560SEL stalls

[elsevillano]

My 1987 560SEL occassionally stalls for no apparent reason. Usually while in motion, not while stopped. It's done this 3 times in about the past 3 months. We live in Arizona - no temperature extremes. Seems like it happens after driving between 5-15 minutes. What should I check?

[greenacres2]

I'd start by checking the fuel pumps and/or fuel pump relay. Do the pumps buzz? Good info in the archives here. Good luck.

[Q]

Fuel pump relay. I resoldered mine and have had no recurrance in over a year. Mine left me stranded one day, so be proactive on this one. Fortunately, I was in my subdivision.

Resoldering is easy. The culprit is going to be the three large pins that hold the relay to the board. My broken solder joint was visible.

[elsevillano]

Thanks for the suggestions. I'll check the relay this weekend when my son brings it up from school. BTW, I forgot to mention that when it stalls I can start it right back up and it keeps on going. Does that still indicate the relay, or could it be something else?

[Pili380SL]

You might try pulling a spark plug and see if any unusual wear/fouling is indicated. It might give you a direction to search if the realy checks o.k.

[Q]

when it stalls I can start it right back up and it keeps on going

ABSOLUTELY. Mine would sometimes not die at all, just lose power and come right back up. If it did die, I could put it in neutral while it was still rolling and restart it every time except the last time. I thought it was the fuel pump failing. Once it died completely, I went through the diagnostic procedure of pulling the relay and jumpering the two pins that cause the pump to run and it ran fine. Put the relay back in and nothing. Opened the relay up and spotted the broken solder joints. 3 minutes later, popped the relay back in and fired up immediately. Never failed again.

I have also resoldered and thus repaired my failed Idle Speed Control Module and my Cruise Control Computer.

[mikaelw2001]

Interesting, this sounds like what happens to my 1984 500 SEL from time to time although It always starts up immediately after shutting down. Abyone has a picture on were the fuel pump relay is located?

Thanks in advance,

Mikael Westerberg
1985 500 SEL
Vanersborg, Sweden

[elsevillano]

Please, if anyone can tell me, or send a diagram/picture, of where the fuel pump relay is for my '87 560SEL, it would be so helpful!
A.

[Q]

On my 380SE, it is in the fuse box toward the rear. It is a black module about the size of one of those jumbo packs of Juicy Fruit gum. The bottom was glued, but came apart pretty easy. I put a thin bead of silicone glue around the sealing edge when I replaced for good measure.

Here is a photo of what the circuit board looks like:

http://www.peachparts.com/shopforum/showthread.php?threadid=74032&highlight=fuel+and+pump+and+relay+and+location

[elsevillano]

OK, on my '87 560 SEL, the fuel pump relay is within the engine compartment, by the firewall, just below the driver's side windshield wiper - there are 3, it is the center one. I removed the relay by pulling straight up. I carefully ran the tip of a very small screwdriver around the edge to remove the glue, then pried between the edge of the PC board and the housing and popped it out. I found a microcrack on the contact pin that makes contact for the relay. The crack was barely visible to the naked eye (I used a magnifying glass).

When soldering, be careful that this pin doesn't go out of alignment. Apply light pressure from the underside as you heat up and solder the joint. Make sure to use good quality flux-core solder. Before closing the housing, I used QD Electronic Cleaner and cleaned the contacts on the relay and pins and socket wells.

I also found that once mounted, the relay and socket had some free movement, so I cut a tennis ball in half, and wedged it between the relay and the firewall. I'm hoping to minimize any vibration. Email me if you would like pictures.