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Discussion Starter #1 (Edited)
Hey all, I have a 2001 748 Mono. It has Termignoni slipons + UltiMap UM211 chip. The sidestand is also bypassed. I picked it up about a month ago, it had full history + services (latest at 12.5-ishk), currently has about 13.4k miles on it now. Battery is charged, usually on a tender. Prior owner didn't experience this issue.

Summary:
Bike runs up to rev-limiter then motor dies. The RPMs just drop to 0, no noises, just off. Trying to crank bike results in nothing, doesn't attempt to even turn off. Flipping key off and on clicks a relay near the battery and the lights, indicators, etc all work but there is no fuel pump priming noise. Eventually after a period of time, turning it on results in the fuel pump priming and I can crank the bike and it runs like normal. This happened 2 out of 3 times at the rev limiter. Until it hits the limiter the bike pulls hard like normal and has no issues. There is no surging, popping, loss of power, odd noises, etc. Once it hit the limiter though it just died...

Longer:
I'd never run it up to the rev limiter before this weekend, but when I did it bounced then the motor just died. The RPMs dropped to 1k then it pretty much stalled, even with clutch pulled in. The rest of the electrical system worked fine; still had headlights, brake lights, indicators, horn. No warning lights popped on when this happened.

I pulled over to the shoulder of the road and flipped it off then back on and I noticed that the there was no primining noise (that is what I believe that whirring-ish sound is when you turn the bike on?) I played around with the kill switch, side stand, in gear/neutral, no combination would allow me to crank the bike. Everytime there was no priming, just a click from the relay by the battery and pressing the starter button resulted in no noises.

Pulled one of the side fairing and checked fuses and battery and everything looked good. Finally, after pushing it to a store and calling some friends for a trailer, I played around with combinations again.

One of the times I turned it off and then back on and bam, the fuel pump primed and I was able to crank it up. It started up like it normally does at that point. I had no issues turning it off and back on at this point. Waited for a trailer then had them follow me home while I rode back. The bike ran like normal, pulled strong, no weird noises, but I didn't go to the rev limiter.

When I got home, I decided to test it out and rode to the rev limiter on a backroad behind my house. Sure enough the exact same thing happened, the motor died. I checked everything again, but all the fuses and battery looked good. Got it back home and took the other fairing off and started looking for loose connections. Nothing stuck out and eventually (after about 30 minutes), I was able to turn it back on and hear the fuel pump prime. At this point it started up like normal again.

I took it out for a 3rd time, but this time it didn't die when I hit the rev limiter, instead it did like I expected it too and just dropped power, but the motor kept running fine. I searched around to see if anyone has experienced this before, but I couldn't really find anything matching my symptoms.

Was wondering if anyone has experienced anything like this? Or any tips to start looking at for this problem? I'm thinking maybe try replacing the ECU?
 

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It does sound like an electrical issue to me. The fuel pump turns on and off via signals from the ECU. I'd first start by insuring your EPROM hasn't come loose, this is a very common issue. Then I'd make sure all your connectors look good to the ECU. Finally, the timing sensor could cause this problem, though its unlikely. Make sure the sensor has no issues by pulling it out and making sure it has no physical wear and insure the connector has no water or corrosion in it.

On the flip side of the coin, it could be a battery issue. The higher the RPM's, the more it draws on the electrical circuit. So I'd also make sure the voltage is up around 12.5 or greater, whilst the bike is running. Also make sure you don't see any wear on the yellow/white plastic connector to the generator unit.



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Check your fuel pump relays. If your fuel pump is not turning on that could be the cause. When you turn the key you should feel them click. they are located under your seat. you can pull one out and take it to autozone to get a replacement for about $13.00. Good luck!
 

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Discussion Starter #5
It does sound like an electrical issue to me. The fuel pump turns on and off via signals from the ECU. I'd first start by insuring your EPROM hasn't come loose, this is a very common issue. Then I'd make sure all your connectors look good to the ECU. Finally, the timing sensor could cause this problem, though its unlikely. Make sure the sensor has no issues by pulling it out and making sure it has no physical wear and insure the connector has no water or corrosion in it.

