The TPS "tweak" myth
 

This has been discussed MANY MANY times on a variety of forums and there have been people "in the know" (IE, people who work for SCT, Ford, designers of the TWEECER....etc) who have tried to get the message across that this is nothing more than a myth, yet it continues to propagate across message boards "set your TPS to .98" and the like.

This post is designed to dispell that myth and perhaps give an idea of why the myth exists to begin with.

Many years ago, the entire idea of "modifying" what was going on in the ECM was a very new thing, people were much more accustomed to working on Carbureted cars and knowledge of Computer-Controlled Fuel Injection systems was very limited.

Many people would gain a limited understanding of how part of the system (or its feeback devices, IE, sensors) functioned and would often design "performance" modifications around this limited understanding. This is how I think this entire myth came to be.

A TPS is a potentiometer, basically, its a variable resistance device. The ECM views a variety of feedback sensors in order to make adjustments on how the car runs and responds. The TPS simply tells the ECM where the throttle blade is in relation to where it was when closed. Obviously, the further open the blade is, the more timing the ECM will throw at the engine (over base) and the more fuel it will provide. Many people think that "tweaking" the TPS will cause the ECM to percieve that the blade is further open than it actually is, thus "seeing" WOT sooner as well as reach full advance sooner as well. This is a great theory, but unfortunately, its completely false.

When you turn your key on, the ECM quickly probes all the sensors in the system and then uses some of those values as "base" reference values. So, if you set your TPS voltage to .98 like people recommend, the ECM views that as closed and any value higher than that is relative to .98. BUT, if the TPS is at .52, THAT value is used as the closed value and any value higher than that is relative to .52, the advance curve and fuel curve ARE THE SAME and are relative to base in either instance. WOT is percieved at ~3.8 volts, this typically happens at 3/4 throttle, not actual WOT, so matting the pedal is matting the pedal, no matter what your "base" voltage for the TPS is.

Hopefully, people will find this information helpful. There is a lot of cool, factual information floating around about finding easy/cheap performance out of these cars, unfortunately, this "mod" isn't one of them.

Correct, Always was amazed how this one got around.

I found setting my tps then resetting my computer helped big time with my hanging idle.

You probably just have a baffed TPS then. They can develop flat spots on them which will give out wacky readings.

This kind of info is always helpful............... :tup

Well, that's what I'm hoping for! There are lots of REAL performance mods for the venerable 302, this unfortunately, isn't one of them.

I would think if the TPS is made for "tweaking" or making adjustments on it would have oval mounting holes on it when it doesn't......

Very true :) No, Professional Products catered to this myth by releasing their BBK rip-off TB's with adjustable TPS's..........!!!!!!

Awesome thread, great to hear someone finally clear this up, I've been wondering for years if there was any truth to it.

Having heard everyone and their uncle always tell me to "set my TPS voltage", I have to admit I'm a little skeptical about this. Even so, it makes sense that the ECM would use whatever "X" voltages the sensors are sending as a "base" value and go from there.

If that is so, it leads me to ask: what would happen if I were to have my foot on the gas when the ECM comes on? What if the pedal's at part throttle? What about to the floor? Would the values be completely out of whack until I turn the car off, then on again? How would the car handle acceleration?

Now I can't field-test this question yet myself (since my car is still sitting in storage), but would love to hear what anyone else has to say.

Any guinea pigs willing to try this out, in the meantime? :wiggle:

Well, to the floor prevents the injectors from firing because the "base" voltage is now 4.0V, which is the universal "WOT" value (or somewhere in that range, might be 3.8v) If you held the pedal down, and it was beyond 1.1-1.2v but not at WOT and you held it there for the entire "probing" period, I think its quite possible that the ECM would see the TPS as out of range and not use its input. Of course if you were just holding the gas for a few seconds while cranking, as soon as the car catches and you let off, I think that is when it does another reference voltage check (when the engine is officially "running") so if its in the proper position then, I think you'd be OK.

This does not apply for older vehicles like the 5.0's.

You need to reset the KAM (keep alive memory) and this is why disconnecting the battery needs to be done for the change to occur

Well, the 5.0 crowd is where the myth first propogated from :)

:confused: Just a little confused... so with a car like mine ('89 5.0)... does the TPS require adjusting or not? Is the 'magic' 0.98v value that important?

Its a myth period.

On a 5.0 car, I would put a volt meter on the car, set it to .99-1.00V, reset the battery to clear the KAM and be on your way. This will not make the car go into WOT any sooner or things like that but it will help the car idle much better because your IAC functions, dashpot functions and other idle controls will be much more accurate

On newer vehicles, it is not necessary to do this but if you look at certain company's who make CRAPPY TB's the screw still has to be manually adjusted to OEM spec's. TB's I would never use include BBK.

These settings should never be touched as they are fine from the factory. Once you start changing thins, using crappy TB's you get into problems

well even ford sold a kit to adjust the tps...?

Well, as far as the EEC-IV ECM's go, it would be pointless to adjust it unless the TPS mounting holes are so far out of line that its over 1.2v and then the ECM would see the TPS as bad.

As I said, the people that have access to the actual code for the EEC-IV are the ones who are providing this information, people can spend their time doing better things to their car that actually ENHANCE the performance, rather than "Honda modding" by screwing with sensors and thinking they are acomplishing something.

I agree with OVERKILL.

The TPS mod is a bunch of hogwash... I generally make sure mine are in the range of .87 - .90V. I think the magic number for for wot is 4.5v, and like was mentioned the car will go into power enrichment mode well before that voltage [4.5v] is reached.

Waaaay back in the day in my 89 GT I did the TPS tweak to .98v and the car never ran any different. You have to watch to because at some point over 1.xxv the EEC is going to think you are on the gas and will idle high... i've seen that before.

I remember reading some where you want the tps set at no higher then .98v or it could spike over to 1 volt. What that would do I have no clue ?? Would this statement mean anything to you guys."spike over"

If the "base" reading for the TPS is ~1.2v, the ECM sees it as bad, so that's what you could be referencing to.

Set your TPS to .95-.99, then adjust your TB to stock idle rpm and you are set. If you wish to adjust the idle higher, do it properly, with a chip.

This is the only and proper way to do it

ok cool and stock idle would be ??? 700-800 rpms ???? And is this the same with a blower car ??

Yes, its the same with a blower car. The rather stringent voltage range mentioned above isn't really necessary; keep it below 1v and you'll be good to go as mentioned in my original post. Steeda.ca is correct on changing the idle though, PROPERLY, you are supposed to do it with a chip or a tuning device like a TWEECER.