Temp Sensor solution

Ok, here we go.

This just came to my attention looking at the pinouts I posted.

I had previously thought the ECU looked for a signal from the temp sensor, and then switched the fuel maps accordingly.

But if you look at the schematic, the temp sensor is directly connected to the fuel pressure control solenoid.

What I'm figuring is that rather than change maps, it ups the fuel pressure.

If this theory is right (I can't see it being wrong) just disconnecting the temp sensor from the pressure regulator, rather than unhooking it from the harness, and you should revert to normal not rich mode.

Give me a few hours to get home, and I'll know for sure.

sounds like a good theory. Let us know what you find out for sure.

that's some interesting stuff... i know something connected to my temp sensor is giving me my trouble. maybe it could be the fuel pressure solenoid? i'll have to look into it as well.

i forgot to swap my temp sensor with you when i was at the meet. it would have been a quick check to see if yours was running ok.

Someone stop me from fitting a blow through turbo carb setup.

Well, here's what happened, reminds me of old school christmas lights ... one bulb goes out and you have to check every bulb to get them to light up again.

Temp sensor failed, even after clearing the codes, it comes right back.

So it tells the pressure control regulator to kick it up a notch.

The high flow pump I have was already a bit much for the stock system.

It ran pig rich until the O2 sensor crapped out (it was used)

So not only was it pig rich, it was being neutered too.

BUT ... silver lining here ... I might try and rig up a WOT switch to the pressure control solenoid and just clip the wire from the temp sensor. That way it will richen up under wide open, but stay normal the rest of the time. Maybe even wire a switch in too, so if I need it I can have a switch operated choke.

that's what i've got right now. a switch to the temp sensor. turn off the sensor and you're super rich. leave it on and save gas. it's a compromise. but at least it's easy to do. but it sounds like you just need a new temp sensor. they're only $40 from nissan and worth the hassle of switching on the fly.

i've tried to splice a potentiometer between the temp sensor but even at 10K ohms (the max it shows on the fsm for a cold car) my a/f mixture doesn't richen up. it only seems to richen when there's NO signal from the temp sensor. i bought a 50k ohm pot yesterday to see if that will do the trick.

i'll check out my fuel pres solenoid this weekend. hopefully that is the culprit and i can finally have a regular running car. hopefully you can buy these from nissan. hopefully i can FIND the damn thing.

just follow the wires from the temp sensor. One goes to the ECU, the other to the pressure solenoid

Are you sure you actually need the fuel pressure module? My car (UK spec) dosent have one, the signal from the temp sensor only goes to the ecu and nowhere else?
I wonder if your cars can run with it totally disconected? (not the temp sensor) or are your ECU's different to ours and require this info?

we do run different ECUs. I know the UK spec don't have O2 sensors, so a lot could very well be different.

Well, I unhooked the pressure control solenoid thing, and it really did seem to make the car idle better. I still have to swap out the O2 sensor. I was going to do it yesterday, but it was pouring rain and I was getting pretty soaked.

If the rain holds off today, I'll swap the sensor and actually take it out for a drive.

i'm such a lazy ass. i still haven't fooled with my fuel control solenoid. i did take a look thru my fsm. it may be that i've got some vacuum lines mixed up.

i guess when everything is just 'good enough' they tend to stay that way.

was it only the US S12 that got the fuel presure solenoid or the MKII S12????

It may only be the US models. My S12 is an Mk1 and it has the fuel pressure control solenoid.