Have a 1996 Nissan Hardbody D-21; 2WD, Automatic. Runs good when cold, stumbles when warm both at idle and running. Vacuum is 18", Fuel pressure is 34psi, has a new distributor timing is set to 10 BTDC, spark plugs are a light brown. My Zurich (HF) Scan tool will not recognize any Nissan before 1998, purchased the 14-pin plug to 16-pin plug so it Should be able to read the ECM. No luck. Looking for ideas for a scan tool that will not cost all of my grandchildren and my Harley. Also tested each fuel injector -11-12 ohms. Anybody have any ideas; the owner is retired and doesn't have a lot of money.

I actually make a 3D printed ECU remote tool for those pre-OBDII trucks that plugs into the check connector. One that's just a handheld box, and another style that's designed to replace the ashtray in the center console for constant monitoring. Be happy to give you more details if you're interested.

As for the original problem, do you have the factory service manual for it?

I would like to know more about your ECU tool if you don't mind. I have a '93 D21 so I don't know if your diag tool is applicable or not. Thanks.

It works for a 93. I think the applicable years are something like 88-95, and it just plugs into the check connector under the fuse box. The button switches modes, and for the ashtray mounted version the rocker switch kills the LEDs if you want them off at night. The box version looks like this, and the ashtray like this.
Either version is $50 if you're interested.

I bought one these from Kiv (on another site), and can confirm it works perfectly (the box with cable extension, not the ashtray). I also have a ‘93.

You still have to read the flashes from the box in mode 3 for the codes, just like you would from the ECM, but it saves the trouble of removing the passenger seat each time.

Thanks to both of you. Just to confirm, With this tool I won't have to access the ECU at all? Everything's done through the box?

Correct. I went through and tested all 5 modes in about 5 minutes. You read the flashes from the box, and you use the button on the box to change modes instead of spinning the little screw on the ECM.

It also saves you the trouble of resetting that screw back exactly where it started on the ECM, which is needed because it’s also an idle adjustment screw.

Basically takes all of the hassle out of reading codes or testing your O2 sensor in mode 1 etc.