79 SA 12a with Nikki carburetor.

So I have a couple stumbles in my power band after reverting the engine from the Weber 45dcoe to the factory Nikki. On a whim I decided it may be TPS related so I unplugged it and the hesitation is completely gone. Just wondering, what does the TPS control on a carbureted car? Secondary butterflies? I haven't tried to get on the car hard at all seeing as how I can only drive it up and down the yard (needs new tags).

 

There isn't a TPS. Are you talking about the float bowl vent by chance?

 

The 3 prong connector part on the front of the carburetor. Looks like a prehistoric TPS to me. The extra carburetor that I have off of an 83 had a TPS using the same connectors so I figured that's what it is. Anyway, when I unplug it my stutters go away.

 

My guess is something related to emissions. As there is basically nothing on the carberetor that actually *needs* to be plugged in from what I can remember....

And to me, in my limited experience and knowledge of these cars (I'm leanring though), it doesnt make sense that we have a TPS...what purpose would it serve?

 

yup no tps on the old Nikki or any carburator for that matter. Its all vaccum operated unless you do the mechanical secondaries. Posting a picture would make things easier

 

Yep, it's emissions related. It's in the FSM (4A-37 in '85, 1A-52 in '82) and the Wiring Diagram. 3 prong connector (orange, black/red stripe, green/red stripe on the bottom)

 

interesting.. i thought the TPS stands for throttle position sensor was for the 13b gslse fuel injected

 

It is for fuel injection. Hence why our cars do not have one.

I suppose there could be one on a complex newer age carb'd car with electronic controls etc, but i would just think itd be pointless.

Or at least Ive never heard of one for carbs, maybe someone else has.......

 

I honestly didn't know what it was. It looks like the TPS on my 86 and my old 87 and 88.

I figured since there was no ECU or anything fancy it must be for controlling the amount of fuel at certain RPMS or maybe to mark the throttle position for timing when the secondaries open up... ???

Also what is the part that is right near it? The yellow connector with the solenoid? There is no 79 repair manuals and the 79 is different from all of them.

What actuates the secondary butterflies? Just vacuum from the engine? Or should they open by pressing the throttle without the car running?

 

The 12A cars do in fact have a TPS (or at least the same thing as one). It serves the same basic purpose as on older FI cars (like the GSL-SE) as it reports the throttle position to the ECU. The FSM refers to it as the throttle sensor.

There is a test on the 12A throttle sensor similar to the GSL-SE TPS adjustment (2 light rig). The throttle sensor test can be found in Section 4A, pg. 9 of the FSM. There is additional testing info located on pg. 4A-37.

The throttle sensor is part of the deceleration control system. I would have to look in more detail to see what all it controls.

If I remember correctly, the 12A sensor is electrically the same as the GSL-SE TPS (resistance goes between about 1k and 5k).

Edit: Page numbers are from the '85 FSM

 

weird, i stand corrected.

 

It is emissions related. You don't need it for the car to run. Also, to be clear, ECU in this case is Emissions Control Unit. Most people think of ECU=Engine Control Unit and are shocked to find one lurking in their 12A powered car.

NCross: Check out the test for the sensor. It doesn't control anything fuel related directly, but might be messing with your vacuum solenoids or something if it is out of whack.

 

Pictures...

BTW my rats nest and all emissions are gone. So it's safe to say I can remove these parts?

Also, the single connector on the driver side of the carburetor, black and white I believe going into what looks like the richer plug on the opposite side... Can this be removed/unplugged as well?

 

the 81-85 cars use a throttle position sensor, on those it controls the ACV and the shutter valve, and the distributor vacuum advance(s).

the 79-80 cars i think just have an idle switch. use is probably similar, although id have to look in the book(s)

 

I just unplugged everything. Drove it up and down the street a couple times and seems to be in good order so I'll just keep them unplugged.

 

When stripping emissions, rats nest and cleaning up the extra 'junk' off of our carbs, the TPS is removed.

I'm surprised most of you who have reworked carbs didn't realize that there is a TPS, tsk tsk.

 

we actually had to troubleshoot a BAD one at the dealership about a year ago.

 

I just need to make a couple block off plates for the ACV and remove the TPS and whatever else that junk on it is. I've had it unplugged for a few days now with no problems.

 

Here is my stripepd mani and carb. Nothing left but a throttle cable:

 

Yeah, the presence of a TPS really threw me off when I first learned of it. Only saw them on FI cars before that...

 

I stand corrected. I didn't know that was a TPS.

Out of curiosity: could it, in theory, be used as a TPS in a custom EFI setup using the Nikki as a throttle body?

 

Jeezus...

Did you use JB weld to patch all the holes up?

 

Yes, that and Block Off plates where needed

 

Same thing I did, i retained the choke though. Makes it easier to start on cold days.

 

Perhaps. You'll need to find the ohm range of thqt TPS, then see if it's compatible with your standalone. Interesting idea.