'73 350SL Fuel Pump relay - PeachParts Mercedes-Benz Forum

bsharp8256 · #1 11-20-2012, 03:44 PM

Today my car wouldn't start, and I noticed that the pump didn't spin up when I turned the key on. I replaced the pump about a week ago, so I believe it to be the relay. I probably should have checked for voltage at the terminals, but being a new pump I went ahead and ordered the relay.

After doing some searching, it seems that most of the time the relay is located above the fusebox under the passenger side dash--and I believe I found it (it looks like it's the original too). The problem comes from the fact that it's got 5 pins, and the replacement has 6. Looking at the plug, there is a blank place for a 6th pin to go into, but I believe that extra pin on the relay has a purpose and I don't want to just plug it in and give it a shot before I ask here. In fact, I'm wondering if the relay I found is something totally different, and I just keep missing the one I'm looking for. I just don't see anything around under there that looks similar.

In the pictures, the left is the new, right is the old. Any ideas?

Thanks,
Brandon

ctaylor738 · #2 11-20-2012, 06:26 PM

It should work. The extra pin 50 is for voltage when the starter is engaged. But you will have voltage on 15 - ignition on, which is all you need with the original relay.

This assumes you don't have a bad ignition switch.

Frank Reiner · #3 11-20-2012, 06:34 PM

bsharp 8256:

I may be in error on this, but I believe the FPR is behind the right side kick panel (or just above it). Also the FPR for D-jet engines is usually the familiar "silver cube" with 4 pins (30, 85, 86, 87) or with 5 pins (87a).

ctaylor738 · #4 11-20-2012, 07:59 PM

Frank is correct.

I retract my previous statement.

This relay is for the defrost on the hardtop window.

You need to look for the relay with a large black-red-white wire attached to its socket.

rowdie · #5 11-21-2012, 07:05 AM

As frank stated. PN is 001 542 02 19. The FP relay is the top left relay in the panel. There may be a bracket that has to be removed to access it.

Graham · #6 11-21-2012, 10:23 AM

1973 350SL?

Only 350SLs sold in NA were the early 1972 models before they changed badge to 450SL.

Is this a Euro model?

Presumably they use the same relay. Rowdie has a picture (on BW) showing exactly whee that relay is. OK here it is:

And as Rowdie said, sometimes there is another layer of relays over the ones in pic. My car is like that.

bsharp8256 · #7 11-21-2012, 10:49 AM

Thanks guys, I found it. I asked for the FP relay at O'Reilly's and it seems that they gave me the wrong one, since the pin numbers don't match up anywhere except for the 87 near the plastic post, not to mention the size difference. Am I correct in assuming this? I'd rather go into a store and pick up the correct one today, but I'll order it if I have to. Has anybody managed to get one of these at a parts store?

Edit: Yep, it's a Euro car. I bought it cheap off of a guy who got it in a real estate trade, and I didn't even know what it was until I got it home, noticed the speedometer, and looked closer at the vin.

Thanks,
Brandon

meltedpanda · #8 11-21-2012, 10:56 AM

basic MB cube relay, I have never been able to get one at a parts store, I have a few in a box here somehwere , if you get in a bind

rowdie · #9 11-21-2012, 11:12 AM

You can pull one of the others and try it to see if that is the problem. Pull one from the right side. The one directly below the FP relay is the ECU relay so don't pull it.

Ziad · #10 11-21-2012, 03:09 PM

The 72' 350 SL is an EFI fuel system, it dosen't use the cube CIS relay.

This is what you need.> ( I have new or used )

The 280se 4.5 (sedan) its located behind and low on the passengers headlight.

Relay Fuel Pump Mercedes 280SEL 300SEL 3 5L 4 5L Bosch DB MB W108 W109 New | eBay

rowdie · #11 11-21-2012, 04:40 PM

Quote:

Originally Posted by Ziad

The 72' 350 SL is an EFI fuel system, it dosen't use the cube CIS relay.

This is what you need.> ( I have new or used )

The 280se 4.5 (sedan) its located behind and low on the passengers headlight.

Relay Fuel Pump Mercedes 280SEL 300SEL 3 5L 4 5L Bosch DB MB W108 W109 New | eBay

This discussion is about a 1972 350SL (107.043). It has a 3.5L EFI (D-Jet) the fuel pump relay location and part number I posted is correct for this model.
Check the EPC if you doubt me and the others here.

bsharp8256 · #12 11-21-2012, 04:50 PM

Quick update:
I pulled one of the other relays from the right side and swapped it into the FP socket, and I got the same symptoms--the car will gladly spin all day without starting, and there's no ~1sec spin on the pump when the ignition is in the "2" position. This made me wonder if the pump was bad (despite it being around 2-3 weeks old), so I tested it, and it spun right up. I'll just have to assume that the relay has been good all along.

While I was down there, I also checked for voltage at the wires going to the pump, which was there only when the car was turning over. ctaylor brought up the possibility of a bad ignition switch--does anyone have suggestions on how to test for that?

Thanks,
Brandon

RadioTek · #13 11-21-2012, 05:43 PM

This may sound a bit odd, but have you checked your points recently? I had a bunch of no-start trouble until I replaced my points with an electronic retrofit/replacement. The gap of the ignition points had gone to nothing as the rider on them wore away, not letting the coil work correctly.

There is also a green wire from the distributor to the ICU module (right behind the (US) driver headlight that has been known to go 'open' with time and cause problems.

Just a couple of suggestions.
Scott

Frank Reiner · #14 11-21-2012, 06:26 PM

The absence of power to the fuel pump during the 2 second "pre start" period, unfortunately suggests a fault in the ECU. The timer function is in the ECU, rather than in the relay, as it is in a K-jet system. When cranking, the relay is closed thru the starter solenoid, hence power to the pump in that phase.

As suggested by ctaylor, there may also be a fault in the ign switch. Do you have power to the ign in position "2"?

bsharp8256 · #15 11-21-2012, 07:14 PM

I hadn't checked them at all, so I ran out and gave them a peek. I didn't check the gap because it's getting dark and I didn't feel like wrangling with turning the engine, but the points' surfaces themselves looked almost new. The wire looked good also. I also checked the spark, managing to shock myself in the process, so I know the spark is good.