Update: Data logging temperatures or sensor voltages or signals (to start with). Here are some ideas, places to look and hardware & software links to start with:
Say you want to monitor the temperature of ANYTHING in the jeep, oil, coolant, transmision fluid....This little guy (temperature sensor) is easy to use, very accurate, and waterproof. Features a high-level linear output of 10 mV per degree F, typical accuracy of ±0.4 degrees F at room temperture, and a range of 0 to +300 degrees F (-17 to +150 degrees C, with U3/UE9). $49, at:
http://www.labjack.com/details.php?prodId=36&category=5
The USB data aquisition device itself, LabJack U3 is $99, for complete specs and pdf manual go to:
http://www.labjack.com/labjack_u3.php?prodId=25
The LabJack will read voltages directly from parts like a TPS, O2 sensor, MAP sensor, CPS (I think it will read the DC spike or impulse of the CPS, but you would need to check the signal time and measurement times to see if it is fast enoguh to see the CPS signal. Might depend on RPM! But I think the LabJack is much faster than the engine top RPM)
You might need a resistor in the circuit to lower the peak voltage for the U3 model (it reads up to 3.6 volts max) but the U12 will read +/- 10 volt signals. The U12 is probably the better choice at $129.
http://www.labjack.com/labjack_u12.php?prodId=27
Software (some is free) and how to write software downloads at:
http://www.labjack.com/labjack_u3_downloads.php
Other thoughts:
You might need to use resistors on the data collection wires to increase the impedance (need high impedance) of those lines in order to avoid disturbing the signal strength, voltage that the ECU is measuring to run the engine.
Also the digital I/Os of the LabJack might be able to sense (if configured properly) the DC impulse signals of the CPS, and fuel injector inputs (?) as on/off state signals, and thus be recordable to a laptop.
Discusion forum for Labjack users:
http://www.labjack.com/forums/index.php
Other possibilities:
A pressure transducer can be used to measure oil or fuel pressure.
Something to wet your appetite. Here is someone in the discussion forum working on
RPM to Analog?, Converting engine rpm signals to analog, already:
http://www.labjack.com/forums/index.php?showtopic=102
RPM off an Ignition coil:
http://www.labjack.com/forums/index.php?showtopic=521
Spike protection, Automotive:
http://www.labjack.com/forums/index.php?showtopic=474
Where I found this!
"I used a frequency to voltage converter with limited success. I was not too happy with it overall. I use my LabJack to datalog RPM, manifold, pressure and several temp sensors along with A/F on dozens of different cars. I had to add a bank of dip switches to the F to V converter to change the resistors so it would read in the proper freq range. That worked OK, and then I just ran the crank position sensor to the CNT and that works great. Granted the CPS is not an even signal, depending on the application but a 60-2 or 36-1 or 36-2 tooth sensor can be scaled to give an accurate RPM. So if you have a CPS I would give that a try."
That is all I have time for right now, but this should help get some of you would be doityourselfers started with looking into data aquisition for the older Renix and OBD-1 models.