Need Help Adding MPG Gauge to 1990 Vehicle

[Irons]

Hi everyone,

I have been reading the forum for a few weeks and would appreciate some advice. I have a 1990 Range Rover that I plan to convert to E85 or E100. First I would like to add instrumentation to get instantaneous MPG and possibly a few other engine measurements (tach, vacuum, volts, etc.) to ensure that the truck is running at its best and to measure performance as the ethanol to gasoline ratio is increased.

The truck has an OBD I port, EFI, an existing road speed sensor, and plenty of room and access to install hardware and wiring. What would be the best avaiable option to get an on board system to provide instantaneous MPG?

Thanks in advance for any help.

[Daox]

Welcome to the site Irons. You'll want to do a search for "mpguino". Its a device designed by one of the members here and is avaliable for a very reasonable price (you must solder it up though). Good luck! Instrumentation is very important when doing this sort of stuff, and its a great place to start.

[Andyman]

If you want to try a really simple way to measure fuel flow rate, you can connect a dwell meter (intended for setting points in older cars) to one of the fuel injectors. One wire goes to the positive battery terminal and the other goes to the fuel injector wire that is controlled by the fuel injection system. The reading on the meter will be proportional to the fuel flow but you won't know exactly how many gallons per hour you are using unless you have some way to figure out a ratio of fuel flow to degrees of fuel injector activation. Typically you will use about 2/3 gal/hr at idle if you have a 4.0 liter engine. To calculate MPG, you can divide MPH/GPH.

[wagonman76]

This is cool. I actually have a multi-function analyzer that includes dwell, got it from the Salvation Army. If I figure something out I could just stick a temporary label to the meter. Meanwhile I do have parts ordered for a mpguino.