Misfire at steady cruise

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Smerkal

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Aug 10, 2012
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Location
Lincoln, NE
Just got my first FJR. 2006 AE model. I've wrenched on everything from cars to airplanes to truck and boats, but this is my first fuel injected bike. it seems pretty straight forward as far as fuel injection goes.

I've noticed that when idling, running at steady RPM (any) in neutral or running at steady cruise (light load, any speed) the exhaust has a constant misfire/burble sound. At times I think I hear a ping as well but can't get it to do it consistently. When idling, it sometimes sounds like the ignition misfires against the compression and you get a hard miss. I've done the usual:

TB Sync

Plugs

Checked for vacuum leaks

Messed with CO settings

Fresh fuel

Injector cleaner

No codes

Ground spiders are clean and tight, no damage. Ground voltage drops are acceptable

Main harness connectors are clean and tight

The bike is stock other than a horn and add on lights. It came with StainTune exhaust but I removed that to be sure it wasn't the source of the issue. It runs strong under acceleration all the way to red line, but as soon as you put it under light load it stumbles around.

I'm planning to get an oscilloscope from a friend this afternoon and look at the crank sensor, injectors, TPS, etc to see what I can ascertain. Any suggestions?

 
Did you check your:

Battery for weakness (weak battery can cause some weird issues)

Check you Coil Wires to make sure they are Firmly Screwed in to you Spark Plug Cap.

 
Are you sure it's not the lean serge they all have ? They are set up lean to pass emissions. If so a power commander would take care of it by putting in a richer fuel mapping.

I'm not sure, but I think if you unplug the O2 sensor the ECM will go into rich mode. If so try it and if the issue goes away it's probably the lean surge.

I'm sure someone with more knowledge will chime in.

Also dirty throttle bodies can cause some weird things.

 
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+1 - Yep. Try what Roadrunner suggests above.

If there is a change then it is the "lean stumble" that some riders can feel, others seem numb to it.

There are many ways to "fix" it, but they all involve adding fuel during cruise.

 
Compression is 85-88 all across the board. I have no reason to suspect a mechanical issue. Bike Only has 13k miles on it.

I am unable to isolate it to a single or pair of cylinders either. I can disconnect the injectors one at a time, inducing a dead miss on that one cylinder, but the other three continue to burble, and it's the same all across. The rpm drop on each cylinder is identical as well.

Enrichening with propane/ether smooths it out some but not completely.

Perhaps they just do this? Can others confirm or deny? It drives me nuts especially edging slow in first such as in a parking lot because the bike surges.

 
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I also tested the ignition using an old GM HEI tester. It drives DIS coils to saturation, it has a good hot blue spark all across.

 
If you got those readings with a fully charged battery, hot engine and holding the throttle open while cranking you have an issue.

It could be as simple as sticking rings. Put a tablespoon or so of oil in each cylinder as you run the compression test. If the compression goes up it's rings, if it doesn't it could be carbon on the valve seats. I seriously doubt that all cylinders would have equal carbon.

I would suspect the test and not the engine, after all, you say it has good power and it *sure wouldn't* if you were down ~40% of your compression. Verify the o-ring on the compression tester and redo meeting the conditions in the opening sentence. Put the battery on a trickle charger overnight to ensure that you have sufficient cranking speed.

Before going after major internal issues you may want to take your injectors to a diesel engine shop and have them flow checked and balanced.

Take a couple of minutes and read this, I see you using several different descriptions of what you are feeling.

 
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Also, it's not a surge like the throttle is being moved, it's a distinct but random misfire/burble sound heard in the exhaust and felt it the drive train. If I were to characterize it, I'd say it's most akin to a lean miss. Spraying carb cleaner into the air box smooths it out a lot it seems.

I looked at the crank sensor and injector wave forms, they all looked exactly like what I would expect. The CPS has a distinct and periodic double pulse which I assume is the TDC indicator (without seeing the reluctor it's only an assumption).

Cranking the CO settings WAY up (Richer) did very little to affect it. Nor did disconnecting the O2 Sensor. I wish I had another one to listen to and see if I'm just hyper sensitive. I've become that way from being a pilot. I don't like anything other than steady engines at 10,000 feet ;)

 
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Much more likely to be electrical than fuel.

Have you had the ignition switch recall done?

The coil grounding signal goes directly from the ECU to the coils, not much to go wrong there. The soil's power side goes through a couple of connectors (coupler 17 and coupler 52), through the handlebar Run/Stop switch, the ignition fuse to the key switch. Go fish. :lol:

Edit: Glad you found the missing PSIs.

