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4ZE1 Fuel Injection to Carburetor Conversion Tutorial

41531 Views 118 Replies 30 Participants Last post by  martinjhodges
How to Convert a 2.6L EFI to Carburetor

This tutorial applies only to non-air conditioned vehicles, manual transmission only and to non-emissions vehicle. Additionally, this applies only to the U.S. model 2.6L (4ZE1) which fits the below description. Vehicles with a/c and automatic transmissions will have issues of which I have no familiarity. The following modifications may only be used on vehicles for off road use only and in compliance with all local, state, and federal laws, rules, and regulations.

Parts Needed
  1. Intake manifold with thermostat housing from 2.3L (4ZD1) Isuzu[/*]
  2. Stock carburetor (Federal) from 2.3L (California versions have an Electronic Control Module (ECM) Only the Federal Version will be discussed[/*]
  3. Distributor w/vacuum advance (Federal) and distributor hold down bracket from 2.3L[/*]
  4. If possible, obtain a few inches of the wiring harness and connector which plugs into the 2.3L distributor/coil connector[/*]
  5. Low pressure inline electric fuel pump[/*]
  6. Fuel Pump Regulator[/*]
  7. Tubing for new fuel pickup tube[/*]

Under the Hood (easiest if hood is removed)

Mine did not have the EGR pipe nor any A.I.R. Parts. If yours does, remove any items which would otherwise prevent the removal of the complete intake assembly.
  1. Disconnect and remove battery[/*]
  2. Put vehicle in neutral and apply parking brake / chock wheel for manual transmission[/*]
  3. Drain coolant (radiator petcock) and remove upper radiator hose[/*]
  4. Disconnect heater hose at passenger side lower intake fitting[/*]
  5. Loosen fuel cap[/*]
  6. Disconnect fuel return line from fuel pressure regulator and fuel line from injector rail[/*]
  7. Disconnect fuel vapor line from intake[/*]
  8. Disconnect ground wires from intake[/*]
  9. Disconnect wire to water temperature gauge sending unit (I remove the sending unit and installed it to the 2.3L due to my knowing it was good[/*]
  10. Disconnect all electrical connectors routed to engine which would prohibit the removal of the complete intake assembly[/*]
  11. Remove PCV hose from intake[/*]
  12. Disconnect hose from rear of valve cover at the air cleaner ducting tube[/*]
  13. Disconnect MAF sensor from air cleaner[/*]
  14. Disconnect hoses/lines form charcoal canister / remove charcoal canister[/*]
  15. Remove air cleaner and duct work[/*]
  16. Disconnect throttle cable from throttle body[/*]
  17. Disconnect electrical connector to coil and remove coil[/*]
  18. Disconnect round white connector to distributor/coil[/*]
  19. Disconnect vacuum lines in any manner you prefer[/*]
  20. Remove throttle body and common chamber[/*]
  21. Remove lower intake[/*]
  22. Remove brackets on passenger side inner fender along with remaining vacuum lines and associated parts[/*]
  23. Though it may not be necessary, loosen power steering belt, disconnect power steering pump bracket and lower the assembly out of your way[/*]
  24. Drop the fuel tank or cut an access port through the rear floor so that the fuel pump can be accessed[/*]
  25. Remove fuel pump assembly[/*]
  26. Remove sediment screen from bottom of fuel pump[/*]
  27. Measure and record the overall length of the fuel pump[/*]
  28. Remove fuel pump from bracket[/*]
  29. Purchase, etc, tubing and cut it to a length equal to that measured from the the bottom of the fuel pump to the end of it's fitting which resides in a short section of rubber fuel line. This will now be the new fuel pickup tube[/*]
  30. Insert tubing into rubber fuel line and clamp same[/*]
  31. Reinstall fuel pump bracket with new fuel pickup tube to the fuel tank[/*]
  32. Reinstall fuel tank or secure floor section to floor. (I cut a rectangular opening in the rear floor. I then used metal stock as "stops" for the cut out section. These were attached underneath the floor on the rear side. I attached two small hinges on the front side. This worked out very well.[/*]
  33. Make sure the distributor rotor button has been indexed to the distributor hold down or other location. Do not allow the vehicle to be moved if in gear. This will simplify the installation of the 2.3L distributor.[/*]

