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2018 wr450f misfire / hesitation

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Hi all,

I have a 2018 wr450f that I have owned for a couple of years without any issues to do green landing around Salisbury plain area.

suddenly, just before Christmas, I was out for a ride, everything was going fine, and then it just suddenly started misfiring and having hesitation. I limped home to diagnose what was wrong but I am at a loss now. I also had some horrible noises which I have sorted. Hoping someone else may have some input, but these are the things I have checked / replaced

1. Checked and replaced coil pack - no difference

2. new cam chain - the old one was badly worn and it had skipped a tooth at the cam shafts. No valve contact luckily.

3. New spark plug

4. Cleaned all the fuel lines and injector gauze 

5. Cleaned the fuel filter that is inside the tank

6. Cleaned the throttle body inside and out blowing out pressure line hose.

I took it up the road just now but the bike does not want to idle very well and does not want to Rev at all. Anything past 1/4 throttle and it just bogs and misfires.

before I phone up a local garage to get it hooked up to the diagnostic tool, just wondered if anyone else has some input or suggestions?

thanks in advance

Dan

 

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Normally these are solid motors that will go a long time with only minimal maintenance. I’m surprised your cam chain was badly worn on a 2018 bike. Lots of hours?
You’re absolutely sure you got the cam timing correct when you replaced the cam chain, yes? And the valve clearances are correct? Those are my only two guesses as to the poor running.

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Have you plugged in the tuner to see if it has any error codes?

The air intake pressure sensor is known to cause issues like this but doesn't throw a code iirc

 

Here's a thread about the MAP/Intake pressure sensor

 

 

Edited by GuyGraham

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I don’t know how many hours I have as I don’t really care, but I’ve done about 2000 miles on her. As long as it is well maintained and regular oil changes, they are good to go.

when I took the cam cover off, the 2 notches in the shafts were not flush with the cylinder head. Both were lower, showing that one of the shafts had rotated one tooth. The chain had not stretched, but rather it was very notchy and the links just didn’t pivot smoothly. The new oem chain was of the same length and each link was moving smoothly. Was very odd!

I haven’t plugged a tuner in yet. I’ve asked a local Yamaha dealer to see if I can drop the bike down to them.

will take a look in my service manual to see if the pressure sensor can be checked using a multimeter,  tube good shout though. 
 

valve clearances are good. Even if they are slightly out, the bike wouldn’t perform this badly, and they wouldn’t just suddenly good from absolutely fine to terrible as it did on the ride when this started happening. It was like someone flicking a switch. Fine 1 sec, bad the next.

will keep you updated...

Edited by Arctic silk

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So a bit of an update....

I was looking at the bike again over the weekend and testing as many sensors as I could. I’ve checked as much as I possibly could and everything looked fine and in spec.

in short, I thought I might look a bit further into the TPS. Although the ECU was providing a good 5.04v into the TPS, my service book said this is fine then. I thought I will get it onto the workbench and test it further as all other sensors have been checked and I’m kinda running out of things to check.

I borrowed a dc power supply from work, set it to 5v and then measured the voltage at the signal pin (middle pin). Rotating the butterfly plate through its range of travel, the voltage steadily increases from 0.5v at idle, but there is a definite flat spot around 1/2 to 3/4 throttle. It gets to about 3v and then the multimeter goes to ‘OL’ and then jumps up to 3.34 pretty consistently. It does this when returning the plate too back to idle.

I suspect that this may be the cause of my bogging.

OEM part for the WR is £180. Or......get on eBay and type in ‘JT7H’ (which is stamped on the top of my sensor), and I could find a replacement part for £50! I will buy one and get it replaced, and then give an update, as I hate reading other threads where it just ends and no one knows what solved the problem etc.

im confident it’s not the injector or fuel pump playing up either as I powered these to test for sufficient flow etc, and all seems good. 
 

this is the pic of my TPS. The type JT7H is a standard type of Keihin TPS and I have found out that it was fitted to a lot of Honda motorcycles (cbr600rr 04-07, crf250 models....) and some Honda cars.

D637F239-D71D-436E-9611-9B1EDADFEFE8.jpeg

C29BC420-641B-46E8-A073-67F689B78FB0.jpeg

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So it turns out that the sprocket on my camshaft had rotated slightly, so my intake cam lobes had shifted round slightly, even though my timing marks are aligned. 
I didn’t know that the timing sprockets were only pressed onto the shaft. I guess that my cam chain had worn and then were snatching at the sprockets, pulling them round slightly and causing the misfire. 

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