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Discussion Starter #1
I’m chasing some fueling issues on my track only 01 748 and am not sure where to go now.

A little history: Over the winter I took the fuel pump out to install a new NAPA fuel filter and quick disconnects (it’s a base model that previously had the banjo fittings). After the install, the bike ran fine in the garage and during the quick test ride around the neighborhood. At the first track day of the year in April, the bike died on me on the first lap in the second session coming out of T1/T2 at VIR. I was hard on the throttle, and the bike just stopped accelerating and the revs just slowly went to zero. It would not restart on the side of the track. Back in the pits we checked fuses, relays, spark…everything checked out. Fuel pump would prime but no gas was getting to the cylinders. We poured a little gas in the TBs and it fired right up. We then put on another 748 tank and it started fine. I dug into the fuel pump and disassembled it looking for any cracked hoses, loose connections, etc… but found nothing wrong. With nothing left to do, I put the fuel pump back in the tank and put the bike back together. To my surprise, the bike started instantly. I rode it the next day without issues. Since then I have done another track day in May with the bike running strong and no issues.

Now, yesterday at another track day, I experienced nearly the exact same problem. After riding 4 sessions with no trouble, the bike dies on me in the exact same manner, coming out of T1/T2 hard on the gas. Bike will not restart. So far everything checks out like before. Fuses, relays, pump primes and spins, starts with gas poured in TBs…etc.

What has me stumped is the intermittency of the problem and the fact that it died twice under exactly the same conditions. Anyone have any ideas?
 

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Sounds like fuel starvation … but you knew that. I’d question the filter first, then go from there. I know many use the Napa filter with no problems and not knowing what pressure they are able to take (looks like a regular low pressure filter to me.. but I don't know and question it). Could be something else like pick-up to the fuel pump assuming this problem comes on slowly.

Is the vent on the fuel tank open/clear?
 

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Discussion Starter #3
I'm not opposed to tossing in a new filter, but I would like to confirm that its clogged or somehow the culprit. Last time the bike died, I blew through one end of the filter and fuel came out. Which led me to believe it wasn't the problem. Any way to check for blockage?

As far as the vent, I have not taken apart the cap to check for any blockage, but while on the side of the track I opened the cap to release any pressure and tried to start it with the cap open. No luck.
 

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If something large enough to block the outlet is floating around in the filter (and I’m not saying there is) just blowing on it won‘t necessarily prove anything because the piece would have to be in the right position, even partially blocking the outlet can affect the output pressure . If the filter isn’t made to handle the high pressure of fuel injection, I would think the filter element (paper) would break up and cause problems.

It kind of sounds like the fuel pump itself may be giving up but with all the other track days and no issues….. The only thing left when it does fail is check the fuel pressure. It may sound like it primes but to what pressure?

Could also be heat related. It is actually running while its in the process of dying? (has ignition?). Just wondering if you have a bad connection at the computer or weak ground. Maybe the injector trigger fails. Are the injectors spraying when it doesn‘t start?

Just throwing out a few ideas. Hope you get it figured out.
 

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Discussion Starter #5
Thanks for the tips Yellow Blur.

I think I may just cut the fuel filter open to see whats going on in there. If I find something, good. If not, oh well.

How can I test the fuel presure? I was reading the service manual yesterday and it mentioned some tool used to test the FPR (which I of course dont have). Is there any easy way to test this?

Im not sure its heat related. The session it died, we were on the grid for a bit while the track was cleaned up. However, I shut the bike down as the water temp reached around 200-210 F. But even now, after sitting for a day, no fuel.

It just seems like the fuel quits. It doesnt start to die, it just dies suddenly. In both cases, the bike was pulling strong at about 9-10K and then just stops.

I have yet to test the injectors. Any good ideas on methods? I know fuel is not getting to the cylinders because a: when I add gas manually to the TBs it fires and b: i can crank it all day long and not even get a whiff of fuel smell. What bothers me about the injectors is the fact that when we put on the other fuel tank, it worked. But then again, when we put my tank back on that time it worked as well.
 

