Replaced the (red) TPS on my '88 XJS as it wasn't possible to achieve the recommended 0.32 to 0.36 volts on the red wire at the throttle rest position (as per Kirby Palm). But even with the new one the range of adjustment is only 0.02 to 0.23 volts. The green wire is at 5v as it should be and testing on the bench with a 5 volt power supply gives the same result. My question - does it have to be between 0.32 and 0.36 volts or will anything below that be ok?

 

Firstky it has to be attached to the car. It needs its "signal" from teh ECU.

0.32 to 0.36 is required. Anything below that and the ECU thinks the thing as at idle when you open the throttle until it passes that range.

This is how I have done it for too many years. Easy and simple.

 

I believe you're right. It does think it's still in idle. Then when light pressure on the throttle brings the revs to about 1500 with the ECU thinking the engine's still idling the overrun cutoff steps in and cuts the fuel to the injectors, restoring it at about 1100 rpm making the car lurch along the road as it repeats this sequence. This is exactly what's been happening. I don't know why the new TPS won't let me get to the correct idle setting of 0.32 to 0.36v, the only way I've been able to achieve it is by inserting a 470 0hm resistor (a value arrived at by trial and error) between the yellow (earth) wire and the yellow/black wires it connects to in the wiring loom. This brings the voltage on the red wire into the desired range.

 

What TPS are you using.

I have a few duds over the years, and some people have stated Ford units work, but I have never been able to get them low enough at the idle end. Always 0.50ish, and that is terrible for surging also. Maybe the USA Ford be different, dunno.

 

You can “bench set” a red Lucas TPS by providing 5 volts using an external source, so you’re not doing that wrong.

I’d wonder if perhaps you’ve installed the switch “wound up”. There is a return spring inside the switch, but it should not be installed with tension. I misunderstood the purpose of the internal spring at first myself so this is my own dumassing talking.

 

EAC9634 (red one) just purchased from Barratts UK. Resistance between green and yellow wires is 6.5 Kohms.

 

PM me your phone number, it will be easier. I am too old for this keyboard rubbish.