Z31/300zx ECU/MAF to 280ZXT swap guide

[280Zen]

Generally don't read the L-6 nonsense

:malebitchslap:

[Guest bastaad525]

Afshin - nope I guarantee you, it's an '82 ECU and '82 wiring harness (I've verified both from the info label on the ECU, and the fact that we didn't use the resistor pack for the injectors that you mentioned), but an '81 CAS and 'blank' distributor. I was always under the impression that they would have no problems being 'mixed and matched' like that. However... it is funny that you said "I would imagine that the 82 ECU would not get the right signal and/or advance/retard timing appropriately with the crank trigger 81 system.".... There have been a few bugs that I've had seemingly related to ignition timing, to the point where I was questioning the condition of the CAS itself. But until now I never considered that it might have been incompatibilities between the '81 CAS and '82 ECU. Strange things like a light misfire at idle and low revs, a slight stumble every time the TPS goes open, and timing doing funny things sometimes...

 

Well... after thinking about that and you mentioning it, I'll move getting an '82-83 dizzy up on my list of priorities... it's all I can do for now.

[Tim240z]

Generally don't read the L-6 nonsense [/quote'] :malebitchslap:

ha ha ha!!

[Sean73]

I am almost ready to crank my L28ET w/ 84 ECCS and have a couple of questions.

 

Afshin, can clarify how you hooked up the "burn off" wire for the MAF? I don't think that the S130 flapper AFM has a comparable function (correct me if I am wrong) , and I don't understand why your procedure calls for connecting the Z31 R/W wire to the S130 Y/L wire.

 

The Z31 ECU also uses input from the speed sensor on the vehicle to run the burn-off function, and I wonder how to bypass or modify this to make the burn-off work in an S130 or S30 car.

 

Also, has anyone experimented with all of the various flavors of Z31 ECUs (automatic, 5 speed, California, Federal, various years, etc...), and observed any performance gains by using one over the other? I have an automatic/turbo ECU from an '84 Z31, and I am stuck with it until a 5 speed turbo ECU shows up at the junkyard.

[Afshin]

You are right, there is no clean cycle on the AFM set up. I just used wire 33 y/l form the Z harness because it was not used on the Z31 set up and hooked one end to position F on the MAF which runs the clean cycle then I connected the other end to the Z31 ecu with a new pin in position 12 which powers the burn cycle.

 

My car being an 83 280zxt has a speed sensor, I forgot that the earlier Z don't have one. What you can do is run a wire from position F on the MAF to a push button wired to a + 12 V signal. Then whenever you push the button on for a few seconds +12 V will go to the MAF and clean the fillament. This will work only when the ignition is on powering the other wires to the MAF, and should be done with the engine off (just the ignition should be on).

I would not use a toggle switch that could be left on by mistake resulting in the burning out of the filament. I don't know how frequently the other guys with the Z and no speed sensor clean the filament, but I guess it does not need to be done that often.

[Afshin]

 

The chopper wheel on the left is from the 280ZXT, the one on the right is from any Z31, or similar year maxima. The holes should look like this when being dropped into the distributor. If you flip it over, then it will give the wrong reference point and run poorly.

 

In reference to which ECU would be best, it should be the 88-89 turbo ecu since they have 16 bit processors and have the correct timing/fuel map for the turbo (they are a little harder to find). As mentioned earlier, the 86-89 turbo ecu will require the matching O2 sensor, which will also require a correct size nut to be welded on since the thread is smaller on those O2 sensors than the 280zx sensor.

 

Also, on the 88-89 ecu's, it is better to switch injector 2 and 5 with each other to get the correct batch firing, (it's done on the JWT kit and makes sense with the wiring diagram). I don't know if there is any difference with the pre 88-89 ecu's and need to switch the number 2 and 5 injectors over, but if those ecu's fire the two banks of 3 cylinders in different orders as do the 88-89 ones, then the injectors should be switched.

 

I also found out that at least for the 88-89 ecu's you should use drop down resistors between the ecu and the injectors. A good place to place them would be in the harness comming out of the ecu connectors.

The resistors should be 6.8 ohm/10watt resistors (six of them) and solder them in line.

[Guest Coloradozxt]

Afshin,

 

I posted here hoping that you would be checking this post occasionally. I have completed all connections and am using the 88 turbo auto Z31 ECU. In my case I have used pin 19 to control the air regulator. I grounded the fuel pump to the chassis. I have disconnected the knock sensor and switched the injector wires #2 and #5. I am getting power to the MAF E terminal via w/b on the VCM connectors which are disconnected as you suggested.

 

I am having trouble with the fuel pump shut off when turning the key to the on position and not attempting start. The fuel pump runs for a few seconds as it should, however, with the key in the on position after a few seconds there is a buzzing/humming sound from the fuel pump relay location and the pump does not shut off. What is going on here?

 

Also,

 

Also, the car will not start, but that is another issue, I think. One step at a time.

