i thought i would start a new thread since the old thread was 7+ pages of troubleshooting.

i just watched my jag idle for 5 minutes. by the time it was done the plugs were so foul i couldnt get it started again. issues are no voltage to TPS or IAT. CTS gets 5 volts.

TPS has been replaced with the mustang TPS. ECU has been replaced. TPS is good. wires from TPS, IAT, and CTS all have continuity and theres no break in them according the the ohm meter.

this thing runs 100x worse than when i had the old, bad TPS.

anyone have any ideas. im giving this V12 another week before im lumping it for a 3800 series II.


update* now have voltage to TPS and IAT.

new symptoms are that the jag can consume 5 gallons of fuel in 60 minutes of idling.

replaced injector harness: no change.

 

My car was doing the EXACT same thing. No matter WHAT I did it was running so rich it would foul plugs out in minutes. (I still have a big box of brand new, fouled out plugs in my shed)
I changed ECU's, and the TPS to the Ford unit, also with no change. Finally I said screw it, and replaced the wires to the engine one at a time. I spliced into them where they come out of the fender near the firewall and traced them out one by one, replacing as I went. Now it runs great!

I suspect that several things were happening. Some of the sensors were getting intermittent signals from breaks in the wires, and I think the wires were shorting across and giving weird signals/impedance.

Seriously, even if you just open up the looms and replace the TPS, CTS, ATS and the wires to the microswitches on the capstain I think it might take you a full day, and might be all you need to do. It certainly made a HUGE difference in mine!

 

that CANNOT be the issue. theres got to be a reason why the TPS was getting voltage before i replaced it and now its getting 0.003v
TPS is good, wires have continuity. theres some FUBAR **** going on here.
it ran when i got it home. i drove it 180 miles. it doesnt run anymore. theres something else to this.

 

Because if you short a 5volt wire to ground you will measure 0volts

 

I'll have to think on this for a bit...
On mine, I was getting voltage in all 3 wires of the TPS. Drove me absolutely NUTS.

 

thats what i needed to hear. right there. ill be tracing pin 19 back to the engine bay tomorrow, along with pin 20, pin 7, and pin 5.

 

If you have a couple rolls of wire, cut it as it comes out of the ECU and run it along side the car to where they're supposed to go. That way you KNOW you are getting a direct connection!

 

i was thinking the same thing. but i dont have a couple of rolls of wire. and i live in a dead consumerist town that only sells solid core wire and speaker wire.

 

Speaker wire will be fine for testing just don't leave it in the engine bay on hot surfaces or the insulation will melt.

 

I was going to say the same thing as Warren, speaker wire will work fine, this is just for testing. If it works, you know where the problem is!

 

100% agree. Jury-rig the wires and then you'll know for sure.

 

im making some headway everyone. the CTS gets 5v. the TPS gets no voltage and the TPS gets no voltage from the red wiper wire to the yellow high side wire. the CTS and TPS share that same yellow wire. so if i read at the yellow wire of the TPS and the red/blue wire of the CTS i get 5v! there has to be a short in my wiper/red wire for the TPS. im gonna go look at my schematic again. and see which pin it corresponds too, then jump the pin to the tps and see if i get 5v. if so, then ill have the jag running in no time flat..... after i replace all 12 plugs :P

 

the wire has got continuity. its reading 0.001 ohms from the ECU harness to the TPS pigtail. which can only mean that theres no output voltage from the ecu. right? WTF?!? Jamey just had his XJS running with this god forsaken thing.

update. pin 5 & 19, which are the ECU pins for the CTS get 5v. pin 19 which is the yellow wire, and pin 7 which is the red wire gets 0.14v........??????

fried ECU again?

 

what if i just spliced the blue/orange wire from the CTS to the wiper arm of the TPS? i would effectively achieve the 5v i need? it just wouldnt be coming from pin 7 of the ECU. it would be coming from pin 5 instead.

thats all i really need, isnt it?

 

Not the way I see it. Your yellow/black is 5v supply to all 3 sensors, that Blu/Org coming from the CTS is a direct resistance feed back to the ECU. If you splice anything into that you'd be lucky for anything to run.

Did you try putting the old TPS back on? Could be that the new TPS is no good. At least it ran with the old one. Don't necessarily need to redo the whole swap, just unplug the new one and plug the old one back in. If you're back to the way you were before then Bob's your uncle.

If that doesn't work time to run some temporary wiring over the roof and see which circuit is giving you trouble.

 

i dont think so. if i read the blue/orange CTS wire and ground to the manifold i get 5v. if i do the same thing with the yellow/black wire i dont get any voltage. the blue/orange has to be 5v supply.

also, if yellow was 5v supply then the throttle potentiometer wouldnt function correctly because the green wire wouldnt get any voltage. the wiper arm of a potentiometer is always the power wire. other wise, both the high and low sides would have to be power wires.

 

You could be right but then how does the CTS measure resistance if it sends out 5v and then dumps it to a common ground shared with 2 other resistors? I know on the wiring diagram it's labeled as a ground but it just doesn't jive in my mind.

All I know is the blue/orange wire from the CTS is a home run, if it worked spliced in Jaguar wouldn't have spent the money on an extra wire. I don't think you'll help your case splicing blue/orange into anything.

 

i dont understand this either. theres no reason they wouldve run a seperate power to the wiper of the TPS.

all i know is that the blue/orange wire grounded with my multimeter produces 5v while the yellow does not. and if yellow was power supply then only one half the the potentiometer would be getting power. the green wire would recieve no voltage. the red wire of the TPS has to be 5v supply to the TPS while the blue/orange wire has to be 5v supply as well.

a curious note, according to my multimeter, blue/orange is a negative wire, although it carries 5v. could it be a circuit with a positive ground, such as an austin healey, while the TPS circuit has a negative ground.

that could possibly explain the necessity for an extra wire.

 

Just in case we are at cross purposes, according to my diagram the pins on the ECU North American emissions spec ECU and the wires to them have different colours than UK spec. The pins numbers read RHS to LHS (opposite direction to a book) and numbers start at the bottom row RHS. My diagram says for North Amercian spec:

Pin 5 feeds 5v to the CTS wire colour code UC (do not know what that codes is, sorry).

Pin 7 is the return from the TPS wiper and is colour code YB wire. This carries the variable voltage from the TPS to the ECU.

Pin 19 (top row first pin on RHS) is the other, non-wiper, wire from the TPS and is also colour code YB that also is joined to the return from CTS. So both these YB wires from the TPS and CTS go to the same pin. BUT the colour code on the wires to pin 7 (TPS wiper voltage signal indicating throttle position) and pin 19 is the same, even though they seem to have separate functions. So knowing which YB wire you are testing is important, as they must carry different voltages.

Pin 20 is 5v feed to the TPS and the air temp sensor (code YK).

Pin 21 is the return from the Air temp sensor (colour RU, but I do not know what that colour code is either).

So these five pins between them cover all the inputs and outputs from the ATS, CTS and TPS.

Greg

 

im talking about the yellow and black wire that runs from the high side of the potentiometer all the way back to the ECU. it doesnt change colors. the red wire changes from red to yellow/white.