Help with fuel problem 560SEL - PeachParts Mercedes-Benz Forum

DAS · #1 09-27-2003, 03:00 PM

I need alittle help with a fuel problem on my 86 560SEL. While driving the engine just stopped. After 5 minutes it starts OK. This happened several times over 3 or 4 days. The last time it will not start. I wish I had a manual so I could test a few things, but I don't. I disconnected the fuel line at the fuel distributor and tried starting and didn't receive any fuel from the pumps. I looks like pumps are not getting power. I would appreciate any suggestions or tests. Thanks - DAS

Lurch · #2 09-27-2003, 03:24 PM

You may wish to check the power connections to the fuel pump... they can get corroded. A quick, easy and cheap troubleshoot before taking it to be serviced.

RKreutzer · #3 09-27-2003, 06:17 PM

Hi DAS,

First, if you turn the ignition key to the position just before start, you should hear a buzzing sound for about a second. That would be the fuel pumps at the passenger side inside of the rear wheel.
Sometimes it is easier to hear from the outside.
If you don't hear it, take out the fuel pump relay and clean the connectors/put some dielectric grease on it and try again. If still no go, you have to connect pin 30 (battery) to pin 87 (pumps) and listen to the fuel pumps. They should run now without stopping. If yes, Fuel Pump Relay is suspicious. If not running, pumps are suspicious, but it could also be a problem in the wiring. You would check that with connecting the terminals at the pump to the battery. Connect at fuel pump first, than battery. As a matter of fact, when working at the fuel pumps, the battery should be disconnected, as sparks might damage the relay.
Should pumps be running with direct connection to battery, then the wiring is somewhere interrupted.
Here is a picture of the fuel pumps (before replacement) on my 87 420. The power connections are under the rubber protectors. Do not overtighten, as these old pumps will start to leak out of the terminal.

RKreutzer · #4 09-27-2003, 06:22 PM

The relay is under the hood (at least on my 87) close to the firewall next to the OVP (red head). The AC relay is removed to have better access to the fuel pump relay, which is still in. It says 6000/min on it.

Good luck

DAS · #5 09-28-2003, 12:26 PM

I located the fuel pump relay next to the overload relay. The fuel pump relay part# is 002 545 16 05. The relay was stuck and it took a lot of force to free it. I didn’t have the correct grease so I used some WD40 on the contacts. While I had the relay out I bypassed terminals 30 to 87 and the pumps started. This indicated the relay was probable the problem. I opened the fuel pump relay and it looked and smelled OK except I did find a solder joint on the lower middle back part of the board that looked cracked, so I touched it up with alittle solder. I replaced the relay and it fixed the problem. Driving next week will be the proof, but I feel like it is fixed.
I really appreciate the help I received from the ShopForum. Thanks.

william rogers · #6 09-29-2003, 02:54 AM

Good fix! is it possible to make it home if relay goes bad by crossing 30 and 87 or dose the pump need to shut off and restart while driving?.......
William Rogers.........

RKreutzer · #7 09-29-2003, 08:15 AM

Hi William,

yes it is possible, you just have to disconnect when reaching home. I have a small wire in my glove compartment for that purpose.

Hopefully, we will never need it.

Reinhard

Q · #8 09-29-2003, 08:45 AM

I have about a year on my relay resolder with no return of the problem. It's such a simple fix!