89 560sl fuel pump relay bypass - PeachParts Mercedes-Benz Forum

r134 · #1 10-20-2007, 01:25 AM

Ok, from searching the site I believe the fuel pump relay is behind the glovebox. There is a cluster of 3 black relays, the one i want being the left rear one. Now how do I bypass it so that I can run the fuel pump without the engine running? I can barely get my hand in there and don't think i'll be able to see the socket. Does the socket move or is there another place I can bypass the relay? Please someone help me figure out how to do this properly.

vegadonovan · #2 10-20-2007, 02:34 AM

I don't know the reason why you want to bypass the Fuel pump relay. But you can short pin 30 and pin 87. Thats on my 124 relay. It provides 12v to fuel pump.

Do note that the fuel pump will be on all the time. And you have to remove the short after your journey stops EACH and EVERY time. And you lose the Kickdown feature and the TD safety feature.

Any reason why you want to do this? Is it going to be permanent or just to get it to the stealer?

r134 · #3 10-20-2007, 09:49 AM

I want to do this for diagnostic reasons, the car isn't running now. At least it can circulate some fuel system cleaner. Want to check fuel pressure, I think either my fuel distributer and/or injectors are no good. Never should have left the car sitting for half a year.

vegadonovan · #4 10-20-2007, 10:27 PM

You have suspected the expensive items first. Have you thought of fuel filter?

Does the fuel pump run when the key is turned?

you can crack the pipes at the injectors and see if fuel is delivered to the injectors.

Any symptoms that we can try to assist to help with?

r134 · #5 10-21-2007, 12:44 AM

First thing done was to change the fuel filter. Pump runs with key on and while it is running using starting fuel, it continues to run a second or two after the car runs out of starter fluid or gas poured down the flap. Most old gas was drained and about 5gal of fresh fuel is in the tank.

I've cracked all the pipes and fuel is present, some comes out when I crank the engine. With the pipes drained, they fill back up after trying to crank the motor. Cold start injector is working, the car starts when it's cold out for a few seconds but then dies.

I suspect either the injectors are rusted or clogged up or there is not enough fuel pressure. I just received my CIS pressure gauge and want to check fuel pressures to and from the fuel dist but need to know how to bypass the fuel pump relay so it can run without having the engine run.

vegadonovan · #6 10-21-2007, 02:59 AM

Did the engine stall precisely at the same 1-2seconds after starting?

Tachy will just drop to zero. Seems like something cut it out ?

Are these your symptoms?

Have you shorted the 2 pins that was posted before?

Thanks

r134 · #7 10-21-2007, 11:07 PM

Yes, it stalls 1 or 2 seconds after starting. The tach drops to zero only when the motor rpm drops to zero. Seems like the regular fuel injectors aren't taking over after the cold start injector starts the motor.

So since the cold start injector can start the car does that mean that the distributer is flowing enough fuel/pressure and that the injectors are probably no good?

I haven't shorted out the pins yet, the relay is way behind the glove box in the dash.

vegadonovan · #8 10-22-2007, 02:01 AM

I have this problem with the car starting and cutting out precisely 1-2 seconds after starting. If I constantly cranks, it will continue this way. I will let the car sit for 1 minute and it will start driving fine.

This usually happens after the car stalls in the midst of driving at any speed. I have changed the Fuel pump relay and it has not occured for 1 week. Some suspected the CPS and Coil and even the ICM. But the first I changed is the FPR. Still monitoring.

I have changed the plug wires. Cap and rotor looks fine. Harness are all patched and non-exposed.

I will update as and when I have more updates.

r134 · #9 10-22-2007, 11:18 AM

I'm pretty sure mine is a fuel related problem since it will run if gas is poured down the flat or if i continue to spray starter fluid. The car has always run fine, it's just that I haven't run it in over half a year which is why I think the gas might have caused the problem. The car has sat most of it's life. It has 20k miles on it, the original plugs look good and the wires have low resistance.

vegadonovan · #10 10-22-2007, 06:25 PM

I read in the manual under one of the compliants that it could be the tachy mulfunctioning thats why it receives tacho =0 and cut the fuel. try to reseat the electrical connections to the Ignition control module. Use contact cleaner and see if it helps.... Its free anyway...

The last time I was nearly stranded by the unstartable bouts, I removed and put in the fpr again and the car willl start.

r134 · #11 11-07-2007, 03:47 PM

Ok, now the car doesn't even try to start anymore. Fuel is getting to the fuel distributer but not to the injectors. I've read a post saying it could be the Fuel dist is clogged with varnish and may be cleaned out by running the pump continuously with techron and fresh fuel. Now how do I run the fuel pump?
Is there another way of getting the fuel pump to run instead of jumping the relay behind the dash?

r134 · #12 11-08-2007, 01:33 PM

Ok, I hooked up an external power supply to the fuel pump directly. It ran but now it no longer runs when I use the key. What did I screw up now? I hear relays click but the pumps no longer hum.
Can anyone offer some insight please?