Posted by Rob Kleinschmidt on August 13, 2009, 3:51 pm
> Any-who... The Bob has recently begun backfiring like crazy when I
> decel - at a certain point when the rpms drop to the lower range, just
> before down-shifts. Bang! Bang! Loud!
> But that's not the worst of it. I have to keep throttle on it once it
> starts acting that way because, if I let go, the idle drops so low the
> engine stops almost immediately.
> Another thing that makes this difficult is that the behaviour is
> intermittent; happening about 2 out of 3 of the times I ride it.
> Funny thing is, at all times, the bike seems to run real strong -
> whether it is in the backfire-no-idle mode at the time or not.
> Seems the exhaust is bolted on tight. Check the battery ground,
> having heard that it being loose can cause a problem like this.
> Wiggled wires all over while it's running to see if that affects
> anything to no avail. I'm starting to wonder what else I can do to
> diagnose this.
> I haven't replaced the spark plugs (yet), but they looked okay when I
> re-gapped them a few months ago.
> Any ideas on what might be the cause or some tests I can perform?
Fuel delivery issue ? Crap in the gas ? Flakey pump ?
(injected, right ??) I'd drain and refill the tank on general
pincipals.
You also checked both ends of the +/- battery leads, right ?
Any intermittant electrical connection there can cause really
strange stuff.
I'd wonder too if the problem might track heat, assuming
that you can occasionally find some in Canada. Heat on
an electronic ignition component can also cause funny
intermittant problems.
When it runs crappy, what happens next ? Does it continue
to run crappy until it's parked for a while or does it mysteriously
recover while it's running ? If it stays in running crappy mode
for a while, that might be a good time to check timing and
whatever else you can think of.
Posted by MikeWhy on August 13, 2009, 4:04 pm
> So I've tried checking various things. Figured it would be throwing
> some trouble codes but, nope. No trouble codes. Darn.
> Seems the exhaust is bolted on tight. Check the battery ground,
> having heard that it being loose can cause a problem like this.
> Wiggled wires all over while it's running to see if that affects
> anything to no avail. I'm starting to wonder what else I can do to
> diagnose this.
Backfiring suggests it's too lean. I'm guessing FI from you mention of ECU
codes. Intermittent causes might be fuel pump; fuel filter; tank pickup. O2
sensor problems would show up in the codes, but check the wiring.
> I haven't replaced the spark plugs (yet), but they looked okay when I
> re-gapped them a few months ago.
It's worth a look. Insufficient spark might cause the ECU to lean the
mixture. If the behavior varies with humidity, it might well be ignition
related.
Posted by Road Glidin' Don on August 16, 2009, 2:00 pm
> > I haven't replaced the spark plugs (yet), but they looked okay when I
> > re-gapped them a few months ago.
> It's worth a look. Insufficient spark might cause the ECU to lean the
> mixture. If the behavior varies with humidity, it might well be ignition
> related.
Good advice, Mike. It encouraged me to be a little more thorough with
checking the plugs; adjusting a gap that was a little too big. Just
that minor change might have solved the problem. At least that's the
way it appears so far.
Posted by Road Glidin' Don on August 16, 2009, 1:57 pm
On Aug 13, 8:36 pm, "Stephen Cowell"
> > I haven't replaced the spark plugs (yet), but they looked okay when I
> > re-gapped them a few months ago.
> H-D recommends new plugs every 10K... do this
> religiously; the spark system watches the spark
> happen, and if something funny's going on it'll
> think it needs to mess with the spark. On these
> smart systems, don't use multi-gap plugs, or
> funny aviation plugs... the spark computer expects
> Champion H-D whatever, so that's what it'd better
> see.
First of all, thanks to everyone who offered advice on this. It was
very helpful. I haven't been able to get back on this until now;
having been so busy lately.
I'm responding to this reply first because it looks like (so far!
fingers crossed!) Steve (and Mike as well) might have hit the nail on
the head.
Following the principle of rule out the simple/inexpensive things
first, I took a look at the spark plugs, night-before-last. I half-
expected to see indications of a lean-running condition.
But, dog-gone it, those plugs didn't look too bad at all, so I put
them back in.
After a few sips of beer I decided I should have been more thorough.
