engine just dies
 

Hi everybody,
this is for an '87 420 SEL.
It first started to run uneven and the mechanic replaced two spark plugs as they looked bad. Everything else tested ok.
The next day, the car stopped 3 times on me, twice at a stop, once while going down a hill. When I brought it back to the mechanic, it ran of course fine without stopping. It ran fine for 2 weeks, but today it stopped again twice while driving at about 35 mph. No warning lights seem to be coming on and the rpms are still showing, i.e. it doesn't drop to zero.
I put it in Neutral and it fires right up before I even get to a stop.
Any ideas what that could be? Fuel pump relay? The Park/Neutral switch at the transmission?
Thanks for your advice.

Reinhard:

Sounds like a lot of threads I've seen here where the culprit turned out to be a faulty fuel pump relay.

Just my 2 cents.

Thanks, 1991300SEL
isn't it funny that these things never act up in the 1/2 hour you are at the mechanic. He took it out and smelled it, felt it for higher temp. and thought it was ok.
I'll get one and then try to open the old one up.
Thanks again

Under what conditions?
 

How long do you run the car before the problems arise?

I ran it for about 4 miles, then shopped for groceries and it happened about 1/2 mile into the return trip and another mile later again.

funny, just last week, a friend of mine, who owns a 1987 560sel had the exact same problem. I am his mechanic, and ofcourse it took a little for me to see this problem happen. indeed, rpm showed on the tach, but car simply died.
would start right up, sometimes would come alive before a full stop.
I suspected a bad fuel pump, replaced it, and voila, for the last week no more stalling, and actually the car now will reach redline, something it did not want to do before.
I recommend you either do a fuel pressure check. I did not do this, pump was very very noisy in my case, so was an automatic suspect.
Be aware much like this 560 sel I worked on, the 420 has 2 fuel pumps in the back, in parallel. It is unlikely they both fail at the same time.
So check with a stetoscope, or something similar to make shure that they both work.
In case one is dead, you indeed might get the symptoms you have.
In my 560 case, indeed one pump was dead. the other on the way to its final grave. I burried them both.
If both pumps actually run, than you have a power issue, or relay problem.

However my experience has told me that relays usually do not faill this way.
They will prevent a start, or an intermittent no start, but not a sudden powerloss. in the midst of operation.

May this help.

Henri.

Just to let everybody know, I replaced the fuel pump relay back in March.
As I don't drive the car every day, I waited a while before posting, but the car has not stopped since then. So I guess it was the relay.
The fuel pumps were both replaced in 2002, so I tried the relay first.