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Discussion Starter · #1 ·
Hello all,
I have a 748 that was running fine when I bought it this past summer. I rode the bike a total of maybe 5 miles after buying and then the ECU died after replacing the battery (my fault I gather).
Fast forward a few months later and the ECU is working but now the compression is low on one of the cylinders. (90 vs 125 psi)
(It has been in a shop since the ecu issue happened and I have not touched the bike in months.)

After replacing the ECU my mechanic said the bike ran rough for a few minutes then died. He then replaced the spark plugs and added new gas but says it's still stalling after a few minutes and is suggesting to look at the fuel pressure regulator when I get the bike back.

To keep this brief, I'm scared that the engine is toast given the low compression and have no idea where to look besides replacing the pressure regulator.
I love this bike but can't afford to throw all my money at it.
Any help is much appreciated. Thanks
 

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It is not the fuel pressure regulator most likely so I will guess he is not a ducati mechanic. Figure out the compression first to see if it is worth saving and dont buy any more parts unless you can prove them to be bad first.

Save your pennies and find a local old mechanic who knows the 916/748/996 bikes, it will be cheaper long run to pay someone who knows the bike than to pay someone who does not .
 

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Discussion Starter · #3 ·
It is not the fuel pressure regulator most likely so I will guess he is not a ducati mechanic. Figure out the compression first to see if it is worth saving and dont buy any more parts unless you can prove them to be bad first.

Save your pennies and find a local old mechanic who knows the 916/748/996 bikes, it will be cheaper long run to pay someone who knows the bike than to pay someone who does not .
Thanks ducvet. I should of mentioned that the mechanic is in fact an older guy with the only ducati shop in my state (I guess he's a dealer just very small).

He said 90psi is the minimum needed when I last spoke to him but for some reason also mentioned the pressure reg.
Is there anything else worth checking while it's in his hands regarding compression?

Also, the bike seemed to run perfectly fine when I had it going in late june. I don't get what could have gone wrong.
 

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compression could be anything from rockers that have worn to give you lower lift and poor cam timing, bent valves, spun rod bearing.
when were the rockers last looked at? It should be done EVERY full tune whether the valves are in spec or not. any new noises from the motor? I have a hyper 1100 that just spun a rod bearing and it was running fine just noisy. Once you rule out bad things you can breath easier and look at cheaper fixes.

Where did the new ecu come from?
Is it good?
is the large connector fully attached?
does it have the ground wire attached?
Is the eprom installed correctly as it is easy to miss a pin.
stalling after priming is often a sign of a fuel line leak as it runs on whats in the line and then runs out of fuel.
relays should be checked for function you probably have 2 large ones at the back in the tail. swap them and see if the problem changes.


Go slow and think this through, I have never seen a bad fuel regulator. if it was working before the battery issue look for something that could have been damaged from (reversed polarity install?) that. If not there then next look at the work that was done to fix the first problem. 90% of the time it is something simple that was missed or touched, you have to blame ourselves first and verify our work FIRST. After that look elsewhere because coincidences do happen it may have NOTHING to do with your or the shops work.

Be slow and methodical, think before you buy. The answer is there and you two can find it.
 

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I must qualify my advice by saying I'm not a mechanic, but I've been running 916 series bikes since 2004 and have learnt a thing or 2. If the stalling after a minute is the result of fuel starvation and you've looked in the tank to confirm no hoses are split the first place I would look is the fuel filter, located next to the in-tank fuel pump. These often block with detritus or rust flakes and are an easy fix to replace. The most difficult bit is refitting the pump mounting plate into the tank, which requires practice, patience and I suggest a minimum of 6 spare base o-rings on hand (search on the forum for advice on this and follow it!).
Good luck.
 

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Low compression is not the end of an engine. A set of 748 pistons and cylinders is inexpensive, if that is the issue. And it's not too difficult to replace them either.

Please fill out your profile.
 

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Have you checked the eprom in your new ecu? It's correct for your 748?
I would definitely follow Spinoli's advice and pull the tank, drain it (via removal of bolt at the base), remove the flange and replace the lines & filter.
While you're at it, upgrade to metal quick-disconnects if you haven't already.
 

