from the ECU case to ground?

and engine to ground, as in a manifold or something?

 

I have been doing some measuring on mine and have re-read some of the posts.

TPS wires
(G) Green = 5v from ECU
(Y) Yellow = Return (this is NOT ground but returned via the ECU)
(R) Red = Vref (wiper)

Disconnect the battery and unplugged TPS from loom and disconnect ECU check continuity to earth on all 3 connectors in the loom they should be open circuit (NO reading). THIS IS IMPORTANT. DO THIS CHECK FIRST.

Next re-connect the ECU and battery and leave the TPS disconnected. You should measure 5volts to ground with the ignition ON.

Re-connect the TPS and measure the voltage from Y to R at idle you have about 0.3V and FT 4.7V.

Post back your measurements.

 

Yes on both counts do this first before you tackle my last post

Do you have Skype?

 

uhmm, ive never used skype, but i can get it up if need be.

its 10 pm in my time zone right now, plus its raining and i have no garage.

are you saying that the green wire is 5v source? interesting. f thats the case, then the new TPS is probably fried, or ive got a short in that wire somewhere.

 

Yes thats correct

Do not assume anything is fried lets use an analytical approach.

Measure ECU and engine to ground then go through what I said in post #42

 

M90, Warrjon is correct. That is the wrong pin for 5v: See my earlier post, this is an excerpt:

"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."

Greg

 

wow, warrjon. i was chasing my tail until you told me that pin 20 was 5v supply. so heres the verdict. at the engine bay i read nada from the green wire to ground. when i cut the green wire (pin 20) at the ECU harness and measured to ground i achieved 5.00 volts! when i reconnected this wire and measured it in the same spot at the ECU harness i only measured 0.12v. so thats a definitive short! ill be rewiring pin 20 to the engine harness and to the IAT. WHOOO!

 

Great stuff, it IS nearly always the harness! May I suggest, while you are at it, that you do the same test for all the 5v supplies from the ECU (as laid out inmy much earlier post), and also test for the continuity of the wires sending the return signals back to the ECU from the ATS, CTS and TPS? Chances are there are other bad wires.

Good for you finding it though!

 

i would like to. do you know what the other 5v supply pins are? my schematic is too vague.

 

alright, ive got voltage to the TPS and IATS. the TPS is putting out 0.6v at idle awhich is nearly twice what it should be and 3.89v at WOT which is a volt too low. possible TPS issue?

 

some advantiges of standalone ECU, just turn the knob, etheir lean or rich, takes couple .02 of a second, even while driving.

i use a wideband AFR gage. to know what is happening!

center consol switches for other functions.

DARN ! had a time getting in the car NO door handles,pic.

bottom of door is round, seems most guys got Square corners! DUH!pic

pic of dial indicating wheel roundness(wide wheels can be vibrate),unless perfectly round, surprising how many are not! pic

A lot comes back to me when i actually work on the car!!haha

 

ive never agreed with your wheels or your chop top, but damn. that car has all the right looks about it. i see your wideband mounted there on your console. is that an aeroforce scangauge?

 

Where is the air bag pump located on a xj8

 

THX ,M90, much appreciated!

and williegeorge,,,,,, HUH???

 

whats with these random guys posting in random XJS threads? this dude and the dude in the bumper delete thread with the VDP. lol

 

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.

 

If you are measuring the TPS output at the TPS end (not the ECU end) it might be. BUT, set the idle to 0.32v first and then remeasure.

 

i took the tps off and at rest it read .47v see my beware mustang tps thread.

 

Greg,
Are you positive about this? I just went through rebuilding my harness last week. If you undo the horsehair on the ECU plug, there is only one YB wire going into the ECU. The wiring diagram in the ROM confirms this.

Then if you trace that YB wire out to the passenger's-side inner fender where the harness comes out, again there is only one YB wire. This wire then goes into the TPS connector where it is mated to a second YB wire under one of the plugs; this wire then continues on to the CTS.

The ROM confirms this setup, one YB wire "connected" (won't say "feeding" or anything just yet) to one pin of the TPS AND one pin of the CTS together. Check the emissions annex of the ROM.

This is why I always maintained this YB wire is the 5v feed and not the "signal" since it is spliced into both sensors.

For now, M90 congrats on tracking down your problem, I recommend undoing all the wire wrap under the hood and replacing all the wires that need it exactly as they came from the factory, and for now don't worry about what is sending what where and what's the signal and the feed. Just get everything back to stock configuration, then work from there.

Darel

 

this is horseshit. got the new TPS on, the voltage is a little too high, but its running just as rich as before. wont hardly run, and i think i just fouled out all 12 of my new plugs again. the vacuum advance diapragm is broken, but still. it should at least idle.