1. home
  2. how to
  3. Fuel Injection for 258-c.i. Jeeps

Fuel Injection for 258-c.i. Jeeps

Bolt mo' power onto your 4.2L Jeep

If you own an '81-'90 4.2L (258ci)-powered Jeep, there's something lurking behind your local Mopar dealer's parts counter that will interest you. It's called the Mopar Performance Jeep 4.2 Liter Multiport Fuel-Injection Kit, and as its name implies, it includes everything you need to easily upgrade your carbureted engine to quality fuel injection. And it doesn't matter whether the engine is mated to a manual or an automatic transmission.

Some of you may chuckle at our use of the word "easily," but based on what we saw as we watched Matt Dinelli of Attitude Performance in Arlington Heights, Illinois install the kit on a customer's '89 Wrangler, the kit does indeed simplify the conversion to a level of being almost fun. Developed by Hesco for Mopar, we're told the kit is a duplicate of the system found on '91-'95 4.0L vehicles. Part of the reason it installs easily is because of the easy-to-follow, detailed, illustrated instructions and a helpful installation tip sheet that covers frequently asked questions. The kit's overall parts content seems to also have been scrutinized to allow for a significant amount of assembly to be done at the factory, so you don't have to.

The benefits of the system were immediately clear as we drove the finished product about 50 miles after the install. Smooth acceleration throughout the powerband, great cold-starting manners, and performance unaffected by angles were some of the obvious benefits.

The following photos will give you a basic idea of the kit's major components and their installation during the assembly phase. Obviously, you should read and follow the instructions provided with the kit. Dinelli was installing the kit on a freshly rebuilt 4.2L engine that was prepped in accordance with the kit's installation instructions. This meant that a number of components already had been removed, like the power-steering pump, air-cleaner assembly, production emissions controls, carburetor/intake manifold assembly, fuel pump and lines, radiator, fan, distributor, windshield washer bottle, charcoal fuel canister and exhaust manifold oxygen sensor.

The kit has a street price of approximately $1,900 and requires about 13 hours to install. Clearly, the kit doesn't jump out of the box and right under the hood, but considering the significant upgrade of the install, we think that's a respectable timeframe. Once installed, the powertrain control module takes 15 to 30 minutes during first use to "learn" the best settings for your engine. You will notice improved idle quality and acceleration after this learning period. From there on out, float bowls and needle valves will be a thing of the past, and your rig's performance will be the envy of your 'wheeling friends.

What it Fits
The Mopar Performance Jeep 4.2 Liter Multipoint Fuel-Injection Kit is designed for stock, unmodified, well-maintained '81-'90 4.2L (258ci) engines. Installation on engines with modified camshafts, increased compression ratios or engines that are in poor mechanical condition is not recommended. This kit is emissions-exempt in California under C.A.R.B. executive order D265-7. The tune-up and engine service procedures are the same as a '94-'95 4.0L Wrangler. The kit will not allow for the use of the stock tachometer, but includes a wire in the harness and directions for installing an aftermarket unit. The kit is designed to allow for the function of the "check engine" light, so fault codes can be read.