Edit II: Got any dyno shops within a reasonable distance?

 
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Voltage drop B+ to coil is less that .1v. I haven't owned it for very long so I'll have to check with the dealer to find out what recalls have been performed.

It really seems like a lean misfire. Carb cleaner in the intake clears it up momentarily, though propane did not. Not a dense enough fuel source at low concentrations.

 
I wasn't saying the voltage was low, I was hinting that the connection was intermittent. Acceleration and deceleration are dynamic conditions where engine inertia can hide little problems, whereas a steady throttle will let you feel the hick-ups. As you point out, there doesn't seem to be a pattern to the glitches. Everything is in play, including loose battery terminals (need to go back and see if you checked one of the first things first). They way the ignition switch failed (before the recall) could cause an intermittent problem.

Lean misfire will always cause an engine to run hot. What do the plugs look like? Check plug to plug color and overall plug color, if it is lean enough to misfire it will show in the plug color. If it is rich enough to misfire it will show in the plug color. What is the head pipe color and temperature? If the old plugs have a good color and the color is equal between the plugs you should be looking someplace other than a fuel problem.

An exhaust leak will cause that kind of a sound.

Does the tach flicker during the glitch?

Back to that local dyno....

 
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I'll have to confirm with the dealer as to what recalls have been performed. Lincoln isn't a big enough town to have dyno shops. Were just an overgrown collection of corn heads.

Basics have been gone through with a fine tooth comb. Battery terminals, voltage, charging system (A/C leakage), grounds, etc. Plugs are a light whitish grey color. Head pipes are not discolored at all. No temp reading since my kids broke my infrared thermometer using the laser to tease the cat with.....

The reason I lean away from an electrical issue is that I've had a scope on the primary side of the coils and never see a glitch at all in the patterns. The tach doesn't flicker so much as vary slightly but slowly. Every once in a while I hear a slight backfire through a throttle body, just off idle, that would be very typical of a lean misfire.

 
Best of luck hunting it down. I hate to see people start out with a determination that the problem just has to be (what ever) and not pay attention to some of the other underlying subtleties. Troubleshooting is part of what I do for a living so I tend to follow structured problem solving.

Your town may be small but I'm willing to bet that some shop in the area can test emissions. I'll bet that poking an EGA probe up your tailpipes would give you a hint. Remember that the right and left pipes commingle fumes at the cats. Dunno about your fancy Gen II, but a Gen I as a spec of (with Air Injection shut off) 3% to 4% at the head pipes and 1.5% or less at the tail pipe. 4% at the head pipes translates to 1.5% out the tail pipe.

 
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I'm not trying to discount your theory, just injecting my own. Troubleshooting is also what I do for a living as a network engineer and a mechanic. I completely understand your idea, I'm just having trouble finding any evidence to support it. Not that it isn't there, it's just not evident yet.

There are a lot of places with 4 gas analyzers. Dyno's are a different story, since we're not an mandatory emissions state. I think the cows produce more pollutants than the cars ;)

Though it goes against every fiber of my being, I may just have to drop it at the Yamaha dealer and let them look at it. I'm just running out of ideas and methods to test that are available in my garage.

 
I'm still not convinced that what you are experiencing isn't the normal lean misfiring that all of these bikes have. Have you heard and/or ridden any other (stock) FJRs? At idle, they all have a little miss. On 2nd gens, due to the lower cold idle speed (related to having introduced the AE) the hiccups are far more pronounced. Some owners say they hear a clunking from the drivetrain when it happens. And the lean surging at cruise speeds that I was talking about IS caused by misfiring due the leanness of the mixture. By adding fuel (PCIII, etc.) you can get rid of that.

Before you go crazy troubleshooting and replacing stuff, why not just do a direct comparison to another copy of the same bike?

 
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1+ on what Fred said "I'm still not convinced that what you are experiencing isn't the normal lean misfiring that all of these bikes have"

Being this is your first injected bike, this lean surge condition may feel different to you than what you have experienced on a carb bike or even an injected auto.

My oh 9 surged like crazy until I add the power commander. I knew what it was right a way as this is my 3rd FI bike.

It still stumbles/burbles a bit at idle but no longer has a noticeably surge/misfire when moving.

Used PC3's come up for sale here occasionally. You can selling it for almost what you pay for it

if it does not help. Good Luck

 
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