You can see what I am doing on Sundays, the little woman is off visiting relatives and Iam bored 
[LT1] When does PCM learn TPS WOT voltage?
Thread Starter
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
[LT1] When does PCM learn TPS WOT voltage?
I know that the LT1 learns to zero the TPS based on voltage being with a certain range at key-on. But after the PCM has been reset by a battery cable pull or fuse pull, how and when does the TPS figure out the TPS's upper voltage limit (Wide Open Throttle), before you have a chance to take it out and make a WOT run?
Without knowing the peak voltage limit (WOT) it seems the PCM would not know what percentage TPS value to assign to a given voltage generated from a given rotation generated by throttle tip-in as one presses the gas pedal.
So how does it learn the full voltage range of the TPS before you make a WOT run?
Without knowing the peak voltage limit (WOT) it seems the PCM would not know what percentage TPS value to assign to a given voltage generated from a given rotation generated by throttle tip-in as one presses the gas pedal.
So how does it learn the full voltage range of the TPS before you make a WOT run?
Last edited by Lone Ranger; Jun 12, 2005 at 10:33 AM.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by Lone Ranger
I know that the LT1 learns to zero the TPS based on voltage being with a certain range at key-on. But after the PCM has been reset by a battery cable pull or fuse pull, how and when does the TPS figure out the TPS's upper voltage limit (Wide Open Throttle), before you have a chance to take it out and make a WOT run?
Without knowing the peak voltage limit (WOT) it seems the PCM would not know what percentage TPS value to assign to a given voltage generated from a given rotation generated by throttle tip-in as one presses the gas pedal.
So how does it learn the full voltage range of the TPS before you make a WOT run?
Without knowing the peak voltage limit (WOT) it seems the PCM would not know what percentage TPS value to assign to a given voltage generated from a given rotation generated by throttle tip-in as one presses the gas pedal.
So how does it learn the full voltage range of the TPS before you make a WOT run?
Thread Starter
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Originally Posted by tjwong
The PCM will sees closed throttle for any voltage below .90 volts. If you go over that threshold then its no longer zero. A stock replacement TPS for any LT1 has no adjustment, it is just plug and play. If your TB idle stop screw has been adjusted to compensate for idle speed, and if its been adjusted way out then you need to check to see what the closed throttle voltage is. If its beyond .60 to.65 I would definitely elongate the holes and adjust the TPS to get to <.060v. If I remember right anything above 4.5 volts would be deemed 100% throttle but I am not 100% sure about that number but it is right in that range.
I'm not concerned about the voltage values themselves, they're within spec for an LT1, I was just trying to imagine my self as the PCM after a power off reset (battery juice pulled, etc): TPS is zero'd when the .53v is seen, but how does it learn the voltage range to use as a reference to base TPS % off of? There has to be some hard coded voltage scale in the PCM that is used as a reference for TPS% at any given voltage. I've just never seen that as a table or constant in the PCM when using Tunercat to look. Otherwise, the reference voltage range (to use for computing TPS %) could not be established until the PCM sees the voltage generated when the throttle is held wide open the first time.
That's what I was wondering.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by Lone Ranger
My closed throttle voltage stays rock steady @ .53v, using Datamaster to monitor. Moving throttle to wide open takes it to @ 3.9v, that's with the blades pegged wide open by hand at the throttle body, and 100% TPS is reported by Datamaster at 3.75v. No problems there, all within spec.
I'm not concerned about the voltage values themselves, they're within spec for an LT1, I was just trying to imagine my self as the PCM after a power off reset (battery juice pulled, etc): TPS is zero'd when the .53v is seen, but how does it learn the voltage range to use as a reference to base TPS % off of? There has to be some hard coded voltage scale in the PCM that is used as a reference for TPS% at any given voltage. I've just never seen that as a table or constant in the PCM when using Tunercat to look. Otherwise, the reference voltage range (to use for computing TPS %) could not be established until the PCM sees the voltage generated when the throttle is held wide open the first time.
That's what I was wondering.
I'm not concerned about the voltage values themselves, they're within spec for an LT1, I was just trying to imagine my self as the PCM after a power off reset (battery juice pulled, etc): TPS is zero'd when the .53v is seen, but how does it learn the voltage range to use as a reference to base TPS % off of? There has to be some hard coded voltage scale in the PCM that is used as a reference for TPS% at any given voltage. I've just never seen that as a table or constant in the PCM when using Tunercat to look. Otherwise, the reference voltage range (to use for computing TPS %) could not be established until the PCM sees the voltage generated when the throttle is held wide open the first time.
That's what I was wondering.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
The LT1 has a prety wide range of aceptable voltages but I have found it can get a little tricky.
On my car it doesn't like anything over .5 VDC for Zero throttle (Mine is at .43) And it wil see anything over 3.8 as WOT (Could be 3.75 as lone ranger stated (Mine is at 4.4 VDC at WOT)
I cant see .9 working as zero throttle even though the specs atate .3-.9 are aceptable, and for sure .91 should set a code 21.
