Sudden engine failure

This engine is running fine. It suddenly dies. After a few minutes it will start fine and run again. It is totally unpredictable.

Please give a hint on the model year.

…and the odometer mileage.

This is a 1986 190E, 2.3L Engine

Also, the mileage is 140,000

I’m going to guess it’s an electrical problem, possibly in the ignition circuit.

It could just as well be many other things.

Have you taken the car to a mechanic to have this problem checked out.

Without knowing if the problem is due to a lack of spark or fuel I can only make a guess.

Since this is a CIS injected car the fuel pump is always a suspect because the CIS pumps work under much higher pressure than a “normal” fuel inj. system. This means the pump takes a real beating along with the pump relay and the main pump fuse.
Look at the fuse in the fuse block first and make SURE the fuse connection is both clean and tight.

CIS is great when it’s working; not so when it’s not. I’ve torn apart a number of operating, used CIS pumps and have yet to see one in which the commutator on the armature was not badly worn; and I mean badly.

A close second could be a failing ignition module or Hall generator in the distributor although this problem could also be caused by a bad ignition switch, ign. relay, wire terminal, or whatever.

What I would do as a first step is check that pump fuse connection and then check the current draw (amount of electricity used) of the fuel pump. If the pump is pulling 10 amps, etc. then either the pump is failing or the filter is partially clogged; with the latter being a pump killer over time.

Thank you for your reply. I replaced the fuel filter and seemingly it ran well for a week. Now, it is dying once again intermittently, yet running perfect in between.
If I squirt starter fluid in the intake, it will immediately start and run fine once again. The relay seems alright and the fuse box does not have a fuse for the fuel pump (that I can find). Any help would be MORE than appreciated. Thank you.


Since my last note, I would like to add, I removed the fuel filter relay and the circuit board (which is green in color) has an approximately 1 cm. area of extreme darkness. Could this area of darkness represent overheating and failure, so the fuel pump would intermittently quit? Thanks again whole bunch. Robb

Yes, it could. I assume you mean the fuel pump relay. Have you changed the filter?

And that, especially when combined with the rest of the given information, would make me suspect that the fuel pump may be straining due to old age or perhaps a clogged filter. The excessive current from the straining pump may be what damaged the board.

Thank you very much for the reply, a new fuel pump relay is on order and a new update will be posted later. Thanks again.

I have replaced the fuel filter and the fuel pump relay. So far everything seems to be fine. Thank you ever so much.

Thank you for letting us know how it turned out.

Reiterating: Yes, the darkening of the printed wiring board is probably from heating of the relay. PERHAPS that’s normal. HOWEVER, if it is not normal, then the cause is probably high resistance in the contacts. The high resistance could come from wear or from damage by excessive current. Or, as MB said, maybe it’s just excessive current because of a straining fuel pump. Look out for a repeat relay failure. If you can, check the fuel pump motor current and see if it in spec.

You might also try taking apart the relay so you can examine the contacts to see if they are worn or if they are damaged.