 

Can you help? this is driving me crazy.

Mark McCafferty

[Afshin]

Hi Mark

how did you wire the fuel pump relay ?

Also are you using the correct O2 sensor for an 88 turbo (titania type), they are not compatible with the 280zxt zirconia type O2 sensor.

Did you remember to use the chopper wheel/encoder disc from the Z31 distributor?

Did you insert a new pin into slot 34 of ECU connector then connect it to a new wire going to the + coil terminal (car won't start without this)

[Guest Coloradozxt]

Afshin:

 

I wired the fuel pump relay as you suggested. I actually removed the original black wire and female spade connector and inserted a new wire and spade connector and spliced this to ECU plug 108 wire. I did not cut the 108 wire, just tapped into into it. I connected the harness side of the 16 l/r wire to the b/w wire on the FP modulator plug.

 

I have the correct O2 sensor, the titania type, small diameter, however I can't mount it until I have the nut welded to the cast iron downpipe (requires special nickel welding rod). It should start but run rich without the 02 sensor connected, Right?

 

I have the Z31 chopper wheel/encoder disc installed as you showed in your photo.

 

I inserted a new pin connector into slot 34 and ran that to the coil + as instructed.

 

fuel pump runs, but instead of stopping after a few seconds with the key in the on position, it continues to run with a buzzing/humming sound coming from the FPR. Why is this?

 

Engine does not start, plugs are fuel fouled and wet, looks like no spark.

 

I am afraid I may damage some component if I try cranking and checking for spart with coil lead grounded.

 

Should I try connecting the FPR black to the ECU pin 20? My notes say this controls the FPR coil -

[Afshin]

Mark, disconnect wire 108 and have it directly connected to the FPR, you have it connected, so it may have a weak ground thru the air regulator, keeping the relay on and buzzing because of low voltage. If that doesn't solve the problem, then try pin twenty, if that doesn't work I know what to do next, just send me a PM and we will work it thru.

Also ECU pin 19 should be connected to the 108 original wire going to the air regulator, how did you do that without splicing the 108 wire ?

 

In summary, ecu pin 108 should go directly and solely to the FPR and ecu pin 19 should be connected to the old 108 wire connecting it to the air regulator.

 

Lastly double check all your ignition stuff, coil, condenser and make sure nothing got disconnected.

[Guest Coloradozxt]

Afshin, so others will know, I followed your last suggestions. I have the FPR black wire pin directly connected to plug side of pin 108 only. In my case I removed the original FPR black wire female spade connector and taped it off and inserted a new female spade connector and routed that directly to the 108 wire going into the ECU plug. I had to cut he 108 wire a few inches from the ECU plug to make this connection. The other side (harness side) of 108 that goes to the air regulator is connected to pin 19. All works normally now with respect to the FPR relay. Pump turns on normally with key in the "on" position and turns off after a few seconds as it should.

 

Now if I could just get the car to start! Bernards last suggestion was to check the voltage at the coil power transistor connector which I will do soon and post the results.

 

Everyone's help is appreciated.

 

Mark McCafferty

[Guest Coloradozxt]

Okay, again, I hope others will benefit from my mistakes. After the FPR control was working properly the car would still not start-no spark. I traced the ECU plug pin 5 and found the wire was damaged. This is the igntion signal from the ECU to the coil/power transistor. This was relatively easy to fix-the wire was apparently damaged from a Previous Owner screw up.

 

Okay, now the car actually STARTED. However, it would not idle hardly at all, certainly not without keeping the foot on the pedal. I reconnected the VCM wires that control the AAC valve and EGR valve and the car idled okay. I checked timing-it was formerly set at 24btdc which is stock spec for my 83zxt-however it was now about 10btdc, so I adjusted the distributor again to make it 24btdc.

 

Bernard, what do you have your timing set at?

 

Fuel pressure is another variable I have to adjust. Currently I am running about 50 psi at idle with the vacuum hose attached to the regulator. I am using the first generation SVO injectors that are supposed to flow 30lbs/hr or 345 cc/min. Bernard re-mapped my 88 turbo auto eprom same as he is using with 370 cc injectors and stock fuel pressure.

 

Bernard, can you send me (or us) that link again with the conversion formulae for varying fue pressures and injector capacities?

 

The MAF sensor I am using has the aluminum blind plug removed with the plastic adjustment screw exposed. I assume a 3-gas analyzer is needed to adjust this properly. If I have a shop do this, what CO/HC/CO2 reading should I be looking for?

 

The car is idling with vacuum around 14-15 in. Hg. It used to idle around 15-16 in Hg. My garage for this project is at 7000 ft. above sea level so others vacuum reading will probably be greater.

 

After the car warms up, the idle will begin to "hunt" up and down. When I disconnect the VCM connectors again it will hardly idle like when I had them first disconnected.

 

Bernard, how did you handle this?

