72 D-Jet Fuel Pump Relay Question

[350SL4spd]

Hey Guys,

I'm in the middle of getting my Euro 72 350SL up & running again and I have no power to the fuel pump. It was running 3yrs ago, but no juice now.

I've got power to the Main Relay-Electronic Injection (#32 in your program.. I mean wiring diagram), but nothing to the Fuel Pump Relay. I have good continuity btw the 2 relays everywhere that I should and the fuse btw them is good.

Any ideas?

I know I have a short somewhere btw the FP Relay & ground, but I should still have power to the relay. I did jumper the wire that goes from the relay to the pump to by-pass that and got no where. Hence the finding of this problem...

Thanks!!

[Graham]

Don't know if you saw similar thread on BW - In particular, the trouble shooting diagrams in this post:

http://www.benzworld.org/forums/r-c107-sl-slc-class/1594156-1972-350sl-fuel-delivery-ignition-7.html#post4776475

[meltedpanda]

remind me , the fuel pump when jumperd - runs correct?

[350SL4spd]

Fuel Pump is brand new. Everything from the tank to the engine is.

I definitely have a broken wire btw the FPR & the FP because I have continuity to ground on that wire. But I also have no power to the FPR when I work backwards.

Graham: I'll look at that thread when I get a few free minutes at work here. Thanks!

[meltedpanda]

well that is when your continuity meter is your best friend. BTW nothing wrong with running a new line to the FP relay socket . I am pretty sure that can be done , but would have to review wire diagram
Let us know what you find

[350SL4spd]

Thanks melted. I'm completely ok with running new wires to the FP. Just have to find out how get power to the FPR first.

My big fear is that it's the computer not switching the Main Relay-Electronic Injection to send the power to the FPR...

EDIT: Re-read your post: In my wiring diagram the FPR gets it's power from the Main Inj Relay (which in turn gets it straight from the ignition). Problem is that both go into the computer for some damned reason or another...

[meltedpanda]

ah..well the good thing is there have been a few used ECU's on ebay as of late, and fairly reasonable. I wish I had one to send you to try before getting into buying one.
I think pin # 19 and 25 of the ECU are connected to the fuel pump relay.When the ignition switch is turned to the on position,the ECU energizes the fuel pump to ensure that the fuel system is filled for ease of starting.If the engine is not cranked,the ECU will shut off the fuel pump after one or two seconds.If the engine is started,the fuel pump runs continuously until the engine is shut off.

[350SL4spd]

ah..well the good thing is there have been a few used ECU's on ebay as of late, and fairly reasonable. I wish I had one to send you to try before getting into buying one.

Problem is this is my 2nd ECU already. Might switch to Mega Squirt if if it's the problem again...

I think pin # 19 and 25 of the ECU are connected to the fuel pump relay.When the ignition switch is turned to the on position,the ECU energizes the fuel pump to ensure that the fuel system is filled for ease of starting.If the engine is not cranked,the ECU will shut off the fuel pump after one or two seconds.If the engine is started,the fuel pump runs continuously until the engine is shut off.

Maybe I wasn't quick enough with my volt-meter after turning the key on... I didn't hear a relay click though... I'll have to try again with the meter already hooked up to be sure.

Here is my wiring for this. I have the 12v from the Ignition constantly with the key on to the top relay (Main Inj Relay).

[350SL4spd]

No voltage at the FPR even right after the key is turned. I do get .25v on pole 86 of relay 33 when I the engine is cranking. No damn idea what that means...

I also switched out the both relays in question here with one of the others that I know works and all relays check out as working properly.

Does that mean that I'm looking at the computer??

[350SL4spd]

New Tests:

The Main Relay clicks, but only on cranking & not just with key on.

The FPR doesn't click under any circumstance. I did confirm that the relay was OK by swapping it into the start relay slot and it works fine.

Following some of the instructions found on the link provided by Graham I tested for voltage btw terminals 11 & 18 on the ECU harness and got 12v when cranking as I should. However, bridging terminals 11 & 19 is supposed to run the pump, but it gives me no voltage anywhere on the FPR. Also: Bridging #11 & 24 should also give voltage with the key on, but it does not.

In theory this means that the wire to #24 has an issue...

Edit: You can add bridging terminals #11 & 16 to the no-power list too...

