Calling any mechanics.....

Discussion in 'Other Bikes' started by Paul Longstaff, Mar 25, 2021.

  1. Paul Longstaff

    Paul Longstaff Active Member

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    I have ( apart from my blade) a BMW F700gs parallel twin.
    At about 3800 and 4100 rpm it sort of stutters. You can power through it but if you hold a constant throttle in this range there is a slight surging sensation.
    Its best described as , now I am showing my age, when a bike goes onto reserve and that first stutter you get before having to reach for a reserve tap on an older bike.
    It's always there and has progressively got worse 9ver the last 2 years.
    Bike is totally reliable and sounds fine but you can really feel this now especially in rhe top 2 gears.
    I'm going to take it beemer dealer but I don't want to fall into THEIR trap of " it could be this, it could be that, so let's just replace everything" and then hand me massive bill.
    Does anyone have any thoughts?
    Cheers
     
  2. Saqib

    Saqib Member

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    To me it sounds like it could be multiple issues, so it needs some diagnosis.

    Could be something in the ignition system failing - spark plug or coil pack, or wiring leading up to it. Or on the fuel side - dirty injectors, blocked fuel filter.

    I guess that’s not what you wanted to hear.

    You mention a very specific rpm range, so it could be a sensor pickup somewhere.
     
  3. Paul Longstaff

    Paul Longstaff Active Member

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    Thanks @Saqib as the bike is perfect in all other parts of the rev range I too had though its possibly sensor related.
    I don't understand much if anything about ecu electronics etc but wondered if it could be something like an O2 sensor or something similar when the bike is switch between fueling maps or something? I've heard people mention transitioning between a closed loop at lower rpm and an open loop higher up revs but I've never understood what they are talking about :confused:
    It's such a specific 3 to 400 rpm band that I don't think it could be something like a fuel filter as surely if that's blocked or dirty it would affect the whole rev range?
    The bike starts and idles perfectly and runs perfectly throughout the entire rev range other than between 3800 ish and 4200 so quite a narrow and specific band.
     
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  4. CharlieR85

    CharlieR85 Elite Member

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    Throttle position sensor would be high up my list of things to change Paul.
     
  5. Paul Longstaff

    Paul Longstaff Active Member

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    Dealer couldn't offer anything when I spoke to them other than booking it in for a diagnostic £99 could be less if it quickly becomes obvious what the problem is.
    I bought the bike used so its last couple of services ate likely to have been oil n filter changes at an independent so I'm going to book in for a major service at dealers in any event, brake fluids, valve clearances etc at £349 and see what comes of them.plugging it in ref error codes. Can't get it in for a week or two though
     
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  6. dern

    dern Well-Known Member

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    I had a gs that was really sensitive to throttle bodies being syncronised but even when they were perfect it was a bit surgy and snatchy. I think that they run really lean and benefit from being remapped. I didn't bother in the end because it was a unreliable bag of shit in so many ways.
     
  7. Paul Longstaff

    Paul Longstaff Active Member

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    It's a strange one cos the bike is running perfectly and has since I bought it apart from this little niggle which is raising its head.
    It's never put a foot wrong since I got it nearly 2 years ago
     
  8. Saqib

    Saqib Member

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    It could be an O2 sensor. Really difficult to tell.

    Hopefully they find a DTC in the ECU, and that leads them to the exact issue. Otherwise it will cost time in troubleshooting.
     
  9. Paul Longstaff

    Paul Longstaff Active Member

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    Booked in at main dealer for next week.
    Will update on the outcome after that. Have asked for a full service to be done, all filters , brake fluid, valve check, plugs and diagnostic so let's see what happens apart from my wallet becoming hugely lighter
     
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  10. bonjo

    bonjo Active Member

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    hopefuly is a simple case of defective spark plugs.
    interested to know to cause . Popcorn time:)
     
  11. Paul Longstaff

    Paul Longstaff Active Member

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    Going in Tuesday so fingers crossed I get a result
     
  12. Paul Longstaff

    Paul Longstaff Active Member

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    Dealer told me it its the O2 sensor but they want £230 to supply and fit !
    Think i can get it cheaper than that so told them just to finish the big service and i will sort the sensor.
    So £350 for service and now i need to sort the sensor.....
     
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  13. bonjo

    bonjo Active Member

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    You should be able to buy them yourself but make sure it is a genuine denso (or ngk?) by checking the model part on their website. You most probably end up paying around £60

    This is what I did on my car when I replaces 4 sensors over the years
     
  14. Paul Longstaff

    Paul Longstaff Active Member

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    Dealer rang me back saying they had cocked up the parts order for the service so would need the bike at least 1 extra day maybe 2.
    Not really a problem but as he was on phone I bottled it as lazy arse itus kicked in and I told him to order and fit the lambda sensor too :oops:
    Im in the middle of draining, flushing and cleaning out our central heating. I then need to replace the power pump for one of the showers. I then need to lay a base and erect the shed that's just been delivered and then I need to put some bespoke shelving for her majesties shoes so just thought...jeez I can be arsed adding to my list of DIY work :confused:
     
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  15. Paul Longstaff

    Paul Longstaff Active Member

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    Well.i got the bike back fully serviced and a new lambda sensor fitted.
    It's as sweet as a nut and totally smooth throughout the rev range. Not only that the trip computer is recording about an extra 10mpg on my return journey home.
    I knew fuel economy wasn't brilliant but never attributed the fault having so much impact on the mpg.
    So yes I paid top dollar at a main dealer but honestly everything has now been done and she is running do much sweeter.
    Thought I should give you an update and thanks for your input.
    Cheers
     
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  16. Saqib

    Saqib Member

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    Awesome. So the fault lambda was indeed the fault?

    Am amazed it only affected one part of the rev range so much.. perhaps that's where the fuel maps switch over.
     
  17. Paul Longstaff

    Paul Longstaff Active Member

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    Yeah I agree it can only be where the fuelling map is changing from 1 set of parameters to another And mixed with dodgy o2 readings the fuelling was being thrown out in that 400 rpm rev range.
    My biggest surprise was how instantly rhe fuel economy improved by 25%. Had been averaging 42mpg and it immediately jumped up to circa 54's. So given that I think it must have been running a tad rich elsewhere in the rev range though I couldn't 'feel' any issue outside the 3800 to 4200 band. The exhaust had remained clean too, no soot or anything.
    Strange but either way all sorted now so quite happy :D
     
  18. bonjo

    bonjo Active Member

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    Good to hear of a happy ending :)
    I’m a little puzzled why the o2 fault did not activate the engine check light.
    Normally the heater circuit goes open and the sensor performance suffers.
    Running rich could have flooded the spark plugs.
    Don’t underestimate the effect of a service (plugs,oil, air filter) on the mpg. Now you can afford quality windows for your shed;)
     
  19. Paul Longstaff

    Paul Longstaff Active Member

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    No engine check light but it was recorded as an error code when it was plugged in. Just back from a 70 mile run in the freezing cold 6° C and everything seems good so far. 53mpg which is okay by me
    It had an oil / filter change in August so still pretty fresh on that side of things.
    I still would have expected the bike to run lumpy all over the rev range but it didn't so must be something to do with going from 1 fuel map to another which was exacerbating the o2 sensor errors.
    Never mind all sorted for now
     

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