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Discussion Starter #1
I just purchased an 03 zx6r and am having issues. Under 4000 rpm it coughs and sputters, you have to baby the throttle to get it to 4000, once you get past there it revs the rest of the way perfect and doesn't have any issues. (in neutral It isnt as hard to get it to rev as it is when you try to drive it) I have searched the forum and found some that are the opposite where it runs awesome on the bottom and then wont run up top they say anything from fuel pump to injectors to lines. I am wondering if it is a sensor, throttle position sensor or something simple. I pulled the tank and air box off, there are two sensors on the front of the throttle body, I am assuming pressure sensors because one is hooked to a vacuum line and the other is just open. Well at least that is how it is supposed to. Mine had 3 sensors, the one hooked up to the vacuum line was unplugged and another sensor was just lying by that one. If I hook the line up to the plugged in sensor the bike bogs down and dies. I have switched between all three sensors and it is the same. I have tried unpluging the upper butterflies and it doesnt change anything. I have done mechanic work on snowmobiles, four wheelers and dirtbikes. Just haven't delved into the street bike world too much. I am lost any help would be greatly appreciated.
 

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Discussion Starter #2
So quick update, I have a buddy that had an extra set of throttle bodies that came off a running bike, I switched them out with all the electrical on them and it acts the exact same. Anybody have any other ideas, I asked a shop and they said possible ecm???
 

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First, welcome to the forum. An introduction would be nice so we know who we are talking too. Now I'd say just get regular maintaince things out of the way before you go pointing fingers at the ECM. I had a similar issue with my 04, sputtering and sporadic idle, etc. I gave it a full service, and then some sense it was a used bike and I didn't know its history. Plugs and throttle bodies would be my first suspect. Change those plugs out, make sure they are gapped right, then sync your throttle bodies. If you have a power commander, disconnect it, as this can sometimes be the issue.
 

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Discussion Starter #4
Drop2, Thanks for the reply, Sorry about no intro. My name is Tyler, I live in southern Idaho/Utah depending on the day. Been doing mechanic work for the past 10 years and love it. I have never really delved into street bikes, but I came across this one for a good deal and thought why not. Turns out its not the normal stuff I check. I did switch out the plugs and it did not make a difference. I do not see a power commander anywhere on it. I really do not see the ecm being the issue, just something someone had said. I am kinda wondering if it could be the fuel pump, even though normally I would think it would run worse up high.
 

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I actually just moved to Denver from Utah! Crazy lol. Anyway, if I were you I would just keep using the process of elimination. Sync your throttle bodies before spending any more money. There are really good right ups all over for our bikes. Also use the search function on this forum, or Google. Thousands of people have had issues like this, so it wouldn't hirt to look into it and see if anything they did can help solve your issue.
 

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Discussion Starter #7
I got a wild idea and thought about checking the fuel pressure to see if possibly the fuel pump was the issue. Off the pressure would go up to 40-42, running it stayed at 45 psi, to me that seems normal, please correct me if I am wrong. I would assume fuel pump is not the issue.
 

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Discussion Starter #8
ptice, I understand the concept. I am just wondering what I should look for? Because It idles fine and only cuts out bad when I go to test ride it (in neutral in the driveway it seems to want rev fine until I go to ride it, then it will start acting up again).
 

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Welcome to the forum. You're right in that those two sensors are both for pressure. The one on the hose measures throttle body vacuum to determine the fuel amount based on the vacuum level and engine speed at low rpm and low load. The second measures absolute atmospheric pressure, which just allows the ECU to modify the fuel amount delivered if you're at high altitude. The good news is that these are the same sensors, so you can swap them for troubleshooting. Additionally, if the atmospheric sensor is unplugged the ECU defaults to ~sea level pressure. And if the vacuum sensor fails or is unplugged the ECU defaults to calculating fuel delivery via the other method based on throttle position and engine speed.
But basically that all means that those two sensors probably aren't the cause of your problem. The third sensor I'd need a picture of to tell you what it's for though.

Anyway, if the engine performs fine once it's above 4k rpm, then we can pretty much assume it's not a fuel pump or spark plug issue. Spark plug issues will typically always exist and get worse with speed, or they'll often only exist at higher rpm. And when the fuel pump on this model gets clogged up it will typically let the bike run fine at idle and up to roughly 9k rpm and then stutter there.

I'd put a few bucks that your valves are tight on one or two cylinders. Can you do a compression test and let us know the results?
 