On the flip side of the coin, it could be a battery issue. The higher the RPM's, the more it draws on the electrical circuit. So I'd also make sure the voltage is up around 12.5 or greater, whilst the bike is running. Also make sure you don't see any wear on the yellow/white plastic connector to the generator unit.
EPROM was secure and all the connections look and feel tight. Timing sensors seems to check out OK also. Battery seems good.

Check your fuel pump relays. If your fuel pump is not turning on that could be the cause. When you turn the key you should feel them click. they are located under your seat. you can pull one out and take it to autozone to get a replacement for about $13.00. Good luck!
They click normally, but I don't *believe* they were clicking when this problem happened and there was no priming. Can relays be good 98% of the time and bad the other 2%? Or all-or-nothing?

My only advice is to stop thrashing the sh%* out of it! lol Thats why you have a rev limiter.
I know, but I'd like it if it didn't stand a good chance of dying when I accidently hit the limiter :)

Another thought, does the ECU draw a little power when the bike is off, in sort of a sleep mode? Wondering if some condition causes it to kill the pump when I hit the limiter then retain that until some sort of a reset? Thanks for the suggestions everyone :)
 

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When my relays went bad. It would idle rough but work fine above 3k. Then it wouldnt prime at times. It also would prime and not stop priming even with the key removed. Its only a few dollars so its worth a shot. Good luck.
 

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Just my $0.02 - but here goes - and correct me if I‘m wrong:

The fuel pump relays get their signal from the ECU - the Timing Sensor sends a signal to the ECU about RPM and Timing Position, the Chip controls the Rev Limiter RPM. Also the ECU will not send a signal to the TPS or fuel pump relays without the fuel pump being connected - which I guess would mean the ECU will not function without everything connected. Is the Tach included here or just an indicator that has no effect on anything good or bad?

Check the connection at the Fuel Pump/Low Fuel level sensor just to make sure all is clean and correctly connected, no pins pushed back, etc.. It is a connection that sees a lot of use and it does sit in a bad spot - check for wire chaffing also.

Check the connection on the TPS also for the same type issues to rule it out.

Seems funny that the ONLY time it fails is after hitting the Rev Limiter, which in my mind points to a ECU fault or failed connection (power maybe) to the ECU. Does it run all day without hitting the limiter? Ride it without hitting the limiter for a few days and see what happens.

Good luck with it.

Edit: Also, if it’s like my 996 - where the main wire harness comes out of the ECU connector it lands hard against the sub frame where it makes its bend. It may be worth looking in that area for any chaffing through the wire harness.
 

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I had very similar (wasn't bouncing it off the rev limiter, but right after hard, righ-rev acceleration) issue and it all came down to the side-stand relay. EVEN IF IT IS BYPASSED at the side stand switch, the side-stand relay (next to the fan relay at the battery, one of two small relays) failing to close will completely disable your bike. No crank, no run, no fuel pump, nada...
All the side stand bypass does is close this normally-open relay all the time your bike is on. I've been stuck on the side of the road for 10-20 minutes, just like you, due to this relay getting flaky while it was failing. And my side stand switch was bypassed as well.

This might not be your problem, but FWIW, by-pass the relay (not the switch) with 2 spade crimp connectors connected by a 1" section of 14 gage wire plugged into the proper spots in the socket (30 and 87, I believe). Go hit the rev limiter and see if the relay was the issue.
If not, it might also be a ground loop caused by a loose ground somewhere. The rev limiter usually just grounds out a coil to keep it from firing. Could be this grounding causing a relay to stay closed even after it is supposed to return to normal. If you've ever been behind a car with a disconnected ground on a tail light, you'll get the idea. One light goes out while the other brake light goes on... In that case, one taillight is providing the ground path. In your case, a relay might be doing that for you.
Good luck!

