Bob_The_Normal

Well as expected I was getting a 5v drop across ground and the thermosensor lead, with the thermosensor hooked up...

So what do I do to rewire it?

Cut the plug off, splice a wire to each lead, run one to the ECU wire and splice it in (II can identify which one, it has a white stripe on it)... run the other one to where? I'm guessing to a 5v source? But where can I find a 5v source to splice into? The ECU somewhere?

Could I just run it straight to the pos lead on the battery?

The idea is that I have a circuit going from the battery and grounding at the ECU isn't it? And the thermosensor is just a resistor, just has to be in the circuit.

Can anyone clarify all this stuff for me? I know all the basics of electricity and circuits but I have no experience.

--Gary

Kenteth

Be careful with the v5 source, its not protected. Short it and you'll be looking for a new ecu.

It is a resistor, but im pretty sure it runs off the 5v reference signal, not the 12v from the battery. What happened to the stock wiring?

Plus, running more than once sensor with a single 5v ref may cause some funky voltage drop and cause false readings at the ecu.

Bob_The_Normal

Yeah didn't think too much about the frying thing... I was thinking of running it off one of the fuses in the engine compartment but then I don't know the repercussions of drawing current from one of those when it might not be made to handle that extra little bit.

Hopefully someone will know which one I can run a lead off of maybe?

I don't know what happened to the original wiring, the harness is in fairly good condition but it did seem very brittle... so I'm sure it snapped somewhere... I can't measure continuity across the ecu pin to either of the plug pins...

Anyway I was trying to figure it out today and still couldn't... I cut the plug off and spliced the wires... then I couldn't think of where I could draw exactly 5v without effecting other things... so I gave up and went on to trying to figure out what got bent and won't let my headlights go up. ;(

--Gary

Kenteth

well, to do it right, you'ld have to run new wire from the correct pins onthe ecu. I don't really think that there is any easy ghetto way around this one

Bob_The_Normal

*sigh*

That's actually really easy... if it wasn't for one thing... the FSM doesn't say where that other lead comes in at... just says it's one pin... obviously isn't heh.

Any idea how to find out what pin it is?

--Gary

680RWHP12A

whats up?!
your car is running, with your track record, id leave it alone!
its running!!

havent been blocked in by the rain lately? nice., huh? im sick of this weather!!
nice day today though

Bob_The_Normal

Hey Robert,

i was gonna call you 'cause I need to get this thing smogged sooner than later, as you know... and if it wasn't for this thermosensor making it run way rich I'd probably pass... and actually you're right about my track record... there's some broken stuff now... I'll tell you about it on the phone heh.

No use if the car is running but isn't legal!

I swear I'm cursed... running on some hard times right now, but I'm way too addicted to the rotary to give up completely... I might have to get out for a little while though. =/ I would have already but I doubt anyone will pay me what my car is worth to me for it... =(

--Gary

680RWHP12A

yah, ill hook you up with the smog guy ,dont worry....ps , whats up with the second gen section? dam
call me

NZConvertible

Sounds like haven't looked at the wiring diagram. Assuming you're talking about the coolant thermosensor, the green/white wire goes to the ECU, and the black wire is a ground shared by numerous other sensors (plus the ECU itself) that eventually terminates at the main EFI ground on top of the engine.

Bob_The_Normal

Doh... now it comes out... I don't know how to read the wiring diagram! =(

But... so you're saying I just need to ground the black plug and the ECU feeds the 5v from itself?

I don't know anything about it, I just assumed the ECU wouldn't be the source of the power... but hey if it is that's awesome, no need to be pulling 5v's out of my ***. ;D

Does that also mean I can ground just about anywhere from the black wire? (Like say, onto the negative terminal... or onto the back of the engine, with the condensor?)

--Gary

HAILERS

The green/white wire should go to pin 2I on a series four. That is the source of voltage. The other wire on the water thermo sensor should go to a brown/black wire. That brown/black wire is spliced into several other brown/black wires and is the ground for the sensors. They all eventually tie into pin 2C on the ECU. That's for a series four car.

It SEEMS to me both the green/white and the brown/black wire should still be there at the water thermo sensor, or laying nearby.

Bob_The_Normal

Doh, forgot to mention S5 N/A... yeah that'd be useful haha...

Well I DID find the ecu pin diagram, it's in position 2E for the green/white wire...

Funny enough I looked for 2I and the FSM says it's "Sensors" and it's an output! I bet that's what I need to splice into to grab that 5v.. but that kind of sucks since I'll be cutting open the wire that goes to all the sensors..

Oh well I guess... not like this wiring harness is all that great anyway heh.

But that solves the problem... I run both wires through the engine bay into the ECU and splice them at their proper locations, white/green to the 2E pin and the black/brown to the 2I and that should do it right?

Sound right?

--Gary

HAILERS

If your car is a series five DISREGARD the wire colors and pins I described. I don't have a series five manual to look at right now ( I do have series five on disk but that disc ain't here right now). I'll look at the disc later, but that disc does not have series five wire colors in it. PLEASE disregard what I said if your looking at a series FIVE. It works the same but the pins and colors are probably different.

