TPS is messing with me, and winning

[beachsuburban]

Alright I have the 220 tbi, base volts should be .5 to 4.5 at WOT. Now I have read all about the new ones being out of spec so I bought 2 aftermarket and 2 OEM. The one in there I slotted a few years ago the get the base down but in doing so the max WOT was like 4.3 which is the reason for this attempted fix.
So the aftermarkets were .78 at base but under 4.5 at WOT even with the bench test. The OEM, from 2 different suppliers are coming in at .98 base 4.68 WOT.
Anyone out there have a good solution?
Thanks!

 

[gmbellew]

none of those numbers are out of whack enough to cause a problem. Just run them....

edited - 0.98 at idle is a tad high, although i think is still below what will throw a code. I'd just bend the TPS tab to get it closer to 0.7 and run it.

 

[Ricko1966]

@gmbellew I was just about to jump in and say turn it all down .10 - .15 and run it it's close enough. But I see he's in good hands,a great night.

 

[beachsuburban]

Thanks for the idea, but wont that drop the WOT number too low? Another thing is the idle goes up if the base is above .5 so will all that have to be adjusted if the new base will be .7?
Thanks!

 

[gmbellew]

Thanks for the idea, but wont that drop the WOT number too low? Another thing is the idle goes up if the base is above .5 so will all that have to be adjusted if the new base will be .7?
Thanks!

How are you adjusting the TPS voltage? The actual voltage shouldn’t affect idle speed. Bending the tab will drop the top end voltage. But not enough to matter.

 

[beachsuburban]

Not sure what you mean by adjusting but I have the meter hooked up and I'm pressing in on the throttle arm to see voltage movement.
So I bent the arm and have it at .75 base with the idle screw all the way out. Wot is at 4.48.
I have read into this and from my understanding, PLEASE correct me if I'm wrong, if the ECM sees anything above .6v it wont signal its at idle and not run correct.
Because the ECM assumes the throttle is already slightly open at idle.
It can cut back the IAC steps and idle control will be unstable or high it can deliver a bit of extra fuel at idle and tip-in with a rich stumble, could mess with decel fuel cut-off (may not cut fuel properly on coast) and could trigger idle learn issues (it thinks “closed” isn’t really closed)
On the WOT side anything below 4.5 V risks the ECM not recognizing true WOT and therefore not switching into full-throttle enrichment. I guess at WOT it’s supposed to ignore O₂ feedback and dump fuel from a rich open-loop table. If TPS never reaches that threshold apparently the ECM stays in part-throttle enrichment so the mixture is too lean under heavy load, and that can causes bog, ping, or TBI backfire and can also limit spark advance.
Thanks!

 

[gmbellew]

The ECM reads the TPS each start and uses it as a reference to know when to enter idle mode. It will assume WOT for voltages below 4.5. I don’t know what the actual threshold is, but I’d guess it is anything over 4. This is all laid out in the GM emissions and drivability manual.

And you shouldn’t be making these adjustments at the idle screw. Bend the TPS tab. Using the idle screw to do it will mess up what the IAC is trying to do to maintain target idle speed.

 

[beachsuburban]

Interesting, thanks!
When I put the new TPS in, at idle it was noticeable higher.
I didn't make any adjustments at the idle screw, just wanted to get a true base voltage for the TPS without any interference. I'm resetting ECM and the idle when finished.

 

[beachsuburban]

So when its being adjusted it has a see saw effect, if I lower the base the wot also lowers. Question is where should it be favored, should I be closer to a lower base voltage or a higher WOT volt?
Thanks!

 

[gmbellew]

IMHO you are really over thinking this. A wide range will give good results. I think anything below 1.25v doesn’t set a TPS voltage code. If you are in the 0.5-0.8 range at idle I’d not sweat it. And if you have that and also >4.0 at wot on the skinny pedal then all is good.

 

[beachsuburban]

Alright cool, thanks again

 

[Sad Sack]

Remind me to stick to carbs.

 

[Ricko1966]

Remind me to stick to carbs.

Oh this isn't hard at all. You know how some guys can over analyze tire pressure or plug gap,or mixture adjustment. This is one of those deals. Somewhere he heard it has to be this and that blah blah. If he had just set it so he had roughly .5 and 4.5 there would have been no problems a little higher,a little lower nbd it's a very forgiving system. TBI is a very simple,very dependable system.

 

[Sad Sack]

Oh this isn't hard at all. You know how some guys can over analyze tire pressure or plug gap,or mixture adjustment. This is one of those deals. Somewhere he heard it has to be this and that blah blah. If he had just set it so he had roughly .5 and 4.5 there would have been no problems a little higher,a little lower nbd it's a very forgiving system. TBI is a very simple,very dependable system.

Cool, I have little experience in the more complicated fuel and electrical areas, and my learning comes mainly from observing or learning the hard way to fix things. Love the older stuff though EZ PZ! Just didn't grow up with a lot of gear heads for friends so a lot of self-teaching was needed. I'm ok with a wrench but I have so much to learn that's for certain.