K1100 - Stuttering and Loss of Power

[toomuchhype]

I have a 1992 K1100 that I did a full tear down, engine paint and re-assembly. When I got the bike back together it isn’t running very well.

Bike is stuttering and has complete loss of power at sustained (half) throttle. Could often blip the throttle and have it pull again and run fine. But Seemed to get progressively worse. At low or mid throttle it would have a ton of stuttering and hesitation. Literally feels like it is shutting the fuel off.

I started playing with the TPS. I find if I turn it nearly fully clockwise the bike runs much better until it hits the very top end. If I adjust the TPS to voltage XXX then it doesn’t idle, sputters way worse at low RPM and is completely terrible. TPS adjustments definitely have an impact on how it runs so it sure seems like the culprit…

I have a parts bike so I have swapped the following with no improvements:
- fuel tank (different filter, pump, etc)
- TPS unit itself
- Throttle bodies

I have checked the following:
- voltage amplifier (battery tray) - cleaned and reapplied the heat sink grease
- Checked Z hose and all other hoses look good
- Intake boots have no cracks
- Done the “propane test” and does not increase idle at throttle body boots

I am really scratching my head on this. Questions:
1. What impact does the TPS have when it is turned fully clockwise?
2. When the tps is adjusted to 450 volts (halfway position) it runs even worse. Why is this?
3. What else can I check or swap to resolve this?

I have exhausted searching and reading these forums (which is such an amazing resource). Any ideas or tips is greatly appreciated!

[Laitch]

If you painted the frame, ground points on the frame need to be bare metal for the electronics to function optimally.

[Laitch]

Here are two ground points on a 2V Brick that should be bare metal contacts—the right rear engine/frame connection and the frame backbone connection for ground wires. The K1100 is likely to have similar connections.

[frankenduck]

Have you pulled/inspected the spark plugs?

Also, if you have a parts bike you might want to try swapping the coils.  Note that you don't need to remove the "old" coils to do this. You can just attach the wiring and spark plug leads to the spare coils without mounting them and then see if the bike runs any better.

[toomuchhype]

Thank you for the suggestions thus far.  The bike does have new spark plugs in it, but I haven't pulled them to see the condition after I've been running it.  I will do that.

I did paint the frame, so I will also check my ground connections.

The bike runs amazing and pulls like a freight train until you are wide open throttle, and then it just bogs and it's like the fuel is completely shut off.  And that's with the TPS turned nearly fully clockwise.  It also seems to run better when it's cold and gets worse as it gets hot (if that means anything).

[Laitch]

It also seems to run better when it's cold and gets worse as it gets hot (if that means anything).

This a classic symptom associated with faulty coils and faulty Hall effect sensors but first, clean up all the ground connections and be sure all electrical connectors including the ignition control unit's plug terminals and the fuel injection control unit's plug terminals are clean and that the plugs or connectors are securely connected.

[The Mighty Gryphon]

When you adjusted the throttle position sensor, did you adjust for a voltage reading or use the temperature light in the instrument cluster?

There is a procedure for using that light that is described in a write up on Motronic trouble codes and the 3 prong diagnostic plug.  I have found that using that procedure is easier and gives better results than trying to adjust for .375 volts when the throttle is closed.

Along with the grounds, you might also want to shoot some Deoxit on all the connectors that carry the throttle position signal.  Any additional resistance caused by a dirty contact will upset the mixture in some portion of the engine's operating range.

[Scott_]

Seeing as no one has mentioned it yet, I'd suggest that you also check the water temp sensor(and connections)... make sure it is reading in the proper range, as you did say that it gets worse as the temp rises.

[Martin]

Check to see if the fuel supply and return lines aren't partially collapsing as the bike warms up. And check the fuel cap breather.
Regards Martin.

[gkanai]

If the ground was an issue, would it result in intermittent power? Wouldn't a bad ground = no spark at all?

[Laitch]

If the ground was an issue, would it result in intermittent power? Wouldn't a bad ground = no spark at all?

It does equal no spark at all, just intermittently. 

[toomuchhype]

Check to see if the fuel supply and return lines aren't partially collapsing as the bike warms up. And check the fuel cap breather.
Regards Martin.

Hi Martin - Can you expand on what you mean when you say the "fuel cap breather"?  The two fuel tanks under the tank are free and clear and open to the air (no hoses, etc).  Is there something I need to check on the fuel cap itself?

[Martin]

There is a valve built into the cap which allows air to be sucked into the tank to replace the fuel that is being used. If the valve is not working fully, as the fuel is used air is unable to enter the tank. This will cause a vacuum to form in the tank causing fuel supply problems. Link to fuel cap rebuild   
Regards Martin.

[toomuchhype]

Hi All,

Just wanted to loop back to this thread and provide an update. 

Per the suggestions I:
 - Removed all ground connections, cleaned and sanded the connection
 - Adjusted the TPS back to .375v (measured via pins 1 and 4)
 - Removed the coil cover I installed and checked the ignition coils (coils passed).

I rode the bike after the above and it was 100%.  I believe the issue was either the ground connections, or it may have been the coil cover pinching the spark plug wires.  Before re-installing the coil cover, I cut out some of the plastic to relieve any stress on the wires.  Bike was running 100%, pulling hard through all gears, no sputtering whatsoever.

Thank you to the folks that replied to this thread and for this forum as a whole - fantastic resource!

Ride safe!

[Laitch]

Thanks for the followup. 

[Areshuan]

Thanks for the follow up . I am having EXACTLY the same problem for over a  year.
I changed:
fuel injectors
fuel pump
fuel filter
TPS
Spark plugs
all rubbers and  vacuum leaks
My next change was going to be the fuel pressure regulator. Until i read this post and another that mention it  can be an electrical problem and not a fuel problem.
I havent change the ignition spark plug wires.
An hour ago i gave it a visual check and i can see the ground bolt completely loose.
I will come back also with a follow up . I think this post can be useful to many.