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You may already have done so but if not then check the fuse under the seat; there are two in individual holders near the back of the subframe (at least there are on my 916) the larger one is for the fuel pump, mine had actually melted the plastic of the fuse body - it hadn't blown the fuse but it could be damaged so that it breaks contact occasionally?

I had a similar thing happen to my headlight fuse and it would work most of the time but cut-out occasionally, yet would test OK with a multimeter.
 

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Discussion Starter #7
You may already have done so but if not then check the fuse under the seat; there are two in individual holders near the back of the subframe (at least there are on my 916) the larger one is for the fuel pump, mine had actually melted the plastic of the fuse body - it hadn't blown the fuse but it could be damaged so that it breaks contact occasionally?

I had a similar thing happen to my headlight fuse and it would work most of the time but cut-out occasionally, yet would test OK with a multimeter.
I have checked that fuse under the seat and it appears to be fine. No damage.
 

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I also had an intermittent problem with the relay on mine, it sometimes wouldn't start - it was the yellow relay near to battery, again it tested OK but would sometimes not make contact, if the contact breaks the ignition/fuel pump would stop.
 

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Thanks for the tips Yellow Blur.

I think I may just cut the fuel filter open to see whats going on in there. If I find something, good. If not, oh well.

How can I test the fuel presure? I was reading the service manual yesterday and it mentioned some tool used to test the FPR (which I of course dont have). Is there any easy way to test this?

Im not sure its heat related. The session it died, we were on the grid for a bit while the track was cleaned up. However, I shut the bike down as the water temp reached around 200-210 F. But even now, after sitting for a day, no fuel.

It just seems like the fuel quits. It doesnt start to die, it just dies suddenly. In both cases, the bike was pulling strong at about 9-10K and then just stops.

I have yet to test the injectors. Any good ideas on methods? I know fuel is not getting to the cylinders because a: when I add gas manually to the TBs it fires and b: i can crank it all day long and not even get a whiff of fuel smell. What bothers me about the injectors is the fact that when we put on the other fuel tank, it worked. But then again, when we put my tank back on that time it worked as well.
With the new info provided, and giving this more thought, you probably won’t find anything in the filter, even if it is breaking up, but it would be nice to know if it can handle the pressure.

Given it just stops like the key is shut off, just not as abruptly, you hear the fuel pump prime (pressure unknown) and can crank it but no fuel spraying into the TB’s, tells me to look at what triggers the injectors. Not sure but I think it’s the timing sensor where this signal is picked up and sent to the computer. I don’t think I’d fault the injectors themselves as they do seem to be working correctly.

The computer sends the signal through its ground wire to the injector, so if it has power at the injector and still doesn’t spray (assuming there IS fuel pressure at this time) the ground signal could be the problem (or vise-versa, no power but trigger ground, or neither). My bet would be on the ground signal. If the fuel pump relay died you wouldn’t hear the pump at all (could still be weak). If there was enough pressure in the line and the injectors were firing it should start momentarily but die when the pressure was depleted. Per your description, it sounds to me like the injectors stop receiving the message to fire.

Electrical components tend to get heat soaked and if there is a questionable or poor connection the added resistance from heat or moisture will usually allow it to announce itself. Just shutting the bike off won’t stop the part from getting hotter if it hasn‘t yet reached the temp of its surroundings.

When you swapped out the tanks I was thinking the connection at the tank (pump power/fuel sensor) could be questionable, but you always hear the pump, just no spray. Just disconnecting and reconnecting contacts can partially clean them to work for awhile. Maybe you should look at doing this to the computer connections, and checking wire harness grounds, etc. Not just look at them but remove, inspect and clean them if needed.

The TPS function, settings/voltage and connections is another area to check.

Oh, and to test for fuel pressure you'll need the correct fittings with a pressure gauge.

