BEWARE the mustang Throttle potentiometer upgrade. when i finally got voltage to the TPS, i was reading 0.47 ohms at idle and 4.1v at WOT with the kickdown screw turned completely out. which means its too rich at idle and far too lean at WOT.

so i checked the resistance at idle. about 570(ohms? kohms?)
then i went to advance auto and checked the other BWD brand TPS (part # EC3019) and it read 400, which would be FAR too rich at idle properly. so i went to the advance auto across the street and it read 520 (still too rich). then i went to autozone and their duracrap (part # TS215) read 800 (too lean). so beware the mustang TPS from the local autoparts store.

ill be going to the ford dealership tomorrow and trying one of theirs.

wow, they wont let you say "steal her ship?"

 

The TPS should have the following specs
Green to Yellow across the pot = 6KZ
Yellow to Red Vref
Idle = 400Z
WOT = 5.6K

The voltages this will give you are
Idle = 0.34V
WOT = 4.7V

Also important is how far and in what direction the pot turns, The throttle turns about 1/4 of a turn so those resistance values need to be over 1/4 of a turn

 

Just did some quick calculations to get the same voltage out of the 3.9k TPS you will need

265Z at idle will give 0.32V
3.7KZ at WOT will give 4.7V

One thing to be aware of is that there will be 50% more current flowing in the circuit I do not know if the ECU can handle this or not.

 

so was i getting 570Z at idle?

if thats the case then the TPS i found with 400Z would have had the perfect idle mixture. i assumed there would be more resistance at idle to get less voltage.

 

It's a little more complex than that. The potentiometer forms a voltage divider, we will call green 5V A return yellow B and wiper Red C

All measurements are referenced from B the return.

Reistance between A and B is 6000Z (6KZ) at 5 volts so the current is 833uA, we will use this later.

If you put C in the middle there is 3KZ on each side of the wiper. so the voltage so the voltage out is 3000Z x 833uA = 2.5 volts

Ok so lets look at your 3.9K TPS at 5volts the current is 1.2mA or 1200uA, so the voltage with C in the middle is 1950Z x 1200uA = 2.5 volts.

I can hear you saying how can the voltage be the same when the resistance values are different - this is because Voltage is a product of resistance and CURRENT and as you see with the second TPS the current is much higher.

The point here is you can use a TPS with different resistance value if the RATIO of minimum to maximum resistance is the same. The only IF is IF the ECU can handle the additional current flow.

You see Voltage does not fry electronic circuitry current does. Lets put that into perspective.

Take a 12volt car battery and put your voltmeter across the terminals and you will read about 13.5volts, but if you drop your spanner across those terminals WATCH OUT as the spanner vaporises.

Ok with the meter across the battery there is only minimal current flowing a few microamps maybe less, but with the spanner across the terminals there would be hundreds of amps and if you could measure the voltage with the spanner across the terminals it would be less than a 2volts. The current frys the spanner. This is what happens in electronic circuits.

 

i would say that Warren, does know his stuff!!!!

my ECU used a universal potentiometer, from Radioshack $8. !

ECU just needs a movement of any type and calculates automaticly, SDS engineering?

 

damn, i googled that SDS the other day and didnt find anything.

 

Here you go

Simple Digital System EM-5

 

Warren, does this mean the Mustang TPS he was using was okay after all? This is all going over my head now....lol

 

the one i was using was definitely not ok. .47v at idle is not ok.

 

Coming in late.

What does it read if you remove it from the throttle pedestal?

Cheers
DD

 

.47 volts. thats the absolute at rest voltage.

 

Now I'm going to have to recheck mine because it's making me paranoid! I was thinking it measured .38 or .39 at idle...can't remember what WOT was.

 

did you ever get yours wired up correctly?

 

Yup, made a big difference too.
I've been babying it, treating the engine like a newly built break-in. Today I brought it briefly up to 70mph with no problem. I pass over a 1.5 mile long hill that is 11% grade and it didn't even notice.

 

wish mine ran like that. mines still screwed.

 

Dude I really, REALLY know exactly how you feel! I messed with mine for months! I was soooo close to pushing it out of the garage and setting it on fire!

I don't know how many plugs I fouled out, I've got a box full of them. That's why I figured I had nothing to lose by replacing all the wires. I didn't know where the break was or which one...so I just replaced them all!

 

mine ran fine until i pulled the TPS off and put the new one on. ive been chasing ****ing grimlens for days.

i drove this freakin turd 180 miles home, and it ran like bitter **** but it didnt run rich and it didnt foul plugs. something has changed since then and i cannot figure out what the hell it is.

 

Okay...hang on a minute. You know the engine itself is good, this is electrical.
Everything was fine until you pulled the TPS? That gives you a good idea of where the short occurred. There are 3 wires coming from TPS. 2 wires to the CTS and 2 to the ATS, plus 2 wires to each of the micro-switches. Plus I believe there is a ground wire in there somewhere.

You already know those wires were questionable just by looking at the so called "repairs" made by the previous owner.
The wires from the ECU to where it comes out of the fender are usually protected and are in good shape, but once it exits into the engine compartment it's a different story. Oil, heat, etc. This is where I started.


If this system has a bad ground, it will cause it to run rich! Just something to keep in mind.

 

I am not famillar with mustang TPS. If the pot at minimum is zero ohms it should be able to be adjusted for the correct idle operation. It all depends on what minimum and max ohms are.

There may be another way around it - can you post Z values for 3 points green to yellow and yellow to red idle and wot for the mustang TPS.

Basically any LINEAR pot with the correct values will work (like a balance or tone control pot for an amplifier) if it was apporx 0 to 6kz over 1/4 of a turn. Be careful with this the pot has to be linear, volume controls are logrithmic and are not suitable.