MoparMarv

Im suspecting a cps issue with my truck. No charge no speedo and the isspro tach doesn't work. I have not been driving the truck much and this just turned up suddenly th last time I drove it. Short of visual inspection of wires and gap is there any kind of troubleshooting to verify a bad cps? From what I read the PCM can cause similar issues along with grounding as well. Also where is a good place to get a cps?

j_martin

At the connector, with the CPS connected,
The black wire with a light blue tracer is sensor return, PCM pin 4 (ground)
The tan wire with a yellow tracer is 8V supplied by the PCM pin 7.
The grey with black tracer wire is the signal. It pulse between about 5V and ground as the engine is cranked. Might be hard to see with a meter, easy with a scope.

There's 3 suspect connections between the CPS and the PCM. One is top front of the engine (3 wire). One is under the intake manifold near the rear of the engine (10 wire) and the other is the PCM connection. In addition, the sensor return wire is spliced to all over in the harness, and the 8 volt wire is harness spliced and also goes to the VSS. If the 8V supply is current limited (should be, but who knows) repairing a short to ground or a shorted sensor should restore the voltage.

I think the speedo works if the CPS fails. Common item is the 8 V supply from the PCM.

Good luck.

MoparMarv

Just to close this one out. I ended up changing the cps and that was a no fix. I then found my PCM had no power to pins 3 and 9. The wire at the fuse able link was broken. Spliced it back together and everything works.

j_martin

Just a note on this.

The fastest and least expensive path to repair is proper diagnostics.

Had you probed the pins and found 5V missing (it was missing for sure) you could have gotten to the repair without buying a CPS and probably waiting for it.

KRB

Thats why this forum is so helpful. We learn from other's misfortunes!

Dave F

First rule of proper diagnostics; When in doubt consult the DTS Brain Trust!btw where is this fusable link located? (my truck is a 93)


edit; found that info here"https://www.dieseltruckresource.com/forums/engine-compartment-wiring-diagrams-t301830.html?&highlight=crank+sensor+gap"

Me n the dog are headed out to the shop.

j_martin

Get your dog a stool. He'll find the burned link with his nose.