Bob_The_Normal

Ah darn!

Well the leads coming OFF of the thermosensor plug (I cut it out) are a GREEN/WHITE STRIPE and before I couldn't identify the other one... looked like dirty black or faded black... but from what you said I'd definately say it's a BLACK/BROWN STRIPE.

And the lead at the 2E pin is a GREEN/WHITE STRIPE wire... so I have that one... so by deduction the BLACK/BROWN STRIPE must be the + wire that goes to the 2C (which in the S5 FSM is labeled as the output for the sensors 4.5-5.5v "Vref (Power Supply)" (F1-80 in the S5 FSM).

If you could still look at the disc later I'd really appreciate it! What discs are those?

--Gary

HAILERS

Ok. The green/white must have stayed the same on series four and five.

The other wire goes to ground. The design is for it to go to the same ground as is used by other sensors such as the tps, boost sensor, afm, etc. On a series fouir, that wires color is brown with a black stripe i.e. brown/black. On a later series four, like a 88 model they used a pure black wire instead of the brown/black configuration.

So its possible that that other wire is just black. We're going to have to have someone else who is reading this post to tell us what pin that ground is on the ECU.

Bob_The_Normal

Alright, well if no one else answers I'm gonna try to run the wire as soon as I get some time to... and hopepray that they're the right ones! hah..

--Gary

HAILERS

The other wire goes to either 3A, 3B, 3C. Sorry, no series five wiring diagram to prove which. Either should do. All three are grounds.

WAYNE88N/A

Whoa, guys, there's some misinformation going on here...

The water thermosensor is NOT a resistor, and it does NOT receive 5v from the ECU. It acts as a reverse thermocouple, that is, it produces its own electrical current inversely proportional to the amount of heat it receives (much like our O2 sensors, but backwards). Accordingly, this voltage is tiny (.4 to 1.8 volts is spec, the hotter the coolant, the lower the voltage).

The ground wire is there only to complete the electrical circuit (it could just as easily ground itself through the pump housing, but with the small voltages it produces, the ECU receives a "calibrated" signal compared to the other sensors using the same electrical potential, or ground in layman's terms).

The important wire in the circuit is the green/white, it should be in tip-top shape to carry a good signal to the ECU...

Bob_The_Normal

My bad, I'm new to this... I measured 5v across the green-white (while plugged into the ECU and on) to the negative battery terminal... so I thought this mean the ECU was feeding 5v?

--Gary

WAYNE88N/A

Look at it this way- that little bugger only has two wires going to it. If one was 5v power and the other ground, how does the ECU receive its signal???

Besides, a cursory glance at the wiring schematics will show that there is no 5v going to the sensor

Bob_The_Normal

Ok well I wired it up... ghetto style...

Trying to reset the ECU and it isn't resetting... whaaaat the hell... I took of the neg terminal and let it sit for like 15 minutes, pushed the brakes and everything... I'm thinking that ground is now grounding the entire ECU through that one wire! =/ geez.

I'll go pull it off and see what happens... apparently if I don't ground it to the neg terminal the ECU will never lose power.

Not sure on all that though, I'll be right back (this was the first I thought to pull off the ground wire I made... it grounds at the back of the engine)

--Gary

WAYNE88N/A

DO NOT ground that black wire- that wire is part of a "gang" circuit that grounds THROUGH the ECU. In other words, none of the ground wires on these 5v sensors actually go to a "real" ground, but go to the ECU (which then provides the ground through yet another circuit).

Grounding that thermosensor wire may lead to the same problems that some guys have when they ground the black wire at the boost sensor- the car will run like ****, because now the ECU has two different ground potentials to choose from...

Bob_The_Normal

Argh! Thanks Wayne!! I would have never figured that out... so I need to splice this black wire into the ECU ground?

Does it matter which one? S5 N/A there are three of them!

I'll take a look at it more tomorrow.

--Gary

WAYNE88N/A

If the original black ground wire is still intact, find a way to reconnect it to the thermosensor, the way it was from the factory. This will effectively put the sensor back into the electrical "loop" shared by the other sensors, which will make the ECU happy...

If it's impossible to wire everything up to OEM spec, just cap off that black wire, and don't ground it. Hopefully the sensor will then find a ground through the housing, although that may skew the input voltages to the ECU...If you must do it this way, read the sensor's input at the ECU pin (see FSM wiring manual for pin #) to make sure the signals are near spec, or it'll mess with your fuel scheduling. How much? Who knows, lol

NZConvertible

Really? I always thought is was just a thermisto, since there's a temp vs. resistance chart in the FSM. Plus all the thermocouples I've seen generated far less than 1V, usually only a few millivolts.

That's what the NA ECU wiring diagram shows, but on the Turbo ECU wiring digram there's a link between the ground wires on pins 2A and 3C, meaning there is a direct path to ground for those sensors. I have no idea why they're different.