Help! Firing on One Cylinder

333 Views 19 Replies 3 Participants Last post by jjmaine, 15 d ago

motopreserve

Discussion Starter · 1 mo ago (Edited)

Need a little help here folks. Had some weird power loss/surge/loss issues at the track the other day. Most dramatic display was one lap the speed/power was fine on the straight, next lap WOT capped at 65mph, lap after that was closer to 90mph. I was able to ride through it by smacking the throttle, which usually seemed to bring the power back. So it was coming and going for the entire first session, which was not ideal. Back in the pits the bike would start immediately, but idle and throttle was lagging. No CEL or error codes. Had to bail on the day.

Back at the shop, Day of Diagnosis began today. Again, started right up. Checked the basic stuff first (vapor lock, clogged air filter etc). No difference. Determined it is only running on 1 cylinder (#2). I've checked the following:

1. Compression (outstanding and near equal in both cylinders after the rebuild)
2. Checked coil packs for damage (slight rust, but no cracks etc)
3. Swapped #1 and #2 coils (no change)
4. Battery checked (solid at rest, cranking, idle and 3000rpm)
5. #1 coil/plug sparked against engine
6. Fuel Injector resistance (within spec)
7. Fuel Injector power source (correct)
8. Fuel Injector voltage output (correct)
9. No vacuum leaks at manifold or air-box boots
10. Cleaned Fuel Injector
11. Swapped known good Fuel Injector to bad cylinder (no luck - so both are working in Cyl #2, but neither in Cyl #1)
12. Swapped in a spare ECU (no change)

So at this point the bike runs (quite well) on one cylinder, despite running the known good coil packs and fuel injectors in the bad cylinder. My latest thought it that perhaps the fuel pump is not providing enough pressure to move the fuel down the pipe to Cylinder #1? The fuel hose enters the pipe closest to Cyl #2, and maybe it just can't make it down the pipe to the furthest cylinder? Not even sure if that could be a thing.

Any thought or advice welcome.

Thanks,

Scott

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jjmaine

· #2 · 1 mo ago

Was it firing on both cylinders when you got it or was the engine in need of a rebuild so who knows? Just wondering if maybe something got tweaked during your rebuild or if the PO had the issue well before you got it…
Seems the only thing it could be is an issue with something to do with the fuel injector? Not the injector itself obviously but maybe an issue with the wiring or ecu and it isn’t telling that injector to send fuel?

motopreserve

Discussion Starter · #3 · 1 mo ago (Edited)

No idea if this issue existed for the previous owner. It needed a rebuilt straight away. But ironically the cylinder with water in it when I got it is the one running well now.

I am wondering about the data being sent too. But I literally have no idea how that would work. All the FI reading were correct (resistance, input voltage and power voltage from ECU to FI (measured back at the ECU). Those are the only tests I found in the manual.

I forgot to mention that we also swapped a spare ECU in and it produced no change.

Where I’m lost is in the timing of the fuel injection/ignition. It’s coming from a black box that’s a mystery to me. If it was a points system, great. I can figure that out. But this shit gives me a headache!

jjmaine

· #4 · 1 mo ago

Timing? How about cam timing? Maybe it slipped a tooth somehow before you got the cylinder head all bolted back on?
I’ve never experienced the cam timing being off but I have heard it can cause some pretty strange issues like the bike will start and idle okay but under load the engine acts weird.

motopreserve

Discussion Starter · #5 · 1 mo ago

We thought of that earlier. But I assumed if it was off it would cause both cylinders to act weird at some point. I could be wrong. But it’s odd how the one cylinder seems to be humming along fine.

Looking like I may need to head back in to the motor and take a look. I’d love to rule out all the electrical first - but I’m reaching the end of my knowledge when it comes to these fuel injected systems.

motopreserve

Discussion Starter · #6 · 30 d ago

Well, looks like I’m going to need you fellas to smack me in the head with a 2x4”.

Ran through another series of electrical tests with all readings in spec. I’ve poked so many wires the harness is probably Swiss cheese. I was at a loss.

