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  #1  
Old May 11th, 2020, 07:33
alexbrown64 alexbrown64 is offline
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MPG Gauge for OBD1 Jeeps

A lot of guys are chasing bad fuel economy on their modified Jeeps. We know the modifications don't help and already poor performer when it comes to economy. Being OBD1, we dont have an overhead fuel computer, and scan gauges don't work.
Anyway, my modified 95 4.0 XJ in Australia is returning around 12.5 mpg. I was hoping better numbers.
To help me work out what modifications, including driving style would help, i needed a mpg gauge, showing real time data for the OBD1 Jeep.


A lot of research on ecomodder websites led me to a local guy that has built a touch screen mpg gauge for our Jeeps (still in trial phase).


The wiring only takes a basic 12v and ground for power, and 2 inputs which come from the ECU. You pin into the VSS wire and any of the injector wires.


After some initial setup and calibration, which can include a few tank fills and a test drive, the system uses the vehicles speed/distance, tank capacity and microsecond of injector time per litre of fuel to show a lot of different parameters on a color screen such as Distance to Empty, real time MPG, average MPG etc..



This system is still in development, but has been returning 99% accuracy levels.
The system can be swapped between mpg and litres/100kms.


Just thought i would share a pretty cool mod that can really make life a bit more economical.


I am currently installing the gauge in my '95 RHD 4.0 XJ. Will report back with more pics and details over the coming weeks. Sorry, the pics of the gauge are set to metric, but it is simple to switch over. Once i have it up and running in the truck, i will swap it over and show real time data in mpg.



Cheers,







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  #2  
Old May 11th, 2020, 07:40
alexbrown64 alexbrown64 is offline
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Re: MPG Gauge for OBD1 Jeeps

The Jeep the touch screen fuel economy gauge is going into.


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Old May 12th, 2020, 08:13
alexbrown64 alexbrown64 is offline
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Re: MPG Gauge for OBD1 Jeeps

Initial fitting today. Lots of time due to Covid 19 lock down.
Anyway, spliced into #1 fuel injection line, and VSS.
Switched power was stolen from my stereo.
Brackets fabricated and computer placed in a location that made it easy to program, read, and be unobtrusive.




Initial thoughts were great. Its only a small screen, but all data is there. RPM's were spot on straight off the bat. Hot idle fuel burn was set for around 3/4 gallon per hour, and needs to be set for 1/2 gallon per hour for initial set up.
Only problem is the Speedo function. Its bouncing. I am trying a few things to work this out, but the owner of the system wants to come down with an oscilloscope to look for a dirty signal.
All in all, very happy with the initial product. Will be amazing for pre-update Jeeps when up and running.
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Old May 12th, 2020, 23:01
alexbrown64 alexbrown64 is offline
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Re: MPG Gauge for OBD1 Jeeps

Fixed the speedo bounce. My speed sensor is attached to a "yellow box" electronic speedo calibrator. The yellow box then sends the modified signal to the PCM. I do this so that i don't have to change speedo gears at regear/tire size changes. Just adjust the yellow box to make speedo corrections. Anyway, the MPG computer didnt like it. I spliced into the output wire directly at the speed sensor and ran that to the new gauge. Works like a charm. So now i have to start the calibration process before i can get live data. Once up and running, i will also have a "Distance to Empty" function. It works well with over size fuel tanks like mine, as you can input any size fuel tank into the configuration.
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Old May 13th, 2020, 08:44
Jim Malcolm Jim Malcolm is offline
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Re: MPG Gauge for OBD1 Jeeps

Pretty cool. Peaked my interest. I'm guessing you "press a button" to tell it that you're refilled? So much you could do with enough hardware. AW4 control instantly jumps into my mind. I started on a Touchscreen to mount in the steering wheel to control lights, hvac, etc, since I can't reach the dash when strapped into a 4 pt harness but well, that XJ still isn't done and honestly may be given away here before too long. Life... I'd be interested in updates as they progress into production.
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Old May 26th, 2020, 06:14
alexbrown64 alexbrown64 is offline
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Re: MPG Gauge for OBD1 Jeeps

Gauge is working well. It has a wizard that calibrates the machine for you. The very first time you use it, you just set the injector microsec/litre (or gallon) so that your hot idle is using roughly 2lt/hour. When you fill your tank again, it will ask you how much you put in. It will then calculate the difference and calibrate the injector setting. I am now officially running at 18.2 lt/100km, which is 12.5 mpg. Now that i have the gauge sorted, i will be looking at some mods to get the mpg up a bit.



Fitting a new NTK O2 sensor soon, giving the tires a bit more air, and pulling the ZJ clutch fan out and swapping in a Hayden XJ clutch fan. Ive got an MT2500 OBD1 scanner so i can go in and check out everything. It all looks pretty good except for a lazy O2 sensor. I also reset adaptive memory using the unit.
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