no tach after trans swap!

[sltlytwkd]

So I did a major swap in my 12v 47rh 94'. It is now a ppump 24v with a 4r100 . I am still using the stock wire harness and PCM. The only sensors I am still using is the tach, oil press, coolant temp, and TPS otherwise I completely deleted the wires all the way to the stock PCM plug. The stock trans part of the harness is still intact and tied on the side. The grounds, power wire, starting circuit, and the rest of the cab and truck harness is still stock. I am using a PCS controller for my trans, and need a tach signal. My dash nor the PCS will give me a tach reading. I completely unhooked the PCS controller and still nothing. I have checked everything, I had the whole harness in my lap checking for any damage. The tach sensor does not have any resistance between any of the wires, and I set the air gap to .049" and also tried .040". Still nothing! I just want to make sure I'm not missing something before I blast a $100 sensor at it for nothing! Is there any other tests I can do first?? Sorry for the novel, thanks in advance!
Willie

[BigPapa]

Is this in the '94? I'm guessing you're using the 12V ESS. Which damper are you using, the 12V or the 24V?

[sltlytwkd]

Yes, I'm using the stock 12v sensor with a 12v fluidamper and relocation bracket. The only odd thing is I am only 4.6 volts at the ESS plug, but the service manual says it's a 8 volt source?

[BigPapa]

12V's aren't all the same. Got to know what year the PCM and ESS are from.

'94-'95 uses an 8V supply, PCM pin 7, Orange wire.
'96-'98 uses a 5V supply, PCM pin A17, Violet/White wire.

[BigPapa]

There was a thread here a while back about ESS voltage. From what I understand he ended up using 12 volts and it worked fine. I imagine the sensor can handle the 12volt fine but if you have an 8volt '94-'95 sensor and a '96-'98 PCM putting out 5volt it may not be enough.

[sltlytwkd]

The entire harness, all sensors, and PCM is original to the truck. The only thing different is the engine block, head, and trans. Yes, it's the orange wire in pin 7. I ohmd pin 7 across every other pin in the harness and ground. Nothing crossed, so it's not like there's a short or rubbed through spot in the harness. And, since the tach don't work the alternator won't charge either. Silly dodges.

[BigPapa]

It's either the sensor, the wiring, the PCM, or any connections in between. I have been hearing of more issues with the older PCM's lately.

I'd suggest applying 12volt to the Orange wire and see if it reads. If not, try to find another sensor to try. From there, I would try a PCM.

[sltlytwkd]

Ok I guess I will try that tonight, thanks!

[BRE]

I will throw this out there. The same voltage reference that feeds the ESS, also feeds the VSS (vehicle speed sensor).


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[sltlytwkd]

Yes, that it does. The VSS is not hooked up due to having the different trans. Does the PCM need to see something through the VSS in order to "complete" the ESS circuit?

[BRE]

I wouldn't think so no.


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[sltlytwkd]

Well I tried putting 12v on the orange pin 7 wire. Nothing happened. Now I ordered a new sensor for tomorrow and will try again!

[sltlytwkd]

Update! New ESS, still don't work!

[BigPapa]

Wiring, connectors, or........PCM.

[sltlytwkd]

I unplugged the PCM, took a pick to all the the terminals to snug them up a bit and it didn't change. I finally got a signal to my PCS controller but my dash tach nor alternator work yet. Im working on getting a buddy to lend me his PCM!