TPS readings
 

HI,
Can anybody confirm the TPS readings that you are supposed to get using the FSM?

This is a 87 NA and is failing emissions on high hydrocarbons.
Page 4A-50 of the FSM provides the following info:

A-B
Idle 1 kOhm
Full open 5 +/- 1 kOhm

A-C
Idle 5 +/- 1 kOhm
Full Open 5+/- 1 kOhm

My problem is that on the A-C test @ full open, resistance drops to about .6 kOhm. I have another TPS that behaves the same way. Can anybody confirm that resistance is not supposed to change on the A-C test between Idle and Full open. (Just want to make sure there's no typos)
It would be nice to narrow this down to the source of my emissions problems but I don't want to replace a part if it is not bad.

Thanks
Charlie

Weird...

The A-C test is supposed to be opposite of the A-B test, so the FSM is wrong???

A-B 1k -> 5k
A-C 5k -> 1k

I recommend to try and set A-B to 1k-ohm at idle rest and engine warmed up fully.



-Ted

Additional information
 

Ok - I have looked at Bob_the_Normal's (Gary) post. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/how-things-work-inside-tps-360803/

It does look like the resistance should not change when measuring the A-C leg.

I dialed down my TPS to 1kOhm and now I am throwing a code. 1 long 1 short which is the indication for bad TPS.


Has anybody tried any of the aftermarket TPSs out there?
I note that Niehoff Ignition offers p/n FE40172 which is supposed to replace oem part number N326-18-911a Their parts are carried on parts america website.

http://www.partsamerica.com/SelectPa...ition%20Sensor

The problem is that when you bring up the part information, "Oxygen sensor" is listed.

However if you go to the niehoffs site at
http://www.niehoff.com/pdf/NieEmission.pdf That part is listed as a TPS.

I don't want to advertise but the price does seem almost as low as used units on ebay.


I also note that KEM parts has a part number for the TPS, 141-7002, but can't find any information as to weather or not this part is in production.

I two more part numbers for the TPS:
NAPA 2-16704
Borg Warner: EC3237
Both are supplied by Niehoff so you will get the same product, just a different box.

I also called KEM and they do not have that part number in production.

Actually, the fsm is right. JPG attached.

I THINK where your going wrong, is that the plunger needs to be fully depressed with YOUR FINGER, not the throttle linkage. Thats the only way your going to fully depress the plunger.

As for your question, A-C reads approx 4.8K and A-B reads 5.1K on my throttle sensor.

When the throttle is fully closed, and NOT riding on the fast idle cam, the reading should be apporx 1K, A-B. Or if the plug is fully connected, and the key is to ON, pin A should read 1volt approx.

Or when you set your tps using the light method, the end result is approx 1vdc on the pin A (green/red wire of the harness side of the plug).

And I've no idea why the A-B and A-C should read alike when at opposite ends of the spectrum. Got me. Ain't normal and fully unexpected. But true.

As far a the emissions go, after setting the tps I'd concentrate on the proper operatinon of the acv, especially input of the relief and switching solenoids to the acv and to make sure the dump pipe of the bottom of the acv isn't dumping all the time.

Both solenoids are related to the tps setting, along with the water temp switch on the bottom of the radiator. If the water temp switch on the bottom of the radiator is showing OPEN, then the relief solenoid will not get energized and the airpump air will dump overboard instead of going to the exaust ports.

A properly set tps at idle, will result in the relief solenoid being energized and the switching solenoid de-engergized. At idle.

Also some gains can be had from leaning the variable resistor out. But make sure the engine will still idle fairly well after adjusting it.

Hailers,
Thanks. My A-B is within range it is the A-C reading that is off. The manual indicates that the resistance should not change with the position of the plunger. After looking at the photos and taking apart my spare I can see why it should not change. If I get a chance I will post a sketch which explains the workings of the TPS. I suspect the A-C leg is there to tell the computer that the TPS is working and connected. I have ordered a new TPS from pep boys.
Again thanks for the info Hailers. I have been a avid reader of information on this site for quite a while and have always found your posts accurate and informative.
Regards,
Charlie

Yeah. I re-read part of what I wrote, and I think I fudged up on the A-C in the way I did it this morning. Simple thing to checkout but I think I screwed up on doing the A-C. I'm going to re-do that later today. You almost have to work at it to screw that up, and I did.

Tps Sketch / Schematic
 

I hope this sketch helps further demystify the workings of the tps and better explains why the resistance should not drop on the A-C circuit.

I checked my tps again. A to B when showing 1K at idle........the A to C reads 4.6K at that time. So the FSM is right.

A to C when the plunger is full open, reads .609K

A to C when the plunger is full closed, reads 5.16K

A to B when the plunger is full open reads 5.3K

A to b when the plunger is full closed, reads .596K

I'm going to print out your jpg and take a look. Off to business right now. Later.

Didn't I say that earlier? :P


-Ted

Yes. What I shoulda, coulda, woulda said, was the fsm is right in respect to the
A-C reading when A-B reads 1K.

When the A-B reads 1K the A-C on my tps reads 4.65K, just like the manual.