infrequently I didn't even think about it until it started doing it much more often

[GeorgeMurphy]

First - check alternator output - should be no less than 13.8 volts at the battery posts at 1500 rpm . Nor more than 14.5 volts. if not, change voltage regulator - brushes could be worn.

Next - OVP (overvoltage protection relay may be faulty - at least pull it and clean contacts . . .

Check flywheel rpm pickup - flex the cable to see if engine dies . . .

[IKE]

Thanks for the tips. I'll work on it this weekend and let you know if it solves the problem.

[IKE]

Thanks for your help. I checked all those things and on the suggestion of another forum I changed the fuel filter. I think the one in there had been there forever. I went through and cleaned every electrical connection I could lay my hands on. All of this has made the car run better, but it has still died twice in the last week. I'll keep looking. This weekend I'm going to replace all of the fuses. They're all pretty old and as you know they tend to deteriorate over time and lose contact.

Any more suggestions would be appreciated. I sure hope it isn't something expensive like the chip.

[IKE]

Apparently it was the fuel filter. I put in a new one and the car has run fine for a week and a half now, with no problems.

Thanks for all the help.

[IKE]

Back in August I posted this and thought I had solved the problem by replacing the fuel filter. Well, as luck would have it it started doing it again after a few days. My son was driving it and didn't tell me he was having problems so I didn't know for at least a week until I took it for a drive and it died. About three weeks ago it got so bad the car died at least ten times in one day. I was really frustrated. Frankly I was on the verge of dumping it a buying a new car and it wasn't going to be a Mercedes! My wife was so afraid the car would die she insisted we use my son's 91 Honda civic.

I could put a long list up here of everything I checked or replaced. None of which seemed to do any good at all. (But at least my car has a lot of new parts, most of which weren't all that expensive.)

Finally though, I think I have found it! It has run perfectly without quitting for a week but I'm still keeping my fingers crossed. The last three things I replaced are the voltage regulator, over voltage relay and fuel pump relay. The voltage regulator brushes were worn very badly, so I decided to replace it, and while I was at it, the over voltage relay. Right next to the over voltage relay is the fuel pump relay so I replaced it too. I had checked these two relays previously and they seemed to be operating perfectly, and that was my mistake. They were. They were shutting down the car because the voltage regulator needed replacing. I suspect that because of the worn brushes that the voltage regulator was intermittently losing contact or arcing causing everything to shut down.

I am putting this up to let you know this because I have recieved e-mails from members who have the same problem, asking me if I had ever solved it and I wanted them to know what I had done. For the first time in at least a year this car actually runs like a Mercedes should.

[David Bernhard]

Yes! Replace brushes every 100k miles. I lost a set at 120k, one side was badly worn. Checked my other car which looked original at 167k -- worn down to little tiny nubs! Replaced them too. They are cheap (from FastLane -- dealer is high) and oh so easy to replace.

[IKE]

In got mine from the Benz Bin. I could have bought the off brand for about $19.00 but I got the Bosch for $42. At Mercedes they're about $80. I've bought quite a few parts from these guys and they deliver in a couple of days by UPS.

I also buy used or rebuilt parts from Potomac German Auto in Frederick MD. Great place. The Greater Washing Chapter is taking a tour of the place this weekend. I've been there so many times I don't need the tour.

[vnoronha]

This is probably your problem. The central electrode of the distributor cap is probably broken or worn. If you car has 100k miles or more, this is more than likely.

You'll need a small Allen (5mm?) wrench to remove the cap and cover and it might be easier to replace the cover along with the cap since separating the two is quite difficult. You can just clean the rotor and replace it but once you're in there you might as well replace it.

Try it and you'll feel the difference. My 89 300TE and 87 300E had the same problem earlier this year. While you're at it replace the plugs too ($2 apiece) and watch it fly!

Vivian

[IKE]

I did that a long time ago. It didn't solve the problem. Some one made that suggestion and so I said Why Not. Anyway that is just one of the many new parts that got changed.

Unfortunately this is one of those problems that is almost impossible to diagnose unless it happens to do it when it's hooked up to the computer. Of course, it never does.

[john m]

Hello Everyone
I have several ideas.
Don't whish to waste time with duplication.
Could you please post list of parts replaced?
We have had two like this in three months, fuel pump was the cause on both.
We drove each for roughly four days before the problem surfaced.
Very irritating to isolate.
A couple of months past, we had a marginal crank sensor that would shutdown the engine at random times.
Have a great day.

[IKE]

I started with a tune up, new plugs, distributor, rotor. I replaced all fuses (and I do mean all) I checked all relays and replaced any that appeared weak (but they didn't happen to be the right ones). I replaced the fuel pump (it was leaking slightly) and the fuel filter and the fuel line from the tank to the fuel and and the fuel line between the fuel pump and the filter. I replaced all the ignition wiring. I found and cleaned all electrical connectors I could get to, and replaced some that were falling apart. To put it simply I went through any part of the electrical system that might have an affect on the engine and checked it, cleaned connectors, and replaced as needed.

I had the Electronic Control Module (the computer) checked and cleaned all of it's contacts. By the way, even on the after market these things cost $1200 and up. You can get used ones but don't replace it unless you have to.

I went through half a dozen cans of spray contact cleaner cleaning the electricals.

The valves seals were leaking through the head into the cylinders, and it need doing, and I thought it might be contributing to the problem so I had it completely rebuilt. The car ran a lot better and I got through my smog test but it had nothing to do with the problem. ($2300). (Mercedes shop.) I also had to buy a catalytic converter which had nothing to do with this but also cost about $2200 parts and labor.(Mercedes parts)

Some one suggested that it might be the transmission neutral safety switch. I had had problems with that on my diesel so I replaced that. It had no affect on the engine but my shift lever isn't so sloppy anymore.

There are other things I checked that I didn't write down and don't remember.

What it amounts to is all the electrical systems on these cars are integrated. There are literally dozens of things that can cause the engine to stop. Each one has to be checked. The computer gets signals from lots of sources and if any of those it seriously out of spec it can shut it down.

First you have to determine if the problem is fuel or electrical. That's why I checked the fuel sytem first. It's a lot easier to check the fuel system for problems than the electrical. Once you determine it's getting fuel then you start on electrical.

Here it was a combo of both which fooled me. When the voltage regulator would arc or lose contact the fuel pump relay would trip and shut of the fuel pump. These are autoreset circuit breakers so after about a minute it would reset and I could restart the car.

Knowing what I do now, the first thing I should have checked was the voltage regulator. I did do a voltage check with the engine idling and the voltage was in the correct range. It would have been better to take it to a shop and have them test the alternator output under load. It probably would have spotted the problem. I also would have replaced the relays regardless. There aren't that expensive and they all had 200,000 and 14 years on them so I should have just replaced them.

[john m]

Hello Ike:)
Splice a fuse in ahead of autoreset circuit breakers, with any luck the fuse will blow soon, showing which circuit is killing vehicle.
This would normally be the hard way.
With your case, I would say it is easy compared to what you have been through.
To bad you are so far away.
I would like to drive it for two or three weeks to find what kills your car.:)
You are amazing.
I would not tollerate what you have on a personal car. :(