Question about TPS voltage

[r_simmonds]

Question for some of those that have tuning experience here.

So I tried a couple of searches on here and didn't come up with anything, so here's my question- On a cable driven L36, does it need to see a full 5 volts to reach 100% FE? I'm curious, as I'm trying to do some more tuning work on the throttle body itself before I get into actual ECM tuning. If it needs to see a full 5 volts to reach 100%, then my goal is to rework the throttle body so that it will hit 100% at WOT as opposed to just trying to trick the computer. The biggest thing I've noticed with mine is that while it's set at 0.5V at idle, and even with some modification done to allow more throttle opening, it still only hits 4V at WOT with a full 5V reference signal.

As of right now, I've cut out the stand around the MAF and filled/smoothed the pocket just before the blade. I've also ported the bore, radiused the transitions, knife-edged the blade, and cut down the shaft and screws. The car definitely feels stronger through acceleration, but I know that there has to be a little more in it with just a little more work. I do intend to at some point take the upper and lower plenums off and play with some porting work on them, possibly even some decking and other little tricks. So I'd like to make sure that when I start getting into changing the tuning in the future that the computer will allow me to take full advantage of the work.

I do know that the 04 GTO like mine can have similar problems with reading full voltage at WOT, and thus create tuning problems which can be remedied by tweaking the throttle body. So if I need to do some more tweaking to allow more rotation of the shaft to get the full 5V, then I'm certainly up for the challenge.

Mostly this is just a kind of science experiment for me, something to play with in my downtime. And it's certainly fun to make the Mustang GT guys scratch their heads at how a nearly stock V6/A4 Firebird was able to keep up with or pull slightly ahead of them.

[3.4grapeofwrath]

Re: Question about TPS voltage

The throttle position reading should not go any higher then 4.5 volts. If you go over that it will affect the transmission shifting and lock up. I found that out experimenting years ago. You can rotate the tps slightly from side to side to change the voltage readings slightly. I even slotted the holes to change the readings but it only ended up messing up the idle rpm's. You should be seeing WOT at 4.0 volts though. My advice would be to leave it only.

[r_simmonds]

Re: Question about TPS voltage

When I reworked the bore, I opened it up a little more so full closed position is a degree or two further. And then modified the throttle stop so that the blade opens to a fully flat position. Afterwards, I bent the roll pin that engages the TPS so that it would see 0.5V when idling. I'm thinking about ellipsing the bore a little more, to get a little more travel, as well as possibly trimming down the blade a little more to help. I'd like to find another throttle body for cheap to toy around with on the bench, since the Firebird is my DD. Then once I get it fine tuned, swap it on.

One thing that made me curious about the voltage, was that the Casper voltage booster jumps voltage up to a full 5V above about 75% throttle position. I may be mistaken on that, but after reading the description of it and some owners talk about it, that was my understanding.

[Hib Halverson]

Re: Question about TPS voltage

I've done a lot of data logging with my 275-hp engine and I have never seen a TPS voltage more than 3.35V at WOT.

I've decided that the exact voltage doesn't matter much as long as the TB, be it cable or ETC, is at a WOT and the system delivers enough fuel. I know that's happening from my wide band O2S readings and my chassis dyno numbers.