Should have re-checked the gaps on those plugs (even though I'm quite
sure I did it over the winter).
Hmmm. The gap on the front plug is a bit on the wide side. Not way
out (about .044"), but slightly out of spec (should be .038" - .043"
IIRC). And it's all sorta ballpark anyway, using the circular ramp-
style measuring gauge I have... So I adjusted it to .040".
The next day (yesterday) I took the bike out for a good, shake-down
run. 11 hourts of riding (up to Wabasa, Slave Lake and back to
Edmonton). Aside from one, brief re-occurrance of the problem early
on, the bike ran perfectly the entire way!
I think I'm going to replace the plugs now, to be real sure. It might
be that this EFI system is more picky about plug performance than my
other bikes (which I rarely change plugs on). The current plugs do
have 18K miles on them already.
> Make sure that you wait for the engine check light
> to go out after key on before starting... very strange
> behavior can result if all the peripherals don't get
> to do a happy boot (CAN-connected serial data stuff).
You could be right on that, but I've never noticed any down-sides to
starting before the pump stops. The problem with my bike sometimes
appears after awhile of riding.
Posted by Thumper on August 16, 2009, 3:04 pm
On Aug 13, 8:36 pm, "Stephen Cowell"
> > I haven't replaced the spark plugs (yet), but they looked okay when I
> > re-gapped them a few months ago.
> H-D recommends new plugs every 10K... do this
> religiously; the spark system watches the spark
> happen, and if something funny's going on it'll
> think it needs to mess with the spark. On these
> smart systems, don't use multi-gap plugs, or
> funny aviation plugs... the spark computer expects
> Champion H-D whatever, so that's what it'd better
> see.
First of all, thanks to everyone who offered advice on this. It was
very helpful. I haven't been able to get back on this until now;
having been so busy lately.
I'm responding to this reply first because it looks like (so far!
fingers crossed!) Steve (and Mike as well) might have hit the nail on
the head.
Following the principle of rule out the simple/inexpensive things
first, I took a look at the spark plugs, night-before-last. I half-
expected to see indications of a lean-running condition.
But, dog-gone it, those plugs didn't look too bad at all, so I put
them back in.
After a few sips of beer I decided I should have been more thorough.
Should have re-checked the gaps on those plugs (even though I'm quite
sure I did it over the winter).
Hmmm. The gap on the front plug is a bit on the wide side. Not way
out (about .044"), but slightly out of spec (should be .038" - .043"
IIRC). And it's all sorta ballpark anyway, using the circular ramp-
style measuring gauge I have... So I adjusted it to .040".
The next day (yesterday) I took the bike out for a good, shake-down
run. 11 hourts of riding (up to Wabasa, Slave Lake and back to
Edmonton). Aside from one, brief re-occurrance of the problem early
on, the bike ran perfectly the entire way!
I think I'm going to replace the plugs now, to be real sure. It might
be that this EFI system is more picky about plug performance than my
other bikes (which I rarely change plugs on). The current plugs do
have 18K miles on them already.
> Make sure that you wait for the engine check light
> to go out after key on before starting... very strange
> behavior can result if all the peripherals don't get
> to do a happy boot (CAN-connected serial data stuff).
You could be right on that, but I've never noticed any down-sides to
starting before the pump stops. The problem with my bike sometimes
appears after awhile of riding.
Don, you need a Valkyrie.
Thumper
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> decel - at a certain point when the rpms drop to the lower range, just
> before down-shifts. Bang! Bang! Loud!
> But that's not the worst of it. I have to keep throttle on it once it
> starts acting that way because, if I let go, the idle drops so low the
> engine stops almost immediately.
> Another thing that makes this difficult is that the behaviour is
> intermittent; happening about 2 out of 3 of the times I ride it.
> Funny thing is, at all times, the bike seems to run real strong -
> whether it is in the backfire-no-idle mode at the time or not.
> Seems the exhaust is bolted on tight. Check the battery ground,
> having heard that it being loose can cause a problem like this.
> Wiggled wires all over while it's running to see if that affects
> anything to no avail. I'm starting to wonder what else I can do to
> diagnose this.
> I haven't replaced the spark plugs (yet), but they looked okay when I
> re-gapped them a few months ago.
> Any ideas on what might be the cause or some tests I can perform?