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Discussion Starter #1
I searched around a found some mildly related threads but nothing with the same issue.

Bike ran when I got it in Sept. It's since been completely dismantled and rebuilt.

Finally got it back together enough to try and get it running. Turn the key on and right switch to run. Fuel pump primes, and I hit the starter switch and it fires right up. It start and runs and I notice I've got no tach. Tach has power for lights, and oil light, but doesn't move.

Turn right switch to off, and key off. Double check wiring at tach, seems ok. So I turn the key back on, and the right switch to run and no fuel pump. The relay for the fuel pump just keeps clicking over and over and over again.

So I shut everything off again, and pull the relay for a few seconds. I install it back on the bike, turk on the key and run switch, and the pump primes again. Hit the start switch, and she fires right up.

I shut it off again, swap the two relays and try again. It fires right up, but after I shut it down and try again same thing. Relay for pump just keeps clicking away.

The ECU has been sitting in a drawer of my tool box for over 6 months. I haven't popped the plug off to look inside and see if there's any crap on the board.

I am thinking of asking my friend or coworker to borrow the ECU from one of their 748's to rule that out.

Anyway....any thoughts on why it would do this? Seems bizarre that the bike will only start if I pull the relay and hook it back up. Thanks for the help.
 

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Discussion Starter #2
Alright seeing as how no one had any idea what the hell I was talking about, I'll update this with a few more details. Plus pictures and a movie! everybody likes those right? lol


Anyway, got another good harness from a 2000 748 (same bike) and it stills doesnt work right. Once start is all it's got, and the tach still doesn't work. At this point, I'm pretty sure the ECU is fubar but I wanna run this past you smart people here.

This is what the wiring on the main relays on the original harness looked like when I got it.

The green arrow indicating the spliced power source from the right switch (going from fuel pump relay to ECU relay) and the blue arrow indicating the spliced ground circuit feeding off to a separate wire that goes right to chassis ground.

Below on the wiring diagram is what I 'think' these wires correspond to here, though I don't have the relays in front of me to see what terminals go to which wire specifically (plus the colors don't match...typical).



Here video of exactly what the damn thing is doing.
On the first attempt, I've already pulled both relays and plugged them back in. The bike starts and runs, but no tach. I shut it off, and turn it back on and (you'll have to turn the sound WAY up) you can then here the fuel pump relay just ticking away. Pump does not prime, and as you can see the bike does not start.

Relays are good, and I even pulled the housing off at one point, watched it tick and even forced the connection closed yet the pump still did not run.

Now the funny thing is that the bike ran fine and the tach worked when I got the bike original, with all those wires spliced together like that.

My only conclusion is that the grounds in the ECU are fubar and not operating the relays, hence why whoever spliced the power leads and ran a direct ground did what they did.

As I mentioned before I am going to borrow my friends ECU from his 748 and see if it makes any difference. I have a feeling that the ECU was toast when I got the bike and that the wiring fix was just a makeshift way of bypassing the failed circuitry.

Thoughts?:D


And again, since everybody likes pictures. Here's the bike, if anyone was wondering.
 

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Old Wizard
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The zero tach reading suggests that the ECU isn't outputing the rpm signal it gets from the crank rotation sensor. Since the bike will run, the pump is running, so the ECU is getting the signal and energizing the pump relay (but not reliably), but not sending it to the tach.

What the ECU is doing here is not clear. Perhaps a bad ECU as you suspect.
 

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Discussion Starter #5
@TheSouthAfrican

The Bike has not been ridden in 8 months since I had it shipped up from Virginia, road it 15 miles to my garage and stripped it down to bare frame. It does have a PCIII and had Akro slip ons and pod filters though no idea about what tune. It will be getting a custom map when it's road worthy. That messed up harness was on the bike when I got it, and the tach worked and the pumped primed every time.

@Shazaam
I also suspect the ECU is internally faulty. Like I said it appears whoever did the wire job on the harness realized the ECU wasn't grounding out the relays.

I will run by my friends house and "borrow" his ECU from his 748 and see if it makes a difference as I know his rear harness is unmodified and the tach and pump both function fine.

This wiring issue is killing me as the bike is so close to done. All that's left is making a new tail and sorting a new exhaust. Just this wiring problem giving me a headache.


Thanks guys for the replies back. Nice to know someone cares :D
 

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2001 ST4, 2002 M750S, 2008 848
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@TheSouthAfrican

The Bike has not been ridden in 8 months since I had it shipped up from Virginia, road it 15 miles to my garage and stripped it down to bare frame. It does have a PCIII and had Akro slip ons and pod filters though no idea about what tune. It will be getting a custom map when it's road worthy. That messed up harness was on the bike when I got it, and the tach worked and the pumped primed every time.

@Shazaam
I also suspect the ECU is internally faulty. Like I said it appears whoever did the wire job on the harness realized the ECU wasn't grounding out the relays.

I will run by my friends house and "borrow" his ECU from his 748 and see if it makes a difference as I know his rear harness is unmodified and the tach and pump both function fine.

This wiring issue is killing me as the bike is so close to done. All that's left is making a new tail and sorting a new exhaust. Just this wiring problem giving me a headache.


Thanks guys for the replies back. Nice to know someone cares :D
I'd put 10 bucks on the ECU being "gone" on this one. I had to replace the 1.6m in my ST4 and really the quickest way to diagnose it was to swap mine out for a known working unit from a 748 project bike my local shop had. You may want to remove the make-shift ground wires from the relays before you try out your friends ECU... just as a big fat preventative measure!

If you find out you need a new one, check with gotham cycles and look for a used 1.6m (I believe the 748, 996, and ST4 all share the same ECU) and make sure you keep the EPROM chip that is in your current ECU for re-use.

Best of luck!
 

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Discussion Starter #7
ducati_750, that seems to be the consensus at this point.

I already have another harness off a 2k 748 I bought thats on the bike now, that is 'un-molested' still grounding out through the ECU which is prob why nothing works.

I'll make sure to be careful with my buddies ECU though. That thing I want to do is by two haha. Yeah I'll prob snag one from Gotham. I think they were going for 250 and change for a good used one which isn't bad.
 

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Finally a video...

Thanks for posting this! I can't believe I never thought of a video, but stuck to stupidly mimicking the sounds to people I spoke to about it.... I've been rebuilding my 05 749 and this is my main sticking point after switching the battery, fuel pump, and R/R with the generator (fingers crossed that I don't have to) in my sights after I change the injectors and plugs. Was the harness/ECU the issue?
 

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Discussion Starter #9
I pretty much narrowed it down to the ecu at this point. I'm using one of the relay sockets from the old harness for now so I could get it running without hacking up the new harness till I can afford an ecu.

Tach still doesnt work but i did accidentally knock it off my workbench onto the floor a few months back so I prob just broke it lol.
 

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Discussion Starter #12
Siemens is definitely an upgrade but they make some crap too. I know cause I gotta deal with their problem ECUs everyday lol.
 

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I just got done with an intermittent no start problem. What we found was the two Siemens relays on the side of the battery box were junk. I replaced them and it's been smooth running since then. When the bike would die, I would only get ~7 VDC at the ECU relay, which isn't enough to power all the gizmo's.

Worth a shot anyways- relays are cheap compared to other pieces of these things.

---Matt---
 

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update from the mechanic

Talked to the mechanic and he found a short in the harness in the actual pump assembly, the flange I think it's called? Just something else to look into.
 
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