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TBI issues

Just an FYI, I'm pretty sure GM didn't use adjustable sensors for a reason on these setups. GM had a few ways of adjusting the idle voltage that they used or could have used:

ECM uses throttle position when vehicle is started as a "baseline" and works off of that, checking every time the vehicle is started. (TBI?)

Slotted TPS units. (TPI for one)

Idle adjustment.

I'd have to check the GM manual to see how they say to "set" TPS on the TBI rigs. Since idle is controlled via IAC/ECM, I would ASSUME any minor TPS voltage changes needing made would be done through an idle air adjustment. I can't imagine they required that the sensors be modified, but I don't know that for certain.
 
^^^ that sounds about right. I remember my tps had different numbers then that.


I'd call up a mechanic or dealer and ask them if those voltage numbers need to be dead on. I'm guessing they don't because of the reasons dyeager posted.

Pretty sure they run off a basline when the vehicle starts.

EDIT: just read that article and it sounds like you got her figured out.
 
I took the sensor off the TB and it did the same thing, max voltage with the lever pushed all the way back, which I think is farther than the throttle shaft will push it, was just over 4 volts and my service manual says at WOT it would be about 5 volts. and mine is not the adjustable type with slotted holes.
 
What does the service manual talk about for "setting" TPS, or how the codes for TPS problems are set? Somewhere in there should describe the operation of the TPS other than just voltage.
 
Which means GM sets "base" TPS every time the vehicle is started, and voltage is irrelevant, assuming the TPS works correctly.
 
dyeager535 said:
Which means GM sets "base" TPS every time the vehicle is started, and voltage is irrelevant, assuming the TPS works correctly.
Click to expand...

Yuppers....

Although voltage is still somewhat relevant. Do some searching or make some calls and see if you can figure out what the normal voltage range for it is. My guess is it's fine but you never know.


Start looking REAL close for cracked vacuum lines or broken nipples on sensors.
 
Well thats the thing...in adjustable TPS', GM stated .54+/- at idle, but since we are saying that the TBI TPS is non-adjustable, the ECM sends a reference voltage, and calculates off of startup TPS voltage, if 5V is the reference, and it sees .5V(10%) on startup then .5V becomes idle TPS value, or 0% throttle. Everything off of that, say 1V, would be calculated to arrive at the corresponding throttle opening. So the ECM in this case would then "know" that 1V=20% throttle opening.

Assuming we've determined its operation correctly (which begs the question why people would bother modifying the non-adjustable mounting) things like power enrichment (pump shot for a carb) would simply be based off of throttle %, not voltage.

Again, all this hinges on whether or not the TPS "output" to the ECM is smooth and consistent, and has no electrical dead spots in it's travel. Yes, that's voltage, but not important the way it would be if the ECM were expecting X voltage at Y throttle opening.
 
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