ReefShark

Just put a new fuel pump on. Now I am not getting any power to the relay. The fuel pump fuse is good. I thought first, bad relay, replaced relay. No help there so I placed a jumper between the correct connections, nothing. Now I've tested the jumper connection and I am not getting any power to the relay. Found the fuse for the fuel pump and it is tested visually and with the tester on the panel.

Why am I not getting any power at the relay?
All replies appreciated.

Mrmerlin

Umm let me guess its a 1978 or 1979, or a 19??

ReefShark

Yep, got so wrapped up in the problem, I forgot the car...

1985 Euro Auto, 928S

ROG100

Crank position sensor.

Kevin in Atlanta

No power to the pin 30 on FP relay with the key on or off? If no power to 30 than I'd start looking at the ignition switch.

Also, are you doing continuity or actually using a multimeter to read voltage. Continuity can be misleading. Test with a multimeter from 30 on the FP relay to 87 and 30 to a known good ground.



Power only goes to the FP fuse while the car is cranking if the CPS is functioning properly and the computer is doing its thing.

ReefShark

I'll be getting one saturday, will let you know. Thanks

[/QUOTE=Kevin in Atlanta] No power to the pin 30 on FP relay with the key on or off? If no power to 30 than I'd start looking at the ignition switch.

Also, are you doing continuity or actually using a multimeter to read voltage. Continuity can be misleading. Test with a multimeter from 30 on the FP relay to 87 and 30 to a known good ground.[/QUOTE]


Used a multimeter. Am trying the crank sensor first, but looking at the ignition switch also. No voltage at pin 30, ignition off, ignition on, and while cranking.
Thanks much!

Kevin in Atlanta

It is not the CPS. Do you have the WSM or at a minimum the wiring diagrams?

Why did you replace the fuel pump in the first place?

dr bob

The 30 pin on the fuel pump relay comes directly from the battery positive post via an almost-dedicated conductor. It's one of the smaller red wires that connects at the battery positive clamp. Power comes in from the battery to the CE panel via U12. It splits there internal to the panel to feed the fuel pump relay in position XX, and the LH Jetronic relay pin 30 in position XXV. For the fuel pump wiring, it connects to relay pin 87, through fuse 42, from where it splits to cover the fuel pump via U15. It also feeds the aux air valve via CE connection Q14, then through the 14-pin under the hood pin 7 to the front-of-engine harness KS2 and the valve.

Start by thoroughly cleaning all the connections at the battery positive terminal. Get everything shiny and pretty, snug things up, then a thin coating of Vaseline before you put the plastic cover over the terminal. Leave the spare wheel well open as you finish up the diagnosis of the fuel pump, as the wiring for that comes back through the well at a connector at the forward end. There's a ground at that spot that needs cleaning while you are there. It serves the fuel pump, plus the transmission safety and gear indicator switches. Again, clean well, assemble and snug the bolt, then a little Vaseline.

Note that the ignition switch plays no direct role in getting primary (pin 30) power to the fuel pump relay. Instead, the ignition switch tells the LH controller to get to work. The LH controller waits for pulses from the CPS via the ignition controller before it pulls the fuel pump relay pin 85 towards ground. The other side of the relay coil (pin 85) does get power via the 15 bus from the ignition switch, true when switch is in "run" or "start" positions.

For those playing along at home, this info is known good for the 1985 car, but may not apply to yours if it's a different year. Check the wiring diagrams, as they are the definitive resource for the various model years.

Kiwi'79

^^^^
dr bob, that write up and explanation is gold!!! for my brain at least, thank you.

Can anyone confirm if this write-up will be the same for my cars? (If so then I will print that into my "special folder".

I get terribly lost in wiring diagrams.

Apologies OP for the partial thread hi-jack.

dr bob

These DO NOT apply to your cars. The later cars use the engine management controller to generate a signal to operate the fuel pump relay. On the K-Jet (CIS) cars, the fuel pump relay uses a tachometer signal to determine that the engine is spinning. The starting and running systems for ignition and the CIS injection are totally different. ;(

Kiwi'79

Thanks dr bob, I really ought to have known that.

jpitman2

AFAIK the CIS cars should have a pump relay that runs for a few seconds at switch on to prime things, then goes off until it sees tacho signal on cranking. The non-cis cars DONT do this! The relevant relays are quite cheap from Roger. An ordinary relay will work, but will not stop running while the ignition is on - normal behaviour is a safety feature in case of accident.
jp 83 Euro S AT 57k

ReefShark

I've just ordered the shop manual on disk, will have those diagrams soon. I had shop manuals originally but sold them when I thought I'd replaced them with a disk, but to my dissapointment, it turned out it was only the parts manual.

The car was running intermttently. I've had the car for 23 years and the fuel pump had never been changed from the original.

Kevin in Atlanta

Only 23 years? I think you deserve a prize. :-)