Z31/300zx ECU/MAF to 280ZXT swap guide: 1981 supplement

[280Z Turbo]

I recently did the Z31 MAF swap on my 1976 280Z 2+2 with a 1981 280ZXT motor. Afshin’s write-up is on a 1983 harness, so I thought I would do a write-up on the 1981 harness and include a few other helpful hints for Hybrid Z'ers interested in the swap.

 

Like Afshin, I also used a 1984 Turbo ECU, but there are other possibilities. For some information on which year ECU is best for your needs, check out redz31.com: http://www.redz31.com/pages/fuel.html

 

I find it odd that the Z31 MAF swap isn’t more popular. The plugs on the 280ZXT harness fit in the 1984 ECU perfectly, you just need to add a couple pins.

 

Why do this swap? Reliability, for one thing. I never got my 1981 ECCS to work right. It ran pig rich sometimes and ran dangerously lean at other times and I never knew why. I installed the 1984 ECCS and it’s been running great ever since and it always starts quickly. Even when it’s cold.

 

You also get better performance. That silly flapper door AFM is a big restriction and a MAF will flow much better. People have picked up an estimated 15 peak horsepower at the wheels from this swap and say that the throttle response is much better. I can’t verify the estimates, but my car sure does run good now that I swapped it!

 

It seems like everybody on the 1970-83 forum on Zcar.com uses Megasquirt. MS is cool, but it’s a helluva lot more complicated and expensive, IMO. I was told on Zcar.com recently that nobody uses the 300ZX ECCS because it is “untuneableâ€. Certainly not true. Visit www.Z31performance.com or www.redz31.com to dispel that myth.

 

Supposedly, you should use the 300ZX harness instead of using the 280ZXT harness because the ECU connectors are more sealed off from moisture in the air and don't corrode so easily. A lot of people have problems with these. Using a Z31 harness would be a real pain, so just make sure that you clean the 280ZXT contacts every once in a while. Pulling them in and out a few times can help.

 

The first thing you’re going to want to do is read Afshin’s write-up from HybridZ.org. I also have the same disclaimer as Afshin. I also have no formal training. If you fry your ECU, electrocute yourself, or blow your car up, it's your own damn fault.

 

http://forums.hybridz.org/showthread.php?t=91250

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DISCLAIMER:

 

First, electrical shorts can burn out your EFI and/or cause a car fire. I have no interest in anyone doing this and don’t know if it will work for you or not. I have no formal training and am only sharing what I did for myself. There is no guarantee nor should any inference whatsoever be made that anything posted below is correct or safe.

 

PURCHASED PARTS:

 

1984 Z31 turbo ECU, MAF, any 84-89 300zx crank angle sensor/chopper wheel (the wheel has a top and bottom, do not reverse or car won’t idle properly) and MAF and ECU connectors with several inches of wire attached. Also need wiring diagrams of both cars.

 

NOMENCLATURE:

 

Mass air flow sensor = MAF

Air flow meter = AFM

Fuel pump relay = FPRz = from 280ZXT

zx = from Z31 / 300 ZX

Example: zx 30 y/b = # 30 wire/pin which is colored y/b (yellow with black line) on the 300 ZX system

 

Also, I crimped every cut wire to connectors so I could plug and unplug all the changes.

 

CONNECTING THE MAF:

 

Cut the wires to the AFM a few inches back from the clip

Take clip and wire from MAF then:

1) Connect MAF Position A/wire 30 y/g to 30 y/b wire from z harness

2) Connect MAF Position B/wire 31 b to 31 y/r wire from z harness

3) Connect MAF Position C/wire black to body ground

4) Connect MAF Position D/wire 26 b to 26 b wire from z harness

5) Connect MAF Position E/wire 27/35 b/w to any ignition activated + powered wire (pin 27 and 35 are + ignition wires on the same circuit, they are b/w (black with white strip) and can be tapped into from either b/w wire going to the 2 V.C.M solenoids that are located under the AFM bracket

6) Connect MAF Position F/wire 12 r/w (for cleaning cycle) to 33 y/l wire from z harness

 

CONNECTING THE Z31 ECU TO THE Z HARNESS:

 

There are a few of the ECU connector pins that are different. I got an ECU connector clip from the junkyard and then cut it open and took out three metal pins with several inches of wire to it so I could plug them into the empty connector slots of the z harness.