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The most difficult bit is refitting the pump mounting plate into the tank, which requires practice, patience and I suggest a minimum of 6 spare base o-rings on hand (search on the forum for advice on this and follow it!).
Good luck.
Agreed that refitting the base into the tank is the difficult part ,, but it requires nothing more than patience , & definitely does not require the purchasing of 6 O-rings for a “just in case” scenario.

Personally that is a waste of money.

My pump has been removed & refitted without damage & without spares at least 5 times in a 2 week period for an electrical fault ( & I have no idea how old the o-ring is)

Instead of having spare O-rings , have 3 longer bolts on hand so that the base can be slowly & evenly jacked out of the tank 1/2 turn at a time & the procedure reversed for installation.
The damage to the o-ring occurs when the base is removed or installed unevenly.

Can’t help the OP with their problem, but as someone stated , don’t waste money unnecessarily ( the extra o-rings are exactly that , sorry Spinoli )
 

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Two things stand out for me.
First the ecu has been replaced, second the motor stops after a short time.

The fuel pump gets it's turn on signal from the ecu to prime the system at prestart.
Once the motor turns the ecu receives a signal from the crank sensor telling it it's OK to start pumping fuel continuously.

It's possible the ecu isn't getting that signal from the crank sensor and just maybe it's because the long plug on the side of the ecu isn't wasn't seated in it's socket when the ecu was swapped.

Alternatively it could just be the pump itself is stuffed
 

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Discussion Starter · #10 ·
Thanks for all the help thus far. Am picking it up on wednesday and will report back once I'm physically with the bike.
 

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Discussion Starter · #11 ·
Two things stand out for me.
First the ecu has been replaced, second the motor stops after a short time.

The fuel pump gets it's turn on signal from the ecu to prime the system at prestart.
Once the motor turns the ecu receives a signal from the crank sensor telling it it's OK to start pumping fuel continuously.

It's possible the ecu isn't getting that signal from the crank sensor and just maybe it's because the long plug on the side of the ecu isn't wasn't seated in it's socket when the ecu was swapped.

Alternatively it could just be the pump itself is stuffed
Right, that was the initial reason I brought the bike into a shop. I replaced the battery when I bought the bike and immediately after doing so the pump wouldn't prime anymore. Now since the ECU has been replaced the pump is back on and running so I'm not suspecting that as an issue. He said the crank sensor checked out fine too when he was first addressing the ecu problem.

As far as EPROMs go, I'm running fast by feracci forza pipes but don't know what EPROM is in the ecu.
Could that be a reason for the fuel starvation?
 

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Right, that was the initial reason I brought the bike into a shop. I replaced the battery when I bought the bike and immediately after doing so the pump wouldn't prime anymore. Now since the ECU has been replaced the pump is back on and running so I'm not suspecting that as an issue. He said the crank sensor checked out fine too when he was first addressing the ecu problem.

As far as EPROMs go, I'm running fast by feracci forza pipes but don't know what EPROM is in the ecu.
Could that be a reason for the fuel starvation?
No

Just because the crank sensor "checks out" that doesn't mean it's not the issue.
Remove it and reduce the air gap to just a couple of thou and see if it cures it
 

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Discussion Starter · #14 ·
It is not the fuel pressure regulator most likely so I will guess he is not a ducati mechanic. Figure out the compression first to see if it is worth saving and dont buy any more parts unless you can prove them to be bad first.

Save your pennies and find a local old mechanic who knows the 916/748/996 bikes, it will be cheaper long run to pay someone who knows the bike than to pay someone who does not .
Hey Ducvet I just got the bike back now and am going to look into the pressure regulator. Based on what my mechanic said, the unit may be clogged with debris (since the bike hasn't run much over the past few years) thus causing the stalling problem at idle. If that checks out okay however, is there anything you'd recommend checking next? I looked over the ecu/ eprom when I picked it up today and it all looked okay connection wise
 
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