FYI: Fuel Temperature Sensor

FUEL TEMPERATURE SENSOR BASICS

The "Fuel temperature Sensor" located on the "Fuel Pressure Regulator" attached to the fuel rails sends the current temperature of the fuel in the rails to the ECU to command certain operations depending on which model year you have. All model years have the "Fuel temperature Sensor", but the function changes between years.


1984 & 1985 (EARLY) MODEL YEARS

For the 1984 model year (and possibly early 1985 model years that might share the same ECU), as the fuel in the fuel rails gets warmer the "Fuel temperature Sensor" relays the temperature increase to the ECU, and the ECU adjusts the fuel map to "enrich" the currently referenced fuel cell to add more fuel.

Below is page EF & EC-20 from the 1984 FSM.
As stated, it shows that the "Fuel Temperature Sensor" increases the amount of fuel injected based on the resistance of the sensor (Refer to page EF & EC-53, which is not shown, for the temperature/resistance scale that the ECU sees based on "Fuel Temperature Sensor").

Note: The last point on the left side of this diagram is "When fuel temperature is high".

[attachment=2:2vfsi7uh]EF & EC-20 - 1984.jpg[/attachment:2vfsi7uh]



1985 (LATE) & LATER MODEL YEAR

For the 1985 and later model years, the FSM does not indicate an enrichment in fuel maps based on the resistance of the "Fuel Temperature Sensor".

Below is page EF & EC-22 from the 1985 FSM (every year after shows the same diagram/data).
It DOES NOT make any indication as to the Fuel Temperature Sensor contributing to the fuel map by adding an enrichment modifier to the current fuel map cell.

Note: Comparing this diagram to the one from 1984 model years, you will see "When fuel temperature is high" is missing. It is fair to assume that this feature was removed/revamped from later model years perhaps due to issues with the early model years, being the first of their kind.

[attachment=1:2vfsi7uh]EF & EC-22 - 1985.jpg[/attachment:2vfsi7uh]

SURGE-TANK INFORMATION

Below is page EF & EC-31 from the 1985 FSM (every year after shows the same diagram/data).
[attachment=0:2vfsi7uh]EF & EC-31 - 1985.jpg[/attachment:2vfsi7uh]

The surge tank is only equipped on 09/86 and later Z31's equipped with Turbos. (Needs verification).

It is located in the DRIVER SIDE wheel well, infront of the wheel itself-near the frame rail… By looking at where your MAF is, you will see two rounded vacuum hard-lines that come down from the strut tower area near your ignition coil and transistor, and ultimately make their way through the sheet metal just above the frame rail- and lead into the surge tank.

The purpose of the surge tank is to store "above atmospheric" manifold pressure via a one way check-valve connected to a vacuum line that goes to the intake manifold. When the pressure in the intake manifold is above atmospheric pressure, some of that boost pressure is stored in the surge tank for later use. The check valve prevents pressure from coming back out of the vacuum line. The tank may have some sort of relief valve to vent off excess pressure above a limit set from factory.

This pressure stored in the surge-tank is not released until the car is shut off and re-started. If the "Fuel Temperature Sensor" tells the ECU that the current temperature in the fuel rails is above 40*C or 104*F, the "Pressure Regulator Control Solenoid Valve" that the outlet vacuum line from the surge-tank is hooked up to is activated. This causes the pressure that is in the surge-tank to be routed through the "Pressure Regulator Control Solenoid Valve", and to the "Fuel Pressure Regulator" for a certain amount of time based on the current fuel temperature- thus increasing fuel pressure during hot starts.