OK, so I just got my Megajolt installed and running. The only thing is my tach doesn't work anymore. My truck is an OBD-II 1996 Ford Bronco with 351W engine. I have read all the posts about the tack adapter and such. I had hoped I could just hook up the IDM circuit from the EDIS to the IDM circuit in my EEC. That did not APPEAR to work.
However, after messing with it a while, I plugged in my OBD-II logger and bingo, it reads RPMs. In other words, the IDM signal from the EDIS is driving the tach in the EEC and it appears to be correct. However, my dash tach is not working (fuse is good).
Any ideas? I assume the tach on the dash must have seen driven by a different coil fired circuit than the dash in the PCM. However, I have no idea where that circuit might be.
Help.
Baxter
Weird Issue with Tach
Moderators: JeffC, rdoherty, stieg, brentp
Okay, I figured this out and thought I should share what I learned.
Indeed, the IDM circuit from the EDIS module will properly drive the IDM/Tach signal on a Ford EECV PCM. On my PCM, the input is labeled IDM. The same input is labeled "tach" on EECV PCMs with the EDIS built in.
The tach in the console, however, is not connected to the engine computer at all. Rather, it ties directly into the ignition coil firing circuit. I have no idea exactly where it tees off from the ignition coil firing circuit, but the wiring diagram I reviewed makes clear that it does. I went ahead and connected pin 5 (the coil circuit) from the unplugged ICM plug to pin 8 (Coil A) of the EDIS8 module. Since the coil circuit is disconnected from the ICM (which is no longer in the truck) and also disconnected from the original coil (which is also no longer in the truck) I would not have expected this to do ANYTHING. Low and behold, my tach is working again, so that circuit does in fact tee off to the tach somewhere in the wiring harness. Off course, it reads 75% low since it is only reading off of one coil. No worries. I ordered the tach module and will get it working correctly next week.
Baxter
Indeed, the IDM circuit from the EDIS module will properly drive the IDM/Tach signal on a Ford EECV PCM. On my PCM, the input is labeled IDM. The same input is labeled "tach" on EECV PCMs with the EDIS built in.
The tach in the console, however, is not connected to the engine computer at all. Rather, it ties directly into the ignition coil firing circuit. I have no idea exactly where it tees off from the ignition coil firing circuit, but the wiring diagram I reviewed makes clear that it does. I went ahead and connected pin 5 (the coil circuit) from the unplugged ICM plug to pin 8 (Coil A) of the EDIS8 module. Since the coil circuit is disconnected from the ICM (which is no longer in the truck) and also disconnected from the original coil (which is also no longer in the truck) I would not have expected this to do ANYTHING. Low and behold, my tach is working again, so that circuit does in fact tee off to the tach somewhere in the wiring harness. Off course, it reads 75% low since it is only reading off of one coil. No worries. I ordered the tach module and will get it working correctly next week.
Baxter
Just wanted to report that the MJ is correctly driving the EDIS8 on my '96 Bronco w/ 351W. I had an issue getting the SAW command to the EDIS unit, but when I connected pin 7 to the trigger sensor and PIP/SAW shield (and nothing else) then everything started working as advertised.
Thanks. Awesome product.
Thanks. Awesome product.