George West

The TPS adjustment seems very critical as to how well my '85 'Vette is going to perform. I set .62VDC at idle, for a crisp throttle. Too much higher throws a code. For sure .7 volts at idle is too high.

Then I adjusted the WOT for 5VDC. I do this by sliding the TPS further along the arc of the throttle valve shaft linkage. Idle voltage remained.62VDC, and the car pulled very aggressively.

But then I threw a code, and the car dropped into "limp home" mode. The code would clear, only to set the next time I nailed it. So I adjusted the TPS for a range of .65(idle) - 4.8(WOT). Same deal.

The car ran great when I first raised the WOT TPS voltage. This leads me to speculate that the WOT voltage needs to be as high as possible.The fact that it didn't work for very long is somewhat puzzling.

What do you guys with the really fast iron head C-4s do about this adjustment? Mine seems hairy now, but perhaps that is because the battery has been disconnected, so it does not have a good TPS/Voltage map in memory any more? What about those switch things that turn on at 70% throttle? Are they better than just a good TPS adjustment?

This was a good threat earlier this year, but it did not really conclude. Is there even an advantage of a high WOT voltage? I know 4 volts is high enough to work well, but I do not know if 4.5 or even 3.5 volts would be better. And those $100 magic TPS boxes....

Thanks for listening and
all the help.

George

CFI-EFI

I have a 1984 Crossfire. As far as the TPS is concerned, I doubt they are very different. I asked everyone I thought might know, the effects of altering the TPS adjustment. All I got was a bunch of blank stares. So I played with it myself. Spec for my TPS is .525v + or - .075v. I started out at the high end of the tolerance, .600v. It seemed a little different, but I couldn't quantify it. I bumped it to .650 and headed for the track. At cruising speeds I found it difficult to maintain a steady, constant, speed. The throttle was super sensitive. At the track...no difference. Needless to say, I set it back to spec. I keep it right at .525v. If you think about it for a second, all you need is sufficient voltage for the ECM to go into the closed loop, PE mode. I have heard some who liked the enhancer for around town driving. At the track, you hit WOT so quickly it makes no difference. *I* wouldn't give you $0.02 for the enhancer. Good luck, and...

RACE ON!!!

65Z01

The reason our L98 like an "agressive" TPS is that the ECM sees harder throttle all along the throttle position path, so it's giving more timing advance as well as more fuel. You might have to settle for a little lower max setting and bump base timing to achieve best performance.

I adjust my '88 TPS in similar manner; the idle reading is .67 Vdc and WOT reading is about 4.7Vdc (the max I could get).

What code are you getting, TPS or MAF? Does it throw the code at idle or higher throttle position?

Check the throttle plates & linkage for excessive play, as this might account for your problem.

jmrl98

.57 at idle, most I can get at WOT is 4.7 also. :seeya

0ski_dwn_it

Set it to .57 at idle position, and if you get ~4.2-4.3 volts at WOT your fine.

scorp508

Your ECM is probably programmed for something around 69% = WOT if it is unaltered. Crazy isn't it? As long as you get over 3.45v I think you'll be ok.

George West

65ZO1,

If I set the WOT to 4.9 or 5.0 volts, I get a code 21 (TPS voltage high). The code only occurs about 1 or 2 seconds after the pedal is nailed. It clears after a minute or so. If I set the idle voltage too high (.7), I also get code 21, but it sets right away.

It is easy enough to find voltage limit at idle - the code sets right away. But I didn't even know that there was a limit for WOT. And it is difficult to determine the exact voltage where the code sets and engine stumbles.

Since some people have set 4.7 volts with no problem - and since I can get 4.7 volts easy enough - let me try that for WOT.

George

65Z01

Going much above .67 Vdc at base idle I've seen the code 21 set upon start up with two TPI cars so I guess that is about the idle limit value.

