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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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New here, I have a 1991 SpaceCab that was dealer converted to a dually that I purchased new 32 years ago. Brought my eldest son Caleb home from the hospital with it. Later I gave it to him. He was killed in a motor cycle accident 10 years ago and the truck just sat as I was too heartbroken to do anything with it. Well now my youngest son, who was 8 when Caleb died asked if he could have it so now the two of us are restoring it. We are following the above instructions to remove all of the fuel injection as it seemed more manageable to me than replacing all of the old clogged and cracked air system that was stock. And it looks SOOO much cleaner, BONUS! I don't know if you are still following this but I have some questions, Thanks

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4 Posts
Wow, thanks for the help! I knew this thread was old but I still had hope! I'm an "old car" guy so trying to get the injection and emissions stuff sourced and then figured out was just beyond me so carbs it is!
1. First question was about the Ignition coil. On the 2.6 it is on the back of the valve cover but it appears from pictures that there is one on the 2.3 intake. Are they different? do I need a 2.3 one and get rid of the 2.6 coil?
2. The mention of the brass to cover the unused ports has me a bit baffled. I just figured I'd plate the exterior where the old units were bolted on. I've done that a bunch in the past getting rid of the mechanical fuel pumps for electric ones. To be fair though I don't have the new manifold yet as it is in transit from a scrap yard out of state. Maybe once I get it it will make sense.
3. Next question was about the return fuel line, Shooter said he ran with the fuel cap loose and would get back to it but I didn't see that thread. I was planning to use the "relief" side of the fuel pressure regulator to handle that. Would that work? Again my history is old vehicles mostly old jeeps and they do not have a return or pressured tanks so I'm iffy on that.
4. EGR valve? does this get totally delegated? Again old vehicles don't have that.
5. PCV valve, where did you run that vacuum to?

Thanks again for your help. My son is over the moon excited as am I to get this little nod to Caleb back on the road!

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41 Posts
To Martin,
1. The 2.6 coil will work however if you can source the old wiring from the 2.3 it will be plug and play with the vacuum advance dizzy. I bought a new dizzy and new 2.3 coil, but used that old jumper wire. Mounted it on the valve cover with ground to firewall. Heads up there is only 2 wires a 12 volt source and the tach feed back. And they were opposite of what I thought they’d be. I believe the black with red stripe was the tach output…

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41 Posts
2. I don’t know about the brass reference? But yes, I just cut out aluminum plates for all the open holes not being used. Along with black sealant. Fuel pump, egr, I also recommend cutting the egr line at the exhaust and welding up a bit of the end to create a plug. We measured it at orielys auto and it was a weird thread, $12-20 plug used on a dodge oil pan?
It was 22.150 thread by 12mm. If you don’t have a welder. Hopefully you can get that fitting loose at the exhaust to weld or plug, they can be a real bear!

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41 Posts
3. Fuel return will not be needed unless you plan to use a fuel bypass valve. If you use a Weber carb which I recommend unless your gonna be rock crawling, the desired fuel pressure is 3lbs.
Do not use the mr gasket fuel pump, I had 2failures on my first tank of gas. I just switched to a carter pump designed for 1-4psi . See attached pic. Ihe had no problem with tank venting.
The problem I had was the Weber uses hardly any gas when idling and once fuel pump has been running it pressures up and gets hot and shuts off . Hoping the carter holds up, but if I have the same problem, I’m gonna add the above mentioned fuel bypass and put a 2.8 factory pump back in the tank to keep it cool, the bypass will keep it pumping all the time while only allowing 3psi at the carb. Problem is that bypass valve capability of 3psi is $200+.


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41 Posts
5. Pvc - there is a special bent hose,, or you can just run a normal vacuum hose to the base of the intake on the inside. I have seen some running a catch can for oil on this hose? Maybe someone else can chime in on that..
Get a small filter for the back of the intake port. Not sure on the size, got one too big on my first try.

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ok I'm past that now the question is about wiring. Shooter talks about the wire going to the distributer/coil so is that the same wire going to both units? Meaning 1. the distributer then 2. the coil? and on both there are 21 wires I assume they are grounds?. my wire is the Green with black stripe, not red not that that makes a difference...
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