Jeep JK 3.6Liter Unichip Project
Unichip started working on Jeeps with the YJ and the XJ about 15 years ago and has been working on lightly modified daily drivers, rock crawlers with stroker kits, and SC and turbo monsters ever since. We have PnP kit on XY’s, YJ, TJ’s, and JK’s including the MY11 JK that the reflash guys can’t do because the OE locked the ECU…
Our MY11 JK kit is identical to our earlier JK kit since the only change to the factory set up was locking the ECU code… the engine and the performance data in the OE ECU didn’t change, so our kit didn’t change. Getting into the MY12 JK with the new engine was something we were really looking forward to. Time to buy a JK!
We got a JK in February 2012 and dove right in… the first step with any development project is verifying the electrical schematics match reality by using a good old fashioned oscilloscope to test the circuits we’re going to tie into. After we verified those signals, the next step is connecting a Unichip and ensuring it’s electrically “invisible” to the OE ECU… in order to ensure there’s no footprint left in the OE computer, the OE computer must not see any altered signals from the Unichip’s installation.
This process doesn’t have anything to do with changing the signal’s values… that’s something we’re going to do and that the OE ECU really can’t see because it expects those values to change… for example changing the MAP sensor signal’s value from 0.50 volts to 0.52 volts is something the OE ECU expects to see during normal operation and is the key to what we’re doing.
The biggest challenge during this step is really ensuring the extra circuitry we’ve added doesn’t cause any signals to arrive too early or too late at the ECU during the startup and shut down sequences as you change the ignition key… even a few milliseconds can cause a Check Engine Light. Once the Unichip electrical connection makes for a happy OE ECU, the tuning process can start.
Initial tuning isn’t about making power but learning about the OE engine management solution… not the lines of code in the OE ECU but what’s really happening in the engine.
- What sort of AFR does the engine operate at?
- When does the engine transition from Open Loop Fuel System management to Closed Loop?
- How much fueling change will the OE ECU accept without throwing a CEL?
- How much ignition timing can we add without generating a CEL? Not yet looking at how much power can we make but looking at those things we’ll need to change to make that power.
The good news the JK responded like we expected and there’s lots of room to play. Now the R&D project splits into two different paths… calibration development and harness design.
Designing a Harness
Just because we can tune a vehicle, doesn’t mean we can make a kit… we have to be able to create a harness so JK owners can install the kit at home.
Our design goal for every harness is reliability, installation simplicity, installation simplicity, some more installation simplicity, and above all it’s got to be simple to install! Since we’ve already identified the signals we want, our challenge is finding the most reliable and easily accessible points in the factory electrical system to pick up those signals so we can manipulate them.
For the JK, we tie into the three sensors using male/female connectors that are easily accessible… here’s the harness…
You can see the harness on the JK in the installation instructions…
Bolt-on Part Testing and Tuning
The next step in all of our testing is putting various bolt-on parts onto the vehicle and building unique calibrations for each of the combinations… that is a Brand X CAI, a Brand X CAI and a CatB exhaust, a Brand X CAI, headers, and a CatB exhaust. Then we pull all those off and do it again with Brand Y, then Brand Z, etc…
We don’t do all that work because it’s fun putting parts on and taking them back off… the calibrations for the different combinations look very different.