It's strange that you are also getting the code when you go to WOT. Here's my info on when the code gets set:
-TPS voltage >2.5 Vdc
-Engine is running
-Aif flow <15gm/sec
-All three conditiions are met for >3sec.
OR
-TPS voltage >4.5Vdc with ignition On.

Further it is stated that the idle voltage should be .54Vdc +/-.08 Vdc.

So, this explains the idle voltage setup but not the problem you are having with the WOT setting.

I'm wondering if, when you go to WOT, it is taking more than 3sec for the MAF to register that 15gm/sec of air flow, but you said it comes up 1-2 sec after nailing the throttle...hmm.

Anyway, lets hope you still get agressive performance with 4.7Vdc and no code tossed.

George West

65Z01,

I think that you found the answer! What must happen is that I get over 4.5VDC with the ignition on, whenever I mash the pedal to the metal. I think that what the numbers are saying is not to exceed 4.5 volts on the TPS wiper, ever. Thnks for finding that info.

Gee, and I just finished setting 4.7 volts at WOT! Let me go and fix it. Thanks again - I could find nothing on too high a setting at WOT, only that idle voltage should be .54 volts. I see no reason to try 4.7 volts anymore - with what you just told me, it could set a code at WOT.

I see that people have trouble getting over 4.7 volts. Elongating the slots on the TPS allows for more voltage swing. But I should never have done it! :_dupe:

I think I can just set .62 - 4.5 volts, and forget it. :auto:

Thanks everyone!

George

Corvette0096

:iagree:

coopsl98

I have a 1990 vette and my TPS readings are .60 @ idle and 3.52 @ WOT. Is my WOT voltage to low or is this normal.

George West

1.) I know that the factory spec is .54 volts at idle, with 800 mv tolerance. So anywhere from .46 to .62 volts should be a good setting.

2.) I know that many Forum members like to set the idle setting a little high.

3.) I know that my car has some hesitation when I set the TPS for .48 volts. This goes away at .6 volts. Above .7volts my car does not idle properly.

4.) I know that the WOT voltage can be set too high, causing an error and very poor performance.

5.) I know that 65Z01 found that a code 21 may set if:

"......-TPS voltage >4.5Vdc with ignition On."

6.) I know that the "performance switches" claim that they:

".....(are)...designed to engage at 60% throttle in every gear. Once it's activated at 60% it delivers a full 4.6 volts to the computer. The computer reads this as a valid wide-open throttle signal and delivers maximum fuel and timing ......"

"......Not to be used with any other power chips....."

That suggests that 4.6 volts is as high as you can go with a stock chip. That is somewhat confusing, as >4.5 volts with ignition on can cause code 21. Perhaps 4.6 volts is just on the edge.

I believe that the computer learns the TPS curve as you drive. It must match a model stored in memory somewhat. If it is close enough (does not set an error code), then the TPS voltages are matched to air flow for that car.

Custom power chips can change the TPS internal model. I believe that is why they caution against power chips in the throttle switch description.

With the above facts and suppositions, I tried .62 volts/idle and 4.48 volts/WOT. That setting is fine. But .62 - 3.48 volts might be just as good. Even if the car was a little off, I suspect that things would improve as the new TPS response curve was learned by the computer. If the WOT was very low, you would lose throttle resolution. It would tend to be either idle or flat out. I would not expect that trouble until there was only a few hundred millivolts swing. Like .5 volt/idle and 1 volt/WOT.

That means that the WOT voltage must be over 1 or even 2 volts, and less than 4.5 volts. But 3.5 might be just as good. I will run some tests over the next few days.

And that is all that I have figured out about TPS adjustments, to date.

George

JAKE

I have my TPS voltage set to .65 with the engine idling. Now if you look at the instructions for setting the TPS voltage it specifies, ignition key "on" engine "off".

Since my Fluke took a hike recently, I can no longer set it with the engine off, so I set it using Diacom and use .65.