 

1) Insert new pin into slot 12 of ECU connector then cut wire 33 y/l before it goes into ECU connector and attach to new pin #12. So 12 pin from the Z31 ECU thru wire 33 y/l will be connected to the 12 r/w wire on the MAF (marked as F). Now the ECU will be able to go into auto clean mode and keep the MAF filament clean.

2) Insert new pin into slot 34 of ECU connector then connect it to a new wire going to the + coil terminal

3) Insert new pin into slot 3 of ECU connector then connect to a new wire going to the – terminal of your coil. The car seems to run OK without this step, but I still wired it since it was done on the 300zx. I have a MSD and the car is doing well with it.

 

 

CONNECTING THE FPR TO THE Z31 ECU:

 

This way if the car stalls out, the fuel pump should shut off as it’s supposed to.

 

Now on the 280zx the FPR is always grounded and does not get turned on until the ECU thru pin 16 l/r (blue wire with red line) sends a + signal. On the 300zx it is reversed, the + is on whenever the ignition is on, and the ECU thru the fuel pump modulator sends the – signal to activate the FPR. Hence, I needed to rewire the + and – signal used to turn the FPR on.

 

1) Black wire (- source used to turn on relay) wire cut right before FPR, connect to new wire and take to pin 108 on the ECU connector

2) 16 l/r ( + source for turning on relay), wire cut right before the ECU connector end and connected to + ignition source (I tapped into the b/w wire going to my 280zxt fuel pump modulator which sits above the ECU).

 

 

Now the ECU controls the – power that switches the FPR on thru the ECU pin 108, and the 16 l/r wire is ignition + to the FPR. Now I have no explanation for this part, but according to the book, pin 20 from the Z31 ecu should activate the FPR, which then loops back thru the FPR to pin 108. This did not work for me. However, it worked perfect when I connected the new wire going to pin 108. Again I don’t know why pin 108 is working for this and pin 20 did not, but it sure is working well on my car.

Also I disconnected the knock sensor and did not switch any of the injector wire.

 

Lastly, to run the air regulator, it was controlled thru pin 108 on the z set up (which control the FPR in the z31 set up) as opposed to pin 16 on the Z31 set up. So I connected the 16 pin/wire coming out of the ECU connector to the 108 z harness wire (black which goes to the air regulator) and now the Z31 ECU will control the air regulator from ECU pin 16 thru the 108 wire. (While ECU pin 108 now controls the FPR)

I hope this helps others map out there own swaps (there are many ways to do this).

 

It would be most useful if others who did this could add in their tips, cautions and related experience reguarding this swap such as Z31 maps/ chip burning, adaptations for 370cc injectors, data on actual HP/torque gain and timing/tuning for the set up…..

 

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Okay, now that you've read Afshin's write-up, here's a few more things you're going to want to know.

 

DISTRIBUTOR MODIFICATION:

 

The 1981 ECCS used a magnetic CAS mounted near the crankshaft pulley. As far as I know, this cannot be made to work with 1984 ECCS. So, you need to use an 82-83 distributor with the CAS built in as well as the slotted degree disc from any Z31 distributor.

 

Since I had an entire Z31 distributor, I used the CAS, bearing, degree disc, and some other hardware since it was in better condition than the one I had. The Z31 CAS is also said to be an upgrade from the 82-83 sensor. I’m not sure about that, but it looked a lot cleaner to me and it’s been working great.

 

Just about everybody says that you MUST swap out the oil pump shaft in order to use a 1982-83 distributor. That’s not true, but I did have to have the 82-83 shaft and collar machined to make it work. The 1982-83 distributor has a splined shaft that holds it in place better than the stock slotted shaft which is too sloppy for the 1 degree resolution on the CAS.

I had the 82-83 collar machined to the same inner diameter and overall length of the 1981 distributor collar, but I left the splines in on just the top part of the collar so that the collar would stay centered on the distributor shaft. I tried to use the 1981 collar, but it just flopped around too much on the pin and wouldn’t stay centered.

 

If you look at the end of the oil pump shaft in the engine you’ll notice that the slot that fits into the distributor shaft is off center and one side is bigger than the other. The 1982-83 distributor shaft has a half-moon shape. This can be filed down (or milled, I suppose) until it fits perfectly on the larger side of the oil pump shaft. You should have little or no play in the distributor shaft if you did it right. WannaBREz's "half-moon", on the other hand, needed no filing to fit nice. I guess the tolerance was not very precise.

