Blue throttle pot problem
Discussion
I may have a solution using a Tilton contactless (hall effect) TPS but to test it out I need some help from someone with a good working and well tuned standard 4.5 with the MBE ECU as I’m on an aftermarket system so my figures are non standard. I need to know the output voltages at idle and at full throttle. If a few people can reply so we can get good average data that would be great. The Tilton one never wears out and zero noise so despite the price it’s a permanent solution if it can be made to work.
I’ve just ordered one so when I have numbers I can compare.
How to measure:
one pin is always ground (0v)
one is always 5v
the third is variable with throttle position.
once you ID the one that’s always 0v put you black meter lead on this one a find the one that varies with throttle position and measure the voltage at idle and wide open. You will need to slip the boot off and obviously do this with engine off, ignition on and not immobilised, throttle pot must be connected too.
I’ve just ordered one so when I have numbers I can compare.
How to measure:
one pin is always ground (0v)
one is always 5v
the third is variable with throttle position.
once you ID the one that’s always 0v put you black meter lead on this one a find the one that varies with throttle position and measure the voltage at idle and wide open. You will need to slip the boot off and obviously do this with engine off, ignition on and not immobilised, throttle pot must be connected too.
Has to be a 4.5
The percentages in the manual are the same but no way to know if those percentages map to the same voltages in the ECU tables. There seems to be less of a problem getting the white 4.2/S6 ones anyway so this would be an expensive solution for them.
Although on reflection it might be handy to see some 4.2 figures I suppose. If they are the same this mod might work for both as these TPS's have both clockwise and anticlockwise outputs.
The percentages in the manual are the same but no way to know if those percentages map to the same voltages in the ECU tables. There seems to be less of a problem getting the white 4.2/S6 ones anyway so this would be an expensive solution for them.
Although on reflection it might be handy to see some 4.2 figures I suppose. If they are the same this mod might work for both as these TPS's have both clockwise and anticlockwise outputs.
fatjon said:
How to measure:
one pin is always ground (0v)
one is always 5v
the third is variable with throttle position.
once you ID the one that’s always 0v put you black meter lead on this one a find the one that varies with throttle position and measure the voltage at idle and wide open. You will need to slip the boot off and obviously do this with engine off, ignition on and not immobilised, throttle pot must be connected too
You probably ought to know the actual voltage on the 5v feed at the time of measurement as well.one pin is always ground (0v)
one is always 5v
the third is variable with throttle position.
once you ID the one that’s always 0v put you black meter lead on this one a find the one that varies with throttle position and measure the voltage at idle and wide open. You will need to slip the boot off and obviously do this with engine off, ignition on and not immobilised, throttle pot must be connected too
Happy to help out on this FJ.
I have an ok 4.5 V8 to test with if you have no one else.
A few years ago, off work with a broken neck, I built a 4.5 AJP engine simulator and connected it to a scrap MBE ECU I found on ebay.
I recall that the Throttle potentiometers are 5K Ohms (or 4.7k).
It might be useful to perhaps test the replacement TPs in simulation first using my simulator [which roughly translates to a few wires and potentiometers on a breadboard]
Aide
I have an ok 4.5 V8 to test with if you have no one else.
A few years ago, off work with a broken neck, I built a 4.5 AJP engine simulator and connected it to a scrap MBE ECU I found on ebay.
I recall that the Throttle potentiometers are 5K Ohms (or 4.7k).
It might be useful to perhaps test the replacement TPs in simulation first using my simulator [which roughly translates to a few wires and potentiometers on a breadboard]
Aide
That would help if you have throttle bodies too? In theory the maths should be simple ohms law if a fully closed throttle is 0 ohms and an open throttle is 4.7k but I know for sure that there is no way an AJP idles on 15% throttle, it would chuck a rod at that angle while unloaded. Also pretty sure that wide open is not at the end of the pot as the pot range is more than 90 degrees.
My guess is that despite what the ECU shows, the true fully closed is about 12% TPS , idle is about 3% more and wide open is about 60%-70% of full pot travel. Will measure full travel of the pots tomorrow to test that theory.
My Cerb idles at 900rpm with a true throttle angle of 4% of WOT angle. At 15% you would be dodging flying rods.
My guess is that despite what the ECU shows, the true fully closed is about 12% TPS , idle is about 3% more and wide open is about 60%-70% of full pot travel. Will measure full travel of the pots tomorrow to test that theory.
My Cerb idles at 900rpm with a true throttle angle of 4% of WOT angle. At 15% you would be dodging flying rods.
The ECU IS 8 bit.
There are 256 throttle positions.
The percentage that is displayed, on the original diagnostic software and verbatim on my App [which represents what the ECU thinks the position of the butterfly's in the Throttle bodies is] is not leliear. There are many more throttle positions, of the 256 availiable, dedicated to more finely representing the position of the butterfly when it is at idle.
There are 256 throttle positions.
The percentage that is displayed, on the original diagnostic software and verbatim on my App [which represents what the ECU thinks the position of the butterfly's in the Throttle bodies is] is not leliear. There are many more throttle positions, of the 256 availiable, dedicated to more finely representing the position of the butterfly when it is at idle.
Edited by aide on Friday 10th December 23:31
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