Megasquirters and electrionics experts- help needed

[Philip A]

As I have advised on the forum, I am currently fitting a Motronic "thor" manifold to my 3.9 and hope to initially use my 14 CUX, before later swapping to a Megasquirt 2.
Checking the Throttle Position Sensors last nght I found that the motronic TPS has a resistance to earth ie from the 5Volt input wire to the earth return wire of 1750 Ohms, vs the 14 CUX TPS of 6000 ohms. The earth is shared by the water temp sensor, the fuel rail temp sensor,and the MAF.

My questions are
Does this matter? I assume there will be a higher voltage returning to earth with a lower resistance.
Will this affect the other sensors? Will it cause component failure in the ECU?

Can I add a resistor to the earth return to increase the resistance to spec 4000-6000 Ohms as long as I have the specified voltage swing from 0.5 volts to 4.9.
Regards Philip A

[F'n_Rover]

I'm no expert.
adding a resister to the earth side of the tps will do no good as you wont have full rail voltage swing you may end up with say a 4 to 5 volt range.

i would think using the lower ohm tps would not be a problem as basically the are just voltage dividers. 1000ohm or 100000 ohm will do the same thing. However things will change depending on the ecu input impedance.

the lower ohm tps will draw more current from the ecu 5v rail but we are talking poofteenths.

the only problems you may have will relate to the input impedance of the ecu. I doubt you will do any damage but you could have problems with
obtaining full range swings.

Can you fit the original tps ?
how are the original tps units calibrated? trim pots on the ecu ? or mechanical ?

I have never had much to do with rover ecu's so dont do anything based on what i say ( i doubt you would anyway )

[Philip A]

Thanks for the input.

Re the original TPS. The mountings are very different but this is not insurmountable. I have not yet removed the new TPS from the manifold because it has tight 5.5MM bolts holding it. Who ever heard of 5.5MM bolts??? ( I will go to Jaycar and see if they have a spanner)So I do not yet know what the new TPS connection to the shaft looks like. The old one is a raised blade which fits in a slot in the end of the shaft.
The ECU is tolerant of the starting voltage and apparently automatically compensates ( I guess it remembers the last start up voltage). It can be between about .05 and 0.5 volts so I guess the best way is to connect the new TPS and see the voltages.
I called Bosch and the tech guy suggested that an additional resistor may work, but as I thought about it, you are correct and it may reduce the range. ARRRGH!!!!
Reagrds Philip A

[Philip A]

I bought a 5.5 mmm spanner and dismantled the motonic TPS from the throttle body.
Worked out I could modify the throttle shaft to use the old TPS.
Currently am in the middle of the mod, which involves cutting off the end of the throttle shaft, cutting a 2mm slot in it, spacing out from the original mount by 12.5 MM with a piece of nylon bread board.

At least I feel I am now getting somewhere.
WHY, do they make EVERY rubber hose on the new manifold a different diameter from the old manifold????? Has science progressed that far???
Regards Philip a