Jeepers And Creepers Throttle Body Upgrades
The Jeep 4.0L engine found in TJs, XJs, ZJs, and WJs is a trusty powerplant, and the '91-and-newer high-output versions make respectable power for a long time if well cared for. We recently ran across an easy mod that can provide a quick power boost and help renew an aging throttle body on these engines.
The stock throttle body bore is 55mm and a common upgrade to increase intake flow, and ultimately power to the wheels, is to bore the aluminum body to 62mm to match the diameter of the bore in the intake manifold. Combine this with a free-flowing air cleaner and muffler, and you can unlock some performance for not a ton of money.
Jeepers and Creepers in San Francisco, California, has been boring the Jeep throttle bodies for almost 10 years so they know the 62mm bore mod is a valuable upgrade. However, they started seeing the results of aging throttle bodies: housing cracks and wear at the throttle shaft bearings (which can result in leaks and poor idle).
They solved all these issues by introducing a billet machined throttle body bored to 62mm that is a bolt-in replacement for the stock unit. We performed an install on a stock '97 Jeep TJ in about an hour and a half and also dropped in one of their new throttle body spacers while we had the induction parts off the engine. Here's a brief tour of the install.
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7. The electrical connectors and throttle linkage were reassembled. With the new spacer in place, it's a good idea to recheck throttle cable for any binding or limits to its travel.
After reinstalling the air intake tube, we fired up the Jeep and it settled to a quiet idle so we took it for a short drive. We found the off-idle response to be smoother overall and the mid-range power to be more responsive by the seat of our pants. Next up would be an air cleaner upgrade and we'd enjoy more benefit by letting our 4.0L breathe better through a 62mm bore.