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Discussion Starter · #1 · (Edited)
I hope I can get some help here as I'm at wits end with this bike. I have viewed a lot of threads with similar issues, but I've yet to find anyone else who either successfully fixed it or had any solution. I have rebuilt many motorcycles and claim to be a mechanic since I do all of my own work and rebuilds, but this problem has beat me.

I bought this bike from the original owner as a 2008 ZX6R with about 1100 miles, so yes, it sat for a good while. The fuel in the tank was foul but it wasn't much left so I ran it through in combination with good gas.

Initially, the only problems that I noticed: had to let it warm up for about 10 seconds before touching the throttle, or it would die; a slight loss of torque on takeoff/clutch engagement; and at about 8 to 9000 rpm during acceleration, you would lose power and the engine just wouldn't push itself any further, almost as if it was choking itself of either fuel or air. At this point I assumed that I just needed to run fuel system cleaner through the bike, and so I started doing so.

As time went on, this problem progressed. The bike is now at 1500 miles, and since then, I discovered the following consistent traits of the issue.

  • Upon cold start, you have to let it warm up for about 10 seconds before touching the throttle, or it would choke itself and die.
  • Initial throttle blips, most of the time, try to choke the engine, but you usually get right through the choke without dieing.
  • At WOT (wide open throttle), the bike ALWAYS chokes itself out. Not enough to die, but it sputters like a son a of bitch.
  • The engine will choke itself at somewhat consistent percentages of throttle, e.g., at 30% throttle the engine chokes, but at 40% throttle, it will do fine.
  • The issue does not seem to be load dependent, only throttle position.
  • The secondary intake valve (throttle body) actuator ended up getting fried around 1500 miles. I was notified via code on the odometer, and replaced the throttle body assembly (used) immediately. This provided no relief whatsoever to the issue at hand. What concerned me was that this might have been an electrical frying of the component. Note that this also replaced the throttle position sensor and all other components on the throttle body.
  • The bike must be running lean/hot because the exhaust is getting so hot that it has melted some of the plastic around the muffler. I no longer run it long enough to get that hot since this issue is so bad now.

Here's what's been replaced/done in an attempt to fix the issue based on self-diagnoses and using forums: spark plugs, coils, lower fuel rail and injectors (came with prior mentioned throttle body), fuel pump rebuild (replaced the pump and sock with a rebuild kit), and ECU. Also, the fuel lines were pulled and checked for clogs, and were also cleaned. When I first pulled the fuel pump and disassembled it, the sock (filter) was clogged with a hardened clay like material. Because of this, I believe the fuel flow might have been affected.

Also worth noting is that it seemed that running fuel system cleaner through the bike didn't help at all. In fact, it seems as if as I rode it with the cleaner, the problem only got worse. But I have no way of knowing if this was a contributor to the problem other than I was simply running the bike.

Finally, I will say that it truly seems that the engine is choking of either fuel or air.

Thank you for taking the time to read my thread. I'm about to give up completely and take the bike to a shop, and I HATE paying another mechanic when I have the ability myself. So, if you have any ideas, I'm open to hearing them.
 

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Discussion Starter · #4 ·
No power commander. Fuel mapping is through the ECU is it not? I feel like putting in a second ECU would cover that base if so. I have thought about buying a power commander just to try the solution though.

All breather lines etc. are hooked up properly. I did a thorough check of that during initial disassembly. I also tried opening the gas cap to see if it was a ventilation issue.

A very important note I apparently forgot. The problem gets worse with engine temperature. Once it gets to 215 F, or the point when the fan turns on, you have a couple minutes before it chokes itself completely out. Then it won't fire at all until you let it cool off a bit.
 

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Discussion Starter · #5 ·
Haven't checked the rectifier. I figured if the batteries charging the rectifier is good. You think that's a bad assumption?
 

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Sounds like it's running super lean..... I haven't seen anything that says you have looked in the air box to see if it's clogged....... that's so basic, I feel like I might be insulting you.
 

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Discussion Starter · #7 ·
RJ I completely agree with you. But yes, part of my initial inspection was that the filter and all air intake paths were clear. Thank you for giving me the benefit of the doubt haha.
 

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RJ I completely agree with you. But yes, part of my initial inspection was that the filter and all air intake paths were clear. Thank you for giving me the benefit of the doubt haha.
It can only run hot if it's starving for air..... I'd have to think it's related to the intake.

On a mostly unrelated note, have you done a compression check on the thing?
 

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Discussion Starter · #9 ·
Yeah I keep reverting back to the starving for air thing too. What I'm imagining is that the secondary butterfly valves are starving the air flow due to not being properly actuated based on throttle position.

No I haven't done a compression check. I assumed it wasn't an issue since everything ran fine in the beginning, except for what I mentioned of course.

Also, what still baffles me is the inability to fire at all when the bike gets to fan temp (215 F). You would think the air starving wouldn't be an issue there at idle/start.
 

