any electrical engineers out there?

hey guys- i'm in need of some information that i can't find in the chrysler xj service manuals that i have. I need to know what sort of signal the ecm/pcm in a '99 xj gets from the motor in order to decipher engine rpm. I'm swapping in a diesel and i'm not sure about where exactly the 4.0 gets its' information on this matter so i'm not sure about how to go about wiring up a sensor (or what sort of sensor i might need) in order to replicate this signal. if anyone out there has information on this, i'd appreciate you passing it on to me. if not, any ideas on where i could look? I'm also asking at several diesel forums and 4btswaps.com, but i thought maybe you guys would have some different insight. thanks.

CPS?

Yeah. Specifically what range of voltage (assuming it gets a positive voltage signal) does the ECM receive from the jeep crank sensor in order to actuate the tach.?

I believe it is a 5 volt/0 volt TTL pulse signal on 91+ XJs but I'm honestly not sure, it may be analog. You should see a pulse for each opening in the flexplate/flywheel. The ECU uses this to tell what position the crank is at and also calculates the RPM based off it. The data is then forwarded as a message to the instrument panel via the CCD bus (on 97+ XJs anyways.) If you know of a place to get info on the CCD bus protocol you can rip a CCD bus transceiver chip out of an old 97+ TCU, ECU, ACM, or IP and combine it with a small microcontroller to send your own tach signal based off whatever sensor you want, else you could mill the proper slots into the flywheel on your 4bt and find a way to mount the CPS on your transmission bellhousing.

http://www.kolumbus.fi/juha.niinikoski/CCD_bus/ccd_display.htm may help you figure out what data to send to the IP via the CCD bus since the example code includes portions that decode the same info.

Thanks, kastein. That's exactly the kind of info I was looking for. I can probably deal with something like that.