 

Here's some pics of the assembled distributor:

 

Strip out all the guts and swap out bearing if necessary. That pedestal that you see there is pressure fit in there really good! A small vice grips is your friend here! Just grab on to it really good and pull up. You may need to use a vice grips for the old screws too.

 

The shaft and bearing goes in first, then the CAS, then the pedestal, and then there's a thin black spacer, then there is another washer with tabs on it that holds the degree wheel. Remember there is a top and bottom to the degree wheel. Don't mix them up!

 

 

After you have the Z31 degree wheel on, put the top pedestal thing on and replace the screw. The rotor mounts to this top piece and it's good to go!

 

 

 

Here's the modified collar. As you can see the splines were bored out to match the 1981 oil pump shaft on the motor. The collar was also shortened to the same length as the 1981 collar. You only need the splines at the top to keep it centered.

 

DROPPING RESISTOR PACK MODIFICATION:

 

For some reason, the 1981s used a resistor pack on the driver’s side of the engine bay. 1982-83 280ZXTs don’t need this and neither does the 1984 ECCS.

 

To bypass them, I simply cut off the resistors and twisted the remaining wire together. You could just slip some universal connectors into the slots of the male end of the stock plug, but I wanted to take advantage of the female connector that secures the connectors in place. This distributes the positive voltage to all 6 injectors (the ECU controls them through the ground).

 

Make sure that you properly insulate and solder the connection!

 

 

NOTE: 1988-89 ECUs will require the use of dropping resistors as they were designed for high impedence injectors. I’m not sure if the stock 1981 resistor pack could be used with this ECU, but you will need something to protect the ZXT's low impedence injectors.

 

 

 

CLEANING CYCLE FOR MAF:

 

This was originally automatically controlled by the speed sensor on the Z31 and since 76s didn’t have that, I needed to find a manual way to control it. Ignore the part in Afshin's write-up about connecting MAF terminal F to the ECU if, like me, you don't have a speed sensor.

 

I just used a push button ignition switch. I removed the bracket for the hood release and drilled a hole. It was the best place I could think of that didn't require making a hole in the dash or console. I have heard that you just hold the button down for 1-5 seconds and release to clean the filament. You don’t want to burn up the filament, so be careful!

 

This is where I mounted mine. It's convienent and out of the way.

 

 

OTHER NOTES:

 

If you run an electric fan, I would recommend using a sheilded wire for your MAF signal wire. The electric fan can interfere with the MAF signal. I have heard of people running rich just because the fan is running: http://www.redz31.com/forum/viewtopic.php?t=327

 

I used a wire that I had on another harness that was for the knock sensor. It had 2 wires on it so I used the black one for the MAF signal wire and the red one I used for the cleaning cycle. The cleaning cycle wire doesn't need to be shielded, but since I had that wire there anyway, I took advantage of it.

 

Notice that the wire shielding is grounded to the body. Do this on both ends of the wire.

 

 

For the fuel pump, don't move pin 16 to pin 20. I did that and got almost no voltage. Not sure why, but Afshin had the same issue.

Use any switched power source to energize the coil in the relay and then run it back to ground through pin 108 (which is used for an air regulator on the 280ZXT harness, I think)

 

The relay has "NO" (normally open), "COMM" (???), and 2 "COIL" (for the signal, not the actual power) prongs.

 

The fuel pump is connected to "NO"

Fuel pump power source goes to "COMM"

One "COIL" prong is connected to pin 108

The remaining "COIL" prong is connected to that switched power source.

 

TOTAL COST:

 

1984 300ZX Turbo ECU w/ manual trans: $55 shipped

300ZX MAF w/ MAF harness: $35

1982 280ZX Turbo distributor: $46 shipped

Z31 distributor: freebie

Machining of distributor collar: freebie

Connectors & switch: a couple bucks, probably

 

About $140 invested and it runs SO much better. That's a lot of bang for the buck!

[bumble zee]

Sticky?

[AdreView]

Can someone clarify, which coil terminal does this new wire connect to?

 

3) Insert new pin into slot 3 of ECU connector then connect to a new wire going to the________terminal of your coil. The car seems to run OK without this step, but I still wired it since it was done on the 300zx. I have a MSD and the car is doing well with it.

Edited August 10, 2015 by AdreView