91 K100RS - Runs poorly when warm

[IanC]

Greetings! I'm hoping to get some insight before I yank my hair out. I'm working on my dad's 1991 K100RS. The bike was parked 5 years ago due to a no crank/no start. He bought a used ignition switch and that was replaced but didn't solve the issue. I replaced the load shed relay, starter, and cleaned the grounds. It cranked but no start.
Found the fuel system had been ravaged from sitting. Replaced the pump, filter, hoses (fuel and vacuum), fuel pressure regulator, injectors, intake o-rings, and fuel cap gaskets. Also put on a Remus exhaust. Now it ran but was hard to start but otherwise ran well when cold but seemed to fall on it's face when it got out of the cold range.
I checked the codes and got an 1133 code for the Hall Effect Sensor #2. Replaced the ignition pickup now it starts right up but seems to run very lean when coming out of cold start. I've adjusted the Throttle Position Sensor to .375v with throttle closed, check the resistance of the potentiometer and it's near 500 ohms resistance,  replaced the spark plugs, and replaced the temperature sensor. I've also checked the coils (8 ohm resistance primary, 12k secondary) and the plug wires (6k resistance) as well and cleaned the coil connections. Still does the same.
To me it seems like it's coming off a cold start enrichment and then leaning out. Code 1133 is still present. I'm at a loss on what to look at here. I have dad looking to see if he still has the original ignition switch as it ran well prior to being parked with the no start but that's just grasping at straws at this point.
Any ideas about what I'm missing?

[The Mighty Gryphon]

I can't offer any insight into why the 1133 code keeps coming up.  You may not be canceling the code correctly.  The codes don't self cancel after you address the problem that caused the code.

Have you checked the engine coolant temperature sender?  A failed sender or dirty connector will cause the mixture to get overly rich when the engine warms up leading to poor performance.  It is a not uncommon problem. 

If the mixture is lean, the cause is usually and air leak someplace, usually in the boots and bushings around the throttle bodies.  There are checks you can do with propane or carb cleaner.

You may also be dealing with dirty injectors.  You can pull them and send them off to be serviced or you can get a bottle of Techron fuel system cleaner and dump some in the tank.  Run the engine for a couple minutes and let it sit overnight.  Repeat a few times.  Sometimes it will clean out the blockage. 

How is the compression?  A bike that sits a while can sometimes have a stuck ring that lowers the compression in a cylinder.  I have had good luck with putting a shot of Marvel Mystery Oil in the cylinders cranking the engine a couple times and letting it sit.  It is good for breaking up carbon deposits.

[IanC]

Hi Gryphon. I disconnected the battery to reset the code. Does the Motronic retain codes through a battery disconnect?
I replaced the sensor in the pipe directly below the radiator.  I assume that's the sender you mean.
I don't see any visible cracks or tears in the intake boots or hoses and I replaced the intake o-rings. I'll try some carb cleaner or propane to verify.
The injectors are new upgraded units from EME.
I would think if it were a compression issue it would run better when warm as things expand. Right now it runs like a top when cold both on and off choke.

[frankenduck]

Usual cure: Cheap and easy fix. Refresh the heat sink compound for the ignition amp.

The amp is located on the front left corner of the lower battery bracket. When the factory heat sink compound gets old it does not dissipate enough heat to the battery bracket and the ignition amp overheats so the bike runs like crap when it gets warmed up. (Only on K1, K100RS4V and Gen 1 K1100s.)

Remove the ign amp from the battery bracket, sand/steel wool off the old heat sink compound and apply some new heat sink compound.

Any heat sink compound will work. It's pretty generic sutff.

Example: https://www.amazon.com/dp/B0CBN1R5VP/


 

[IanC]

Thanks Franken. Forgot that one. It's been done too with no change.

[The Mighty Gryphon]

Everything there is to know about the Brick's Motronic and ABS diagnostics.

https://www.motobrick.com/index.php?action=dlattach;topic=7996.0;attach=78083

[Laitch]

You've replace both the coolant temperature sensor and the air temperature sensor?

[IanC]

I have not replaced the air temp sensor.

[Laitch]

Checking for a short in the wire from the air temperature sensor to pin 22 of the Motronic Control unit could be undertaken. I wouldn't run out and replace it yet.

If you're performing the diagnostic procedure correctly, the repeated 1133 code could be faulty, according to the code checking guidance at the link TMG provided. That code pertains to a No Start condition and your Brick is starting. Try clearing the code according to those instructions. If clearance fails, you might review your sensor installation.

The dilemma here is a question of faith in the Brick's diagnostic system. If there is no faith in it, then logic is the only recourse.
 

[IanC]

I've been trying to find a pin out diagram of the Motronic without much luck.

[Laitch]

I don't know where you've been looking but there are two Motronic manuals at Motobrick that are downloadable. Get them from links in a list that can be found in the Technical Directory/Motobrick Shop Manual section prominently displayed on Motobrick's homepage. Here's the link to the subsection list.

[IanC]

Perfect. Thanks Laitch!

[frankenduck]

K100RS4V Motronic Pinouts:

Page 2 of this PDF:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/kwiring/K1.K100RS4V/K1.SLP.Wiring.Diagram.V3.1c.pdf

And:

https://i.imgur.com/3QYpeD3.jpeg