How to Convert a Nissan 720 (1980- 86) truck to Z24i (fuel injection) from a D21 86.5 - 89 truck.

Updated 9/2/2009

I was having problems with the stock computer controlled Carb. Weird idle speeds, stalls and sputters after engine warms up etc. I tried a few aftermarket Weber and Solex 2 barrel carbs. The carbs were xlnt for power gain but the adapters were high maintenance. I had a carb fall off once. The throttle return springs were a constant nightmare. I tried every type of spring I could find. But had a lot problems with sticky throttle and high idle not too mention the smog issues. I decided the only legal and reliable way to go was Fuel injection. There is no aftermarket versions available. So I decided pure Nissan parts was the best way. Unfortunately 1986 was the last year of the 720. But I found out the 86 720 was available with the z24i motor just before the D21 (Hardbody) came out. I decided that if Nissan made a Fuel injected 720 I could convert mine. The big problem is there is no 720 z24i parts laying around in junk yards. So I used all D21 (86.5+) parts with the exception of the fuel pump, hoses and throttle cable.  I have received a few emails on how I did this so I will try to be more detailed on what I used and how I did it.

This picture is from a stock 720 with z24i. Very rare. (Not mine) 

Step 1. collect all the parts. If possible go to a junk yard that lets you get the parts yourself and get most from same vehicle.

Mandatory Parts needed: Assuming the old truck is a 720 80-85 z24 and new is 87-89 z24i. Note the i means fuel injected.

• Used 87 Intake manifold --including EGR electronic water switch etc..

• Used 87 Throttle body complete. including 2 injectors, air flow meter, idle speed switch etc.

• Used 87 air cleaner.-- looks like carb version from above except aluminum spacer and has 2 wing nuts instead of one. On lid it says "electro-injected" and it is two tone, black and silver.

• Used 87 Wiring Harness-- including relays and all connecters related to computer and engine.

• Used 87 5 speed truck Engine computer. There is also a Automatic version. I never connected the computer wires to my 5speed trans.

• Used 87 distributor. This is the crank angle sensor.

• Used 87  Ignition coils you need 2. The new modern transistor versions. note spark plug wires, cap and rotor are the same for carb and injected.

• New throttle cable much longer than carb version. New from dealer for stock 86 720 injected $19 special order. fit like a glove. 

• New 45psi Fuel pump, any external  brand will work ....I used a new 86 Nissan 720 injected pump with hose and bracket. The plug connected right into my wiring harness.  5 minute install. But cost $160.00.

• Used Charcoal canister with 3 hoses. 1985 carb has 5.  I used a 1984 280zx one. The carb has more vacuum lines than injected.

• Update 1/2009: I used a complete z24i motor. The distributor shaft is different from z24i to z24. You may need the z24i timing cover. I need to research part numbers,

• Haynes manual 1980-86. cheap and worth the $12 from any auto part store. I do not like the Chilton manuals.

• New Nissan Service Manual 1986.5 call Nissan at 800 247-5321 or any local dealer, same price.  I have purchased 4 service manuals so far and are very detailed. The Dealer mechanics use these. Service manuals for vehicles built in 2000+ are now available directly from Nissan on CDROM. This is the website for service manuals.  Note: Nissan never made a 87 service manual for the truck because the Hardbody was introduced in 86.5. 86.5 and 87 are the same. 88 engines use different engines codes. See step 10 for more details on engine codes.

Step 2. Lay used wiring harness on floor and connect all the parts to the appropriate connectors. Just make sure you have all the pieces and they fit. 

Step 3. Remove all black tape and cut away all extra wires. This includes 87 fuse box, headlight stuff, heater, park lights etc..YOU DO NOT HAVE TO CUT ANY WIRES THAT GO TO THE COMPUTER. Leave these as long as possible to integrate into the 85 harness if possible.

Step 4. You will need to integrate a few wires into your 85 harness. These wires come from the 87 computer and "tap" into the 85 wires so leave as long as possible. You do not need to buy or extend any wires. 

• starter -- yes the computer wants to know when your trying to start the engine.

• ignition "on"-- tap in near radiator on the way to new coils. reuse old Coil hot lead.

• battery via fusible link.-- 2 white 10 gauge wires.

• fuel pump--remove both old fuel pump relay next to glove box on right kick panel and tap in there.

z24 wiring schematic

1988 z24i wiring schematic

1988 ECCS wiring

1988 TPS

z24 sparks plugs and z24i Sparks plugs

New z24i VACUUM layout. The carb version is more complicated.

