Help! 1982 TPS help please

[Flowjoe]

Went to check the setting on the TPS today. Signal wire shows .624v at closed position. Ran it through the range of motion and at WOT it showed just 4.25v. To further complicate things the hot wire is showing just 5.08v. Before I start messing with a car that runs and drives thought I should seek input here. If I understand the relationship correctly (and I might not ) then whatever I add or subtract to the static/closed position should end up added or subtracted for the WOT figure. But even if I adjust the TPS to .525+/-.025 static this should add only .1v which is not enough to raise 4.25v to 5v. And none of this addresses the hot wire carrying only 5.08v.

Where should I be starting on this? Is the TPS bad? Is something else potentially out of adjustment?

Ground seems solid (connected lead to ground wire and alternator bracket and checked for continuity...strong signal. Then connected voltmeter to ground wire and hot read 5.08v shifted voltmeter ground to alternator bracket and still got 5.08v...no drop).

 

[Antz81]

5v on the 'Hot' wire to the TPS is correct. So that's one issue that you don't need to worry about. This is supplied via the ECM and not direct from the battery.
Your TPS may just need adjustment. Not sure of the procedure for an 82 so can't help there. If what you have said about it is correct though, then i can tell you this one thing:
By the sounds of things you need to make roughly a 0.1v adjustment at closed position with a result of roughly a 1v adjustment at WOT.
Not sure on the type of resistor used within the sensor, but if it is a logarithmic type (instead of a linear type) then you will probably get the results you are hoping for by adjusting it.
As I said above i'm not sure about the procedure for an 82 but hope that helps.

 

[KANE]

Another thought... even if the TPS shows the correct value at idle- and then roughly the correct value through mid level position- it could still be bad if you can't adjust it to get WOT readings that make sense. In other words, it isn't going to give you the right reading at WOT no matter how much you adjust it because it is just worn out.

An easy way to test for that is to manually turn the butterflies to WOT (with the engine off but the key in run position). You should see the voltmeter give you the right reading. If it doesn't, loosen the two Torx screws on wither side of the TPS and then manipulate it until you get the correct readings throughout the range (idle & WOT). You may end up seeing the side of the TPS where the pigtail connects sit up at more of an angle. If you end up running out of adjustment and still can't get to WOT readings- and your butterflies are clearly at WOT- then your TPS is the culprit.

Hope that helps!

 

[Flowjoe]

Both of those responses are very helpful.

I was certain I had read that power-in was full and constant 12v (obviously I was in error) so knowing that I am good at ~5v is a relief.

Had not considered that it may not be a linear relationship. When I started to do this I was prepared to have a number out of spec and adjust accordingly (fairly straightforward it would seem) but what I found left me reluctant to start fiddling without more info. I wanted to be certain that there was nothing else that could be influencing those numbers? Now it seems clear that I just need to move the TPS and see what happens.

For the record, all of my "test data" I provided was done with the engine not running, key in the run position and throttle manipulation by hand at the manifold.

Thanks again, I'll let you know what comes of the adjustment.

 

[Flowjoe]

Update

Did get around to adjusting the TPS (just waited for a Snap-On MTG-2500 to show up after a N EBay purchase). The scanner backed up my reading of .624 at closed position. Adjusted to .52v (scanner started giving me problems - user error I believe - and my multi-meter only goes out 2 decimals at lowest whole volt setting). WOT now reads 4.08v. In order to attain 5v at WOT I would need. To move the TPS in such a way that the closed setting would be way out of spec. Shall I assume the TPS is bad and replace it? Or am I missing something else? FWIW, the throttle did feel slightly more responsive after the adjustment...perhaps it was just me as it was all seat of the pants but it seemed more responsive.

