Suddenly Backfires on Deceleration (constantly)

[faster675]

I commute on my FJR pretty much every day (including last mon-fri).

This morning it is suddenly "backfiring" on deceleration "all the time".

I do all my own servicing, except for major items.

Bike is an '05 FJR, full holeshot system, proper map in PC3, I removed the AIS at 9K miles.

... she has 24,600 miles on her, just had 24K service done (by highly recommended Yammi dealership) 3 months ago, Air filter is clean.

In addition, on acceleration, power seems nice and smooth, but maybe (?) a little soft.

Also seems to have a slight miss at idle on one side (Holeshots are a dual 2 into 1 system)

Any ideas ? Like - if one of the plugs on the AIS ports came off ... would this cause what I am experiencing ?

 

[ionbeam]

All Content Deleted

 

[wfooshee]

The AIS is gone, so the connector is probably irrelevant. If one of the blocking plates is loose, or at least not well sealed, then air would be allowed into the exhaust on decel at all times.

 

[HaulinAshe]

Extra air in the exhaust sounds more like a detonation (sharper, abrupt POP).

Extra fuel in the exhaust sounds more like combustion (lower pitch, longer duration).

If you can carefully listen and determine which one is actually happening, it might give you or the mechanic a head start on the fix.

Even at 26,000 miles I wouldn't rule out a sticky injector or bad fuel. Changed fuel stops lately? Seen any construction work in the area?

I'd start with some fuel/injector treatment and check the PAIR plates. If you left the reeds in place (which I always do after cleaning) the cover plates have to be very loose to leak.

 

[faster675]

Extra air in the exhaust sounds more like a detonation (sharper, abrupt POP).If you left the reeds in place (which I always do after cleaning) the cover plates have to be very loose to leak.

Definately sounds like a sharper POP, much sharper than "normal.... (I've always gotten occasional backfires or pops because my bike is "jetted" a wee bit rich = unburnt fuel)

I put (tight fitting) vacuum plugs on the inlets to the reeds. .... maybe one of them came loose ...

I'll check it when I get home from work

Thank You All !

 

[HaulinAshe]

If you plugged the hoses as opposed to replacing the hose plates with cover plates, I'll bet one of the plugs is leaking. Also check for a collapsed hose, as this is a sign of a reed that's leaking backwards and allowing hot exhaust gas in reverse. That can eventually ruin your day by rupturing a hose.

In any case, I highly recommend cleaning the PAIR system reeds when you cap or plug the system. It's a PITA to do, but do it once, cap the system and you're done forever.

 

[Big-D]

Remember the olden days when you could turn your ignition off, pump the gas pedal a couple times and then turn the ignition back on and get a huge bang. That was caused from fuel remaining in the cylinder and when the ignition was turned back on, that fuel exploded.

Backfiring is usually related to a fuel/ air mixture being too lean. With everything you've done, have you checked and/or re-calibrated your throttle bodies? If not, it probably needs doing anyway. Perhaps after trying the other fixes, you should check the throttle bodies for being in sync.

 

[faster675]

Remember the olden days when you could turn your ignition off, pump the gas pedal a couple times and then turn the ignition back on and get a huge bang. That was caused from fuel remaining in the cylinder and when the ignition was turned back on, that fuel exploded.
Backfiring is usually related to a fuel/ air mixture being too lean. With everything you've done, have you checked and/or re-calibrated your throttle bodies? If not, it probably needs doing anyway. Perhaps after trying the other fixes, you should check the throttle bodies for being in sync.

....I synced em pretty recently ....

I'm betting one of the plugs came loose .....

 

[faster675]

Checked all plugs + hoses + injector to head boots + header to engine connections - everything I could think of to inspect.

Pulled spark plugs checked them all - they all look good.

It is still doing it. And there is definitely a miss at idle on cylinder 3 or 4.

Any more ideas on things to check before I have to break down and ship her off to the dealer ?

 

[madmike2]

At NAFO in Golden CO one of the riders had a bad/plugged injector. IIRC, it was Steve (03SilverBullet) and he played with that thing for days until he figured it wasn't electrical but it was a piece of "stuff" blocking the injector.

 

[03HiYoSilver]

Faster,

Did you check out your Main Wiring Harness Connector?

https://www.fjrforum.com/forum//index.php?s...st&p=268059

Coil Wires

https://www.fjrforum.com/forum//index.php?s...st&p=714281

Possible Loose Coil Wire to Plug Boot Wire where you could trim off about 1/4" and reinstall.

Just some ideas, good luck with your fix...

 

[mcatrophy]

... This morning it is suddenly "backfiring" on deceleration "all the time".... proper map in PC3, I removed the AIS at 9K miles.

In addition, on acceleration, power seems nice and smooth, but maybe (?) a little soft.

... Also seems to have a slight miss at idle on one side (Holeshots are a dual 2 into 1 system)

Any ideas ?...

Just a thought. Without the PC3, I believe there should be no fuel injection on the overrun until the engine speed is near tickover, so no fuel to cause backfiring. Even with the PC3, my (limited) understanding is the PC3 uses the ECU's fuel injection pulses to trigger its own.

That being the case, it sounds as if the ECU thinks it should be delivering fuel, which suggests the TPS area might be worth investigating.

I do speak from supreme ignorance :mda: , feel free to shoot me down; I'll learn something if you do.

 

[wfooshee]

Don't know for sure that there's no fuel delivery on overrun. You'd think so with EFI, but I'm not convinced that's the case.

 

[TownsendsFJR1300]

At NAFO in Golden CO one of the riders had a bad/plugged injector. IIRC, it was Steve (03SilverBullet) and he played with that thing for days until he figured it wasn't electrical but it was a piece of "stuff" blocking the injector.

Do you know how he found the clogged injector on the bike? TIA, Scott

 

[faster675]

Do you know how he found the clogged injector on the bike? TIA, Scott

... and along the same lines .... any easy way (short of replacing injectors) that I could figure out if I've got a dirty injector causing my problem ?

 

[03HiYoSilver]

faster,

Have you Disconnected the PC3 to see if this is causing the problem?

 

[faster675]

Faster,Did you check out your Main Wiring Harness Connector?

:yahoo: :yahoo: :yahoo:

Looks Like Silver wins the prize

onnector A is corroded:

I'll start cleaning them tonight after work ....

 

[RadioHowie]

Do you know how he found the clogged injector on the bike? TIA, Scott

He lifted the tank?

 

[03HiYoSilver]

Looks Like Silver wins the prizeI'll start cleaning them tonight after work ....

Faster,

Yay! Glad you found the source of your problem. The unfortunate thing about these situations is that they don't throw a code... so it takes a great deal of troubleshooting usually on our part.

P.S. You can keep the prize money for the celibratory beer!