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i am now the owner of a 2004 GL1800 with 70k miles. i still have an 2006 VTX that i put over 85k miles on it. my gold wing has a FI 25 code, this has happened a few times in the past 2 weeks with no problems. however, on my way home from work, 60 on a straight road, it bucked a few times, FI light came on, and then it was all i could to keep it running and make it home. i had to keep the RPMs above 1500-2000 when i had to stop. when i arrived home i checked the code again and i still only had the 25. went out the next day and started it, sounded like a sewing machine, no idle. the day after that was better but still no idle. will the right hand knock sensor cause this or should i start looking for a new PCM. any other ideas?
 

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Hey Chips - The Left and Right Knock Sensor on the GL1800 is a small single wire thumb sized part, screwed into the engine block to notify the ECU of the best ignition timing per RPM, load, etc.... When the ignition is spot on, the ECU will actually creep the timing toward an additional "advance" setting as a test until it receives a slight pre-detonation signal (advanced too far). Timing is then slightly retarded until the pre-detonation no longer occurs. This constant testing assures max HP and MPG at all times.

Internally the working circuit of the Knock Sensor is based on having two small crystals or special ceramic discs pressed together. This special circuit will produce a very tiny "Piezo-Electric" AC signal when a vibration (mis-firing cylinder) is felt through the block surface. The ECU will briefly retard the timing to that side of the engine when either the left or right Knock Sensor emits a signal. The timing is then returned back to normal to watch for the next pre-detonation event.

Because the Piezo-Electric signal sent to the ECU is in the milli-volt (.005 vac) range - any resistance in the electrical wiring or the connecting terminal points will throw a "Knock Sensor Signal Missing" FI 25 (Right) or FI 26 (Left) code from the computer. Sometimes just cleaning the signal wire connecting points will solve the problem.

To test the Knock Sensor output with the key OFF, you simply connect one lead of a multi-meter selected to the ac mill-volt range to the Knock Sensor terminal and the other multi-meter lead to ground. Then use a small hammer to very lightly strike the block near the sensor. The indicated output ac voltage will briefly spike with each impact and then then return to 0 volts. You can also swap the left and right Knock Sensors to see if the error code changes from FI 25 to FI 26. Hopefully your ECU is not the problem.

Hope this helps - Good Luck Michael
272940
 

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Hey Chips - The Left and Right Knock Sensor on the GL1800 is a small single wire thumb sized part, screwed into the engine block to notify the ECU of the best ignition timing per RPM, load, etc.... When the ignition is spot on, the ECU will actually creep the timing toward an additional "advance" setting as a test until it receives a slight pre-detonation signal (advanced too far). Timing is then slightly retarded until the pre-detonation no longer occurs. This constant testing assures max HP and MPG at all times.

Internally the working circuit of the Knock Sensor is based on having two small crystals or special ceramic discs pressed together. This special circuit will produce a very tiny "Piezo-Electric" AC signal when a vibration (mis-firing cylinder) is felt through the block surface. The ECU will briefly retard the timing to that side of the engine when either the left or right Knock Sensor emits a signal. The timing is then returned back to normal to watch for the next pre-detonation event.

Because the Piezo-Electric signal sent to the ECU is in the milli-volt (.005 vac) range - any resistance in the electrical wiring or the connecting terminal points will throw a "Knock Sensor Signal Missing" FI 25 (Right) or FI 26 (Left) code from the computer. Sometimes just cleaning the signal wire connecting points will solve the problem.

To test the Knock Sensor output with the key OFF, you simply connect one lead of a multi-meter selected to the ac mill-volt range to the Knock Sensor terminal and the other multi-meter lead to ground. Then use a small hammer to very lightly strike the block near the sensor. The indicated output ac voltage will briefly spike with each impact and then then return to 0 volts. You can also swap the left and right Knock Sensors to see if the error code changes from FI 25 to FI 26. Hopefully your ECU is not the problem.

Hope this helps - Good Luck Michael
View attachment 272940

Wow, what a fantastic explanation of the operation of the knock sensor circuit.
 

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Hey Chips - Were you able to make any progress in sorting out your FI 25 code ? As previously mentioned one of the most informative "home mechanic" tests is to swap the suspected Knock Sensor to the opposite side of the engine and see if the trouble code changes to 26. If this doesn't help point you in the right direction and the wiring checks OK, the ECM may turn out to be the culprit.

There is one other thing that is sometimes over looked. Since the Knock Sensors are our "Sergeant At Arms" standing guard to watch for even a slight cylinder misfire, a tank of low quality (randomly inferior) fuel can turn on a FI 25 or 26 error. You might try some 93 octane premium gas just to see if the error goes away.

The Honda engineer's installed the knock sensor circuitry so their "King of the Road" could run on the less expensive 87 octane gas, if preferred. At times though, this can generate a boarder line problem that tends to spook us a bit when out on the road far from home. The Pro's and Con's of the Premium Fuel requirement of the BMW bikes is often discussed amongst our local riding groups when we meet for breakfast.

Good Luck - Michael
 

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This symptom is a classic failing ECM. Swap the sensors from side to side and ride it until the light comes on again, then check it. If it changes to a 26, then it’s the sensor. If it still throws the 25, it’s a bad ECM. Knock sensors do fail on occasion, but a failing one won’t cause the engine to idle badly.
 
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