After just putting on a fresh set of PR2s on I took my bike out to scrub in the new tires. When I went for a ride the bike started missing. The bike is a '92 with 20K all stock (engine) and its never had an issue before.
I shut the bike off and let it cool down and tried it again 15 minutes later. I found it was only firing on two cylinders (the #3 and #4 pipes stayed cold). My guess is an electrical problem based on two cylinders completely shutting down. Fuses all looked OK, nothing else obvious. I have since removed the coils looked at them closely, measured resistance and they were both within the manual specs. I re-connected the coil connections and everything was fine. Since #3 and #4 are fired from different coils I doubt the coils are the problem. Next time it happens I want to be sure and check for spark. As I think about it I wonder if there is a related vent or hose for carbs #3 and #4 that could cause the problem.
Other factors, I recently installed a battery and fork springs but had done some riding without any issues.
Any ideas as to what this intermittent issue may have been? I'm heading to WV in a month and I'd like to find a 'solid' problem to hang my hat on.
thx, jd
Obviously the wrong tires. Bike is rejecting them.
That or you've got synth oil, which also causes electrical gremlins.
Otherwise, you may desire to take a peek at the fuel feed into the carbs, at a T fitting, which possibly has a blockage on one side. Next obvious step would be to pull the #4 bowl (easiest to get to) and see if there's fuel in it or not.
I had a issue that has been ongoing for almost a year and it finally turned out to be a bad ground wire.... the main ground from the rear of the engine case to the negative battery terminal.
caused all sorts of weird running issues and eventually toasted the battery.
Kookaloo!
Frank
The later models have a "reserve" switch on the left inner fairing. I believe that it is supposed to simulate running out of fuel by cutting spark to two cylinders. This could be a possible culprit.
For some reason I was under the impression that it would cut power to the fuel pump. Though I'm not sure - maybe someone else can clarify.
Quote from: Marsh White on May 17, 2010, 01:43:29 PM
For some reason I was under the impression that it would cut power to the fuel pump. Though I'm not sure - maybe someone else can clarify.
Yes that's what I thought also, it shuts down the pump until you flip the switch to reserve. Thanks for the idea though, I'm still stumped. I'm going to balance the carbs this weekend and take if for a good 200 mile run and see how it goes. The bike has never stumbled before so I hope it was a one time issue. If it happens again I plan to check for spark to isolate the problem to electrical of fuel. I was hoping someone experienced a similar problem so I could easily locate the culprit and find a 'smoking gun' so to speak.
jd
If i remember, don't both 3 and 4 plugs fire on the same coil?
If one plug or one wire is bad then both plugs don't fire
Check
+12 to coil
coil for spark
bad wires to plugs
bad plugs
bad pickup
bad igniter
1-4
2-3
Would be unlikely that 3 and 4 would have an electrical problem. Swap spark leads on 1/4 and 2/3, and see what lights up on a start, that'll tell you everything about the electrical, which is likely just fine.
Quote from: mikeholzer on May 17, 2010, 11:53:56 AM
The later models have a "reserve" switch on the left inner fairing. I believe that it is supposed to simulate running out of fuel by cutting spark to two cylinders. This could be a possible culprit.
The simulated reserve feature simply cuts power to the fuel pump..... not nearly so sophisticated as that.
Quote from: Travis398 on May 17, 2010, 05:47:35 PM
1-4
2-3
I think this is right. I was going to start a new thread, but maybe I can just jump in here.
Got up this morning, got ready to leave, bike won't start (ran fine yesterday). Engine spins over, never hits. Get home this afternoon, check fuses, battery, fuel pump, etc. Everything ok. Check for spark; nothing on 1 and 4, spark on 2 and 3 (although it looks weak to me). Does this sound like a bad coil? Would it go out that suddenly?
The coils fire 1-4 and 2-3.
It could be a bad coil. Electrical components tend to just fail suddenly like light bulbs. You can check this by swapping the coil power connectors. Pull the plugs, swap the connectors and see if the 1-4 plugs fire (leave the 2-3 coil disconnected when you do this).
However, I would also check every electrical connector you can get your hands on. I've seen this before where one coil will stop firing or get chronic. I've seen it fixed a few times by electrical connector maintenance.
DavidR.
Thanks for the advice. Although they look like a pain to get to, I'll swap the coil connectors tomorrow and see what happens. The electrical connections could be a culprit; I pulled the tank last week and replaced the fuel filter. Things were REALLY nasty under there and I cleaned it extensively with Simple Green and carb cleaner. Maybe I amplified the corrosion?
check the coil grounds real good.
also check the ground/negative wire from the battery to the rear of the engine.... i had some crazy running issues and that cable turned out to be the root source of the problem.... the cable looked perfect on the outside but the inside was completely ate up with corrosion where the wire meets the terminal crimp..... anyway the resistance finally got so bad it melted my battery terminal and ended with a no start situation.
after repairing i also added a frame ground for good measure.
KOokaloo!
Frank
Well, latest development. It's apparently somewhere past the coils. The 2/3 plug wire/coil assembly won't fire when attached to the 1/4 connector. 1/4 will fire when hooked to the 2/3 connector. Crap. I was hoping it was the coil.
Looks to me (and my aviation electronics trained neighbor) like the pickup is OK. Two wires from the pickup out to the ignitor box. If one works (2/3 lead) the pickup is OK. The ignitor box splits that signal into two (one signal to each coil). ???!??
My money (no pun intended) is on a bad ignitor box. Thoughts/advice? I don't suppose the "fake reserve" switch could be involved, could it? Seems like I recall that the reserve function mimicked a low fuel level by shorting out two cylinders?
the ignitor box is one area where the FJ doesnt normally have any problems.... i would lean more towards a pinched wire or cruddy connector... have you done a oil change lately? the pickup wire can sometimes get pinched by the oil filter housing (fairly common)
KOokaloo!
Frank
Quote from: 83elite on May 23, 2010, 09:50:39 PM
Well, latest development. It's apparently somewhere past the coils. The 2/3 plug wire/coil assembly won't fire when attached to the 1/4 connector. 1/4 will fire when hooked to the 2/3 connector. Crap. I was hoping it was the coil.
Looks to me (and my aviation electronics trained neighbor) like the pickup is OK. Two wires from the pickup out to the ignitor box. If one works (2/3 lead) the pickup is OK. The ignitor box splits that signal into two (one signal to each coil). ???!??
My money (no pun intended) is on a bad ignitor box. Thoughts/advice? I don't suppose the "fake reserve" switch could be involved, could it? Seems like I recall that the reserve function mimicked a low fuel level by shorting out two cylinders?
Nope.... it simply cuts power to the fuel pump, to simulate running out of fuel. And, the ignitor box is NOT involved....
Looks like you need to chase the wire back, double-check the connectors it goes thru and look for abraded areas of the wire, it could be shorting to ground or just broken...