Man you guys post fast,
I think it has to have code that takes known 0 position and then once it has established WOT voltage it would do a compare and the range would be the 0-100 range for throttle position ie .47-4.25
On my car it doesn't like anything over .5 VDC for Zero throttle (Mine is at .43) And it wil see anything over 3.8 as WOT (Could be 3.75 as lone ranger stated (Mine is at 4.4 VDC at WOT)
I cant see .9 working as zero throttle even though the specs atate .3-.9 are aceptable, and for sure .91 should set a code 21.
Man you guys post fast,
I think it has to have code that takes known 0 position and then once it has established WOT voltage it would do a compare and the range would be the 0-100 range for throttle position ie .47-4.25
Last edited by FD2BLK; Jun 12, 2005 at 01:50 PM.
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Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Ok now I have done some more reading and am becoming interested. It sees any thing above 80 % as WOT. My new guess is they have a hard coded formula for WOT i.e. 3.70 (80% lets call it) and it uses the zero position to set the range (I.E. .3 would be diferent then .5). Using the range of the TPS sensor it uses the fuel tables form that point on. I think they decided there was a better way to catch the mouse from reading aboutthe LS1 with the TAC system. The TAC system uses two position sensors in oposite voltage refrences. One reads 0 throttle from 0VDC and the other as 5 VDC and the oposite for WOT. This allows for a cross refrence point that I would think would be an extreamly acurate refrence point for fuel calculations.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by FD2BLK
Ok now I have done some more reading and am becoming interested. It sees any thing above 80 % as WOT. My new guess is they have a hard coded formula for WOT i.e. 3.70 (80% lets call it) and it uses the zero position to set the range (I.E. .3 would be diferent then .5). Using the range of the TPS sensor it uses the fuel tables form that point on. I think they decided there was a better way to catch the mouse from reading aboutthe LS1 with the TAC system. The TAC system uses two position sensors in oposite voltage refrences. One reads 0 throttle from 0VDC and the other as 5 VDC and the oposite for WOT. This allows for a cross refrence point that I would think would be an extreamly acurate refrence point for fuel calculations.
Yes that is correct for the LSx strategies. Also those special TPS and TAC sensors were used also for safety interlockings. GM's strategies called for comparisions in all the sensors to insure that there wasn't something goofy going on with their TAC system. Any differential compared to X constant would mandate a reduced power state. You can imagine the amount of liability if that TAC system was to go nuts on someone.
They even interlock the air flow vs TPS vs RPM. If MAF output numbers are greater than X when compared to a look up table the PCM commands reduced power mode, which means RPM is limited to 1500 RPM. I know this because I have installed blowers on SUVs and ran into this problem, the blower causes higher than normal air flow, the PCM sees this and thinks OH S**T theres way too much air going by the MAF so there must be a throttle body problem so SHUT DOWN! and it does this by going to reduce power mode, which incidentally damn near got me killed in my own blown 8.1L suburban one day as I merged onto the freeway with my foot in the throttle, it was not a fun moment to have my engine shut down with a semi-truck bearing down on my back doors
Thread Starter
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Originally Posted by tjwong
Ahh ok, I know what you are asking now. I beleive you are right, in the PCM firmware that is not accessible via conventional tuning tools I am sure that there is a comparator of some sort. Upon start up the PCM does several tests behind the scenes, one is that it checks barometric pressures by looking at the map the moment it is powered up. I am sure it does the same thing with TPS or some similar power up test.
This is what I suspected. I think and you and FD2Black nailed it down.
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
when i open the throttle wide open from inside the car it shows 3.7v max but i can manually open it to 4.2v from outside by hand. is this ok or should i be concerned 
after reading these post im wondering if i could be losing any power from not having full throttle....4.5volts?
after reading these post im wondering if i could be losing any power from not having full throttle....4.5volts?
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Originally Posted by GS977
when i open the throttle wide open from inside the car it shows 3.7v max but i can manually open it to 4.2v from outside by hand. is this ok or should i be concerned after reading these post im wondering if i could be losing any power from not having full throttle....4.5volts?
after reading these post im wondering if i could be losing any power from not having full throttle....4.5volts?THe voltage is fine butt he fact that you can rotate the TB is the concern. If the TB is not opening all the way then you have an aire restriction.
Drifting
Joined: May 2005
Posts: 1,258
Likes: 38
From: springtown Texas
how do i get the slack out of the throttle cable? it looks like the amount of slack in the cable would give full throttle if it were a little tighter. i looked at my asr and couldnt figure out how to pull some slack out. if i look at my throttle body i can see the cable hanging loose on the throttle arm. if ya know what i mean 
Thread Starter
Le Mans Master
Joined: Feb 2002
Posts: 7,858
Likes: 2
Originally Posted by GS977
how do i get the slack out of the throttle cable? it looks like the amount of slack in the cable would give full throttle if it were a little tighter. i looked at my asr and couldnt figure out how to pull some slack out. if i look at my throttle body i can see the cable hanging loose on the throttle arm. if ya know what i mean
Press in on the big rectangular button on the adjuster and while holding it in pull the cable on the right hand side of the adjuster until the slack is gone. Can't remember if you move the cable left or right to take out slack, but try some trial and error, it should work. Take just enough slack out so the throttle pegs to wide open when your foot has the pedal all the way down.
Last edited by Lone Ranger; Jun 12, 2005 at 09:34 PM.