Dug through my spares and grabbed another spark plug. Not even sure what made me think of it, since the spark test was the 2nd thing we checked. Sure it had spark grounded to the frame. But why not try a new one anyway? What could it hurt…

Bam! Cylinder #1 fired up immediately with the new plug. Turns out the plug was the only thing we didn’t swap to the other cylinder. And that was the f*cking culprit all along. Or so it seems so far.

Quick multimeter test showed that the plugs got different readings (coil contact to threads/body). I’ve never had a plug create spark against the engine yet have no spark inside the cylinder. But when I test, I ground to the frame but don’t touch the threads to the frame as well - just letting the arc jump. So this is not a proper test (although it’s never steered me wrong in nearly 20 years).

Visually the exterior of the bad plug looks fine. Turns out that it has broken (deteriorated?) inside the plug itself. Unreal.

Learn something new every time I step up to this little 300

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jjmaine

· #7 · 30 d ago

Damn, sweet! Sucks that it caused such a headache but thank god you didn't completely strip the entire engine back down before you figured it out lol

jjmaine

· #8 · 30 d ago

I'm guessing it was a new plug too? Must have been faulty?

motopreserve

Discussion Starter · #9 · 30 d ago

Yep. We even asked my buddy’s brother whether he has seen such a failure. He’s a supervisor for the sanitation trucks in NYC, so seen his share of abused vehicles

. He said he had seen it - but very very rarely. So I guess that should make us feel a little better.

And yes, very happy that I finally decided to check before tearing the thing apart. Looks like there is another track day a week from monday. Think we will try to hit that and make up for lost time!

Reactions: 1

jjmaine

· #10 · 30 d ago

Nice! Yeah I couldn’t help but think if that had happened to me I would have never figured it out. My first thought would have been “The spark plugs are brand new so those are good” lol

motopreserve

Discussion Starter · #11 · 30 d ago

And it had spark!!!! Lesson learned. Testing plug against the engine tells you the coil is working. And LIKELY the plug, but not guaranteed

Needless to say, I have a pack of 4 on the way!

jjmaine

· #12 · 30 d ago

Thats why ai love these forums. No way I would have ever learned that if people didnt post their issues and solutions. The hard part is remembering it all when/if the time comes!

motopreserve

Discussion Starter · #13 · 30 d ago

Agreed. My brain hurts from 3 days of researching fuel injection. Never thought I would long for the days of carbs so bad

I do have a couple lingering issues I’d like to tie up. One cylinder is running hotter than the other. Might try to rig up gauges to do a throttle body sync. Need to read about that again in the manual.

Also, I have a slight hesitation on the throttle if I crack it quickly. Not sure if it’s related. Or is this typical on these bikes? Seems to only do it from idle. If I’m reving up near 3000rpm and crack it - seems to work fine.

jjmaine

· #14 · 29 d ago

Not sure if the hesitation off idle is normal, mine seems fine especially after the ecu flash (I assume they richened the bottom end).

I know mine used to turn over a fee times before starting cold and now it fires up instantly even after sitting for a week. Valve adjust and ecu flash helped I think.
I’ve been really flogging my bike, I’m debating a manual cct just to be safe….

motopreserve

Discussion Starter · #15 · 29 d ago

I need to sort out that hesitation. But it really only happens when I twist the throttle as fast as I can. I would never being doing that on track anyway. Rolling on the throttle feels perfectly fine.

The bike starts on the first push of the button every time. So I’m good there. Thankfully!

Reactions: 1

Hudson794

· #16 · 16 d ago

Ask me questions

Sent from my TECNO KC8 using Tapatalk

jjmaine

· #17 · 16 d ago

Hudson794 said:
Ask me questions

Sent from my TECNO KC8 using Tapatalk

How’s your sister?

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jjmaine

· #18 · 15 d ago

This guy writes one post that says “ask me questions” and then sends me a private message to tell me his “friend” just so happens to have the Arrow exhaust headers that I was looking for in my wanted post. Just email him at this sketchy email he says lol.

motopreserve

Discussion Starter · #19 · 15 d ago

Good grief! I saw that his “ask me questions” post was his first.
Way sketchy!

jjmaine

· #20 · 15 d ago

I know right!?

“Arrow exhaust headers for sale, will trade for google play gift cards” 🤣

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