The MS45.1 cars like the ZHP came with wideband O2 sensors in the pre-cat locations.
The problem is, the DME only reports the voltage of these wideband O2 sensors, and not the AFR or lambda.
But I've calculated the formula that will convert the pre-cat O2 sensor voltages to lambda, and then its an easy calc to get AFR (lambda * 14.7 = AFR).
So if you want to know how rich or lean you are running at any time, even during wide open throttle, pick up yourself a cable and a copy of Renovelo Bytelogger (http://www.renovelo.com/bytelogger/). Then go for a drive and log some data, and make sure you are logging your pre-cat O2 sensor voltages, either bank 1 and/or bank 2.
Once you have your log, which will be a nice neat CSV file, open it in Excel and use this formula to give yourself a lambda value for those Pre-cat o2 voltages:
=0.684562+(<Pre-cat O2 Voltage>*0.205987)
Or if you want to go straight to AFR:
=(0.684562+(<O2voltage>*0.205987))*14.7
These calcs will get you an AFR reading that should be pretty much spot on.
Enjoy!
PS Bytelogger is an awesome diagnostic trouble code reader too. It not only reads and clears all trouble codes, but it reports additional freeze frame data that was captured at the time the code was triggered. So you get a data logger and a code reader/clearer in one package, I highly recommend it.