Vehicle Cabin / Interior
  1. Remove console[/*]
  2. Disconnect ECM[/*]
  3. Remove ECM[/*]

Installation of 2.3L Manifold / Distributor & Coil / Carburetor
  1. Clean passenger side surface of cylinder head thoroughly[/*]
  2. Obtain a sheet of 20/1000th brass shim material[/*]
  3. Looking at the center of the passenger side cylinder head, you'll see a rectanglar recess. On it's left hand side, you'll observe a small, tube-shaped raised section of aluminum. This is used as an oil return path. The 2.3L intake has an opening which aligns with the recess. This area needs to be blocked or the result will be oil leakage.[/*]
  4. Make a pattern to size and shape of the cylinder head side of the intake manifold opening[/*]
  5. Transfer pattern to brass shim stock and cut[/*]
  6. Sealer should be applied to approximately the 1/8" outside edge of both sides of the plate[/*]
  7. I prefer the much thicker fel-pro intake manifold gasket over the factory gasket. Your choice.[/*]
  8. Install the intake manifold, gasket, and shim stock to cylinder head. Torque to spec. If done correctly, the shim / block is located between the intake manifold gasket and cylinder head.[/*]
  9. An alternative or addition to the brass is to cut to size and shape a good quality intake gasket material and 3/16' or 1/4" steel or aluminum plate. This can be drilled and installed on the "outside" area of the manifold using the two studs to which the 2.3L mechanical fuel pump attached. You'll need two nuts for the studs.[/*]
  10. I chose to remove the studs from the cylinder head and went with bolts only for attaching the intake manifold. I thought it gave a cleaner appearance and it appeared that the two upper center studs would interfere with the installation of the weber 32/36 carburetor.[/*]
  11. Additional block off plates will be necessary for EGR related equipment[/*]
  12. To aid with installation of the manifold, I temporarily installed (finger tight only) studs to the upper rear/front bolt holes. I then slid the intake on, began bolting and removed the studs at the appropriate time and replace them with bolts.[/*]
  13. Install the ignition coil[/*]
  14. Connect wire to water temp sending unit and to the oil pressure gauge if it was disconnected[/*]
  15. Install the distributor (check distributor shaft O-ring and replace if necessary) hold down bracket and distributor (there are two sizes of hold down brackets. My 2.6L bracket would not work, thus the need for the 2.3L bracket)[/*]
  16. Connect heater hose to manifold[/*]
  17. Examine thermostat and replace as needed[/*]
  18. Obtain upper radiator hose for 2.3L and install. I purchased a 2.3L universal ribbed hose[/*]
  19. Install new fuel pump as near and below the tank as possible[/*]
  20. Install the fuel pump regulator in engine compartment[/*]
  21. I removed my charcoal canister, vapor lines and fuel return line. You may or may not choose to follow this path.[/*]
  22. I am currently running mine with the fuel cap loosened for venting. I'll do a more permanent fix soon.[/*]
  23. Run 12 volt power to the fuel pump. I made a new circuit with a circuit breaker and relay. You can use the wiring which powered the factory fuel pump.[/*]
  24. Install carburetor and fuel lines when you're comfortable to do so. Install throttle cable and brackets to carburetor throttle linkage (fabricate as necessary). You will have a much easier time if you replace the f/i throttle cable with the shorter carburetor throttle cable.[/*]
  25. Connect PCV to new carburetor[/*]
  26. Route hose from rear of valve cover to large fitting beneath carburetor, passenger side. I am installing a small K&N breather to the valve cover fitting; doing away with the hose.[/*]

