1978 450SL Location of Fuel Pump Relay?
 

Hi,
My 78' 450SL (california) has problems running once started. It starts fine, but slows down and shuts down after driving for 15-20 mins. Then it will start up again in an hour.

Does anyone know where the fuel pump relay is located?

Below is a picture of my fuse box and relays, but none of these is the fuel pump relay as I bought from an MB Dealer.

http://img479.imageshack.us/img479/2...agrelayto5.jpg

The fuel pump relay looks like the one below.

http://img205.imageshack.us/img205/1...opartswie7.jpg

Any help is appreciated.

It's above the relays in the picture, held in place with a 7 or 8m nut.

Sounds similar to the trouble I had with my SL, and it was not the relay. Ended up by replacing all the old ceramic fuses with new copper/brass conductor fuses. Factory fuses have aluminum conductors that over time can develop a thin layer of corrosion that can interrupt circuits and bedevil mechanics trying to diagnose the problem. Then again, it may be your relay...

230/8

By which you're saying it's not visible in the picture, correct? I'd go check my car but its in another location.

If this is a possible case, I'll likely go ahead and replace all the fuses with copper/brass as you suggest. It'll be inexpensive and at the least rule it out, thanks.

And of course, let's not forget the fuel strainer.

That's correct, you can't see the relay in your picture.

Replacing the fuses is a good idea. But keep in mind that the FP relay is unfused, and powered directly from the battery, via connectors C101 and C105. It is always hot, so if you mess with the wiring, disconnect the battery first. You can remove the relay without disconnecting, though.

I can't locate it. There is nothing else there except vacuum elements behind/under the glove box.

There is a relay held in place by a 8mm nut, but that is in the middle right side of the picture. That relay, however does not exactly match the relay I have as a replacement (it has 5 pins and is silver, where my replacement has 6 pins, is black and states rpm voltage etc.) but it does match the size and does fit into the female cable (but one of the pins on the replacement is put into non-hot (no elec.) hole).

Any other suggestions? I cannot locate this stinkin relay.

thanks

Look for a large white/red/black wire - that's the one that runs to the fuel pump - connected to 87.

I'm starting to think my car was jimmyed in some way to resolve issues with the fuel pump relay, because I just cannot find it. I looked at wire red/white/black wire connected to the fuel pump and tried to follow it forward to the relay area, but it goes directly behind the wall of the trunk, so if I wanna follow that, it's a little bit of work.

Suggest you start from the other end. You should find that wire somewhere in the relay area unless something has really been changed.

Finally found it (but it wasn't the problem)
 

It seems that my fuel pump relay was behind the brake pedal. The ECU in the same area (under the driver's side dash, above the foot area). Also, my fuel pump relay (silver) looks nothing like the replacement (black). Here's a picture of them side by side:

http://img248.imageshack.us/img248/7060/image034pj8.jpg

However the relay was not the problem. The problem was 1) a 25amp fuse for a wire that goes directly from the battery to the fuel pump; that was blown. It's the only fuse in the car located at the battery...never checked for 2 years, but it was the culprit (pretty sure).

2nd, once I replaced that fuse, the car started up fine and was driving good, no stalling, no shutdowns after half an hour on the road. But there was no pickup either, the pickup was real bad. Then I realized that I removed the air intake assembly...which was why there was no pick up. Then I placed the assembly back on...guess what, the car stalled. So I found problem #2...needed a new air filter. Replaced it, car runs good. (one more thing though, I'll put it in another post)

So having a shyster dealer replace all my fuel injectors, which did not solve the problem and letting the car sit for about a year and a half, a new air filter and a 25amp fuse directly connected to the battery fixed the job.