Maxed Out Offroad


1 Since our engine came with most smog and fuel-injection components when we purchased it, we only needed the ECM and wiring harnesses. This ECM and harness are from a '98 Grand Cherokee. A setup like this will cost a few hundred dollars, which we think is a good deal. But it will require hours to figure out what goes where, not to mention installing it.

2 This is the step that gets complicated, especially on late-model vehicles. The trick is figuring out aspects of the management system such as vehicle speed, TPS, mass airflow, and upstream and downstream O2 sensors. Then there's the auto shift relay, injector drivers, and a number of other electronically controlled components to sort out. Lastly, you must determine what not to use, such as electronic door locks, the ambient temperature sensor, and keyless entry. We are still working on the left harness plug-in, but luckily the harness was intact, so we just needed to plug and play. Make sure the OBD-I or -II plug-in is also included for engine diagnostic checks.

3 With the wire harnesses on a workbench, inspect them for damage and clean them. A sanitary install of complicated harnesses is impressive, so you might as well go the extra mile. Keep in mind that over the years some of the wire's protective covering may have become brittle and cracked. At this intersection of wires, the split plastic loom has separated and the factory electrical tape has worn away. The loom should not be installed without being repaired.

4 After inspecting the wires, we rewrapped the damaged loom with a quality electrical tape, and then wrapped that with a self-vulcanizing rubber tape. This will not only protect the wires, but waterproof them. Split-braided sleeving is also a great way to protect the harness, which we will use over the rubber tape, making our harness bombproof. There are many ways to repair and re-cover wiring, but sometimes the large factory end plugs won't allow coverings like heat shrink-wrap to slide over them. Wrappings and split coverings are best.

5 We wouldn't attempt this without the factory manual. It will give you the correct color codes for the wiring and where each is meant to go. The book comes in handy when deciding which wires can be left unconnected and which can be removed or left unplugged. Keep in mind that the newer the system, the more complicated the conversion. On some vehicles every electronic gadget is monitored or run through the ECM. If one wire is improperly connected or missing, there could be problems with the performance of the vehicle. For ease of installation, once it's determined where a wire or plug goes, it should be numbered, along with its respective component.

6 We recommend finding an intact system. This way the electrical connections will plug right into the respective components. And most factory plugs are specific, meaning they will only plug into the right component, unless many components are the same like fuel injectors. The difficult part of the conversion will be determining which wires the engine needs and which aren't so critical.

The scrap-yard Chrysler 5.9L engine bolted in our Scratch Built Scrambler project already had most of the components like fuel rails, injectors, and smog-related parts. But it lacked the electronic control module (ECM) and wiring harnesses, so we called Jason Hulbert, owner of Maxed Out Off-Road in Klamath Falls, Oregon. Hul-bert's family also owns a six-acre salvage yard filled with everything a 4x4 enthusiast dreams about. He sent us an ECM, an engine wiring harness, and everything we needed to get our project up and running.

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