Throttle Position Sensor Adjustment

Thanks to Garry Vander Eyk



On some models of Kawasaki Vulcan motorcycles with Digital Fuel Injection (DFI) there have been some complaints of excessive pre-ignition pinging. These engines require 91 octane fuel and sometimes will continue to ping even on 94 octane fuel. One common cause of pinging is incorrect air/fuel ratio (too lean). 

The DFI system uses an Electronic Control Unit (ECU or computer) that has been programmed or “mapped” to supply a specific amount of fuel to the engine depending on the amount of air that is available to the engine under all riding conditions. The ECU uses input from several sensors to determine the amount of air entering the engine, including water temperature, atmospheric pressure, intake air pressure, RPM, intake air temperature, and throttle position. Since this DFI system does not have a knock sensor or oxygen sensor there is no feedback to tell the ECU if the engine is actually receiving the correct air/fuel ratio at all times, it relies entirely on the factory-set programming.

The procedure outlined here involves rotating the Throttle Position Sensor (TPS) from the factory setting to “tell” the ECU that the engine getting more intake air than it actually is receiving, the ECU will then provide slightly more fuel, resulting in a richer air/fuel ratio under virtually all conditions.

The original purpose of this procedure was to address the many complaints of pinging 2003 to 2006 VN1600 Classic and Nomad motorcycles, while running on 91 octane fuel. This adjustment can also be applied to VN1500s that ping on 91.  In theory, it can also be used to richen the mixture enough to run with lower octane fuel and to compensate for aftermarket intake and exhaust systems. On bikes that have un-usually high fuel consumption and do not ping under any circumstances, the TPS could be adjusted to provide a leaner mixture.  Since the air/fuel ratio is being altered, fuel consumption will change, although in most cases it will be insignificant. 

For the record the Kawasaki factory maintenance manual calls for:

0.584 to 0.604 volts with the throttle opening at idle
4.29 to 4.59 volts at wide open throttle (WOT)

As you'll see below Vulcans come from the factory with a substantial variation in settings between those numbers and even .05 volt change can make the difference whether the engine knocks under load or doesn't and may also give you the option of using regular or mid grade fuel instead of premium. 

How far does the TPS need to be rotated?

No two bikes will be the same, and it depends on how bad the bike pings to start with and how ping-proof the rider wants the bike to be. The adjustment is so delicate that you can not see the amount of rotation with the naked eye, it can only be done by measuring the TPS output voltage before and after the rotation.
Generally speaking, if a bike pings bad on 91 octane, even pings a bit on 93, then rotating the TPS .03 volts will give you bike that will not ping on 91 and will even run well on 89. Adjusting this same bike by .05 volts will cause it to smoke black and be completely ping less on 87 octane. Running this rich will no doubt increase fuel consumption and carbon up the engine.  For a starting point, try adjusting the TPS by .02 volts, go for a ride, and re-set it if necessary.

Be not afraid, the 'how to' for all this is coming....right now!

Tools Required:
TPS 6.JPG (23882 bytes)
#25 Security Torx Bit. This is a 6-point Torx bit with a hole up the center to accommodate a post inside the screw head. Most tool stores should have this, certainly a Mac or Snap-On dealer will. Get the bit only, not a complete socket with bit attached.   

A good digital multimeter to read increments of 1/100th of a volt DC.

4, 5 mm hex keys or allen sockets

8, 10, 12 mm sockets

Phillips screwdriver

Steel pin from a sewing kit, no larger than 1 mm diameter and no longer than 25 mm (or it could come in contact with a grounded body part, or Kawasaki needle adapter set 57001-1457

Silicone sealant, or Kawasaki Bond 56019-120

¼ inch wrench or shallow ratchet (to turn the Torx bit)

How To Do It

1. Turn off the ignition key.TPS overview.JPG (116661 bytes)

2. Remove the seats and fuel tank.   Do not disconnect the speedometer wire harness. Set the speedometer unit face-up on the frame or the liquid crystal display can malfunction. With the tank removed, the throttle body, air cleaner, thermostat housing and hoses can be seen. (photo right)

3. Remove the chrome right-side air cleaner cover. TPS 2.JPG (115625 bytes)
TPS 3.JPG (119895 bytes)

4. Remove the black plastic inside cover from the throttle body, begin by removing the two short ISC hoses, two Phillips head screws, the chrome bolt (10 mm socket), four allen screws near the top (5 mm hex key), slide the large hose out of the front and allow the cover to hang by the wires or support it with a bungee. (photo right)

5. Remove the bracket (held by two bolts requiring 8mm socket) that holds the rear spark plug wire above the throttle body.  Pull  both spark plug wires off the plugs and hang the wire forward and out of the way. You will now have a clear view of the throttle body, the black TPS attached to it and one of the 2 screws that fasten the TPS to the body.  (picture left)TPS 5.JPG (69487 bytes)

At right is the TPS, see the yellow paint on the mounting screw.  Not all bikes have this yellow paint.

6. As shown below left, remove the wire harness from the thermostat TPS 8.JPG (99984 bytes) housing and lay it forward, remove the wire harness from the TPS. This connector will have 3 wires in it, the center wire will be yellow with a white tracer. Insert a sewing pin from the top straight down along the wire until you feel it hit the metal contact.    

