TPS moisture

[Reptoid Overlords]

I've replaced the fuel injector/CHT/Thermo connectors and fusable links. I was thinking of testing and cleaning the voltage drop resistor next. I had an intermittent stall that ended up being a faulty alternator hold down bolt, causing the belt to loosen. Replacing the bolt and re-tightnening the belt fixed it. Any advice or heads up about troubles regarding the voltage drop resistor would be appreciated.

 

It'll be the last electrical connection that I'm aware of that hasn't been tended to. The pocket calculator under the drivers side kick panel has been tested per FSM along with a good deoxit treatment. Ignition module appears to be functioning as intended.

 

[Careless]

I'm not familiar with the particular part you're referring to. is it an Injector impedance box with 7 pins? one input power wire and 6 outputs to the individual injectors? some injection systems are squirted in batches or pairs, so it might only have one input wire and 2 or 3 outputs.

if so, its most likely just a cluster of resistors in there. somewhere in the FSM or online there should be an impedance measurement and pinout you can use to test if the resistors aren't blow or shorted or degrading.

Edited March 26, 2017 by Careless

[Reptoid Overlords]

The dropping resistor, as its called, are indeed 6 resistors that reduce voltage to the injector for protection. Looks like they started using them in 280z's EFI systems. I have no cause for concern that mine is bad, but it needs to be cleaned up and tested just to make myself feel better. I was just curious if you had run into any problems with them.

[Zed Head]

On 3/19/2017 at 11:20 AM, Reptoid Overlords said:

Every few months or so I'm pulling the TPS out of my N/A '80ZX to find tiny amounts of moisture built up inside causing a slight miss at a specific RPM(1600-1800).

That's an odd solution to the problem since the TPS (more correctly called a TVS) only changes state right off idle if adjusted correctly and again at full throttle.  Shouldn't be in the picture at all at 1600-1800 RPM.  Red herring?  Or maybe it's misadjusted.

[Reptoid Overlords]

I should've updated as I think I've diluted the thread a bit. There was moisture in my TVS, but my rpm related problem was due to the alternator hold down bolt coming loose, causing the belt to slip preventing smooth voltage distribution to wherever it needed it. I guess that rpm was just the right spot to make it run weird. Thanks for your reply.

[Careless]

22 hours ago, Zed Head said:

That's an odd solution to the problem since the TPS (more correctly called a TVS) only changes state right off idle if adjusted correctly and again at full throttle.  Shouldn't be in the picture at all at 1600-1800 RPM.  Red herring?  Or maybe it's misadjusted.

It should be noted that Nissan TPS/TVS are known for poor contact buttons and finger-follower deformation which can change its range of response where the open/close circuit will function- mainly due to the center conductor/pin binding up when you jab the throttle sharply instead of easing into full throttle. it's only brief, but by design- over time, it can deform the contacts within the unit because of how the plastic trench that the center pin rides on is designed. the area of the trench that moves it to the open position is a short and sharp zig-zag. 

if it were misadjusted + had misaligned contacts, it might hit that RPM. can't say i've actually tested various units and recorded the number. I just prefer to just adjust them and get them working.

Nissan partially fixed the issue on the Z31 model by adding a linear potentiometer within the TVS, essentially turning the Z31 unit into a TPS, as you've mentioned- there is a difference. Though for some reason, the fix was only adopted on the automatic ECUs, even though all the TPS units had the additional 3 pin sumitomo connector hanging out the bottom/side.

Edited March 27, 2017 by Careless

[Zed Head]

8 hours ago, Careless said:

It should be noted that Nissan TPS/TVS are known for poor contact buttons and finger-follower deformation which can change its range of response where the open/close circuit will function- mainly due to the center conductor/pin binding up when you jab the throttle sharply instead of easing into full throttle

I've never heard of this problem.  Usually they're just corroded from sitting inactive.  Never read of such a detailed flaw in the design.  Where did you get your info?

[Careless]

I didn't "get" my info anywhere, I discovered it on my own through trial and broken parts. I have taken apart many of these TPS units. One of the first used ones I tried to diagnose issues with had a slightly deformed centre contact- the one with the button that rides the trench in the nylon base. I literally chased harness gremlins for months because I had already changed and adjusted the TPS thinking it had to be the issue with why my car was idling weird all the time- it seemed to fix the issue... or so i thought. I was wrong. I just gave up messing with it at one point until I installed Nistune and logged drives on my way to work.

After fitting my 60mm turbo, I was dicking around and seeing how fast it spools by conducting repeated closed-to-wot throttle jabs. I must have done at least 10 to 15 in succession, one after anoter. When I parked the car, it would not idle correctly. I used nistune to check TPS logs and found that it was not closing... I opened both previous units that had seemed to fail, and the one I had just taken off had a noticeable kink in the blade. The one which that one replaced the first time around was deformed, but not kinked. The blade was definitely bowed more than normal. Almost as if the nylon piece pushed it further than it could possibly move in the trench.

I have 3 or 4 more TPS units in storage because I've seen two show erratic behaviour due to the same issue, and because they're inexpensive at junkyard expeditions. 

It's a common mod to intentionally bend the 280zx blades to adjust the function of the TVS, but these were sealed Z31 or other VG30E/T units, so I ruled that out.

It's also possible that the reason they bent is that the grey stick that is what swings the nylon pieces around possibly deformed a bit causing the center pin to bottom out on the end of the trench, but I do know that they were bent before I opened them- I did not modify them. 

If you spray silicon lube on the nylon piece, they move noticeably smoother too. Maybe that says something. In any case, I'm not saying they're all doomed to fail. Manufacturing tolerances probably have a lot to do with it, and that's why they made replacements. It's still a nice and compact design.

Edited March 28, 2017 by Careless