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Throttle Position Sensor - Vfr Running Very Rich

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Hello,

My 5th gen 98 VFR is running very rich. It gets very poor mileage, about 18mpg. The bike is rideable, but not by much. Over the winter I was doing work on the bike, and I removed the throttle position sensor (TPS). I honestly do not recall why I removed the TPS, it was months ago, probably to get access to something. I see now that that is a big no – no, that on page 5 - 69 of the factory service manual it states “do not loosen or tighten the white painted bolts and screws of the throttle body. Loosening or tightening them can cause throttle valve and idle valve synchronization failure” and that the 2 bolts securing the TPS are in the “white painted” group. So, the dealership is now telling me that the entire throttle body needs to be replaced, which is very, very expensive. Prior to removal of the TPS, the bike mileage was 32 to 35 around town.

Specified Actual

Input 5V 5V

Output(throttle closed) 0.4-0.6 V 0.4 V

Output(throttle open) 4.2–4.8 V 4.37 V

When I gradually open the throttle, the voltage increase at the TPS output is smooth. Given this and the above measurements, the TPS passes all the checks, and is not a bad TPS.

Yes, I fess up that I messed up in removing the TPS, but that shouldn’t mean that I have to replace the entire throttle body.

The FI diagnostics is not spitting out any codes.

Any advice or assistance is most appreciated.

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No responses to this yet? I would say your voltages look like the TPS is adjusted fine, but it could still be bad. poor fuel economy is a symptom of a bad tps

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Are 5th gens subseptible to the thermostat warm up issue as 6th gens, I kind of agree, if getting the proper voltages from the tps, its probably just a coincidence, and not the real problem.

Are you at full temp above 160 degrees in about two to 3 minutes on a cold start? Since its winter time, perfect time to test the thermo

But these bikes(6thgens) eat fuel any time below about 160 degrees(5thgens might be the same).

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Trail and error now . More then likely you will have to set it and run it and re-adjust until you find a voltage that matches past performance ..

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is that all the manual gives for tps voltages, while full throttle closed and full throttle open require certain voltages. To actually adjust, requires a Feeler gauge adjustment. where you place a certain size feeler gauge in between the throttle stop , and measure and adjust the sensor till you get the right voltages (at the required feeler gauge setting). I dont see that measurement in your post, so maybe honda is just not releasing it. Assuming you marked the sensor before removing, I doubtt your off enough to lose 15 mpg.

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Running rich can often be caused by leaking, plugged or disconnected vacuum hoses. The one to the fuel pressure regulator is sometimes a culprit. There should be no fuel leaking in to it. If there's fuel in the vacuum hose, your FPR is stuffed. It also would be a good idea to check the MAP sensor for proper operation. To accurately check the TPS, measure the voltages at the ECU (if the TPS is working ok but there is a wiring issue, the ECU won't see the correct voltages).

If it's sat for long periods, there could also be some clogging issues in the injectors. One that won't seal correctly can let too much fuel through and continue bleeding the pressure off in to the cylinder when the engine's shut off. I sent mine out to RC engineering for cleaning and was surprised at the improvement it made.

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