R1100GS stumbling troubleshooting

Discussion in 'GS Boxers' started by cnmjr123, Oct 22, 2020.

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  1. cnmjr123

    cnmjr123 Been here awhile

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    Hello all,

    I have a '98 R1100GS with 67K miles on it. Over the past month, I've noticed a "stumble" at low-mid throttle openings. I'm having a hard time describing it: stumbles off idle and enters a big dead zone with no acceleration(like a carb jet feels when it's clogged). Cracking the throttle more will eventually fix it as the RPM increases.
    During this stumble, the bike sounds as if it's running on one cylinder and has increased vibrations. I've noticed this issue both when the bike is cold and hot and through all gears. Lately, I've noticed some pinging or popping on deceleration with a closed throttle. I typically wear earplugs and have only recently noted this so it may or may not be related.

    What I've done so far:

    Fuel: I've run multiple tanks of good quality gas of different grades through it. 89-95 octane doesn't change anything. I've also treated the gas with HEET with no effect.

    Valves: adjusted.

    Throttle bodies: synced.

    Spark plugs: replaced and correctly gapped.

    Air filter: cleaned, no rodent debris in airbox.

    More ideas:
    Could the TBs have a vacuum leak and need a rebuild?
    HES going bad?
    Coil going bad?
    Plug wires?

    Thanks everyone!
    #1
  2. The Fabricator

    The Fabricator I didn't know it wasn't possible so I did it.

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    have you synched the tb's at part throttle and idle?
    #2
  3. neppi

    neppi Long timer

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    Vac plugs fell off / perished? Injectors clogged? Injector connectors oxidized? Injector connector leads worn through? Injector grounds / earths oxidized? ... for starters.

    I got 3/5 of these on mine... wiggling the injector connectors helped sometimes. Oh, also the injector bottom seats (the thick O-ring thingies at the tip) were hard and dead-ish and caused air to fly by. I bought a pair of new ones and mounted them with a hair of Yamabond. Sealed it nicely. The injector mounting brackets were a bit bent out of shape causing the injectors sit a bit loose.

    Have you reset the Motronic? How’s the Cat-plug doing?

    Sounds pretty electrical to me. Pull out all the related connectors (incl Cat-plug), clean them properly and put back together with a smidgen of diel-grease. Althou some say you shouldn’t use it in super low voltage / Amp stuff. I never had any issues.

    Should do the trick...

    You didn’t mention adjusting the throttle position sensor?
    #3
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  4. Steptoe

    Steptoe steptoe

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    With a meter check the resistance across the electrical connector terminals. Both injectors should read around the 16 mark...... if one is higher or lower there's your problem.
    #4
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  5. cnmjr123

    cnmjr123 Been here awhile

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    Yes I did

    Thanks for the info. I'll be replacing both vac plugs for good measure. I just cleaned both injector connectors with QD electric cleaner, they were both oxidized. The black outer sheath on the right injector wires has become brittle and started flaking off. None of the inner wires seem compromised though. I also noticed the right injector has more "wiggle" vs left, perhaps the o ring is shot. Is the only way to clean injectors is to send them out to a shop?

    I can only find an R1150 Motronic reset guide. Do you know if it applies to R1100s? Pull fuse 5 for 5-10min? Cat plug and wires look intact.


    I haven't adjusted the TPS. Seems intimidating! :D Use the zero=zero method?

    Will do, thanks!
    #5
  6. neppi

    neppi Long timer

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    Pull fuse #5 for the 10min, put it back, ign on, slowly-ish turn throttle 0-100-0 twice, power off, done.

    There are fuel system cleaners you pour into your tank that clean the injectors, but the best way to clean R1100 injectors is to put a matched pair of R1200 injectors in. ;)
    #6
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  7. Steve W.

    Steve W. Boxer Pilot

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    Try unplugging the O2 sensor and then pull fuse 5 for a few minutes. Then reinstall fuse. This will keep the motronic in open loop. See if it improves. Cheers
    #7
  8. cnmjr123

    cnmjr123 Been here awhile

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    16.9 on right injector, 18 on left. No luck with Motronic reset.
    #8
  9. vagueout

    vagueout Long timer

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    Spark plug HT leads/caps deteriorate with age, 20 years or more is high time to replace i.m.o.:*sip*
    #9
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  10. Three Dawg

    Three Dawg Into Africa

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    Wot he said.
    #10
  11. Don-Julio

    Don-Julio Adventurer

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    I would suspect a dirty injector. Start by spraying some brake cleaner around the intake boot, around the throttle bodies so you can rule out intake leak. Do you run a K&N filter? Don't.. Pull the pink relay in the fuse box. Ride it for a bit and see if you get a change in symptoms. Lots of variables there if the problem goes away. I've seen the injectors so clogged that they work better by spraying MAF cleaner directly into the airbox with the filter removed. Hold throttle at appx 2200 and spray. If it gets better, try running an FI cleaner like BG or Techroline by Chevron for a couple tanks at a high density ratio. If you find it is the injectors, it does not hurt to pull them and clean with a stainless steel brush as well.
    #11
  12. cnmjr123

    cnmjr123 Been here awhile

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    Thanks for the reply. I pulled both injectors this evening. The right side has more "wiggle" vs left so possible vacuum leak there (?). The left injector looks more like a "jet" vs a "fan" shape while spraying, so definitely dirty.
    #12
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  13. mouthfulloflake

    mouthfulloflake Not afraid

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    #13
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  14. Don-Julio

    Don-Julio Adventurer

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    Well, that's a good place to start. Glad to help.
    #14
  15. Lasermaster

    Lasermaster Been here awhile

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    I'm not a mechanic, but the two big problems I've had with my 96 1100GS had very simple solutions.

    1. When my bike stuttered and stalled I thought I had a fuel problem. It was a frayed throttle cable that eventually snapped.
    2. When I had another stalling issue it was a failed side stand switch.
    #15
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  16. cnmjr123

    cnmjr123 Been here awhile

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    Sweet victory! Clogged injectors were the culprit. Bike runs great now, no power loss or hesitation. Thanks for everyone’s help!
    #16