Suddenly will not revv

[griswoia]

Ok so my v11 sport has been fine and then the other morning cranks right up but will not revv.

Literally it will idle forever but ANY throttle will cause it to choke and backfire and die.  Dip off throttle and it resumes good idle.  

 

I pulled on plug wire at a time and yep both are firing.  I thought maybe the fuel pressure regulator, and I had a spare, replaced that no issue.

Now I'm wondering if the fuel pump is just weak but it idles great....  Luckily I have another V11 LeMans that is running fine so I can swap parts to try and narrow it down but where to start?

 

Thoughts? Ideas? Insights? Gripes?  I. Fielding all comers.

 

--Ian 

[Tomchri]

2 minutes ago, griswoia said:

Ok so my v11 sport has been fine and then the other morning cranks right up but will not revv.

Literally it will idle forever but ANY throttle will cause it to choke and backfire and die.  Dip off throttle and it resumes good idle.  

 

I pulled on plug wire at a time and yep both are firing.  I thought maybe the fuel pressure regulator, and I had a spare, replaced that no issue.

Now I'm wondering if the fuel pump is just weak but it idles great....  Luckily I have another V11 LeMans that is running fine so I can swap parts to try and narrow it down but where to start?

 

Thoughts? Ideas? Insights? Gripes?  I. Fielding all comers.

 

--Ian 

Same experiences with my Corsa  and Greenie, fuelpressure to low on the Corsa, and rev sensor was installed with wrong clearence, actually touching the sprocket. That one is easy to ohm, I think it should measure 650 - 700ohm.

Just my experiences.

cheers tom.

[JBBenson]

Start with basic tune-up.

If the bike was running fine before, it's more like a checklist. Check all fuses and relays as well. Is the battery fully charged, and holding a charge? Don't laugh, a weak battery can cause very weird symptoms that make no sense, and yes, this can appear suddenly. A weak battery can show what's looks like healthy voltage, but not under load or running conditions.

It could be the crank sensor, as mentioned above, or the TPS got moved somehow. Doubt it's the fuel pump, they tend to fail slowly.

[griswoia]

Bike lives on a battery tender and checks out but can easily swap.  Yes I've been running the bike 3-4 times a week so this was just fine one afternoon and the next morning got this behaviour.

 

Replaced all relays 3 months back with new as the running lights kept flickering.

 

Will check fuses.

 

The reason I replaced the fuel regulator was the bike burped a few ounces of gas on the first start when it would no longer revv.  I figured this was from the fuel reg.  It's not done this again and I do t know where else it could have come from.

 

Ugh I feel snakebit as my BMW dropped an exhaust valve for no reason yesterday.  Two bikes down.... Oof

[LowRyter]

Makes sure the tps hasn't come unplugged. 

[guzzimeister]

Hi, almost certainly a TPS failure. Fuel pressure would have to be very low to give the symptoms you describe, and crank phase sensor failure is on/off ie won't run at all. Weak battery is unlikely but not unknown, but bear in mind the TPS operates at 4.8v so again unlikely. You will need to check voltages at idle (around 150mv) and full throttle (around 4.8v)

[docc]

I have never had any success with my Triplett meter finding a bad TPS using millivolts. On the other hand, they reveal themselves readily reading resistance while slowly opening/closing looking for jumps in the reading (bad).

BTW, idle TPS mV is somewhere in the 400-500+ range, while the 150(157) is the fully closed baseline with the right throttle plate closed against the bore without the linkage, right stop screw, or high idle cam interfering.

[Lucky Phil]

I'm always amused when everyone goes for the complex stuff first. How about the fuel filter? Of course if you have a fuel pressure test gauge that would be the first thing to check.Not saying its the filter but starting with the basic, simplest/cheapest option is troubleshooting 101.

I've had Ducatis do this, enough fuel for idle but not enough for anything else.

Ciao

[Tinus89]

14 hours ago, guzzimeister said:

Hi, almost certainly a TPS failure. Fuel pressure would have to be very low to give the symptoms you describe, and crank phase sensor failure is on/off ie won't run at all. Weak battery is unlikely but not unknown, but bear in mind the TPS operates at 4.8v so again unlikely. You will need to check voltages at idle (around 150mv) and full throttle (around 4.8v)

I'm not gonna say it has to be Phase Sensor, but I have had the experience where the bike would idle and rev up to ~2000rpm, but above that start sneezing/backfiring and die. Revving above 2krpm and then let go throttle, she would just pick up idle again.

Culprit: a non-oil compatible o-ring underneath the phase sensor which had swollen enough to make the gap of the sensor way too large for  a proper reading. So it IS possible.

 

1 hour ago, Lucky Phil said:

I'm always amused when everyone goes for the complex stuff first. How about the fuel filter? Of course if you have a fuel pressure test gauge that would be the first thing to check.Not saying its the filter but starting with the basic, simplest/cheapest option is troubleshooting 101.

I've had Ducatis do this, enough fuel for idle but not enough for anything else.

Ciao

But I agree with Phil: go for the more straight forward stuff first!

[luhbo]

Anyone ever had a stuffed gas filter? Still filling from rusty army canisters?

[Tinus89]

1 hour ago, luhbo said:

Anyone ever had a stuffed gas filter? Still filling from rusty army canisters?

I have actually seen it happen on a '99 bike (Japanese, with a steel tank) a few years ago.

[Lucky Phil]

2 hours ago, luhbo said:

Anyone ever had a stuffed gas filter? Still filling from rusty army canisters?

Anyone ever heard of "bad" fuel from petrol stations with old contaminated storage tanks?

Not everyone lives in big sterile clean European cities.

Ciao

[luhbo]

Hey, we have 2020, soon, and are moving forward, still.

Anyhow, a clogged filter would be a nice and easy solution for his problem. Still it would take a lot of particles to get this filter closed. And not overnight. I'm curious what the cause will be.

[Tomchri]

7 hours ago, Tinus89 said:

I'm not gonna say it has to be Phase Sensor, but I have had the experience where the bike would idle and rev up to ~2000rpm, but above that start sneezing/backfiring and die. Revving above 2krpm and then let go throttle, she would just pick up idle again.

Culprit: a non-oil compatible o-ring underneath the phase sensor which had swollen enough to make the gap of the sensor way too large for  a proper reading. So it IS possible.

 

But I agree with Phil: go for the more straight forward stuff first!

Like Tinus said, my phase - rev sensor acted like his, less than a week ago.

cheers tom.

[griswoia]

Love all the advice.  I just put in a new fuel filter 6 weeks back.  No reason than I was insulating the pump and figured 20 years on the same filter was enough.

I'm going to check TPS in the next day or so.  Looks like there is one on the right hand throttle body.  I'll report back.  Not sure where the crank angle sensor is have to look that up.