Hope this helps some.:cool:
 

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I had a similar problem with my 748 a while ago. I took it to the Ducshop and they explained to me that a relay had gone bad. It only would act this way when it got hot (180-190 +degrees), then it would just totally lose power. They replaced a relay that's under the tank towards the front (rests upon the coolant resevoir). Since then, it's been good to go. I'm pretty confident that that relay has something to do with the fueling system as well, as the problem you're describing sounds almost identical (minus the track).
 

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Discussion Starter #11
Yellow Blur - thanks for the analysis. Im going to try to find a noid light and try to test the signals at the injectors. I will probably have to wait for the weekend to really tear into the wiring harness.

2000Ducati7-4-8 - Was your issue with the relay intermittent? I will take a look at it tonight. Thanks
 

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Yellow Blur - thanks for the analysis. Im going to try to find a noid light and try to test the signals at the injectors. I will probably have to wait for the weekend to really tear into the wiring harness.

2000Ducati7-4-8 - Was your issue with the relay intermittent? I will take a look at it tonight. Thanks
Yeah, it would only happen so often when the bike got hot.. The rest of the time it was fine. They fellas at the DucShop said it was a common problem on the 916 series bikes.
 

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Discussion Starter #13
Well I got a few minutes to play with the bike last night. I checked the fuses again, and unplugged and looked at all the relays. Everything looked good and intact. Looked over the wiring for any loose connections or missing grounds. Again, everything looked like it should. So just to see, I popped the fuel pump back in the tank (I didnt even disassemble it this time. Just checked the wiring) and it fired up. I took the tank back off and checked that the injectors were spraying fuel, which they were.

2000Ducati7-4-8, I think you are refering to the Absolute Pressure sensor. It sits on the main coolant tank around the neck. From the outside it appears fine, but I need to find a way to test it. Of course the manual says hook up the Mathesis tool which I dont have. If this sensor fails, shouldnt I throw a code, check engine light, or whatever?
 

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From the outside it appears fine, but I need to find a way to test it. Of course the manual says hook up the Mathesis tool which I dont have. If this sensor fails, shouldnt I throw a code, check engine light, or whatever?
In the service manual it shows how to test this sensor (and others) with a voltmeter.
 

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I've had a similar issue and been checking all the various sensors. One thing you can try to determine if the Absolute Pressure Sensor is at fault (this will need to be done while you are experiencing the issue) is to unplug it and see if the issue changes. The bike can run without the Absolute Pressure Sensor plugged in. It will not run optimally, since it will not be compensating for air density, but it will run. The only sensor that I've found will not allow the bike to run if it is not connected is the Crankshaft Position Sensor (Timing Sensor). So, in my experience, if one of the "modification" sensors (I call them that since they "modify" the fuel map to compensate for specific conditions)
such as Air Density, Water Temp, Air Temp, etc. is malfunctioning, the bike will not run well, but it will usually still run. If the bike dies outright, look towards the items that are ALWAYS required... fuel and spark. Now, that being said, if one of the "modification" sensors is malfunctioning so badly that it has changed conditions such that the bike won't run, unplug each one in turn and see if the bike functions. If so, you found your malfunctioning sensor. If not, fuel or spark... (CPS, fuel pump relay, etc.)
 

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Discussion Starter #16
In the service manual it shows how to test this sensor (and others) with a voltmeter.
My manual just says: "To check operation of this component, use the "MATHESIS" tester."

Anyone know how to test it with a multmeter?
 

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2000Ducati7-4-8, I think you are refering to the Absolute Pressure sensor. It sits on the main coolant tank around the neck. From the outside it appears fine, but I need to find a way to test it. Of course the manual says hook up the Mathesis tool which I dont have. If this sensor fails, shouldnt I throw a code, check engine light, or whatever?
Yes that's exactly what it is. My appologizies; I had forgotten the name of it. And no, it won't give you the check engine light (at least mine didn't)
 

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I am experiencing a similar problem with a 748 Senna....any luck finding the solution?
 
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