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1998 YZF750R - rev counter cycling between 7000rpm and 0 then 7000rpm and back again?


graham847
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Hi everyone

On Sunday was out on my 1998 YZF750R when I noticed the rev counter suddenly flick to 7000rpm then drop to show 0 rpm then a few seconds later ping up to 7000rpm again. The actual engine revs and power remained normal and no other issues apparent. On arriving home let the bike cool down, then turned ignition on. With the engine not running, the rev counter started cycling between 7000rpm and then back to 0 then 7000rpm again etc and repeat. 

Had a look on a online few threads noting that the "7000rpm" is a Yamaha diagnostic indication that points to a problem with the Exup system. So tank & fairings off and had a look. Examined the cable ends at the valve and one was badly frayed/rusty/stiff. Said cable has been removed and a new one ordered.

I also removed both cable ends from the servo  motor so the servo was free to operate. Then turned the ignition on thinking that the servo motor/pulley would now be free to rotate - which it did and I expected the 7000rpm tacho bounce would not be seen if a seized cable had been the problem. 

However...the tacho continued to bounce to 7000rpm back to 0...7000rpm again.

So I though  maybe there is a fault with the actual servo motor. I happened to have a spare motor I bought last year, so plugged that into the loom and turned ignition on. The fault remains just as before.

I have checked the electric connections hooking up the Servo to the loom and all are clean and in good condition

Beginning to wonder if the 7000rpm code might indicate some other problem.

Any more ideas or things worth trying please? 

Thank you.      

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You might not think my reply is related...but bear with me!

I know nothing about modern motorcycle electronics! however i do own a Vauxhall Astra! it has OnBoard Diagnostics (OBD2) which I am familiar with!

Now there are a couple of things which may be of some help...with my Astra, if a Diagnostic Trouble Code (DTC) comes up, replacing the faulty part with a new one results in the code being cleared....but not always!!....sometimes the DTC is stored in a different part of the memory and you have to 'clear' the codes manually by resetting. In my case via my laptop software. if not the code remains on screen or is shown as a series of a flashing light on the dashboard as it's stored historically.

Your Yamaha is likely to have some version of OBD and the interface socket will be hidden somewhere. It may be the DTC 7000 is on display and waiting to be cleared/reset. Have another read of those threads, does it go on to say how the code is cleared or the procedure to clear it.

it's just a thought. I'm not saying yours is the same, but it may be useful information. 👍

 

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6 hours ago, NE0 said:

You might not think my reply is related...but bear with me!

I know nothing about modern motorcycle electronics! however i do own a Vauxhall Astra! it has OnBoard Diagnostics (OBD2) which I am familiar with!

Now there are a couple of things which may be of some help...with my Astra, if a Diagnostic Trouble Code (DTC) comes up, replacing the faulty part with a new one results in the code being cleared....but not always!!....sometimes the DTC is stored in a different part of the memory and you have to 'clear' the codes manually by resetting. In my case via my laptop software. if not the code remains on screen or is shown as a series of a flashing light on the dashboard as it's stored historically.

Your Yamaha is likely to have some version of OBD and the interface socket will be hidden somewhere. It may be the DTC 7000 is on display and waiting to be cleared/reset. Have another read of those threads, does it go on to say how the code is cleared or the procedure to clear it.

it's just a thought. I'm not saying yours is the same, but it may be useful information. 👍

 

Thanks for those thoughts. Unfortunately the 1998 YZF is a very analogue beast, and there are just analogue clocks, and as far as I can see there is no diagnostic plug on the loom to plug-in a OBD reader. It might be possible to perform some kind of rudimentary manual "fault" reset via some particular sequence of turning ignition on/off combined with engine run/kill switch position or similar - however, that is a guess and I have been unable to find any information or manual that says there is a way to reset a "fault" condition on a 1998 YZF.

The new cables are due in a day or so, and I'll re-install everything, plus connect up the fuel tank and fire her up. Maybe with everything put back together, with engine running the system will reset itself and the tacho 7000rpm bounce will stop

I can add that the Exup Valve is completely free to rotate in its housing (I serviced it last year) and the servo motor is rotating when ignition is switched on.

Thanks for your input.     

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Of have no experience of this bike, but as a member of the Fazer Owners Club (FOC UK), I have seen numerous threads on that site referring to the 7K exup fault. I f I recall correctly, you would have to refit all of the missing parts and then reset (ie zero) the servo motor. It also has to be spotlessly clean and completely free to rotate. You may wish to have a look on there for the FZS1000 Fazer 7K exup fault code

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4 hours ago, neversaydie said:

Of have no experience of this bike, but as a member of the Fazer Owners Club (FOC UK), I have seen numerous threads on that site referring to the 7K exup fault. I f I recall correctly, you would have to refit all of the missing parts and then reset (ie zero) the servo motor. It also has to be spotlessly clean and completely free to rotate. You may wish to have a look on there for the FZS1000 Fazer 7K exup fault code

Thank you mate for that advice, will take a look at those threads

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Well done Graham, hope you get it sorted, let us know how you get on.

Got myself an "Enthusiast" badge with my post!  decided to hand out a few "Likes" and thanks to get the rankings chart going as its been empty for weeks!

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This is an error code...

 

There's 3 of them, one for fuel sensor, one for exup valve and one for your TPS.

I'm not sure which of the 3 you have, they're apparently different from the Thunderaces.

Unless you've had your tank off lately, I'd check your exup first...

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Hi,
I have completed further investigations and it appears the root cause is down to the fuel pump and sensor assembly. Looking in the service manual Pins 1 & 3 from the assembly's electrical connector should show continuity (i.e. 0 resistance when checked with a meter.) Unfortunately mine shows open-circuit 100% resistance.

To prove this further I jumpered pins 1 and 3 together on the loom side - and the fault cleared, rev counter returned to acting normally. So although I had one rusty Exup cable, that wasn't the main problem.
Next step is to remove the fuel pump assembly and see if it can be fixed.

Thanks 

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Hi all,

Just to update, I took the fuel pump and sender unit out of the tank and found the connection had indeed broken from the green wire to the solder joint at the sender unit.

I've attached the photo in case it's useful to others. Re-soldered and will put it all back together next week.

Thanks for everyone's input and ideas. 

IMG_4071.JPG

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No worries.
As I said, the indicated codes on the 750 are apparently different than on the Thunderace, even though they indicate the same 3 faults (who knows why this is...). Or I could have told you exactly which one it was.

The strange thing was, when I looked at the 750s manual online, I couldn't find any mention of the error codes!

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15 hours ago, Snakebite68 said:

No worries.
As I said, the indicated codes on the 750 are apparently different than on the Thunderace, even though they indicate the same 3 faults (who knows why this is...). Or I could have told you exactly which one it was.

The strange thing was, when I looked at the 750s manual online, I couldn't find any mention of the error codes!

Hi Snakebite - I finally found the diagnostic code mentioned in the Haynes Manual but not where you might expect (i.e. in  the fault finding chapter). The Fuel Sensor (7000rpm diagnostic code) and what it means is described in fuel system chapter section 4-26. Great if you know you have a fuel system fault....not so good if you just want to know what 7000rpm indication means to start with...Anyway, hopefully useful info. Cheers      

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