TPS 9.JPG (86571 bytes)



7. Connect the harness back onto the TPS as shown at right. Be sure the pin can not contact any part of the bike.  

8. Rotate the twist grip to wide-open throttle (WOT), check that the metal stop on the throttle body disc contacts the aluminum housing. If it does not “click” against the housing, then adjust the throttle cables so the disc can travel all the way to the stop. 

9. Switch on the multimeter, set it to Volts DC. Fasten the ground (black) lead of the multimeter to the bike frame tps 10.JPG (109340 bytes) or battery negative. Touch the positive (red) lead of the multimeter to the head of the pin in the TPS connector. You should read 0.00 volts. Turn on the ignition key and wait 10 seconds for the voltage to stabilize. You should read from .580 to .750 volts with the twist grip at idle. Rotate the twist grip to WOT, you should now read 4.29 to 4.59 volts. Record this voltage, it is the factory set point and you may some day want to put it back to original.  In picture at left the original setting was 4.40 volts.

10. Turn off the ignition key.

11. Check the 2 TPS mounting screws, if they have yellow paint inside the head you will need to scrape all that out with a pick.

12. Place the #25 Torx bit in the screw head, with a ¼ inch wrench on the bit, loosen each TPS 7.JPG (102928 bytes) screw about half a turn as shown in the photo at left.  The inside screw is a real treat to get to!

13. Switch on the ignition key, wait 10 seconds for the voltage to stabilize then hold the twist grip at WOT,  very gently (we're only looking for a teeny adjustment here, the eye won't even register it) tapTPS 11.JPG (110687 bytes) the bottom of the outside ear of the TPS up with the small wrench, the TPS will rotate and you will see the voltage increase.  In the photo at right the new setting is 4.42 volts.

14. Tighten the 2 screws and re-check the voltage to be sure it has not moved from your desired setting.

15. Remove the pin from the TPS connector, re-connect the thermostat harness, re-assemble the air cleaner housing, install the fuel tank and start the engine. You may need to re-set the idle RPM with the adjuster knob under the air cleaner.

16. Test ride the bike, if it smokes black then it is running too rich and you adjusted a little too far, if it pings it is still too lean so go back in and tap the TPS again to get a bit higher reading.   You'll get pretty good at removing the gas tank before you're finished. 

17. After you are satisfied and won’t be doing any further adjustments remove the tank one last time and apply some silicone to the connector where the pin was inserted, to prevent water from entering the contact.

18. Go ride ping free on lower octane fuel!

Comment(s) from contented user(s)

Sarge posted to the VROC list "

I adjusted the TPS on my 05 Nomad according to the instructions on Gadget's fix-it pages. The factory setting for WOT was 4.485 volts. I set it to 4.510 volts. That's just 0.025 volts change! Made a 20 mile run with 2/5 premium and 3/5 mid grade fuel. From 35 MPH in 5th gear, I went to WOT. No pinging at all! I'll have to see what happens over the next few weeks and I can get more mid grade fuel into the system. The bike ran like it was "re-born"! Throttle response was excellent! I’m really pleased with the results. I'm gonna install new plugs and monitor their condition. Who needs an expensive electronic throttle box/fuel processor/control module?!?!

Feedback from Jim Mann

Having a 1500 and always having a pinging problem I made the same adjustments to mine.  I ended up with 4.46v at Wide open throttle.  After playing with mine for 2 days I feel it is much better.  I can run 89 now.  I tried 87 Octane but it still ping under certain conditions.

Jim Mann (Slim, Nomadrider)

Feedback from Brad Langley (1600 Nomad)

As you know I started at 4.4085 Volts WOT stock and it pinged in warm weather on 91 octane pretty bad at lower RPMS.
I decided to try 4.4300 or .0215 increase in DC voltage.  That pretty much stopped the pinging on premium (fortunately the weather in Southern Cal is still warm for testing purposes). I put a half tank of mid grade or 89 octane in the tank and took off for another warm ride.  It pinged but not as bad as premium did before I started the project so I knew I was headed in the right direction.
This morning I adjusted the TPS further.  This time I didn't have to remove the cover on the throttle side.  I just took off the back two bolts from the tank and propped it up about 6 inches above the bike supported by my bungee cords.  The first adjustment taking off all the throttle covers and bolts took about 1 1/2 hours.  The second time about 25 minutes!
I took the second adjustment further to 4.4505.  The bike is now totally ping less on mid grade 89 octane gas!!  I haven't tried regular 87 but I'm sure it would ping less than premium use to!  The exhaust is clear and my buddies say they smell nothing following me so I haven't over-done the enrichment I think.  Mileage seems about the same so far.  I need to run a full tank at cruising speed to see if I can still get 42 mpg on the highway.
I have noticed another side benefit; the cooling fan only came on once in stop and go driving after the first adjustment and didn't come on at all on the second 4.4505 setting.  Before starting this project it was coming on all the time!  Each time the bike stopped in warm weather at a light the fan would come on after a minute of idling and the heat was coming at me big time!
The bike now seems to run much cooler and I don't hear that metallic ping ping ping sound I used to hear when I shut my bike off.  My bike used to stay hot to the touch an hour after a ride.  Now it is much cooler after shut down.  I feel the bike is much happier because of the cooler temps.  this is probably because of the denser cooling charge of more fuel reaching the inside of the combustion chamber providing more of a evaporative "swamp cooler" affect.