"On the Fly" TPS Adjustment for NON-TURBO FI Datsun Z Cars
  Jim Lucius  


Does it seem like your non-turbo FI Z/ZX has lost some of it's pep? Getting lousy mileage and can't figure out why? Have a look at your TPS (Throttle Position Switch). Located on the left side of the throttle body, it is contained in a small black plastic box that comes off easily with no tools. The switch is made up of two contacts. One for idle, and the other for full throttle enrichment. Ideally, only one set of contacts should make at a time. At idle, the rear contact, and the moveable arm (connected to the throttle valve) should be the only contacts made. As the throttle is advanced, the idle contact should break, followed by a brief range where no contacts are made, then the full throttle enrichment contact should make. There should be roughly 1/3 of throttle travel before the second contact makes.
TIP:  When your engine gets wet, the TPS is responsible for more bad running engines than anything else.  Dry these contacts after an engine wash, and you should notice no ill effects.
What to do? Of course, following the directions in your factory service manual will get the desired results and is the only dead-on way of doing things. There is an "on the fly" way to do it as well. The first thing to verify is the idle contact. At idle (engine off) make sure the movable arm contact and the rear contact are touching. Now slowly move the throttle forward, and make sure the contact breaks as soon as the throttle advances. If the contact does not break right away, or is not touching at all, loosen the two screws on either side of the TPS. Reposition the switch until satisfied that the idle contact operates correctly. Tighten screws when finished. Normally, this contact stays OK, and doesn't need adjustment. The other adjustment requires no tools. This is the one that normally goes bad. Nissan ganged this contact with the idle contact, so that they would remain fixed in relation to each other. The problem is that this arm ends up reverting to a closer position to the idle contact. Adjustment is made by slightly bending the contact arm to achieve the correct distance from the idle contact. Gauge the travel of the movable (center) contact. Estimate where 30 degrees of travel is, and bend the arm of the forward (full throttle enrichment) contact until that is the position where it makes. Operate the throttle several times, and verify that the idle works properly, and that the full throttle contact makes at 1/3 travel, and stays made through full throttle. When satisfied, put the lid back on, and take it for a spin. You should notice the difference right away!