P.S. I keep a jumper like the one mentioned above in my pocket whenever I'm riding my Duc. It's like a tiny little spare tire. :D
 

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Discussion Starter #9
When my relays went bad. It would idle rough but work fine above 3k. Then it wouldnt prime at times. It also would prime and not stop priming even with the key removed. Its only a few dollars so its worth a shot. Good luck.
I removed the relay for the pump and while it didn't prime, I could turn the motor over with the starter. When it died before it acted like the kill switch was on, no prime and not even an attempt to turn over. Hopefully this is progress, heh.

Just my $0.02 - but here goes - and correct me if I‘m wrong:

The fuel pump relays get their signal from the ECU - the Timing Sensor sends a signal to the ECU about RPM and Timing Position, the Chip controls the Rev Limiter RPM. Also the ECU will not send a signal to the TPS or fuel pump relays without the fuel pump being connected - which I guess would mean the ECU will not function without everything connected. Is the Tach included here or just an indicator that has no effect on anything good or bad?

Check the connection at the Fuel Pump/Low Fuel level sensor just to make sure all is clean and correctly connected, no pins pushed back, etc.. It is a connection that sees a lot of use and it does sit in a bad spot - check for wire chaffing also.

Check the connection on the TPS also for the same type issues to rule it out.

Seems funny that the ONLY time it fails is after hitting the Rev Limiter, which in my mind points to a ECU fault or failed connection (power maybe) to the ECU. Does it run all day without hitting the limiter? Ride it without hitting the limiter for a few days and see what happens.

Good luck with it.

Edit: Also, if it’s like my 996 - where the main wire harness comes out of the ECU connector it lands hard against the sub frame where it makes its bend. It may be worth looking in that area for any chaffing through the wire harness.
Will look more at those sensors. It also runs fine normally, no acting weird, just runs like it should, just have to not hit the rev limiter. Easy to do, but hopefully this problem will get fixed so I don't have to even think about it!

I had very similar (wasn't bouncing it off the rev limiter, but right after hard, righ-rev acceleration) issue and it all came down to the side-stand relay. EVEN IF IT IS BYPASSED at the side stand switch, the side-stand relay (next to the fan relay at the battery, one of two small relays) failing to close will completely disable your bike. No crank, no run, no fuel pump, nada...
All the side stand bypass does is close this normally-open relay all the time your bike is on. I've been stuck on the side of the road for 10-20 minutes, just like you, due to this relay getting flaky while it was failing. And my side stand switch was bypassed as well.

This might not be your problem, but FWIW, by-pass the relay (not the switch) with 2 spade crimp connectors connected by a 1" section of 14 gage wire plugged into the proper spots in the socket (30 and 87, I believe). Go hit the rev limiter and see if the relay was the issue.
If not, it might also be a ground loop caused by a loose ground somewhere. The rev limiter usually just grounds out a coil to keep it from firing. Could be this grounding causing a relay to stay closed even after it is supposed to return to normal. If you've ever been behind a car with a disconnected ground on a tail light, you'll get the idea. One light goes out while the other brake light goes on... In that case, one taillight is providing the ground path. In your case, a relay might be doing that for you.
Good luck!

P.S. I keep a jumper like the one mentioned above in my pocket whenever I'm riding my Duc. It's like a tiny little spare tire. :D
I looked at the sidestand switch and noted that if I pop out the sidestand relay the bike seems to reproduce what was happening to me; no pump priming, everything else working, and not even attempting to turn the motor when I hit the starter. Gonna investigate the relay / sidestand switch some more now...

Also, trying to trace to the grounds tonight / tomorrow.

Thanks for the help guys.
 

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Discussion Starter #10
Well, I went out and tried to make it die today and it ran fine, haha. I gave up after about 10 spirited runs. Worked great everytime. I have a sidestand relay bypass in my trunk now, just in case that is what it was/is. I'll just keep an eye on it, but for now it seems like it works good :) Maybe I thought something wasn't loose when I was pushing connectors in, but it really was. For now though it seems to have been fixed, hopefully!
 
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