Wiring Distributor and Tachometer
  1. The 2.6L wiring to the distributor consists of four wires; red, green, blue, white. Red will provide switched hot to the distributor/coil. The other three wires became inert upon removal of ECM.[/*]
  2. Two wires exit from the 2.3L distributor/coil wiring harness. One wire is black/yellow and the other black/red[/*]
  3. Reinstall battery. Connect as necessary to perform any tests[/*]
  4. The red wire of the 2.6L harness connects to the black/yellow of the 2.3L for switched hot. The red wire can also be used to provide voltage to the automatic choke.[/*]
  5. Remove tachometer from instrument panel[/*]
  6. Exiting from the rear of the tachometer circuit board are five wires. One of them is black/red. Be cautious. The black ground wire exiting from the tach has red dots. The signal wire will have a black stripe. I noticed on an 88 model the signal wire was light blue with a black stripe.[/*]
  7. Cut the black/red wire a couple of inches from the tach going toward the electrical connector. Strip the end of the remaining black/red wire from the tach.[/*]
  8. Splice a new wire to that end. There are 3-4 lugs on the back side of the tachometer. An alternative to cutting and splicing at the tach is to crimp a small ring connector to the wire end and attach to the corresponding lug/terminal. Make sure the new wire can reach the wiring at the distributor.[/*]
  9. Splice the other end of the new wire to the black/red wire which originates from the distributor/coil.[/*]
  10. Locate and install all ground wires to the manifold which were removed from the 2.6L manifold[/*]
  11. Fill the radiator with water only.[/*]
  12. Start and run motor[/*]
  13. It may be necessary to adjust carburetor and ignition timing[/*]
  14. My engine is now happiest at 6* BTDC @ 800 rpm when fully warmed. This coincides with the specs for a 2.3L 4ZD1. I've been advised to move my timing back to it's original 12* BTDC for better fuel mileage, etc. I tried 12* several times and my engine would start and run fine, however, It would run on when I tried to turn it off. With [email protected], it starts, runs, and shuts down just fine. The timing advances well; blah, blah, blah. I have since timed my engine to 12* with no issues.[/*]
  15. When all is well, drain water and add proper coolant mix. I would also change the oil/filter.[/*]
  16. When all is settled, I am going to begin removing wiring harnesses from the engine compartment and will update this tutorial as I progress.[/*]


I wish to thank the following people whom without their help I would have never attempted or successfully completed this conversion:
  • moondoggie98. He was the first to respond to my questions, was there for any other question and gave me the confidence to proceed.[/*]
  • Jerry (JLEMOND) who provided parts, instructions, and guidance throughout this endeavor. Many times he had to beat it into me until I finally grasped what he was telling me. Thank you forever and a day Jerry.[/*]
  • To other members at who provided assistance, moral support and encouragement, I thank you too.[/*]
  • To my good friend Mike who provided the expertise on setting up my carburetor. [/*]

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1 - 4 of 119 Posts
Perhaps, indeed! That is an awesome detailed write up, and a daunting project. I'd vote twice if it was legal.
Metal88 said:
perhaps this could be in the hall of fame? i would vote for it :D
Hmm, I'm getting 20 around town and close to 25 mpg on the highway with my stock injected engine. Including the occasional A/C use. Is your mileage before carb conversion (17 mpg) typical of most members' Troopers with the 4ZE1 engine?
cronk said:
I think the intention was to clean up the engine bay and simplify the engine function. Being different doesn't hurt either.

Check out the results of the 1st few tanks, not bad. ... highlight=
I think that could be the difference. My RS is smaller and lighter so in theory that could be one reason it's getting better mileage.
cronk said:
I think my best tank was about 20 in my old 4 door Trooper. 17-22 sounds about right.

I know there is a thread on here somewhere where people have posted their mileage.
Shooter, do you have any photos showing the fuel tank pump access port/panel/hole in your floor?
Thank you!
1 - 4 of 119 Posts