Question about sensors and voltage

[MustangGT1990]

I have always read/been told that the reference voltage for most sensors (Throttle position sensor, coolant temperature sensor, EGR position sensor) is approximately 5 volts. Is this true? Also, my understanding is the computer supplies this 5 volts, is that correct? When I measure mine with the KeyOnEngineOff that is what I get, 5 volts reference voltage for all of the above mentioned sensors.

*IF* this is correct, here is where my problems start. If I put my T-5 in NEUTRAL and measure the same voltages they read 2.45 volts. My understanding was they were supposed to read 5 volts reference voltage at all times. I know this sounds stupid but if my T-5 is in 1,2,3,4,5, OR R they ALL measure 5 volts. BUT if it is in NEUTRAL they all read 2.45 volts.

What I need to know is if the reference voltage is supposed to stay at 5 volts at all times?

Thank you!

[Godslayer]

I'm pretty sure they are suppsoed to be close to 5V. I have a nice reference here but it has been packed away because I am moving. I would think it should stay at 5 in neutral also.

Are you having problems with something or is this just for informational purposes?

Anyway I will be done moving by the end of the week so if no one else helps you out... I'll dig the book out.

Bob

[MustangGT1990]

I am having problems.

When I push my clutch in my idle drops and it barely runs. When I let the clutch out it immediately dies unless I keep the RPMs up. Then it will idle. If I push the clutch in and put my T-5 in a gear (1,2,3,4,5,R) the engine will usually die unless I keep the RPMs up.

I have tested the neutral position sensor on the T-5 and it is working properly. I have also tried a new clutch position sensor and it made no difference. The code I get is neutral position sensor circuit failure (67).

I have measured the reference voltage all the way from the computer to my neutral position sensor (light grey/red stripe) and I have 5 volts. As soon as I reconnect the harness to the sensor my voltage drops to 2.45 volts. BUT I tested the sensor and it is working so I disconnected it and jumpered the 5 volt reference over to the signal return wire (light blue/yellow stripe) and it immediately dropped my voltage to 2.45. So, if my reasoning is right I have a problem some where in that light blue/yellow stripe wire. It is the signal return back to the computer (pin 30 I think).

Also, since the reference voltage drops from 5 volts to 2.45 volts it ALSO drops the reference voltage to my throttle position sensor and my egr position sensor and my engine coolant temperature sensor (and who knows what else) since they ALL share the light grey/red stripe wire for their reference votlage.

So, essentially when the tranny is in neutral or the clutch is pushed in the voltage drops to 2.45 volts and my engine idles like crap if at all.

[Godslayer]

Hmm... that is interesting. Have you checked the signal return wire back to the computer for continuity?

I will go dig my book out now and see what it says about your code.


According to this book you should make sure your A/C and heater are both off when you run the test or it will throw this code.

If that's ok then do this:

Check voltage @ pin 30 of the ECA. If the voltage is greater than 1 volt, inspect the wiring and connections between the neutral safety switch and pin 30 of the ECA. If the wiring and connections are good, replace the NSS.

If the voltage is less than 1 volt, and the vehicle is not equipped with A/C, replace the ECA.

If the vehicle is equipped with A/C, check the voltage at pin 10 of the ECA. If the voltage is greater than 1 volt, trace and repair the short to voltage in the A/C clutch circuit. If the voltage is less than 1 volt, replace the processor.

I assume by "processor," they mean ECA.

Hopefully that will help you. Keep me posted on this problem.

Bob

[MustangGT1990]

Ok, for everyone who has helped and gave their input I really appreaciate it. I FINALLY figured out what my problem was. When I rebuilt me engine I noticed some of my wiring and connectors were looking pretty rough so I bought a new wiring harness from Ford Racing. Well to make a long story short, the connector for the bottom end part of the wiring harness (connects under the MAF and goes to the O2 sensors and low oil sensor) is not made right. It connects up just fine BUT the light blue/yellow wire is supposed to make a loop and reconnect to a black/yellow wire that goes back to pin 30 on the computer. Since the new harness was made wrong the 2 wires were never connected so the circuit was open. Hence the error code 67. So, I put my old lower harness back on and it works like a top now. So, now I'm going to modify the new harness to make it work right. Oh well, we live and learn (usually the hard way).

Thanks for everything!

[PKRWUD]

That's the harness for an automatic tranny. They sold you the wrong one.

[MustangGT1990]

That's what I was thinking but the kit came with 2 different lower harnesses, one with a black connector and one with a white connector. Since I could never find a mention of auto or manual I ASSumed that one might be auto and the other manual but apparently not. Anyways I finally figured out where the circuit was open and now it is fixed. YEAH!

It's been a year and a half since I parked it so I have really missed driving it.

Self-inflicted problems are always the worst cause you feel like such a goof when you finally figure it out.