 

I do not yet have the special "titania" O2 sensor installed yet, but I have one. I am using the stock cast iron downpipe and I am told by the local muffler shop that if I want to weld a nut to the downpipe to fit the sensor that it will require a special nickel welding rod to weld the steel nut to the cast iron downpipe.

[Bernardd]

Fuel pressure is another variable I have to adjust. Currently I am running about 50 psi at idle with the vacuum hose attached to the regulator. I am using the first generation SVO injectors that are supposed to flow 30lbs/hr or 345 cc/min. Bernard re-mapped my 88 turbo auto eprom same as he is using with 370 cc injectors and stock fuel pressure

 

Turn down the fuel pressure to 30. Increase it gradually until you get a good idle.

 

After the car warms up, the idle will begin to "hunt" up and down. When I disconnect the VCM connectors again it will hardly idle like when I had them first disconnected.

 

The z31 ecu is not setup to control the stock VCM solenoids. You will have to adjust idle with the throttle stop screw. Installing the o2 should clear it up somewhat as well.

[Afshin]

Some more updates:

I confirmed that the 84-87 injectors are low impedance similar to the 280ZXT, hence those computer don't require dropping resistors.

All 88-89 (turbo and non-turbo) used high impedance injectors, meaning that if you are using low impedance injectors such as the stock or SVO's...and an 88-89 ecu, you will need six 6.8ohm/10watt resistor to be put in line with the injector signal/wire comming out of the ecu pins 101-106 (this is real easy to do, cut the wire and place resitor in line)

 

Reguarding swapping injector 2 & 5:

All turbo 84-87 and all 88-89 ecu's (turbo and non turbo) use a batch firing system when:

-engine is warm

-RPM is less than 3000

-injector pulse is short (defined as less than 6.5ms. e.g. part throttle, crusing on the highway...)

 

During this time (batch mode) the injectors are divided into two banks consisting of injectors # 1,2,3 and 4,5,6. In order to keep this working best, one must switch the # 2 & 5 injector wires on the 280ZXT harness. This can be done from the wires/pins comming out of the ECU or at the injector level.

So even though most people can't notice the difference, it is better to do this (it takes no time) so you get better/more accurate fuel delivery when the car is not under load.

So when you floor the car or when the RPM's are up or the engine is cold both EFI system will fire all 6 injectors simulataneously and it does not matter if the injector wires are switched or not.

[Bernardd]

Update on my z31 ecu adventure:

 

I've got 440cc injectors from an early to mid eighties 5.0 ford (CSI) running nicely. These have a barbed connector and fit onto the fuel rail perfectly. To run these you will have to get smaller clamps as the barb connector is smaller in diameter than the stock injectors or the modified ford 370cc units. There are two different barrel sizes in these injectors, on the smaller size you can use the svo seals, on the larger size the oem seals work fine.

 

As an experiment I've tried set the idle to lean out the car enough to stall it. Easily done so it appears there's room left for larger injectors.

 

This was done using an 88 NA ecu, modifying stock Nissan code. I used the stock 83 o2 sensor. I didn't do the harness swap suggested by Afshin (which is the correct way) nor did I install the dropping resistors. I ran an ecu like this most of last summer with no problems, but I always have an extra ecu with me.

 

Bernard

[Guest Cronic]

Pardon me if I missed it, but what does this mod do?

[Dacelooper]

hey i only posted mine on zcar.com but i figured some of u might find my writeup a bit easier to understand. (i used pictures, hehe.) http://www.zcar.com/forums/read.php?f=1&i=460887&t=460887#reply_460887

[Afshin]

Thanks for adding the figures Dave, I'm sure it will help.

One question, you have not connected the A pin on the MAF to the wire going to the 30 ecu position. I obviously did since it was is shown to be connected in my Z31 diagram (chilton manual section 6, page 75). Any reason for you not connecting it ? I figure it might be better to connect everything as was done on the Z31, specially since the wire from ecu pin 30 is already there (it was going to the old AFM).

I love this set up

[Sean73]

In case any of you are tempted to use the Z31 CHTS instead of the 280ZX CHTS, I don't think it will work without mods. The Z31 CHTS will screw right into the L6 cylinder head, but it has a slightly shorter probe, and I don't think it makes good contact with the cylinder head (that's my theory, atleast).

 

My car was running rough with a brand new Z31 CHTS, but when I switched back to the 280ZX CHTS, the problem went away. From examination of my Haynes manuals, it looks like the 280ZX CHTS and Z31 CHTS have the same (or similar) resistance values, so for now I will be using the 280ZX CHTS in my L28ET powered by 84 Z31 ECCS.

 

Sean

 

73 240Z, L28ET, 8.8:1 CR, T3/T04E, NPR IC, Z31 ECCS

Breaking in the rebuilt motor @ 6-7 psi.

[KRAYZ]

Just a silly off the mark question...I noticed that all of this was for turbo apps., Any idea if i could use this for a N/A engine?