 

[Antz81]

Did get around to adjusting the TPS (just waited for a Snap-On MTG-2500 to show up after a N EBay purchase). The scanner backed up my reading of .624 at closed position. Adjusted to .52v (scanner started giving me problems - user error I believe - and my multi-meter only goes out 2 decimals at lowest whole volt setting). WOT now reads 4.08v. In order to attain 5v at WOT I would need. To move the TPS in such a way that the closed setting would be way out of spec. Shall I assume the TPS is bad and replace it? Or am I missing something else? FWIW, the throttle did feel slightly more responsive after the adjustment...perhaps it was just me as it was all seat of the pants but it seemed more responsive.

Everywhere I look says you need 4v minimum at WOT. So 4.08 should be fine.
I personally would like to see it higher. Its up to you if you want to replace it to try get it higher.

 

[Flowjoe]

Everywhere I look says you need 4v minimum at WOT. So 4.08 should be fine.
I personally would like to see it higher. Its up to you if you want to replace it to try get it higher.

So far every reference I've run across says it should be 5v...no range, just a flat 5v. ad Not being argumentative, just reiterating what I've read.

Thinking through it all I come to the following:

1) How do I determine if 4.08v is truly signally the ECM that the car is at WOT allowing it to make all of the necessary adjustments to fuel and spark? If it is not truly signaling WOT then would it read lean on the outflow?

2) What else could cause the TPS to not have 5v at WOT?

Your continued help with this is very much appreciated.

 

[KANE]

So far every reference I've run across says it should be 5v...no range, just a flat 5v. ad Not being argumentative, just reiterating what I've read.

Thinking through it all I come to the following:

1) How do I determine if 4.08v is truly signally the ECM that the car is at WOT allowing it to make all of the necessary adjustments to fuel and spark? If it is not truly signaling WOT then would it read lean on the outflow?

2) What else could cause the TPS to not have 5v at WOT?

Your continued help with this is very much appreciated.

When I had a problem with the TPS, I ended up purchasing a new TPS.

Here's another thought... let's assume your TPS is fine. Your 32 year old cable could have stretched a bit too. Mine did.

In that case, even if you manipulate the butterflies by hand, you aren't replicating the real conditions of the pedal because it would still be out of spec. You can use a rat tail file on the bracket to elongate it a bit so that you can adjust it forward / backward to get full travel on WOT. While that may seem like a crude solution, sometimes things won't work out any other way- especially when you start making changes to things and find a new cable is pricey and rare.

FYI- I had to elongate the bolt holes when I went to an aftermarket intake. My cable had also stretched a little over time- and when combined with an out of spec TPS (was getting only 85% WOT), and an aftermarket intake it created a 95% WOT scenario until I adjusted the bracket. Once I elongated the holes on the bracket, got to 100% WOT (only needed 1/2 a centimeter in elongation).


Another question while we are talking about the ECM's control of spark and fuel- what is your base timing?

Everything starts from there. Is it set to at least the factory specs or perhaps 2 degrees or so ahead? If so you are fine.

 

[Antz81]

So far every reference I've run across says it should be 5v...no range, just a flat 5v. ad Not being argumentative, just reiterating what I've read.
2) What else could cause the TPS to not have 5v at WOT?

Perhaps i should clarify, the ECM needs to see 4V minimum to see it as being WOT, ideally the reading would be closer to 5V.
You probably have a worn TPS, or something like Kane said above.

 

[Flowjoe]

When I had a problem with the TPS, I ended up purchasing a new TPS.

Here's another thought... let's assume your TPS is fine. Your 32 year old cable could have stretched a bit too. Mine did.

In that case, even if you manipulate the butterflies by hand, you aren't replicating the real conditions of the pedal because it would still be out of spec. You can use a rat tail file on the bracket to elongate it a bit so that you can adjust it forward / backward to get full travel on WOT. While that may seem like a crude solution, sometimes things won't work out any other way- especially when you start making changes to things and find a new cable is pricey and rare.

FYI- I had to elongate the bolt holes when I went to an aftermarket intake. My cable had also stretched a little over time- and when combined with an out of spec TPS (was getting only 85% WOT), and an aftermarket intake it created a 95% WOT scenario until I adjusted the bracket. Once I elongated the holes on the bracket, got to 100% WOT (only needed 1/2 a centimeter in elongation).


