420 SEL dies while driving
 

A really strange happening, every once in a while the car just dies when on the highway or going down the street. if you are on the highway and still have rpms you can turn the key off and then on and it takes off. if it stalls below 30 mph, you can put it in neutral and it will start. any ideas?

90% chance it's the crankshaft position sensor, that what happened to my car last year. Not too bad to replace and is not particularly expensive, either.
On the ignition module mounted on the driver's side fender well, there is a green cable; trace it back to the back side of the engine, near the top, and it is held on there with one small bolt. You sort of have to get to it by feel; I reached up from beneath, with the front of the car on small ramps, while laying behind the front tire. There is a plastic cover that snaps over the actual sensor. Good luck.

Possible OVP relay issue too.. Have you noticed any dash lights such as ABS coming on?

It has a new OVP and no lights on the dash come on, i am buying a new crankshaft position sensor. I will report back when installed.

Well i put the new crank position sensor in and still have the same problem. Any other suggestions? Intermitent stuff is so frustrating.

Does anyone have any more suggestions?

Fuel pump relay .
i would rig up a light to the pump connection to detect a intermittant fault
mak

Thanks, I will give it a try

I have a similar problem, how do you do that? Could it be the fuel pump?

Well i have been monitoring the situation as you know I have a 81 420SEL that just dies when driving, you restart the car and it takes right off again. I tried all of the suggestions so far and have changed the Jetronic control box, fuel pump relay, ovp relay, cap, rotor, plugs and now am at whits end.

Any more ideas out there?

Ignition Coil/Wire
 

Just change the ignition coil and wire to the distributor...that should fix it...

less than $200
 

that's classic broken core for bosch ignition coils. especially if you have been doing other work with associated components......you didn't mention the coil and that's the first thing i would think of...good luck

Thanks, i'll give it a try

I had the same problem and tried every thing. Found out I had picked up water in gas. put in some water remover Can't think of the brand and I have not had any trouble for the last year

Dennis

I have a 91 420 SEL and I am experiencing the dieing while driving, turn the key off and on and zoom. It has given me trouble at start up as well. It will fire, rev up and die. It tries to fire, so I am thinking there is spark, just not enough fuel, but I have not verified the spark during the no start.

I am definitely loosing the fuel pumps. I can turn the ignition to the run position when I am experiencing the problem and there is not sound from the pumps, or I can hear the relay chattering and the pumps cycling multiple times, (this leads me toward the ignition switch and computer, as the computer is responsible for cycling the Pumps when the key is turned to the run position).

My first thought is the relay is bad. Cycling the ignition cycles the fuel pump relay contacts. If they are fried, they may be making and braking contact.

I tried playing with the key while it died while driving and the engine was still spinning, it had no effect. I am hoping that the computer is not the issue.

Has anyone had any luck?

Here is an update: I haven't changed the coil yet, it arrives on monday; however I checked each fuel pump yesterday by putting power on them individually with a battery. One was dead, so I changed it and the fuel filter. While I was changing the fuel pump, which i did by taking the whole assembly down, a little crud washed out of the feed line. So I think the filter may have been clogged also.

After changing the filter and replacing the pump it started right up without hesitation and hasn't died since. I am cautiously optimistic and will change the coil when it arrives this monday. Fingers are crossed.

I just finished repairing the Fuel Pump Relay.

The car always stated when cold, so I first started the engine and disconnected one of the fuel pumps. The engine still ran on one, but the running pump was definitely straining by the sound it was making. I then tried to start the engine with only one pump, and no go. So mine will run on one pump, but will not start on one pump.

Since the engine would die while running, and when it was a no start condition I did not hear any sound from the pumps, I went to the relay.

I removed the cover and, upon visual inspection, I did not see anything cooked or what not. I then put it under my microscope and low and behold there were two solder connections from pins TD and 50 that were broken. There is not any support on the top of the circuit board, so it must be vibrating and the only thing holding the board in place is the solder connections. This corallites to it dieing after I went over railroad tracks, it really got bad after that.

I resoldered all the Pins and the pins on the actual relay itself. Reinspected under the microscope and all looks good, however I have had better looking solder joints than the ones I found that did not have contact on other boards I and made.

I put the cover back on, resealed it, cleaned the pins, and am off for a test drive. Before it only died after it was hot, so I guess time will tell if I really fixed it.