MS3X v3.0 Fuel pump pin not grounding - first startup

[dunnp2]

Hi all, I've exhausted my troubleshooting abilities on this one...whenever I turn the key to run, my fuel pump relay (and pump) click rapidly and the MS box won't connect to the computer.

Everything works fine on the stim, the FP light is on when it should be (2sec initially, then only while synced). It's only when plugged into the relay that the FP wire is at 12v. When disconnected I measure 0.5v on the purple (FP) wire.

I get 5v on R16 and just replaced all four transistors in that row. I just updated to the latest firmware.

I've never started the car, but the first ~5 times I tried, this didn't happen. It started clicking like this for ~5 more tries, then it didn't click again for a few tries, and now it's been clicking ever since.

Does anyone have any ideas? What am I missing?

MSQ attached. I tried starting a new project and only changing the necessary things, still no luck.

[dunnp2]

I've narrowed it down a bit, the main issue is that the fuel pump wire gets pulled to 12v and Q2 isn't pulling it to ground. I've replaced Q2 twice now with the same results. With the relay disconnected, everything works as expected, but with the relay connected it doesn't.

Using the stim, I jumpered 12v to the FP pin and it stayed at ~6v. There is about 18ohm resistance from the FP pin to ground when it is activated. Circuit is open when deactivated.

[billr]

If you disconnect the FP wire from MS, at the mainboard DB37 pin 37, does everything else behave? Can you connect with TS that way, crank and get rpm readings; even give it a quick blast of starting-fluid and get it to fire/run briefly? Let's establish that this is *only* a problem with the FP circuit external to MS.

[billr]

Did I interpret that last post correctly, the FP coil is only 18 ohms?

[dunnp2]

If I disconnect the FP wire completely, TS will connect but when I crank it doesn't sync.
But if I leave the FP wire connected to the relay and jumper that to ground, the fuel pump runs continuously and I can connect, crank and sync.

However, this engine has never run so I wouldn't be confident trying to test it with starter fluid.

Did I interpret that last post correctly, the FP coil is only 18 ohms?

No, while on the stim I measured from the FP pin (DB37 pin 37) to ground on the board and measured 18 ohms.

[dunnp2]

...which makes sense because the power for the crank sensor is fed from the FP relay. When fully disconnected the MS would work normally but not receive the crank signal.

[billr]

I don't think it will work to have power for the CKP sensor coming through the FP relay. MS needs the CKP signal to indicate engine rotation before the FP relay is turned on. The (unreliable) exception is if you start cranking immediately at power-up, and are using a priming pulse, then the FP is activated for a couple of seconds and you may be able to crank and fire before the FP time-out.

[dunnp2]

Ok, that makes sense. The schematic I have shows everything being powered by the FP relay, but I suppose it should be on the main relay. I'll start switching everything over to the main relay now.

But shouldn't that not matter since the main relay turns on the FP relay and they're basically on at the same time?

*edit: just noticed the CKP sensor is connected to the main relay on the schematic I have. But everything else is on the FP relay.

[billr]

Do you understand now that the main relay does not turn on the FP relay, that the FP relay turns on when engine rotation is detected?

[dunnp2]

Do you understand now that the main relay does not turn on the FP relay, that the FP relay turns on when engine rotation is detected?

I guess I knew that, but didn't connect the two thoughts. That was dumb of me. Of course the CAS needs to get power before the FP relay so the MS knows it's spinning and to turn on the FP relay...

However, I ran a wire to the CAS from the main relay and still have the same problem. But I do have RPM sync when I disconnect the FP wire now, as expected. With the FP wire connected to the relay it still clicks like mad and TS won't talk to the MS.

[billr]

Disconnect all the FP wiring from the MS and pump and run a separate temporary wire from the battery to FP, try starting it that way. Wouldn't it be encouraging to know you only have to redo the FP circuit?

[dunnp2]

Disconnect all the FP wiring from the MS and pump and run a separate temporary wire from the battery to FP, try starting it that way. Wouldn't it be encouraging to know you only have to redo the FP circuit?

I went to do that, and with the FP wire disconnected from the relay and a temporary ground to that pin of the relay, the MS won't talk to tuner studio. Is that normal? Does the FP wire need to be connected to something for the MS work?

[billr]

No, the FP wire should have nothing to do with MS connecting to TS. Disconnect that wire at the MS DB37 pin 37, you probably have a short or other mis-wiring in that circuit. Let's confirm that, and disconnecting at the relay doesn't accomplish that. What is the resistance of the FP relay coil?

[dunnp2]

No, the FP wire should have nothing to do with MS connecting to TS. Disconnect that wire at the MS DB37 pin 37, you probably have a short or other mis-wiring in that circuit. Let's confirm that, and disconnecting at the relay doesn't accomplish that. What is the resistance of the FP relay coil?

Wellll.....I'm an idiot.

Turns out the grounds to the MS weren't actually connected to ground. I ran a quick jumper to them and everything works as expected. Fuel pump primes for 2 seconds and no clicking.

I really, really appreciate the help and troubleshooting advice. At least now I know that the wiring I went over is solid and I don't have my CKP sensor going to the fuel pump relay. And I have a much more in-depth understanding of the wiring...

Thanks again.