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Hardwyre

TPS Throttle Position Sensor Adjustment (Pre)Guide -'76 280Z

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This is my first attempt at playing with the TPS, but I wanted to get some pictures up because I haven't been able to find any good pictures or guides for adjusting these TPS modules.

 

If there is any feedback on this, please feel free to suggest changes, etc. I'm new to Z cars and just going off of what I've read.

 

I'm writing this while I'm doing it, so it hasn't been "tested" yet, but the theory makes perfect sense.

 

Here is the thread I found that lead me to rip open my TPS and check adjustments on it:

 

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

Does it seem like your non-turbo FI Z/ZX has lost some of its 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!

My Z has been getting about 16 miles a gallon regardless of whether or not I'm putting my foot into it (though apparently I need to try driving it closer to it's torque peak instead of aiming for lowest RPMs when cruising). Also, I'd noticed she smells rich even under light throttle.

 

As the quote above states, the TPS module, a '76 280Z in my case, has a tendency to migrate the WOT arm inward towards the rest of the contacts. When I opened mine up, I broke off the housing snaps because the plastic was brittle, so it's probably the factory switch. I took 1000 grit sand paper and cleaned up the disc and ball contact points, but had verified with a volt meter that they had been contacting earlier in the unmodded state.

 

What I found was this:

IMG_2329.jpg

The channel that guides the switch is a three step.

The first step makes full contact with the idle switch.

(I'm assuming) the second step is for partial throttle.

The third step appears to allow for wide open throttle and it is here where the other contact should be established.

 

Between the steps are the ramps that connect the three steps.

As I understand it, a properly adjusted TPS should break the idle contact just as you start to give it some throttle.

 

What was happening with mine was that the idle contact seemed to be about right. But even before I was done moving down the ramp to the middle step, I'd already be making contact with the WOT side of the switch. I figure it would be approximately 5 degrees off idle and I was closing the other circuit.

 

IMG_2330.jpg

 

If I am indeed looking at this correctly and understand things, this could account for a fair amount of my (guestimated) rich running problems.

 

I had already approximated the suggested 30 degrees off idle. The coincidence is that 30 degrees coincides with the start of the third step's ramp. As I said, prior to this adjustment, I was making contact with the second circuit all the way through most of the first ramp and beyond.

 

So I grabbed a pair of pliers and GENTLY bent and tweaked it until it started making contact just after the second ramp started.

IMG_2332.jpg

 

Now there is significantly more gap between both contacts and the center pin when I'm in the middle channel:

IMG_2333.jpg

 

So now I'm going to go reconnect her, adjust it so the idle disconnects just as the throttle opens, and see what happens. A toast to analog technology!

 

Edit: I noticed that she doesn't seem to have as much get up and go at partial throttle now but there is a noticeable point in the throttle where power picks up. This makes sense since she shouldn't be dumping fuel under partial acceleration. I so have a fuel smell coming from the engine compartment, so I think I might have a leak somewhere. Isn't there a dye and black light method of checking for leaks?

 

Follow up: After running a couple tanks of gas through the Z, I have definitely accounted for an increase in fuel efficiency. I went from getting ~15 MPG to over 18. Next step is to adjust the timing and check out the AFM's spring. I have a wideband o2 sensor and gauge coming in so it'll be interesting to see her A:F ratio.

Edited by Hardwyre
Test drive.

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Great pictures, I too just took of my TPS after the car would idle good at 600rpms, then stall/bog/cough/backfire through intake between 1-2.5K, then come on crazy strong.

 

My question, what are the repercussions of just leaving this litter bugger off?

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