Does this sound like a fuel pump relay problem??
 

Driving to work this morning on the interstate doing about 75 MPH, while passing another car there was little to no throttle response. My first thought was fuel filter because I am approaching 30K on the filter. Instead of passing I let stayed behind the other car then all of a sudden the engine started losing power. I was able to limp to the next exit at maybe 40 MPH but the engine was running rough.

Got off at the exit and at the stop sign the idle was fine. I went over to a parking lot and sat there idling for a few minutes, everything fine. I continued to work by way of secondary roads, car ran fine. Could only make about 60 MPH on these roads, due to the roads not the car. Then after making a turn and accelerating, coming off a stop light, I get lit up by all the idiot lights coming on...the engine had shut down. Coasted into the next parking lot and stopped. Sat for a minute, hit the key and the engine came to life. I then drove into the office without problem.

Weather conditions this morning were light snow and 20*F at 0530.

None of the fuel pump relay posts I dug up in the search mentioned anything about "at speed" problems. Nearly all mentioned the sudden stalling at, or coming off a stop.

Instinctively I am leaning toward a filter and a fuel pump relay. Anything else I should be looking at?

This is regarding the '86 560SEL.

Mike.. I had a similar problem.. Just driving down the road, and the car would cut off.. Coast to a stop, and it would start right up. Turned out to be a bad solder joint in the fuel pump relay. Pop the relay out, pull it apart, and look at the solder joints. You will likely see one cracked. Apparently a very common problem..

It's a "one beer job:D "

Jay

Mike

Don't overlook the simple things.
At that temperature, you may also want to consider a bottle of gasline anti-freeze. ;)

I don't think this event had anything to do with fuel line freeze up, but I could be wrong. I do know I have had this car on the road at -26*F without problem. This morning was considerably warmer than 26 below. I will pay close attention on the way home to see if this continues in warmer temps...provided it warms up today.

Sounds more like a fuel pump. Just a hunch.

Only takes 5 minutes to look at the relay for bad solder joint. It's also a "white shirt" job.

It smells like a fuel pump relay problem. A concern is that it could also be an input to the relay (like RPM) telling it to shut down.

Check soldering as mentioned above and get rid of the existing fuel filter as well. I've had more than one clog up right at 30K for whatever reason.

My 2 cents.

Well, I tried to pull the relay before leaving work. I couldn't get a good enough grip to get it out of the box, so I tried to pull the light relay in hope of increasing my purchase on the fuel relay. No joy there either. I don't know if it was because of the cold temp or what...I simply couldn't get a grip on it.

Temp never got warmer than 21*F, been on and off snow all day. On the drive home the car ran fine. They are calling for warmer temps by the end of the weekend so hopefully I will be able to spend some time and yank the relay. I know I have had it out before so it should come out now.

I'll probably be ordering a fuel filter this weekend.

I also had a hard time getting my relay out and I also took the AC relay next to it out first. There are 2 little "mounds" in the middle on each side on the longer sides at the bottom. Rocking it back and forward might help. I also lube all the pins with dielectric grease to make it come out easier the next time, plus the better electric contact.