SU HIF44E

The third and latest device used in the series 2 from 1984 on was the HIF44E carburetor. Basically the same unit as the HIF44 but equipped with a stepper motor on one side and a solenoid switch on the other side of the carburetor and an computer controlled device to control this. A very early stage of the injection system....

In this article I would like to go more into this device. There is not much published in the Haynes manuals and a not very common used device in other cars. In my own car from 1983 I replaced the HIF44 with the HIF44E carburetors in my car and think it is running very well now.

So how does it operate?

The HIF44E is basically the same unit as the HIF44. It is a single jet variable choke type and designed to operate under varying operating conditions and changes of temperature. It produces a constant air velocity and depression over the jet. Opening the throttle lowers the depression in front of the throttle disc and therefore above the piston. When the piston rise a point is reached when the depression above and mixture mass flowing beneath is matched by the weight of the piston spring.

At idle speed fuel is induced from behind the jet through a small port behind the throttle disc. During rapid opening of the throttle enrichment is provided by the piston damper, restricting the state of the the piston rise and thereby increase the depression over the jet. An electronic stepper motor controlled by an ECU management system controls the fuel supply. The ECU gets his input from various devices, coolant thermistor, ambient air sensor, accelerator pedal switch and the ignition coil.

The mixture controller is actually the stepper motor, which operates a rotary valve. The ECU unit moves the stepper motor through one of the 144 steps with a total of 120 degrees, while doing this the first 40 degrees the valve spindle opens the fast idle push rod. The idle speed is controlled by the throttle jack, consisting of a push-rod which is in contact with a cam driven by the stepper motor pinion. A pulse from the stepper motor turns the cam and the fast idle-push rod is moved to operate the throttle lever.

On the V8 models a vacuum valve is used to effect the mixture at low manifold depressions by decreasing the air bleed through the mixture control and so enriching the mixture when accelerating.

At a cold start the ECU receives information from the coolant thermistor and ambient sensor. This information is used to determine the amount of enrichment that need to be given for fast idle start. As the coolant temperature rises the stepper motor is rotated in opposite direction causing the mixture to weaken. The engine speed is received from the coil, giving the ECU the possibility to adjust the idle speed when any failure causing the engine speed to drop below 600 revs/min. One step of the stepper motor is enough to increase the speed of the engine by 100 revs/min.

On the opposite site of the stepper motor at the HIF44E carburetor a fuel cut off solenoid is used to cut off fuel by introducing a partial vacuum to the top of the float chamber. This will only operate when all the appropriate signals are received by the ECU, which are, engine temperature must be above 80 degrees C, ambient temperature must be above 6 degrees C, engine speed must be above 1300 rpm and the accelerator switch must be closed. This situations can occur for instance when you drive of a mountain, and the solenoid switch is not used when your car has an automatic gearbox and cruise control. The solenoid switch is switched on and of in half second intervals to prevent complete cutting off and jerkiness, and the switch is deactivated when the speed drops to quickly.

According to the Rover manual there seems to be a device with LED's that can help you to find any failure or fault and can be used as a fast check. We assume you don't have this device and so we will discuss some measurement that can easily done with a normal multi meter on various connections of either the ECU or the sensors. But first the connections to the various parts of the system.

1: HIF44E carburetor
2: Solenoid switch on the side of the carburetor.
3: Stepper motor attached to the carburetor
4: Vacuum switch (3500 only)
5: ECU unit
6: Ignition coil
7: Ambient temperature switch
8: Engine high temperature lamp
9: Engine temperature gauge
10: Accelerator Pedal switch
11: Engine temperature sensor - engine coolant
12: Ignition switch

But which wire is what?

This is the connector on the ECU, which is mounted behind the left glove box inside the car, in the same direction as seen below. The numbers of wiring count from right to left, starting with a black/white wire for the accelerator switch.

Click on the first picture to see the numbering and wiring colors.

Color codes:

1 Black/white, accelerator switch
2 Black, earth connection
3 NC
4 NC
5 White, solenoid switch
6 Yellow orange, stepper motor control
7 Yellow blue, stepper motor control
8 Black pink, stepper motor control
9 Yellow green, stepper motor control
10 Yellow gray, stepper motor control
11 White black, ignition coil
12 NC
13 Green blue, temperature gauge
14 White gray, solenoid switch
15 Black pink, accelerator switch
16 Yellow black, ambient sensor
17 Black gray, engine temp sensor
18 NC

This is the accelerator pedal switch, located on a bracket behind the accelerator pedal. An easy device which does not do more than switch on and of.
On and off switching can be measured with a multi meter at the two contacts of at pin 15 and pin 1 with the connector removed from the ECU.

And this is the ambient sensor, located in the inner and outer wing just by the battery. It simply measures the ambient temperature and supplies the ECU with that information. You can test if the sensor is working properly with a simple multi meter. Here are the values.

-10 C or +14 F resistance measured over the sensor 6k1
+20C or +68F resistance measured over the sensor 1k25
+50C or +122F resistance measured over the sensor 400
Any other out of range measurement means the unit is defect. Note: these measurements can also be done inside the car on the connector, removed from the ECU, at pin 16 and pin 1.