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Do this swap each coil to #1 sparkplug if one is bad you can hear it rev slow should start missing. I have had same problem done what you did and read 1000000 post try it. What sucks is coils are not cheap.
 

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Revs fine in neutral then bogs, sputters when you ride it sound like bad fuel pump man.
I think OP is correct thought that if it were the pump, it should get worse with higher RPM, not better, right?
 

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Discussion Starter #13
Steel, thanks for your thoughts

The third sensor I'd need a picture of to tell you what it's for though.
The third sensor is the same as the other two, it was from the owner before me, he just put an extra one on there because the bike doesnt want to run with the one plugged into the vacuum line.

IMAG3085.jpg

Anyway, if the engine performs fine once it's above 4k rpm, then we can pretty much assume it's not a fuel pump or spark plug issue. Spark plug issues will typically always exist and get worse with speed, or they'll often only exist at higher rpm. And when the fuel pump on this model gets clogged up it will typically let the bike run fine at idle and up to roughly 9k rpm and then stutter there.
That is what I was thinking and have seen on other, non bike machines.

I'd put a few bucks that your valves are tight on one or two cylinders. Can you do a compression test and let us know the results?
My compression tester does not have the right threads for this bike, I will grab one shortly and get back with the readings.

Thanks again for your input!
 

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Discussion Starter #14
Do this swap each coil to #1 sparkplug if one is bad you can hear it rev slow should start missing. I have had same problem done what you did and read 1000000 post try it. What sucks is coils are not cheap.
I switched all the coils and it didnt make any difference.
 

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Check the wiring harnesses for fried wires. I had the similar situation except in reverse, higher throttle inputs and I would lose power.

It's also worth noting that my issue was not in correlation to a certain RPM. I could duplicate it at any RPM, it was related to throttle position. But at first I thought it was a certain RPM because obviously when riding, you usually don't get to full throttle until your later in the RPMs.

Warm the bike up, REV it up high, release the throttle quickly and then very quickly add a little throttle as the RPMs are coming down. If the RPMS are still relatively high and the bike bogs down, you have an electrical issue or a throttle body issue and not necessarily an engine issue.
 

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Discussion Starter #17 (Edited)
Ok, so here comes some more info, I traced down the previous - previous owner, and this is the story I got. He bought it and it ran great. He was riding it home one day and the drive chain broke. He ordered a new chain and while he was waiting he took the cover off of the front sprocket (where the speed sensor is) and after that is when it started acting up. So he switched out the speed sensor and it still acts up. Sometime during his ownership he laid the bike over on the left side and broke the stator cover, which he replaced with a billet aluminum one. He then sold it to this next guy who rode it twice then sold it to me.

Also this afternoon I checked compression, but I do not think that the harbor freight compression tester was giving me correct info because it only said 80 psi give or take 5-10 per cyl. Normally with compression that low I do not see machines that start so easy and run so good (aside from the cutting out issue). I checked the valves as well and they are all in spec (a little on the tighter side, but in spec).

I really am leaning to some sort of electrical/fuel issue because when it cuts out I can spray starting fluid across a couple of the throttle bodies and it picks up. I pulled the fuel pump out of the tank and it and the inside of the tank are super clean, no dirty/gummy stuff anywhere.

Hoping that this may help someone with an idea of something for me to try next. Thanks for all your help!
 

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I actually just moved to Denver from Utah! Crazy lol. Anyway, if I were you I would just keep using the process of elimination. Sync your throttle bodies before spending any more money. There are really good right ups all over for our bikes. Also use the search function on this forum, or Google. Thousands of people have had issues like this, so it wouldn't hirt to look into it and see if anything they did can help solve your issue.
Damn dude. Where did you learn how to spell? What the phuck?
 

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did you ever figure out what it was? my 04 636 has a little issue thats been bugging me, any time im in the lower rpm like coasting around a corner where im just barely on the gas it sounds like its being starved of fuel and it just sounds like shit just busts up and sounds horrible but if you get on it a little more it kinda starts sounding normal again it just does its sputter thing like they all do but when you really get on it shes fine tons of throttle response picks up like crazy
I do have a power commander im thinking about disconnecting it and seeing how it runs, ive already replaced plugs and stick coils and ive cleaned my throttle body bores and ran seafoam into the vacuum lines, I attempted to sync the throttle bodies with a homemade manometer but it didnt work worth a shit so im going to save up and buy a motion pro one
let me know if you figured it out man
 
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