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Discussion Starter #1
Hi Guys,
I'm new to this forum, and have learned alot on here in the past few weeks.
This past summer, I purchased a used 2014 T4 with 900 miles and 192 hours.

Because my machine was due for the 200 hour service, I performed all the tasks in the owners manual.
I changed all the fluids: Engine oil and filter, Front diff, Rear diff and cleaned the air filter.
Ran the valves and adjusted them within spec.
upon my first ride down the dirt road, while holding steady throttle- the engine seemed to bog down- slower and and slower until suddenly, it came back alive and back up to the speed I was running - 26-30 ish.

It sounds like it drops a cylinder or is running too rich until it almost dies and then comes back up to the rpm that you are holding.
I've checked everything I can think of:
pulled the fuel tank, cleaned and drained all the fuel, performed the vent tank mod, replaced the fuel screen on the bottom of the pump.
replaced spark plugs
checked all the wiring and connections- even pulled on the coil wires and plug boots while riding down the road- no change.
Checked the air intake and ensured there was not any unmetered air going into the intake ports. all clamps and bands are tight.
Cleaned the spark arrestor.

I can recreate the issue just by holding the throttle at a steady spot while driving- around 1/3 or 1/2 throttle. it does't do it at full throttle, or at idle. if you are constantly on and off the gas- like riding a trail, you'll never notice it. because it only happens when going steady.

last week I tried something that may add to the confusion- riding down the road at constant throttle, the engine started to bog down again, so I pulled the transmission back into Neutral, and it immediately rev'ed back up! After I coasted to a stop, reengaged the transmission, and took back off. Now i'm thinking could it be related to the load the clutch is putting on the engine?
*note that this bog never happens in neutral- I've tried by holding steady throttle while parked. The motor purrs like a kitten.
I've disassembled, cleaned and inspected the entire clutch assembly, didn't see anything wrong.
I've been a mechanic all my life- but this one has me stumped.

I was thinking maybe fuel pump or Throttle position sensor, but it only does it under load, while driving.
I've seen several other guys have a similar issue, but not a definitive answer.
Thank you in advance for you help and advice!
 

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Good job there with all the analysis. Yes, to me it seems like a fuel issue for sure really. If possible check the fuel pressure especially while you're running part throttle. Even with replacing pump filters and screens sometimes damage gets done it seems to the regulator portion...
 

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Discussion Starter #4
Well, the good news is, I have a new fuel pump assembly, but the bad news is that the engine still bogs down and stumbles at steady throttle. However, with the new pump installed I noticed an overall better throttle response and smoothness to the engine.
Also, I found out that the issue only occurs once the engine is warm.
It won't do it on a short 1-2 mile ride- that's why I thought I fixed it with the new pump. Other than a crack in one of the coils, which could expand with heat- I"m truly at a loss. oh well, I'll just ride it and enjoy it.
 

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Where did you get the new pump assembly? Sometimes even brand new parts can still be odd or intermittent at times. To help eliminate the fuel issue, can you check pressure when cold and then hot when the issue arises?
 

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I'm on the fence thinking a coil issue in other type motors act the same way with heat issues causing some breakdown in performance.
 

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ROCKSOFFROAD
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One question when you did the vent mod did you blow both ways through the check valve
Mine was acting that way (dead spot at bottom end then when applying more throttle it would lunge then go I haven't changed plugs yet but taking of the in line filter and check valve and blowing thru both ways fixed it then I put a new in line filter in my 2014 t4 now has 6800 miles never done anything to the fuel pump ect only regular services full & short and new belt & clutch spider & rollers at 4400 miles
 

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Discussion Starter #8
One question when you did the vent mod did you blow both ways through the check valve
Mine was acting that way (dead spot at bottom end then when applying more throttle it would lunge then go I haven't changed plugs yet but taking of the in line filter and check valve and blowing thru both ways fixed it then I put a new in line filter in my 2014 t4 now has 6800 miles never done anything to the fuel pump ect only regular services full & short and new belt & clutch spider & rollers at 4400 miles
Yes sir, I did, just to make sure it wasn't blocked. However, I guess I should just simply remove it and go for a run and see if that makes a difference. Thanks for the responses and feedback, I appreciate the help. maybe I should just drive the heck out of it and stop being so OCD.
haha.
 

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Discussion Starter #9 (Edited)
Hey guys,
Thinking about what you said- even though I blew air through the check valve weeks ago- I wanted to test it without the valve on the fuel tank, just in case it was causing some strange vacuum or pressure situation. I simply disconnected the check valve, and connected on some spare vacuum hose I had in the shop- I ran it up along side the passenger seat so I wouldn't ingest any dust while riding.

Well, I was hoping it could be that easy, but not even 1/2 mile into my ride, it stumbles and studders again- like it's down a cylinder until suddenly, with no throttle change, it comes back to life and runs fine.

