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Old June 2nd, 2015   #1
Wjbertrand
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Default Ignition problem?

I noticed this on Sunday when riding with Jim, Dave and Tim. Took the car yesterday but rode the bike again today and noticed the problem again. Usually happens when riding around a constant 70 - 75 MPH. I back off the throttle just a tiny bit and the engine feels like someone completely shut the key off, then before I can react it resumes, but with a semi-violent surge. This is much larger than the subtle lean spot issue these bikes are known for. As I'm riding to work I'm wondering about the fuel pump, possible vacuum leak, spark plugs (48K on them), injectors gummed up, what could it be? Then I happened to be looking at the dash when it did it again and notice the tachometer, basically shuts off (drops to "0"), and then bounces back in sync with the power. Now I'm pretty sure it's an ignition problem, based on that observation and assuming the ignition also signals the tachometer.

Gonna check all the obvious stuff like loose wires, etc. but wondered if there was any experience with this kind of problem out there?
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Old June 2nd, 2015   #2
Rob2m
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Default Re: Ignition problem?

Unlikely to be all 4 plugs or all 4 injectors. I'd start with battery connections and in general suspect an electronic issue, reseating connectors may well solve it. Anything happening on the Fi light?
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Old June 2nd, 2015   #3
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Default Re: Ignition problem?

No FI light, I'm beginning to think the problem lies with the kill switch contacts. I recall having a problem where they became very touchy before. Just touching the switch and making it move a little, like pressing it more toward the on direction when it's already on or wiggling it would interrupt the ignition. I wonder if that's what's happening again and the particular RPMs are just the right vibration frequency or some such? Commuting on the coast with the salty air / fog has caused other corrosion issues before (most notably the front brake light switch).

Gonna make this my #1 suspect, squirt some contact cleaner in there and work the switch back and forth a bit. Solved the problem last time.
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Old June 2nd, 2015   #4
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Default Re: Ignition problem?

Flick the switch when your riding, if the symptoms are the same you have proved it.
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Old June 3rd, 2015   #5
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Default

Played with it last night and although the symptoms are the same, the switch didn't seem particularly touchy like before. Only had one or two episodes on the way home. Maybe just moving the switch (I rarely use it) helped a little. I took apart the switch pod and sprayed everything out, but had to use the car today for work reasons.


-Jeff
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The original ST1100 LiST is at www.st-riders.net
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Old June 4th, 2015   #6
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Default Re: Ignition problem?

Well, it's not the kill switch. The problem resumed today in spite of the cool morning temperatures and a topped off fuel tank. I did refine my observations this morning however. First it happens exactly at 4,250 RPM, but only when decelerating or using extremely light throttle. If I just let the bike coast from say 4,500 RPM down through that range, without touching the throttle (completely closed) the tach needle will drop / swing rapidly down and back up a few times right as I hit 4,250. Of course when coasting I don't feel the surging or bucking. I can accelerate back through that RPM with no issue at all. I also proved that it doesn't matter what gear the bike is in, I'll get the same behavior in 3rd, 4th, or 5th at that specific RPM. Weird.

No other electrical gremlins at all. Still no FI light, no clock resetting, nothing just the momentary loss of power and signal to the tach, happening simultaneously. TPS maybe?
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Old June 10th, 2015   #7
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Default Re: Ignition problem?

Well, no joy. I've taken apart every connector that carries the tach signal from the ECM to the tachometer (thinking there's a relation to the tach behavior and the hesitation drop out), tested both coils, the HT leads to the spark plugs. Also disassembled and cleaned all the harness connectors under the left main faring. I have not found anything the least bit suspicious looking, in fact all the connections looked pristine but the problem persists. I'm going to tear into and test the TPS tonight I think. Except for the very specific RPM (exactly 4,250) where the problem occurs, the symptoms are closest to a bad TPS. Unfortunately you can't buy a replacement TPS from Honda (if that's what it turns out to be) you have to replace the whole throttle body assembly for $1200! Luckily, I think I've found some cross references to Honda car TPSs for as little as $14. Gonna hold off buying until I have real evidence this one is bad. It's really a shame because the bike runs perfect under all other conditions. This one's a real head-scratcher....
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The original ST1100 LiST is at www.st-riders.net
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Old June 14th, 2015   #8
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Default Re: Ignition problem?

Update. Eliminated 3 more possibilities: I performed a TPS test, by back probing the connector with the key on. Getting 5.5V where I'm supposed to, ground where I'm supposed to and the ~0.44 to ~4.6V from throttle closed to wide open is exactly what it's supposed to be. Rotating the throttle very slowly from fully closed to fully open gives an extremely smooth response on my analog meter. I even tried tapping on it whilst I changed the throttle position. It's not the TPS.

Next Hal came over and we swapped ECMs. The problem follows the bike, not the ECM. Hal's bike runs fine with my ECM and mine still stutters with Hal's ECM. It's not the ECM.

This morning I tried by-passing the side stand switch. That made no difference and I validated that my jumper stayed in place by lowering the side strand at the end of the test with the bike still in gear, which when not bypassed, should stall the engine. The engine remained running. It's not the side stand switch.

I had Hal run the engine, moving the throttle back and forth around 4250 RPM while I held my hands near the exhausts, I can feel and hear both banks stuttering in sync with the tachometer dipping. Whatever is wrong I believe is affecting all four cylinders.

I went to examine the clutch switch and the connector lug broke off when I tried to remove the wire. It's pretty corroded and due to the broken lug, now needs replaced anyway. Not sure if a dicey clutch switch could cause this problem.
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2015 ST1200

The original ST1100 LiST is at www.st-riders.net
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Old June 22nd, 2015   #9
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Default Re: Ignition problem?

Update: Replaced the iridium plugs that had done 50K, but there was no improvement. The old plugs coming out looked fine other than a slightly widened gap by a couple thousandths. The mystery continues.
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The original ST1100 LiST is at www.st-riders.net
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Old June 23rd, 2015   #10
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Default Re: Ignition problem?

Just keeping this thread alive with an update. Last night I pulled the throttle body assembly far enough out to access the TPS screws. The advice on the Honda car forums to cut a slot in the headless screws to remove them didn't work because they're made of cheese or something, stripped out immediately. This left me no choice but to drill out the screws (shudder). That done, the new TPS comes with conventional screws and fits perfectly. Tonight I will attempt the calibration procedure to get the voltage set to 0.48-0.50 volts, throttle closed, and 4.5 V throttle fully open. The TPSs have slotted holes to allow for adjustment. I measured the old TPS before disturbing it and found the voltages to be pretty close to this range. I recorded the numbers but the information is at home and I don't recall the exact values. Since the bike was running fine when cold, I figure these measurements are probably good.

I'll either get this fixed or screw it up beyond all hope! My fall back plan is to source a used throttle body assembly, including the TPS if my $15 fix fails.
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2015 ST1200

The original ST1100 LiST is at www.st-riders.net
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