Last time I checked with the Fluke, though, WOT gave me a max of 4.52 volts. I tried elongating the slots on the TPS and moving it around (I had just installed a new one), but even that wouldn't give me any additional voltage at WOT. So I'm stuck at 4.52; which isn't a problem at all.

There is a noticable difference in my engine's performance characteristics depending on the TPS voltage setting. Anything close to .54 up to about .59 give me a very slight hesitation at tip in. .65 cured that completely.

One of the things I always do is let the engine tell me what it wants and likes. I don't get locked in on numbers, per se, except in torquing bolts and nuts.

As I understand it, once the TPS voltage becomes high enough to signal the ECM that you're in WOT, the ECM switches to Power Enrichment Mode. This does not give you maximum timing, because when I'm driving at less than WOT, closed loop, part throttle operation, I'm seeing over 48 degrees of timing advance, yet in WOT MAX timing is 28.2 degrees.

My daughter is in her Junior year at Harvard, majoring in Electrical Engineering so I was about to call her and ask about all these electrically related questions. Then I remembered that 'joker' can't even locate the oil dip stick. LOL

Keep us posted.

Jake

scorp508

Right, because at WOT there is a much heavier load on the car. If you tried 48 degrees in PE you'd probably toast a piston or something from excessive knock if you engine hated it.

George West

I agree. That caught my eye when I read it also. They must mean maximum centrifugal but minimum vacuum advance. Heck, I don't know what they mean. It is a dumb claim.

George

65Z01

The TPS voltage can be adjusted on the earlier L98s and the ECM does not change base & WOT settings but starting in '90 the TPS mount used round holes instead of slotted and the ECM simply learns the setting.

But in all cases the ECM "learns" the fuel curve in closed loop mode so that enrichment as the throttle is depresset, till WOT, is learned.

George West

This is my gut feeling, but I have little evidence of it. Lately I have been working with the EFI electronics, so the ECM is powered down as often as not. So I would like to match the expected PE vs % table, without any delays while the ECM is learning. The way I am driving now is annoying. The car runs weak for the first half hour or hour. By the time the car is learning to run well, I am shutting down the ECM to run more tests!

I feel that the ECM is having similar trouble learning how to run well in open loop. Perhaps my high fuel pressure is one factor that is making the ECM delay in getting good values for open loop running. It will start out (on powering up the ECM) either rich or lean (possibly depending on fuel pressure). Again, by the time open loop is becoming stable, I am powering down.

If I could set the TPS to the values the computer expects BEFORE learning my particular settings, I might by-pass this 1 hour learning curve. Of course I can easily set factory fuel pressure, which may also help.

Is there a way I can determine the actual voltages, expected by an initialized ECM, for a particular % throttle position? I can't even get this info from HyperTech - and they programmed my chip.

George

George West

As I reread these posts, I realize that 65Z01 may have given me my answer. If PE is depressed until after the TPS curve is learned, then I have to stop disconnecting the battery, or the car will never run right!

A lack of PE is certainly what it feels like when I drive the 'dumb' car ('dumb car' = nasty 'vette before learning TPS!)

I guess it is normal for the older (1985) 'vettes to be quite slow for a while after power down? I suppose that sometimes it is better not to clear all the intermittent codes collected, as you will have some sluggish driving ahead!

Thanks
George

scorp508

PE is pre-programmed values. I've cleared my ECM many times in the staging lane and run times back to back within a few hundreths of each other to times where the ECM has been learning for well over a week. If there are any "learned" values for PE then have to be miniscule.

65Z01

Exactly Brian.

Out ECM only "learns" when in closed loop mode and then it uses data from the O2 sensor to trim fuel values (via the Integrator & BLM cell data) in closed loop only.

At part thorttle in closed loop the ECM is set up for a compromise between power, emissions and economy; at WOT in open loop it ignores the fuel trim data completely.

It is my understanding that the ECM doesn't "learn" to adjust any parameter other than fuel and that is done with the Integrator and BLM trim data.