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Matt
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21125
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a Honda CBR600FS 2001 that is miss firing intermittently.

Resolved Question:

Hi I have a Honda CBR600FS 2001 that is miss firing intermittently. It started when it was stooling at idle. I took it to a garage and he said that my idle screw on the throttle body was seized so he striped the bike down took it apart applied some heat to unsize it. After that was when the problem started. All plugs were changed to brand new. I had a split HT coil so replaced that for a second hand 1 but did do a resistant test on it. The miss fire was diagnosed by another garage went to another one as 1st garage had no idea blamed my bike not him charged me for work that I didn't ask for and over charged on labour. So 2 nd garage finds fault on cylinder 4 possible injector fault so injector replaced again with second hand one still there. They also found small breather pipes in wrong place redone still there. So far paid £425 for work done still not fixed bit reluctant to take to another garage and pay more. The bike has a power commander 3 fitted K&N filter and non standard pipe. Any ideas
Submitted: 1 year ago.
Category: Car
Expert:  Matt replied 1 year ago.
Hellodoes the bike seem to lack power or struggle to accelerate with any flat spots? also how many miles are on it?
Customer: replied 1 year ago.
Lacks power and now 24000 miles was doing it at just over 16000 miles
Expert:  Matt replied 1 year ago.
Hello this sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank. If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and outand the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,Ideally measure the pressure at the injector rail and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.
Customer: replied 1 year ago.
Ok I can only do this at the weekend so cannot tell you if that was correct.
Expert:  Matt replied 1 year ago.
thats no problem just get back to me on this post on what you found
Customer: replied 1 year ago.
But can this fault only affect 1 cylinder as there is only 1 miss firing
Expert:  Matt replied 1 year ago.
hello OK if you're sure only 1 cylinder is effected and you've already replaced the coil, injector and plugs then I'd next check over the state of the wiring loom and connections to the injector and coil for damage and corrosion - if this is OK then I'd suggest sending the ECU off for testing and also doing a compression test across all cylinders as they should all be within 10-15 psi of each other
Customer: replied 1 year ago.
Ok I no all wiring is fine as for ECU wouldn't the FI light up with a fault code. Also reading up ECU very seldom go wrong
Expert:  Matt replied 1 year ago.
hello the fault detection system is pretty simple on these and you can have a corroded connection which drops a voltage enough to stop the injector working properly without it flagging up as a broken wire but again if you believe that this is OK I'd push on with a compression test to prove out the engine mechanically
Customer: replied 1 year ago.
Ok I will have that checked.
Compression test I would like to think with the bike only done 16k at the start of the fault and only started when 1st mechanic played with it would like to think he did something we cannot see at the moment
Expert:  Matt replied 1 year ago.
Hello I agree that its likley the 1st guy has damaged something or disconnected something but as the bike was stallign at idle beforehand I feel its worth checking the basics If the compression test is OK then I'd next check if all the throttles are balanced / opening at the same ratethis is best done with a flow meter on a running engine and there shoudl be adjustment screws to move each throttle individuallythe airflow meters look like this
Customer: replied 1 year ago.
The idle speed stall has been corrected. I will ask the 2nd garage if they did a compression test as I no they checked plugs and coils. They looked at what the guy had done and all they could see was breather pipes in the wrong order.
They seem to think that the breather pipes on the throttle body have a very small hole that is expanding with temperature as when the air temperature outside is warm it misfires. This does not happen everyday I travel 60 miles in of which is dual carriage way and then filter in traffic aroun London so this would be about 20 miles then 60 back home same route. Somedays I get 2-3 days with nothing then I may get couple of days misfire but may get in no misfire then back home misfire.
So not all the time of which is really annoying.
Expert:  Matt replied 1 year ago.
Hello I doubt the breather pipes are the issue to be honest as it makes very little difference on how they are connected, as long as they are connected if the misfire only occurs when its warm I'd suggest also checking the state of the throttle position sensor and the cam position sensor
Customer: replied 1 year ago.
Funny you should say that as I had thought of that. How would I test it would it be with a Avo
Expert:  Matt replied 1 year ago.
Hello if you unplug the TPS and probe it for resistance whilst your assistant slowly opens the throttle, the resistance value should slowly increase with no sudden step changes in resistance if its does do this then replace the sensor the cam sensor I think is a 3 wire device so not easily tested without an oscilloscope - however they aren't that expensive ( about £30) so you can try disconnecting it to see if that helps in any way and if it does then replace it
Expert:  Matt replied 1 year ago.
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. so if my answers have been helpful please rate my answer.
Customer: replied 1 year ago.
I will be looking at the tps this weekend as I work during the week I cannot check if I rate now it will be closed then I will need to pay again for another session.
Expert:  Matt replied 1 year ago.
understoodalthough you can rate at any time and the question remains open until it expires ( typcially the period is a week)
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 21125
Experience: BEng hons Mech engineering, in auto industry 22 years
Matt and other Car Specialists are ready to help you
Customer: replied 1 year ago.
Matt I have taken off the complete throttle housing as I believe this to be were my problem is as the first merchanic had that off I have renewed all the small breather pipes and replaced the throttle position sensor. I have put it back together and did not take note of which way the throttle cables go looking at the handle bars there are 2 on top of each other I would take that the top one goes on top of throttle body and the bottom one underneath
Expert:  Matt replied 1 year ago.
Hello that sounds right as you have cables to pull it open and pull it closed so they need to run round the grip in both directions
Customer: replied 1 year ago.
Thanks
Expert:  Matt replied 1 year ago.
no problem

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