KrZy8 Stumble off Idle

[dcarver]

KrZy8 has developed a pretty significant stumble off idle, but not all the time! Seems more prevalent when hot.

"significant stumble off idle"

as in I've stalled it several times now, once placing me in a less than ideal traffic situation.

Several summers ago, she ran very bad, even quit running all together at the Yosemite run Tyler put on. KrZy8 died at park entrance. After cooling down, she started and I made it back to hotel.

Quick diagnosis, fixed what I thought was fuel cap problem (not venting) then rode with PanMan and Niehart and Loud Jeff IIRC.

Of course, PanMan put us on a freaking goat trail a KLR 650 wouldn't even like, it was hot and slow going.. and KrZy8 was throwing conniption fits. I rode ahead of the pack at a slightly faster pace to provide more cooling and even coasted downhill when possible.

Reading the mighty FJR forum, all indications were that the TPS was heat soaking and failing, sending the ECU into fuel mixture crisis.

Replaced said TPS with new. All has been good till now. Symptom is ONLY right off idle!

Facts

• Did valve adjustment about 5k ago, she ran freaking GREAT until now
  New plugs, filters, heavy maintenance. https://candybuttorg.ipage.com/cba/node/679
  New TPS. I didn't get the EXACT TPS numbers per the book, IIRC they were off by about 5 or so. Will check again later.
  35 - 47 mpg which is normal data for KrZy8 depending upon rider friskiness, weather, and fuel.
  Only run top-grade fuel. Chevron regular.

Plan of Action

• Check air box for mice activity
  Check compression
  Do Leak Down test
  Get TPS numbers
  Replace injectors. I have 4 matched spare injectors at the ready. They were the '2nd' best set of 4 as worked on by RC Engineering. https://www.rcfuelinjection.com
  Take KrZy8 out back and shoot the bitch! :whistle:

So, before doing all this thought I'd post up and see what all of y'all think the POA should be.

Any ideas, oh great collective?

This bike HAS to make 250k miles before I either part her out or shoot her or whatever!

Thanks in Advance,

dcarver

[wheatonFJR]

For those few mechanically inclined persons on this board who DON'T know what a KRZY8 is, can you provide model and year?

[raYzerman]

Perhaps adjust the TPS again to be in the range, but also a bit of water in the fuel (if it sat for a while and was ethanol fuel or high humidity).. never hurts to put a couple ounces of Seafoam in to take care of it. If you still have issues after that let us know.
It is possible a blockage of the vacuum line to the MAP sensor might cause idling problems, but I'm not so sure that's the case. Again, as a preventative measure, make sure the port is not blocked on the MAP sensor itself and run a wire down the hoses to ensure they are clear.... but I don't think that is it.

[ionbeam]

Don is a pretty resourceful guy, there is no need to guess about the TPS. Back-probe the TPS connector. Black DMM lead on the Black/Blue wire and the red DMM lead on the Yellow signal wire. At idle read .63 to .73 volts. Don't sweat a few milli-volts if it out of range. The way the TPS is attached to the main throttle body shaft the TPS idle voltage reading will change if you adjust the idle speed using the manual adjuster on the right side frame area. The ECU is mostly looking at throttle rate of change and span of throttle change instead of absolute voltage. If the TPS is bad in a narrow portion of the resistive track the ECU will see the sudden drop as a fast throttle change and will chop the FI off via the decel fuel cutoff and then when past the resistive track defect the ECU will see the sudden voltage rise like the rider is pinning the throttle wide open for a brief second and it's this rapid off/on that the ECU sees that makes the engine run so rough or outright stall.

Leave the meter back-probed to the TPS, Velcro/rubber band the meter to your handlebars and for a ride until it heats up. When the off idle misfire happens watch the meter. If it's the TPS, the voltage on the meter will notch down dramatically then come back up as you get the throttle beyond the (potentially) damaged spot inside the TPS. Steady, linear voltage = good TPS = look elsewhere.

The ECU provides +5 volt reference to most sensors and uses an isolated ground from the ECU so it is best to ground the meter to the Black/Blue wire and not chassis or battery ground.

If Don has an updated TPS it should be good, I haven't seen any Gen I/II fail a second time with a new style TPS. But if it is to happen, well Don would be that guy

[raYzerman]

Alan's method is the good only real way to tell if the TPS is good or not...... the other methods of using the DiAG screen aren't as sensitive and a bad TPS can seem good on that screen... DiAG more useful for TPS adjustment when replacing an old one. You guys with '16's and up have to use OBD and an app that shows throttle position. Again, it can show OK while backprobing gives you the real poop on the resistive track.

[dcarver]

Hey Guys, found the solution.
https://candybuttorg.ipage.com/cba/node/757

Seriously corroded #4 spark plug wire at connector. Test ride today wonderful. 42 mpg, snappy throttle, Woo-Hoo!

Then the smell of burning oil and hot right foot.

Sigh. I should fire that bastard tech who installed the valve cover gasket!

Sorry for link, but pics don't crossover from blog to here.

https://candybuttorg.ipage.com/cba/node/757

Most importantly, Many Thanks for all the great ideas offered up. Just wanted to follow up with the resultant findings.

Don

[ionbeam]

Hey Guys, found the solution...Seriously corroded #4 spark plug wire at connector...Then the smell of burning oil and hot right foot.

Sorry for link, but pics don't crossover from blog to here.

Congratulations on finding the culprit.

Pics don't crossover or shouldn't cross over due to bandwidth or some such arcane issue? If this is a problem I will remove the pics.

[raYzerman]

ha... trapped gasket...... just coulda loosened it, lift it enough to get it in the groove and re-snug it back up. Iff'n ya cut it, still might work but look at the new one to check out how it seats.
As fer the plug wires, as mileage goes up and with spark plug changes, wayers can get pulled on and loosened... corrode. Once in 5 years, pull the sparkie ends off, clip 1/4" off the wayers, spread the strands and screw the sparker things back on.
Glad it was an EZ one.

[dcarver]

Hey Guys, found the solution...Seriously corroded #4 spark plug wire at connector...Then the smell of burning oil and hot right foot.

Sorry for link, but pics don't crossover from blog to here.

Congratulations on finding the culprit.

Pics don't crossover or shouldn't cross over due to bandwidth or some such arcane issue? If this is a problem I will remove the pics.

THANKS IonBeam, no problems at ALL except I'm lazy... I simply can't cut and paste from candybutt.org to this site.. have to modify the html like you did.

[dcarver]

ha... trapped gasket...... just coulda loosened it, lift it enough to get it in the groove and re-snug it back up. Iff'n ya cut it, still might work but look at the new one to check out how it seats.
As fer the plug wires, as mileage goes up and with spark plug changes, wayers can get pulled on and loosened... corrode. Once in 5 years, pull the sparkie ends off, clip 1/4" off the wayers, spread the strands and screw the sparker things back on.
Glad it was an EZ one.

Wish I had thought of that. Was too focused on getting compression numbers. Sometimes one needs to back away, come back later with a fresh look. Live and Learn!