I suspected my car might have had a bad temperature sensor for a long time now. This week I finally bit the bullet and bought an apexi pfc. This morning at ambient temperature after sitting all night and before starting the car I checked my temp readings with the monitor, air and water temp agreed with each other at 28c, and 27c. Then I went into etc. and the sensor check option. Air temp and water temp sensors were about 1.6v and fuel temp was all the way up at 3.5v. By my reasoning the fuel temp sensor should have the same voltage reading as the others sense they use the same sensor with the same resistances at the same temperatures for all three. They all use a 5v reference voltage. Thus my fuel temp is reading much lower resistance(high temperature) and thus is enriching the mixture because it adds more fuel because high temp fuel is less dense. Unless the fuel temperature sensor uses a different PCM internal resistance on the circuit than the other sensors(I have no idea why it would). So for those more experienced in what these readings should be, do you agree with my logic that the fuel temp sensor and/or circuit is faulty?

 

The water temp sensor located behind the water pump housing is the same as the fuel temp sensor located on the secondary fuel rail. The only difference is with the seal they use.
One uses a metal crush washer and the other an "O" ring seal.

It is also possible to wrongly swap their green identical connectors.

Most aftermarket secondary fuel rails for larger injectors are not fitted with an attachment for the sensor. Thus you go to the DATALOGIT Screen 2 Inj vs Fuel Temp table and set the 1.020 value to 1.000 and forget it.

 

They are not swapped, they are in the correct locations. I've already checked that, the water temp is exactly what you would expect it to be at ambient first thing in the morning and after the engine heats to operating temperature, I know that one is working correctly. Even if they were swapped wouldn't they read the same at ambient temperature first thing in the morning before starting the car?

While I do need bigger injectors(hitting 96+% duty cycles) at the moment I have the factory fuel rail and injectors and thus a fuel temp sensor. A fuel temp sensor that seems to me to be reading incorrectly. I don't have a datalogit to change the temp table setting, can I do it with the commander? With the original setting how much would an incorrectly reading temp sensor affect the A/F ratio? And what is it supposed to read in volts if it's working correctly?

Also I forgot to mention in my original post, this is a '93 R1. Obviously running a PFC, currently on the factory apexi base map. Pettit street ported engine, Pettit ported factory twin turbos. Full 3 inch exhaust. Aluminum AST, koyo radiator, bigger aluminum v mount intercooler. 180 degree thermostat, lower temp fan switch. EGR disabled but still present, air pump deleted, accelerated warm up deleted, pvc deleted.

 

You got two choices:
(1)take the sensor out and test it per page F-184, sensor or wiring problem, fix it
(2) borrow DL and change value as I stated