[Graham]

Originally Posted by 350SL4spd

New Tests:

The Main Relay clicks, but only on cranking & not just with key on.

The FPR doesn't click under any circumstance. I did confirm that the relay was OK by swapping it into the start relay slot and it works fine.

Following some of the instructions found on the link provided by Graham I tested for voltage btw terminals 11 & 18 on the ECU harness and got 12v when cranking as I should. However, bridging terminals 11 & 19 is supposed to run the pump, but it gives me no voltage anywhere on the FPR. Also: Bridging #11 & 24 should also give voltage with the key on, but it does not.

In theory this means that the wire to #24 has an issue...

Edit: You can add bridging terminals #11 & 16 to the no-power list too...

Have you tried jumpering pins 30 and 87 on the FP relay? (That is the TOP left hand one - right?) That gives you 12v from ignition switch via fuse. Pump has to run if wires back to pump are good.
If it does run, then unjumper 30/87 and ground pump relay pin 85. I think that should simulate what ECU does once certain conditions are satisfied. If pump then runs, problem may be with ground from ECU. Have you checked if pin 11 is grounded? If not, check grounds on top back of intake manifold (under air cleaner).

Don't know if it changes your thinking, but your wiring sketch upthread is not same as one in trouble-shooting. The connection to pin 30 on main relay is straight from battery - pin 86 comes from Ignition switch (as does pin 30 on FP relay).

[350SL4spd]

Originally Posted by Graham

Have you tried jumpering pins 30 and 87 on the FP relay? (That is the TOP left hand one - right?) That gives you 12v from ignition switch via fuse. Pump has to run if wires back to pump are good.
If it does run, then unjumper 30/87 and ground pump relay pin 85. I think that should simulate what ECU does once certain conditions are satisfied. If pump then runs, problem may be with ground from ECU. Have you checked if pin 11 is grounded? If not, check grounds on top back of intake manifold (under air cleaner).

Don't know if it changes your thinking, but your wiring sketch upthread is not same as one in trouble-shooting. The connection to pin 30 on main relay is straight from battery - pin 86 comes from Ignition switch (as does pin 30 on FP relay).

Mine is set up exactly as the diagram I posted earlier. There is no power into the FPR from the ignition switch. Power comes via the Main Fuel Relay (from the ignition). that being said I have no 12v to the FPR (yes, the upper left one) at any time.

I DO need to check the ground @ pin 11 on the ecu still...

I just cleaned the ground behind the intake manifold near the left valve cover. Is that the one you mean?

[meltedpanda]

strange that 2 ecus could be bad, it is rare to have them fail, I wonder if something is shorting them out ?
Graham's test makes sense, did you try it?

[Graham]

Originally Posted by 350SL4spd

Mine is set up exactly as the diagram I posted earlier. There is no power into the FPR from the ignition switch. Power comes via the Main Fuel Relay (from the ignition). that being said I have no 12v to the FPR (yes, the upper left one) at any time.

You may want to recheck the 350SL wiring diagram, the shop manual section 7.4 040/10 and the troubleshooting sketches in the BW post. Maybe someone changed the wiring?

I just cleaned the ground behind the intake manifold near the left valve cover. Is that the one you mean?

[350SL4spd]

Terminal 11 is good to ground.

strange that 2 ecus could be bad, it is rare to have them fail, I wonder if something is shorting them out ?

My tests right now are showing no voltage to some of the fuel system, ECU not-withstanding. Have to track those down first before I look at the computer.

Graham's test makes sense, did you try it?

I jumpered 30/87 on the Top Left Relay and got nothing because I have no power to that relay.

I have 12v to the one below it (Main Fuel Relay) @ 30 (to battery) all the time (key on or off). I have .28v at 86 (ignition) with the key on. That seems wrong to me... Origin of my problem??

You may want to recheck the 350SL wiring diagram, the shop manual section 7.4 040/10 and the troubleshooting sketches in the BW post. Maybe someone changed the wiring?

I did most of the tests from the BW sketches. That's where I'm finding no power to anything. I'm going back through 7.4 040/10 right now to see if I missed anything.

Edit: I see due to a cross-eyed wire-diagram moment, on my earlier diagram where it says "to 86 on 32 via fuse", I actually meant that both went to the ignition. And both are only showing .28v w/ the key on...