i have an engine swapped rig, 87 f250 with a 96 PSD. the tach is intermittent. im just wondering where all the locations on a 96 engine, where the tach could be potentially hooked up.

 

I've never heard of anyone every doing it. CPS is digital to the computer and most would be some sort of scanner that would work with the OBDII port.

 

What tach are you using?

 

its the 87 tach,

 

What did you do with the tach sensor wiring from the IDI harness?

What harness(es) are you using under the hood?

 

i didnt do the swap so i have no idea, i have the 96 PSD on the engine and the rest is the 87

 

You're going to need to find out, or figure out, exactly how this thing is rigged up. The differences between the two generations of truck, AND the control systems/mechanisms of the two engines, are vast. If this was not done right, it could be a money/time pit.

The tachs are nothing similar. In the case of the IDI, there's a sensor on the injection pump that simply pulses with each IP gear tooth, and the tach is calibrated to that. With the PSD, there's a cam position sensor on the block that feeds an irregular signal to the PCM, which in turn uses it not only to determine ignition timing, but to provide a signal to the PSD tach. Completely different technologies. The tach you have could be picking up some stray magnetic signal. The original tach sensor could be just hanging loose under the hood somewhere, picking up some stray magnetic signal and activating the tach you have. Or the OP might have been some Doc Brown mad genius who was able to put the PSD tach guts behind the bricknose gauge face, and calibrate the needle just so. Without some information/documentation from whoever did the swap, or some very detailed forensic inspection/investigation of what you have, you're stabbing in the dark.

In short, such a swap could be the result of some careful planning and ingenious fabrication, or a complete cluster-blank.

 

time to awake this again...

I have finally nutted up and bought a PSD cluster, took out the tach gauge. used a hot knife to shape it into my bricknose cluster. The 3 prongs on the back where to short so i used a soldiering iron and extended the prongs to make proper contact. ( actually looks factory besides the pointer doesn't match). Checked resistance on each prong through my soldiering job and have no resistance. I know have the signal wire from the bricknose (green) from the back of my cluster, ran down into Pin #50 white/pink out of my ECM of the powerstroke, which is labeled "tach signal to cluster"

Issue being now is that at about 2000 RPMS ( I know this by watching my scanner ) is that my gauge only shows 500 RPMS. I can see that my CPS is working correctly as ...again i can watch it on my scanner. I have a 12v supply to my cluster that is gone through a regulator and distributed to each gauge at 5v's, Zero resistance from ground to negative battery terminal. What else could i be missing here?

is there a way to test the PSD tach to make sure it is working correctly? Or to check the signal that the ECM puts out to the tach?