Twice now!!! Engine cuts off at speed.

[Bigfish]

First time this happened I had just put the tank back on the bike. Was low on fuel and heading to a gas station down the street. Was going along just fine in 4th gear when the engine just quite.

 

Second time, this past Sunday I had gone 80 plus miles and was starting to ascend a mountain (Idyllwild) when the engine just cut out with no warning. This time I was in 5th gear.

 

Thankfully both times there were shoulders on the road to pull over. I did not panic. Brought the bike to a complete stop, turned off the key and restarted. Bike worked fine after both episodes.

 

This last one I did notice a fuel starvation upon restart. It was a little slow getting to smooth idle. By slow, I mean a couple seconds.

 

Are these signs of a failing fuel pump?

 

Could it be some kind of vapor lock? (both instances the tank had been removed prior to the ride)

 

Anything else it could be?

 

Very concerned because I have an 800 plus ride this Thanksgiving weekend.

 

[Boffin]

Check for partial vacuum in the tank - it is possible to pinch a vent line under the tank on re-fitting. Also check the quick-disconnects are properly connected - do a physical check, they can be misleading.

 

Andy

[T__]

Bigfish, what else did you do when you had the fuel tank off? Maybe that will lead us somewhere..

 

If you also disconnected the battery it’s possible it took a while for the fueling computer to re-acquire the TPS hi/low parameters if you didn’t do a TPS re-learn at first key on..

 

There is also a possibility there was something like a little water in the bottom of the L/H side of the tank that you disturbed when removing the tank..

 

 

If it only stalled that once then re-started & ran fine after the first dropped throttle stall it very easily could have been the TPS low threshold re-learn (only IF you had the battery disconnected)..

 

Did it run OK right after the tank removal? If it was not running smoothly after the tank removal maybe you had a throttle cable pulled up out of it’s furrel at one of the TBI’s & it finally re-seated at the re-start..

 

You don’t have an aftermarket fuel controller on that bike, (like a Techlusion) do you? If so, let us know as that could be the problem..

 

Twisty

 

 

[Bigfish]

Twisty1,

 

Thanks!! I think you hit it right on the nose with the TPS reset.

 

Yes, in both cases I had the battery disconnected.

 

Did the bike automatically reset after the stall or do I need to perform the TPS sequence?

 

I remember looking in my Clymer and doing the TPS after the first encounter. All worked fine until recently when I disconnected the battery again. Makes great sense to me now.

[T__]

Bigfish, it will eventually learn the TPS threshold but it will only learn the high threshold if you go to wide open throttle with it running a few times..

 

It probably learned the low threshold on the restart after your stall..

 

If you want to be sure it found the high/low limits just remove the #5 fuse for about 30 seconds,, then re-install the fuse,, then turn the key on (do not start),, then FULLY open & close the throttle a coupe of times.. (make darn sure the choke isn’t on when doing the re-set)

 

Twisty

 

[Bigfish]

I'll do this when I get home today.

 

One question though... which one is fuse #5.

 

If I remember correctly, there are two rows and many fuses.

[T__]

Bigfish, there is only one row of fuses.. You want I the 5th one in counting from the L/H (shifter) side..

 

 

Twisty

 

[Bigfish]

Thanks! I'll give it a go this evening.

 

You are a godsend to this forum. I read your posting help daily.

 

[David R]

Thanks! I'll give it a go this evening.

 

You are a godsend to this forum. I read your posting help daily.

 

 

Ditto!

[Linz]

Me too. Twisty, you've almost single handedly enabled me to work on my own bikes.

 

Thanks mate, from OZ.

 

Linz

[Peter Parts]

Let's say the ECU doesn't get the full two-twists. Let's say it gets only to 50% (and I am sure I rarely go past 50% in ordinary riding). To my poor understanding, that scales the TPS by double.

 

Then, when you go riding and flick your throttle to the 10% location, the ECU sets the fueling and spark advance maps for a 20% point.

 

What would be the consequences?

[T__]

Peter, it won’t scale the TPS double,, keep in mind that all fueling computers have built in threshold limits so they don’t do just that.. I have no idea what the out-of-limits on the Ma 2.4 TPS is but at least in a runable converter friendly configuration ..

 

The system might even use the initial first key-on voltage for low wiper output reset after a battery disconnect (if the choke is on for first start that could skew the learned low output until it learns the hot curb idle output) or it could just substitute a given XX voltage until full cycle learn enable is established..

 

There are other factors that figure in to this also.. Once it knows low limit it knows that WOT is only capable of X number of volts on the low TPS output to middle range & X number of volts full sweep on the TPS high output so if the voltage is grossly out of expected it will try to do a substitution based on programmed in algorithms (don’t ask as I have no idea what the limits are)..

 

Most everything on the modern fueling computer is based around catalytic converter protection in a failure mode..

 

The TPS is one of the few fueling sensors that the system has a very difficult time substituting for so I’m sure the failsafe is pretty general, it knows it can’t go over TPS supply voltage at WOT (around 5v dc) so maybe that is the high limit until a learned high is established..

 

 

Twisty

 

[Peter Parts]

Peter, it won’t scale the TPS double,, keep in mind that all fueling computers have built in threshold limits so they don’t do just that.. I have no idea what the out-of-limits on the Ma 2.4 TPS is but at least in a runable converter friendly configuration ..

 

The system might even use the initial first key-on voltage for low wiper output reset after a battery disconnect (if the choke is on for first start that could skew the learned low output until it learns the hot curb idle output) or it could just substitute a given XX voltage until full cycle learn enable is established..

 

There are other factors that figure in to this also.. Once it knows low limit it knows that WOT is only capable of X number of volts on the low TPS output to middle range & X number of volts full sweep on the TPS high output so if the voltage is grossly out of expected it will try to do a substitution based on programmed in algorithms (don’t ask as I have no idea what the limits are)..

 

Most everything on the modern fueling computer is based around catalytic converter protection in a failure mode..

 

The TPS is one of the few fueling sensors that the system has a very difficult time substituting for so I’m sure the failsafe is pretty general, it knows it can’t go over TPS supply voltage at WOT (around 5v dc) so maybe that is the high limit until a learned high is established..

 

 

Twisty

 

Thanks for your deep-thinking response. These are issues that have puzzled me for years. Not sure I have as much confidence in the Bosch's rationality as you have!

 

For example, if your conception is true, there's no reason why the 2.4 needs the WOT scale-anchor voltage since it will always be roughly 5 v. Is that your experience?

 

However, the low anchor, about .48, is crucial to set in terms of the software idle switch. But then again, as you point out, that is simply the turn-on voltage, eh, and so needs no two-twists, as I think you correctly imply.

 

In the absence that kind of rationality and inherent fail-safety in the ECU, then maybe the TPS voltage does get scaled, although as you say, maybe 50% or worse would light the "tilt" lamp. Which brings me back to my original question: OK, what happens then?

 

It would be a nice world if the ECU substituted canny values when needed. A lot of the sensor information aren't "recoverable" - for example, if the Hall sensor is way off (just 'sposin' here), the engine might run backwards!

 

Finally, I have trouble believing there are functioning cat converters on any bike over 10,000 miles, benign ECU, O2 sensor, or not.