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Just to be sure, you said you have replaced a ton of parts. Have you actually tested anything though? I get a lot of new parts out of the box that dont work, more likely when using all used parts. Get in the manual and start actually testing things like the throttle position sensor so that you can make a list of know good parts instead of just different parts that may or may not be good. And I second the compression check to make sure you dont have some shitty valve clearance issue or something. Always always test before replacing parts unless the part is free and in your garage already.
 

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What about fuel injectors? I'm by no means an expert mechanic, but do situations happen as to where the injectors become so clogged that simply pouring a fuel system cleaner into the bike doesn't help? Have you checked the spark plugs? I'm curious to see if the problem is across the board or if only some of the cylinders are showing signs of running lean.
 

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What about fuel injectors? I'm by no means an expert mechanic, but do situations happen as to where the injectors become so clogged that simply pouring a fuel system cleaner into the bike doesn't help? Have you checked the spark plugs? I'm curious to see if the problem is across the board or if only some of the cylinders are showing signs of running lean.
Good suggestion but the way he is explaining it is that there is a lack of power, but no shaking or anything that would suggest a single cylinder misfire. Injectors very rarely all go bad or all clog at once unless there was a ton a crap going through the fuel system. He probly would have caught it when replacing the pump and fuel strainer in the tank if there was a bunch of sand or something in there.
 

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[*]The engine will choke itself at somewhat consistent percentages of throttle, e.g., at 30% throttle the engine chokes, but at 40% throttle, it will do fine.
[*]The issue does not seem to be load dependent, only throttle position.
To me this is just screaming throttle sensor, do you have a meter with any type of graphing to see dead spots in the tps voltage sweep? Could also be the intake pressure sensor, its very hard to distinguish between load and throttle position since throttle affects load.
 

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Discussion Starter · #15 ·
So yes, I definitely replaced some components without testing their electrical resistivity or any other thing specified by the tech manual. I do agree that testing each one would be a great way to eliminate those parts as the problem. However, the parts I replaced were cheap and I wanted that quick fix. Now however, I'm trying for a thorough understanding of the symptoms and probable causes before I start doing hours of work just to get to a sensor and test it.

The good news is I still have the original throttle body, so I will test the sensor on that tomorrow per the tech manual.

I agree. I believe the bike runs hotter lean, not rich. Anyone have input on that one?

Snowday, I already cleaned the fuel system. Only two of the fuel injectors had any blockages, and they were small pieces of white "goop." I imagine it was a product of the sour gas and some of the system cleaner.

Based on what we're all talking about, I think I want to try to get a diagnostics tool that reads all the sensors, as long as it's reasonably priced. If it's too expensive, my next step based on brainstorming with my father, a lifetime car mechanic, is checking the oxygen sensors in the exhaust. They would definitely be susceptible to sour exhaust and whatever nastiness comes out of seafoam combustion (seafoam is what I had in the system to clean it up). It would also be sensitive to operating temperature as its literally in the exhaust. Additionally, as far as the issue with the first 10 seconds of startup being unique, the ECU ignores the oxygen sensor readings during the initial warm up since their readings are inaccurate cold. Then again, maybe I'm just putting myself on a happy trail that doesn't exists and I'm destined to test every damn sensor in this thing.

Sad Panda, I'm also on your wavelength. I will be checking that TPS first before anything else on the original throttle body I replaced. If that one is good, that means the symptoms are not from the TPS. I might just scream hallelujah if it is the TPS though.
 

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Discussion Starter · #16 ·
Both the main and the sub throttle sensors checked out to be within resistance range per the tech manual. I really hope this isn't an engine tear down type problem, like valve clearance. Especially with only 1500 miles!

Doing this reminded me to consider that the sub throttle valve actuator died during the problem. Perhaps something is shorting out along that wiring route...
 

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How did you go about cleaning the injectors? If there was white goop then there is a serious problem, normally clogged injectors have no visual signs because it is buildup on the pintel that you cant see. However, if it was injectors it would not be a problem at specific loads, it would be almost anything off idle. I would check the intake pressure sensor next as that will have the most influence on how the computer reads engine load, and when your checking these sensors you should do it while its running and blipping the throttle to see a full voltage sweep. Did you check the full range of the tps or just at closed throttle?
 

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Discussion Starter · #18 ·
Sad Panda, thanks for all your help! So I bought a 2013 zx6r fuel pump for shits and giggles, since I only rebuilt my previous pump and cleaned out what I could actually access. Turns out it was the damn pump! At least initial rev tests proved true. I'm completely reassembling the bike tomorrow morning and putting it on a test drive.

All those symptoms, and it was the fuel pump. I don't get it. I'll post confirmation of the fix after tomorrow's ride. Thanks everyone who helped me brainstorm and figure this out!
 

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Discussion Starter · #19 ·
Everything works great now. I have full power through all RPM's. In fact I pulled the front wheel off the ground after upshifting to 2nd from 15000 RPM's. I was grinning ear to ear haha. My last personal bike (so not including my rebuilds) was a Suzuki SV650S, so that wasn't really something I was used to.

Thanks again guys. My lesson learned from this: when your ECU isn't spitting any codes, look for a "no code" list in the tech manual. The fuel pump was one of 4 or 5 possible problems.
 
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