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1978 Jeep J10 Fuel Injection Install

1978 Jeep J10
Verne Simons
| Senior Editor, Jp
Posted January 29, 2014

50-state-legal, bolt-on fuel injection

Long about 1991, pretty much all Jeeps came directly from the factory with fuel injection installed on their engines. This change was for good reason. The later years of carbureted Jeeps are a horrible mixture of old-school fuel delivery technology plugged up with some rudimentary computer controls that in theory should have made these Jeeps run cleaner and better. Its not, and they don’t run nearly as well as Jeeps with fuel injection. These computer-controlled carburetors are known for their lack of reliability and generally have a negative reputation now that 20 to 25 years or so have passed. Other earlier carburetors are simpler, and while most are more than adequate for on-road use, not all do well in the hills. Some work pretty well off-road if they are tuned properly from the get-go, but this is the exception rather than the rule. The fact is you’ve probably heard someone recommend fuel injection as a cure for any and all carbureted Jeeps. In order to get a Jeep with a carburetor to run well off-road takes more than just having the physical parts. You need to know how to tune that carb for off-road use, or have access to someone who knows how to tune it. Fuel injection allows for a much more plug-and-play situation where the fuel and air mixture going into your engine is controlled by a computer that knows what it is doing (computer-controlled carburetors are much less forgiving). A good fuel-injection system can compensate for altitude as well as other driving conditions. Also, fuel injection generally works much better off-road than some properly tuned carburetors and is much more robust with regard to changes in weather, altitude, and wear-and-tear.

So what does one do to get fuel injection on a Jeep if all it currently has is a lowly carburetor? Well, one of the most common routes is to adapt a relatively simple, mass-produced, factory-available fuel-injection system in place of an old cranky carburetor. The name Howell Engine Developments is practically synonymous with Jeeps and reliable fuel injection conversions. For years this company has offered several different fuel-injection systems for Jeeps. Some of these systems use a GM-based throttle-body injection system. It just so happens that the GM TBI system for a GM 4.3L V-6 can be adapted to fuel an AMC 258 I-6 or Buick even-fire V-6. Also the GM TBI for 305ci V-8s and 350ci V-8s can easily be adapted to an AMC 304ci V-8, AMC 360ci V-8, or AMC 401ci V-8. To this end, Feature Editor Simons has been running a Howell TBI system on his Buick V-6-powered ’49 Willys for about five years without issue after fighting another aftermarket injection system for years. This meant when the carburetor on Simons’ ’78 J-10 died a slow death, it was an easy choice to move to Howell’s 50-state-legal TBI kit for AMC V-8s. Follow along as we install the system and enjoy its reliability and consistency.

Step By Step

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  • Here you can see Howell Engine Development’s 50-state-legal TBI fuel-injection system for ’72-’92 Jeep 304ci, 360ci, and 401ci AMC V-8s (PN K247JPV8, $1,400) installed on the AMC 360ci V-8 in our ’78 J-10. We’ve been running this system for a few months now, and it is seamless as compared to the old carburetor. No more hard starts or vacuum leaks. On-road throttle response is better, and off-road the engine runs like a champ despite any angles we encounter.

  • The first step in installing the Howell TBI fuel injection is to make sure it has a good base to sit on. The Pig Truck’s intake manifold looked as though it had been on the AMC 360ci V-8 since the Jeep rolled out of the factory. We decided it was prudent to pull the intake and toss some new gaskets at it. This gave us time to clean any carbon out of the lifter valley and the bottom of the intake manifold. A new valley-pan gasket and intake gaskets will make sure the AMC 360ci V-8 remains happy for years to come.

  • Installation of the Howell TBI kit makes the air-injection pump obsolete. This will clean up the engine compartment of the Jeep significantly. This also means removing the diverter valves and air tubes that bolt to the factory exhaust manifolds. To do this without causing exhaust leaks, you need to plug the holes in the exhaust manifolds with shorter 9⁄16-18 bolts and copper washers. You can sell your functioning emissions parts to other fullsize Jeep enthusiasts. These parts are hard to find and necessary for emissions compliance in several areas…unless upgrading to the Howell system is a possibility.

  • Once we got the cast-iron intake back in place (with help from a friend, its heavy), we started addressing the factory vacuum lines, ports and switches. The Howell system has a different vacuum-line system than the carburetor that we removed from the truck. All connections are laid out in the instruction manual, as well as the new CARB sticker that also comes with the kit. Once installed, the CARB sticker and fuel injection should keep the emissions authorities off your back when the time comes.

  • After we bolted the included adapter plate to the AMC intake, we were able to install the GM TBI unit in place of the two-barrel carb. We were able to remove the vacuum port (arrow) and close it off with a 1⁄8-inch NPT plug.

  • Next, we installed the hard parts of the TBI system to the adapter on the intake manifold. Another minor stream we needed to cross was that the Howell TBI system needs a return line that routes unneeded fuel from the throttle body all the way back to the gas tank. Luckily for us, Piggy came from the factory with a fuel filter with a port for a return fuel line. We just checked the factory return line to make sure it was in good shape and hooked it up.

  • Our Howell kit came with a wiring harness that has several GM factory-style Weatherpack connecters. Also the harness is well labeled so that all connections are easy to make. Relays for the fuel pump are also integrated in the very comprehensive wiring harness that also is wrapped in factory-looking wire loom. The installation instructions are also very detailed and clear.

  • GM TBI, like most fuel-injection systems, requires relatively high fuel pressure to operate properly. The factory AMC fuel pump is a low-pressure mechanical unit that is good for sending fuel to a carb but is useless for the Howell system. Howell addresses this with its kits by supplying an electric inline fuel pump, a couple of fuel filters, and a mechanical fuel pump block-off plate for the AMC engine. We mounted our fuel pump and filters on the framerail of the truck. The multiple filters help protect the fuel pump and the injectors, which don’t tolerate junk in the fuel well.

  • Another important part of the Howell TBI system is the O2 sensor which uses the exhaust gases to adjust the fuel/air ratio during driving. We were able to sneak in and drill a hole and then weld in the supplied O2 sensor bung in one of the exhaust’s downtubes without tearing any of the exhaust out of the Jeep.

  • The brain of the TBI system is a refurbished GM CPU that has been flashed by Howell. We chose to mount our CPU under the dash with an industrial grade hook-and-loop from our local hardware store. The wiring harness also has a few system fuses and wiring for a check engine light, both of which need to be mounted inside the vehicle’s passenger compartment. Unfortunately, our Arizona summer heat is apparently too much for the adhesive on the hook-and-loop. We’ll either have to come up with a Plan B mounting system or add more hook and loop to the computer and dash.

  • One difference that we noticed between this 50-state-legal TBI kit and the kit on the Buick V-6 in our ’49 Willys is that this system needs vehicle speed information. It gets it from this sensor that we installed between the speed cable and speedometer drive gear on the Dana 20 T-case. Then all we had to do was plug in the sensor to the supplied wiring.

  • Piggy came with an aftermarket 14-inch air cleaner, but the paper filter was tired and worn. We hit up our friends over at Airaid for a new 14 x 3-inch SynthaFlow oiled air filter (PN 800-351, $57.90). Howell says that you can reuse the factory V-8 air cleaner if you live in a cooler climate. We don’t, neither does The Pig, and our factory air cleaner assembly is long gone anyway!


Howell Engine Developments
Marine City, MI 48039
Phoenix, AZ 85050