Problems I Ran Into
Along the Way

Of all the dumb things, I ended up breaking my factory coolant temperature switch with a majority of it still inside the intake manifold. At this point, I really though game over for me and was ready to put the TBI on hold while I extracted the intake/exhaust manifolds.

As lazyness would have it, I decided to attempt to extract the remaining switch with the intake manifold still on the engine. Using a Dremel and a cutting bit, I worked off what I could try very hard not to damage any of the manifold threads. This action seemd to work well but also caused the back end of the switch to fall into the water jacket. Argh!! After about an hour of working with a coat hanger and tweezers, I was finally able to get all the pieces out.

In the end, I was able remove the broke switch with minimal damage to the threads (nothing a little RTV couldn't fix) on the intake manifold and I was able to continue with the installation of the Howell TBI.

Another problem I encountered was that I accidentally broke a plastic nipple on the charcoal canister while attempting to remove a vacuum line. (Note to self: never pull on a rubber hose connected to a plactic nipple. Just cut it off with a razor!!) A touch of Zap-A-Gap, some JB Weld and a day later, the nipple was usable again.

Troubleshooting Tips

The number one reason why your engine won't start after installing the Howell TBI is that the 12V source you chose to power your ECM is incorrect. The ECM power wire needs to have an un-interrupted 12V supply when the key is in the ON position and while cranking. If the ECM light turns off when cranking the engine, you have picked an accessories lead. The ECM light should not turn off while cranking the engine.

If you cannot locate a 12V power source, you may want to consider hooking up a direct lead to the battery with a toggle switch in between.

The Howell TBI instructions come with all the other troubleshooting information you might encounter.
Howell Throttle Body Fuel Injection (TBI)
for a Jeep CJ - 258 California Emissions Engine

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24. Remove your glove box from the dash board.

25. If your Jeep doesn't have an ECM behind the glove box like mine, you will have to drill a large hole through the firewall for the new wiring harness. The Howell TBI kit comes with a large rubber grommet to help patch up the hole once the wiring harness is through. I used a 1-3/4" metal drilling hole saw to accomplish this task. Make sure nothing will get damaged by the hole saw prior to drilling away.

26. Lay your new Howell TBI wiring harness on top of your engine, drill and then mount the relays (show in the image to the left) onto the firewall using self-tapping metal screws. You will see that every other connection on the wiring harness will extend correctly from this point.

27. Carefully feed the ECM connections through the new hole in the firewall you made and then seal off the hole using the large rubber grommet supplied with the kit. I used some black RTV to insure the grommet stayed in place and was sealed off good.

28. Thoroughly clean the top of your heater box. Use some alcohol to insure there is no grease on the surface.

29. Apply one half of a strip of velcro tape to the top surface of the heater box and the other half to the bottom of your new Howell ECM.

30. Through the glove box opening, insert and affix the new Howell ECM to the top of the heater box and then plug the 2 wiring harness connections into it.

31. Using more velcro tape, affix the new fuse block and diagnostics terminal to the side of the heater box.

32. My Jeep was built for California and so it had a "Check Carb" indicator lamp mounted on the dash board just to the left of the steering wheel. I decided to recycle this lamp and attached the new "Check Engine" light wiring to it. If your Jeep does not have this lamp, you will need to purchase and attach an indicator light to your dash board so that you can see error codes or be alerted to any problems the system may experience in the future.

33. The new Howell ECM needs to be powered by a 12V source that has current when the ignition key is in BOTH THE CRANK AND RUN position. I found and used an ignition wire that was located on the steering column under the dash. It is the thick red wire with a white stripe as indicated in the photo to the left.

34. Back at the work bench, assemble your new electric fuel pump to the fuel filter using a piece of the high pressure fuel line and hose clamps supplied with the Howell TBI kit (see photo to the left). Both the fuel pump and filter indicate the fuel flow direction and should be assembled accordingly. Leave the red cap on the fuel pump end but remove the one attached to the fuel filter for later use.

35. Now, climb under the passenger side of your Jeep just behind the transfer case skid plate. Look up on the frame rail and using a small tube cutter, cut the hard fuel line a few inches back from the skid plate. Make sure your face is not directly under the fuel line as gasoline will pour out and soak you. Use the red cap that you removed earlier from the end of the fuel filter to cap off the fuel line after cutting it. It's a pretty good idea to keep a fire extinguisher handy during this part of the project.

36. Cut off another piece of high pressure fuel line and attach it to the end of the fuel filter and hard line along the frame rail using hose clamps provided with the Howell TBI kit.

37. Secure the fuel pump to the frame rail using the strap provided with the Howell TBI kit. I attached the strap to the frame rail using one of the bolts from the old hard line mounts.

38. Connect the fuel pump power lead to the wiring harness.

39. Attach the rest of the high pressure fuel line to the fuel pump, run it up the firewall, over the engine and attach it to the fuel port on the Howell TBI on the driver side of your Jeep using hose clamps provided with the kit. The other port is where you will need to hook up the bypass fuel return line.
Howell TBI Vacuum Diagram

40. Connect all the vacuum lines to the Howell TBI unit, CTO, distributor and charcoal canister using the diagram provided in your instructions and engine sticker. In a nut shell, all you have to do is connect the PCV valve line to the top port and then 'T' it with the large line running down to the charcoal canister. The port below needs a 'T' that connects the distributor's vacuum advance and to 2 points over on the CTO valve. The EGR valve needs to get connected to a third port on the CTO and the fourth port on the CTO is connected to the charcoal canister's purge control port. Plug all the remaining ports.

41. Slide the form fitted rubber grommet onto the edge of the Howell TBI unit and then plug in the fuel injector electrical connectors as shown in the images to the left.

42. Attach your new Manifold Absolute Pressure (MAP) sensor above the base plate of the Howell TBI unit. I decided to attach this sensor to the wiring harness next to the brake booster. Once in place, connect the MAP sensor to the vacuum port located on the back of the Howell TBI unit between the fuel and bypass return lines.

43. Start hooking up the electrical connections from wiring harness to the various points on the Howell TBI unit. Each connector will only fit on its specific port and so you won't be able to screw this up. There should be a place to hook up the ground wire to the firewall near the engine. Also, be sure to hook up the coolant temperature switch, O2 sensor and throttle linkage back onto the Howell TBI unit at this time.

44. On the passenger side of the Jeep, grab the orange and purple (these are labeled) wires and attach them to the starter solenoid on fender well. The orange wire needs to be hooked up to the positive or batter power terminal and the purple to the opposite side as shown in the photo to the left.

45. The remaining white wire needs to be hooked up to the negative terminal on the ignition coil in order to pick up tachometer signal.
46. Climb back under the driver side of your Jeep and remove the speedometer cable connector from the transfer case.

47. Now, attach the Howell TBI speed sensor to the transfer case and then re-attach the speedometer cable to it. Plug in the speed sensor to the wiring harness.

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