I’m in the process of swapping a late-model fuel-injected engine in my truck, but I’m not sure where I should place the computer. Should I put it somewhere that will keep it protected from the elements, such as inside the cab, or is it OK to put it under the hood? I’ve done a lot of searching but there’s no really clear answer.
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Where you need to put the computer depends a lot on the computer itself. While you are somewhat limited by the length of the harness you use, the main priority should be whether or not the computer is weatherproof. If the computer doesn’t appear to have a sealed case, such as the computers used in TBI Chevys, then place it in the safest place you can. Usually this means inside the cab, but if you have an open-air vehicle like a Jeep, then we’d recommend putting it up high somewhere under the cowl. This will keep it protected from the elements and reduce the chance of it taking a dip if you decide to dive off in a big mud hole one day. Conversely, if the computer case appears to be well sealed and the connectors have O-rings and other weatherproofing features like late-model Chevy LS computers have, then placing it under the hood is just fine. While mounting the computer to the bottom of the oil pan probably isn’t a good idea, anywhere reasonably high on the firewall would be fine.
As a rule of thumb we like to use the donor vehicle’s computer location. If the original location was inside somewhere, then that’s where you should put it on your rig. If it’s under the hood, then anywhere in the engine compartment is just fine. In underhood situations, we would still recommend a location that’s going to be reasonably clean and dry. Mounting it in a location where it’s going to be subject to heavy spray from the front tires or down low where it could be submerged should be avoided if possible.
Lastly, you should always try and mount any computer with the connection between the computer and the harness pointing downward, not flat or upward. The reasoning here is that you want to avoid any situation where water could pool around the connector seal and eventually work its way inside. By keeping the computer vertical or at least angled, gravity will draw any water that reaches the connection away from the seals, reducing the chances of the seals being compromised.