I can connect my fuel pressure gauge in-line with the system tomorrow, just to triple check; but the pump is brand new, and it only happens under load. The fact that I can't re-create it while in Neutral, tells me the basics of the engine are good. But while driving, it's easily repeatable.
Fuel pressure shouldn't change at a given throttle position whether sitting still or moving at a 20 mph.
i'm wondering if it could be computer related?
 

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Correct the fuel pressure shouldn't change... Remember, pressure is just resistance to flow. If the system needs flow (more fuel such as under load) and the pump isn't up to it then there is less resistance (pressure). Once you hook up the gauge and the problem is easily repeated and monitored you can then probably easily rule out the fuel pump.
 
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Bill Pelka
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Might want to test the Throttle Position Sensor. Could be a dead spot on the pot. Hooking it up to a meter and running it thru the full range would give you a GOOD-BAD indication. Might want to put a resistor in series with the meter leads to get a very fine resolution and watch the full meter range. Digital will work, but analog meter sweep is easier to see. Good Luck.
 

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Did you ever get this problem figured out ? I have 2014 T2 that is doing the exact same thing. I have done all the things you have done. I also had access to another clutch and changed that out to see what happened. It seemed to make the problem less. So still have the problem.
 

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Discussion Starter #13
Hi Tryreno,
not completely, the new fuel pump definitely made it run smoother and come out of that 'bog' situation with less pressure on the pedal.
but in short, no.

the fact that it doesn't do it in neutral completely frustrates me.
logic tells me the clutch or something putting a load on motor is triggering it. But what?
I did pull the clutch shives and blow all the dust out and clean them with just compressed air. I also inspected the belt and all moving parts of the clutch.
no broken springs or fingers.

I agree with Pelka, it could be a bad spot on the TPS, but I'm not very motivated to remove the panels for the 20th time, haha.
plus, if it was a bad spot on the TPS< wouldn't that also happen in neutral?
I really love this machine, but man, it's frustrating.
 

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Hi Tryreno,
not completely, the new fuel pump definitely made it run smoother and come out of that 'bog' situation with less pressure on the pedal.
but in short, no.

the fact that it doesn't do it in neutral completely frustrates me.
logic tells me the clutch or something putting a load on motor is triggering it. But what?
I did pull the clutch shives and blow all the dust out and clean them with just compressed air. I also inspected the belt and all moving parts of the clutch.
no broken springs or fingers.

I agree with Pelka, it could be a bad spot on the TPS, but I'm not very motivated to remove the panels for the 20th time, haha.
plus, if it was a bad spot on the TPS< wouldn't that also happen in neutral?
I really love this machine, but man, it's frustrating.
Even with a "new" fuel pump, did you confirm you have good pressure while under load and experience this issue? Is the "new" pump a factory one?
 

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Thanks for the reply. I have also checked the power in and out of the TPS. both are whitin spec. and also checked the resistance also within spec.
 

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Discussion Starter #16
I dont have the correct adapters in my fuel pressure kit- and I don't want to cut the factory line.
so I was unable to test the pressure while running.
I need a male connection that is the same type as what comes off the top of the fuel pump, so it will click into the factory line.
I was able to simply attach the pressure gauge to the nipple of the pump, and got 40 psi.

it's not a factory 600 dollar pump, I got my pump assembly from HFP fuel systems- by referral of one of the guys on here.
thanks!
 

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Mine was bogging down bad so I took it to the dealer. They said I needed a new top end so they replaced it under warranty. First ride since they “fixed” it and it is doing the same thing. It seems to happen when it gets hot but stumbles under steady and heavy throttle. Anyone find a cure yet?
 

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Discussion Starter #19
Been riding all spring and summer here at my property, and it's still occurring. I know something's not right, but at least I'm not the only one with this issue.

The one thing I can't seem to get around is the fact that it never does it in Neutral.

For a test, I set the parking brake, transmission in neutral. blocked the tires.
I held the throttle at various stages for several minutes, and it never stumbled or loaded up once. It purred like kitten!
Idle, 1/4, 1/2, and 3/4 throttle- it all sounded great!

So, while still in the shop, I put the rear axle up on jack stands, blocked the front tires and then restarted the engine. Carefully, I sat in the Teryx, and put the transmission into H. I throttled up to roughly 1/2 throttle or 20 mph, and after a few moments, the engine started to stumble and cut out; then, after 10 or 15 seconds, it jumped back up to the position I was holding it and back up to 20 mph. So, with little rolling resistance, other than the drive train, I was able to recreate the issue.
( I know the risks of testing like this, but I've been drag racing for 15+ years and I'm familiar with warming up on a stand )
Anyhow,

could something in the transmission or clutch assembly be spinning faster than the crank and causing a sort of engine load?

I appreciate all the comments and ideas, thanks guys!
 

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Wondering if anyone has had any luck resolving this issue. Same thing happening on my 2016 T4. Thanks!
 
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