Fuel pump relay not closing...?

[supernaughtIX]

89 IX Auto, recently replaced the harness
Fuel pump was not pumping so I changed it, still no good.
Checked relay, it works ok,
faked the pump out by jumping pins 30 to 87, pump works ok.
Pin 86 is putting out 12V when key is in run and start, but pin 85 is not closing to gnd or 0v, etc so the relay is not operating.

I checked my wiring and it looks like 85 goes to the ECU but I don't know what the ECU does with it.

Can anyone tell me how the ECU uses this wire? I heard somewhere that the ECU needs the crank sensor to signal before the fuel will pump. Any other states that MUST be true before that circuit will close?

Any and all help is appreciated.
Cheers
Rob

[StereoInstaller1]

Rob, when the ECU sees ignition, it powers the pump for a few seconds, then shuts down, waiting for cranking.

If you aren't getting signal from the ECU when the key is turned on, there is some other issue.

Do you have the wiring diagram?

Luke

[supernaughtIX]

I've only got the wiring from the Haynes manual handy.
And I'm still getting the 12V from the ign being in run/start, but the relay will not close. I don't know what the ECU does with pin 85 but i would think it should close it to 0v, allowing the relay to function? but im guessing there is something in the ECU that waits for crank sensor before it closes?

[supernaughtIX]

found the 89 325ix electrical troubleshooting manual and its showing pin 85 BR/GR goes to "Fuel Pump Relay Control" on the ECU.

Still no idea what makes this part work though.

[supernaughtIX]

i think its my crank sensor after all
it has a good resistance but no rpm on the tach while cranking...

[jmc1590]

A little insight may be of help...

The fuel pump relay is grounded through the ECU. As the ECU sees signal from the CPS, it grounds the relay, operating the fuel pump. As mentioned earlier, the ECU initally operates the relay for a few seconds after key on to build presure. Then it shuts off. Afterwards, the crank must be moving and the CPS must be generating a signal for it to re-engage.

Hope this helps.

[jmc1590]

I'll also throw this out there. Could you have possibly managed to switch the CPS sensor with the Cylinder ID when you changed the harness? That would explain the no rpm, no fuel, and possibly no spark. (Guessing on the spark.)

[supernaughtIX]

yes, that does help, I wasnt sure if there was anything besides the CPS that determined if the pump was to function.
Either way, I am going to get a functioning sensor and get it in there. While I'm waiting I will make sure my wiring to the ECU is complete.

[supernaughtIX]

I'll also throw this out there. Could you have possibly managed to switch the CPS sensor with the Cylinder ID when you changed the harness? That would explain the no rpm, no fuel, and possibly no spark. (Guessing on the spark.)

I thought that could be it as well, so I double and triple checked I had it right.

[noke325]

I would confirm that the ECU is grounding that pin 85 during key-up for fuel prime. You could do this with a simple test light. Hook the wire end to a B+ source and the test light probe end into the cavity for pin 85 of the relay block.

If it doesn't do it even during key-up, I would say somthing else is going on. Where did you get this harness. Is it new? Is it from the same year? From an ix auto? Could you use a ohm meter from pin 85 in the relay block to whatever the corresponding pin at the ECU connection to confirm continuity?

Also, I have seen harnesses from one year to the next change pinout locations. Not in BMW's though. Not saying thats what the problem is but, better to be thorough. Just make sure the wire for fuel pump relay control is in the same cavity as your old harness.

[supernaughtIX]

I know the ECU is not grounding the pin 85 during run/start, but did not check for the momentary close while switching on. I checked for continuity to ground using my Fluke meter and there was none in any keystate(doing this by myself I didnt think to check for the priming condition). Either way, the pump did not output to my bucket at any point.

The harness came from my 89 Auto IX parts car.

I have not yet checked cont from the relay block to the ECU connector, but that is first on the job list for when I get to the car next. Its not hard to do, it was just delayed by rain until another day.
I'm looking for a good CPS in the meantime.

Thanks for the suggestions.

[noke325]

Which Fluke do you have? Does it have AC Volts capability? If so, you can check your crank sensor with the Fluke. You just need to probe across the terminals on the sensor while its being cranked. The crank sensor is no more than a Hall Effect switch. Just like wheel speed sensors used on ABS. The sensor will output AC volts when the magnet inside is excited by the wheel on the crank.

If you get volts when cranked, check the continuity of the wires from the crank sensor to thier destinations as well.

BTW, what was the reason for changing the harness? I'm assuming the car DID run before you changed it?

[jmc1590]

A couple of other thoughts...

First, have you identified your "mystery" wire(s) by the ECU? I would hate to find you've been pulling your hair out when it could be something like an OBC code...

Second, do you have another ECU you can test with. Assuming that the harness checks out, the "no tach" while cranking screams ECU issues. (Been there, called the tow truck.)

I would also verify your conductivity by checking engine electronics from the ecu connector. That will help rule out any harness related issues.

[supernaughtIX]

i can check VAC when i get out to the car next, can't believe i didn't think of that earlier.
I am willing to consider that the wiring to the ECU could be messed up. Lots to check next weekend.
The car was running before I did a top end rebuild, replaced a ton of stuff, and the old harness had some shitty splice and patch jobs that the PO had done, so I thought I might as well replace the harness since I had a complete one handy.
Also replaced the CPS sensor when I did the harness, but its been sitting for a couple months so I couldnt test it right after install.
Things Ill be checking:
VAC from CPS while cranking.
Continuity from CPS connector to ECU and Ground
Continuity from Fuel pump replay to ECU

[supernaughtIX]

A couple of other thoughts...

First, have you identified your "mystery" wire(s) by the ECU? I would hate to find you've been pulling your hair out when it could be something like an OBC code...

Second, do you have another ECU you can test with. Assuming that the harness checks out, the "no tach" while cranking screams ECU issues. (Been there, called the tow truck.)

I would also verify your conductivity by checking engine electronics from the ecu connector. That will help rule out any harness related issues.

have not yet identified them, but I am home now with my Bentley so I've got it on the desk as I'm typing now.

I do have another ECU, but its got a chip and I was hoping to get the car running before I started messing with it.

The no tach issue im guessing is directly related to the no fuel pump control and a secret part of me hopes that it is simply a problem with the CPS.
This is my first time doing a rebuild of this scope so I'm doing my best.
Thanks again for the suggestions.