Another question while we are talking about the ECM's control of spark and fuel- what is your base timing?

Everything starts from there. Is it set to at least the factory specs or perhaps 2 degrees or so ahead? If so you are fine.

I had considered the cable or maladjusted throttle linkage. The difference between operating the throttle linkage by hand at the manifold and at the pedal is ~.08-.12v, so not a lot really. Certainly not even close to the .92v I am short overall. But an excellent thought none the less.

Good point about 32 year old parts ...most of my hobby cars are pre 1970 so worn components are a regular occurrence. I still think of the '82 as a "new" car (I remember the year Crossfire Injection was released and what a big deal it was before it was eclipsed by TPI) even though intellectually I know the car is 32 years old.

Timing is is a good point too. I just started by checking the TPS ('cause it was simple to do) and found it out of spec so started chasing it. The car runs fairly well. The main issues are slightly hard starting (cranks over a bit before catching) slightly high idle when cold and stays that way a bit too long, not quite as much "punch" on kick down as I would expect (making me think WOT is not truly achieved) and it takes awhile for it to come down to a 650 idle when stopped sometimes (stays around 1000 then drops down to 650 in intervals of about 75-100RPMs over the course of a few seconds). Just want to try and make it run at its best.

 

[Flowjoe]

Perhaps i should clarify, the ECM needs to see 4V minimum to see it as being WOT, ideally the reading would be closer to 5V.
You probably have a worn TPS, or something like Kane said above.

OK, got it . Any way other than what I have done to verify the health of the TPS? Hate to just buy parts and throw them at the problem.

 

[Antz81]

OK, got it . Any way other than what I have done to verify the health of the TPS? Hate to just buy parts and throw them at the problem.

Unplug the TPS and measure the resistance between pin 1 and 3. It should be somewhere around 10Kohm (8K-12K is possible) from memory.
Then measure the resistance between pin 1 and 2 while slowly moving from idle to WOT. You should get a smooth change is resistance. If you get any jumps or dead spots then replace it.
This can also be checked using an oscilloscope, but i'll assume you don't have access to one.

 

[KANE]

OK, got it . Any way other than what I have done to verify the health of the TPS? Hate to just buy parts and throw them at the problem.

I'd consider the replacement of the TPS as as preventative repair / investment at this point.

They can be found for under $70.

Based upon everything you've told us... I'm sure you'll get to the proper reference voltage at WOT at this point of you replace the TPS. And if you don't... that's one less part to fail in the near future.

 

[Flowjoe]

Unplug the TPS and measure the resistance between pin 1 and 3. It should be somewhere around 10Kohm (8K-12K is possible) from memory.
Then measure the resistance between pin 1 and 2 while slowly moving from idle to WOT. You should get a smooth change is resistance. If you get any jumps or dead spots then replace it.
This can also be checked using an oscilloscope, but i'll assume you don't have access to one.

LOL...spot on, no oscilloscope here.

I assume 1 is constant hot and 3 is ground - yes?

thanks!

 

[Flowjoe]

I'd consider the replacement of the TPS as as preventative repair / investment at this point.

They can be found for under $70.

Based upon everything you've told us... I'm sure you'll get to the proper reference voltage at WOT at this point of you replace the TPS. And if you don't... that's one less part to fail in the near future.

True enough, just wanted to sure I had the culprit as I would surely hate to replace the TPS and find that something else is responsible for the low reading

 

[Antz81]

LOL...spot on, no oscilloscope here.

I assume 1 is constant hot and 3 is ground - yes?

thanks!

That's right. Not that it really matters in this test. Since you should unplug the TPS anyway. If you don't unplug it then none of your readings will make sense.

 

[Flowjoe]

That's right. Not that it really matters in this test. Since you should unplug the TPS anyway. If you don't unplug it then none of your readings will make sense.

Right...but I wanted to be certain I was testing the correct pins so the "ground" and "hot" were just convenient designations be sure I was using the correct pins. I might have ended up test resistance between ground and the variable voltage pin...the results of which would have confused me even more