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TPS random fault ?


Mohawk

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Hi All,  I had an issue yesterday with my bike, I was visiting somewhere & when I left the bike started fine, ran fine through the village I was in, but when I tried to accelerate on to a main road, the engine stuttered then died then caught & kept repeating. If I kept the revs low it was fine, but above 5000rpm the bike would exhibit the same as above.

 

During these events the rev counter would drop to zero, but the speedo & other electrical systems kept working fine. I have a volt meter fitted that showed normal voltage.

In my head I diagnosed it as a TPS issue as it repeated every time I tried to increase speed. Luckily 5K/rpm is approx 65mph, so I was able to limp home with it like that. I did stop & restarted the bike in case it was an ECU error. When I got home, same thing would not rev beyond 5K/rpm. So thinking TPS, I stopped the bike, exercised the throttle full cycle for about 20 turns, then the bike started & worked fine. I did another 30 twists with the bike off last night & the same this morning.

 

Bike worked fine on way to work today.  Anyone have any other ideas ?

 

I'll look into it on the weekend, as I was planing to do some pre annual inspection maintenance then anyway.

 

 

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Certainly sounds like an electrical issue Mohawk, given that it has appeared and disappeared. 

 

I have been troubleshooting a carbed ST1100 and this did not want to rev out beyond 4k, turned out to be low voltage reaching the ignition unit due to corrosion in a connector, resulting I think in poor spark plug performance. I'd suggest looking through your connectors and earths, for me the problem was the connector that feeds power to/from the right bar switches.

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I agree, Bad earth or connector. Use conductive electrical lube spray on cleaned or replaced connections and earth points.

Possible diagnosis after reviewing the electrical cct is that bad earth on tacho is somehow running feedback into the tacho output signal from ECU. The tacho has its own earth wire.

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  • Member Contributer

Hi Mohawk

 

Yep look reaaally hard at the earths.

I chased an issue on our MV F3 all season where it would go on to limp home mode randomly.

Replaced lots of parts including throttle bodies/tps

Finally found that a bad earth was the cause.

Cost us a shot at a championship and a rider with a broken wrist!

 

Phil

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Thanks for the advice, I have some maintenance to perform this weekend, so will attend to this at the same time.

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  • 2 weeks later...
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Did you find any reason for it?

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Well I took the advice supplied, I traced the earth, cleaned & re seated them with some conductive grease. There was a little corrosion there.

 

I stripped the airbox off to clean the air filter & checked the TPS connector, plus lubed the TB linkages. Could not find anything wrong there, looked like new.

Been out on it a few times with no repeat so can only assume it's fixed.

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  • 2 weeks later...
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So the issue reared its head again yesterday on the way home, same sort of presentation, started fine, low speed ride, then when winding on for a fast road, bike started bucking like crazy, with engine cutting out & in if the trottle was moved beyonds a few degrees & the revs exceeded 5500rpm.  Below that it was fine.

 

I stopped the bike, switched off, exercised the throttle through full range, turned on & restarted fine was fine for the rest of the trip.

Some research revealed others with similar issues related to corrosion in an earth block hidden in the loom, or a broken ECU wire. So this evening I stripped out the block & it was like new, so pulled & reseated the bridge pins. The ECU was a bit loose in its place & had obviously been wiggling around, but I could not find any broken wires & the earth was good.  Sp all back together & bike starts & revs fine, but it does that most times still anyway.

 

So back to square one, any other ideas ?  I intend to pull the fron t fairing off at the weekend & check the front half of the loom & all connectors.

 

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Intermittent electrical issue, there is nothing worse to fix. 

 

From what you have written it appears that the process of turning off/on the bike runs enough current up the electrics to  arc close the joint again. I would suggest not stopping the engine next time and instead, if the problem occurs and while parked on the side of the road, wiggle all the connectors and wires you can find to diagnose.

Next step would to get home and use that multimeter to check the wiring for bad resistance or earthing resistance at either ends of component plug ins. Again by moving wires about.

After that , get some electrical cleaner/lube spray and drench the connectors and make sure the connector pins have a good fit.

 

After this about the only thing left is to start swapping components. ie: until tested its not possible to rule out a maybe failing ecu or ignition timing sensor or tps.

 

Good hunting and drink lots of camomile tea, beer or whatever does it for you to fight early onset insanity.

 

 

 

 

 

 

 

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Hi, just catching up and I think I caught the details so forgive if I missed this:

 

Have you tested the stator and rectifier? Rev the darn thing to 5500 and test there, when fully warm.

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REG RECT is fine as is charging & all connectors checked & perfect.

 

Next check will be front wiring harness & connectors & possibly the HISS security system but that should cause the bike to die, rather than revert to limp mode.

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Thanks CR QS is switched off at the mo, being reworked. Correction is off too.

 

Had a tip about the engine start/stop relay which is just to the right of the battery box on 5th gen, so checked & its the first connector I've found with corrosion, so may have beennthe issue, time will tell.

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So today I stripped out the front of the bike & checked every cable & connector & apart from being covered in dust, everything was in perfect order.

 

So looking at the wiring diagram, its a bit hard to see how this relay fits into the scheme of things, so a little looking this evening & I found the following which is much simpler to follow. The relay in question is the one top centre marked ESR, a fault on it will stop the whole ECU system, so I believe was my issue.  The ESR on the 5th gen is located the the right side of the battery box under a rubber boot.

 

This diagram although for the 6th gen, is excellent.

 

VFR VTEC PGM-FI Diagram 2002.pdf

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I had an intermittent problem for a long time that progressively got worse to the point that any big bump in the road would make the engine miss and some times cut out.  I was able to trace it by jiggling the wires coming out of the ECU 1 at a time with the engine running.  Turned out 1 of them had a pin prick nick in the insulation and over time a break had developed.  I had to solder it, which was awful given my non skills and tiny wire diameter but it's been rock solid for a couple of years now.

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  • 1 year later...
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OK been a while & this kept happening intermittently, to the point it was at least once a week. So I had to change the clutch plates a couple of months back, so bypassed the Rapid Bike ignition pickup. I looped the Rapid Bike connectors together & put the igition pulse output back on the original ECU connector. It has not happened once since so the error appears to be with the Rapid Bike unit. I'll ask Dimsport for some support next week.

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