EGR cut solenoid is different between z24i and z24. The ECU controls EVAP and EGR as of z24i. z24 is thermal controlled.

z24i Vacuum layout. z24 is very similar.

Harness connecters 88 D21

Harness labels 88 D21

Injector wiring

Step 5. Re tape harness.

Using black electrical tape rewrap the wires coming from computer. This will make it easier to install through firewall and will protect wires. Just leave the few bare ends for the "integration" to 85.

Step 6. Remove old parts:

• unplug and unscrew old computer--under drivers seat

• distributor-- 2 bolts
• both coils
• air canister
• air cleaner
• intake manifold
• throttle cable
• fuel pump-- next to fuel tank on outside frame rail in metal box.
• fuel pump control unit near glove box on right kick panel above speaker.
• o2 sensor--in exhaust manifold, they are different.

Step 7. Install new/used parts:

• intake manifold and gasket.
• throttle body--4 bolts.. gaskets are very expensive because they are heaters. Try to keep intake and throttle body together if bought used.
• New throttle cable--easy 2 bolts and 2 nuts on cable.
• distributor--cap rotor and wires are the same. Stock wires will last 200K and cap rotor 75K
• both coils.-- drill new holes and uses old big screws. I mounted on the square metal wall around head lights.
• mount ECU (computer) under Passenger seat or in a new console under radio.--drill a big 2 inch hole in firewall behind glove box. I noticed 87 ECU will not mount under an 85 seat without modifying the computer brackets.
• lay new harness on engine and connect all wire water tight connectors. Route harness through firewall and connect to computer.
• cut off old coil and distributor wires and use those to connect the "ignition on" on the 87 harness.

• cut off old carb wires these will not be used.

• tap into the starter wire near starter. Wiring harness runs right above starter on fender well.

• connect the 2 white power wires to battery via fuses or fusible links.

• mount fuel pump to frame, connect both hoses and wires to 85 wires. You do not have to run new ones. Use the 87 fuel lines for the supply, yes I used old 1987 fuel lines from a junk yard. These are high pressure (45psi). The return line can be the old 85. Note 87 uses same size fuel lines for both supply and return. 85 has a smaller return. Not a real problem. I had to use 2 clamps were 85 steel return line meet 87 fuel line from the throttle body. 

• Connect the 87 fuel pump wires to 85 at the old fuel pump relay location, under glove box. The 85 relay is replaced by a relay in the relay box under the hood. The fuel pump controller is now part of then new computer.

• o2 sensor--they are different. The engine will run the same with either I noticed. I left mine unplugged with no change in engine behavior.

• mount air cleaner with 2 new wing nuts and adapter. The plastic funnel connects to the 87 air cleaner to the 85 radiator support perfectly. Looks stock.

Step 8. Mount black plastic relay box to inner fender well (drill a hole for big screw) and connect battery. In this 87 relay box you should have a fuel pump relay and I think 1 or 2 ignition relays. blue and orange if I remember. The rest you can remove. 

Step 9. There is 2 wires that connect to the trans neutral switch and 4th gear switch. I never got around to connecting these. The neutral one I read is to prevent stalling during deceleration and the 4th gear is for timing adjustment. or something  Truck ran xlnt without both. 

Step 10. Start the truck check the timing and adjust idle speed if necessary. Check the computer codes for codes. 44 is no errors on 87 engines. 88+ engines are code 55. If the engine does not start check for gas and spark. The engine should still start even if one of the electronics are bad. It will just run poorly. The distributor and computer are the heart of the system the rest just "fine tune" the engine. You should be able to hear the fuel pump "prime" when you turn the key to "on". 

Note: If your truck has power steering. You have to modify the 87 EGR control bracket to mount next to 85 power steering (if you have power steering). 87 uses the old L series fuel pump location for the EGR control bracket. 85 is part of the intake. 87 mounts half of the power steering pump to fender and mounts pump were 85 does. The 85 engines uses water to control EGR operation, 87 uses the computer with the new intake temp sensors. The engine now has 2 separate temp sensors one on the 85 side for the Driver in dash and one for the 87 computer. 

This was my first fuel injection conversion, I was told it could not be done. The hardest part was cutting a 2 inch hole in the firewall for wiring harness. The computer is too big to fit under the seat of a 720 truck. So I installed it in my custom 5 foot long center console. Overall It was quite easy to do. I want to put an Infiniti V8 in a Truck next complete with all the electronics.

If anyone wants to do this, please Email me with any questions.

Done in 1995. Just before I started my first website that same year. I wish I had taken pictures..