Why TP voltage does not matter - Page 2

Post by **cgrey8** » Thu Feb 21, 2008 4:48 pm

He's just talking about the RATCH effect. So if at key-on, your TPS is .95v, but at some point during the drive, it dips to .94v, then .94v is latched-in as the minimum value to assume as Closed Throttle. Later on, if the voltage hits .93v, then .93v is latched in as the minimum. The term Ratch is used because the voltage can go down, but can't go back up until a power cycle and the whole thing starts over again.

Adam McLaughlin · Post by **Adam McLaughlin** » Thu Feb 21, 2008 5:22 pm

Ah, OK. That makes some more sense. Thanks for clearing that up for us Chris.

So, there is some sort of key-on recognition when the EEC is powered up, right?

This would be the base T.P.S. reading, and everything below it would work down as the established base indicator moves lower throughout the engine operation. Do I have this correctly?

Adam

Stern90LX · Post by **Stern90LX** » Thu Feb 21, 2008 8:28 pm

sailorbob wrote:As long as the TPS voltage at closed throttle is below the various self test min values then the eec will cope with it as all of the important TPS related decision processes use the relative TP value (actual TP minus closed TP values). If your TPS is reading between 0.95 and 1.0v then it will be fine as the typical failure value I've seen is 1.25v (in both eec-iv's and v's).

Regarding eec-iv vs eec-v handling of the idle, certainly the early eec-v's don't differ from the iv.

BTW the eec uses a 10 bit ADC so the resolution is better than described above.

Interesting, I've noted my EEC-IV tosses a "Out of Range" error code for the TPS when it's below .75v or above 1.25v when it POSTs @ Key On. So I keep it set to .95 to cope with temp variances and what not. I'm another of those that never bought into the .999...v crap.

Stern90LX · Post by **Stern90LX** » Thu Feb 21, 2008 8:33 pm

Adam McLaughlin wrote:Ah, OK. That makes some more sense. Thanks for clearing that up for us Chris.

So, there is some sort of key-on recognition when the EEC is powered up, right?

This would be the base T.P.S. reading, and everything below it would work down as the established base indicator moves lower throughout the engine operation. Do I have this correctly?

Adam

Yes, that's basically correct. The EEC-IV is just like your PC on power up. It performs a POST. Or Power On Self Test as it were. It polls each sensor to get a base voltage reference(VREF). Compares those VREF's to a variance table and logs what it found... in a nut shell. :) If a sensor can't be read then it should launch into the Limp mode setting and allow the engine to be started anyway.

sailorbob · Post by **sailorbob** » Thu Feb 21, 2008 10:15 pm

Adam McLaughlin wrote:Can you elaborate on that some more?

No need, Chris has already got it covered and beaten me to responding :D

Stern90LX wrote:I've noted my EEC-IV tosses a "Out of Range" error code for the TPS when it's below .75v or above 1.25v when it POSTs @ Key On.

Yes, you will get a error thrown up when at low voltage too. My laziness in not saying this before as most people suffer from a reading that is too high.

Cougar5.0 · Post by **Cougar5.0** » Fri Feb 22, 2008 5:06 pm

Well, for completeness I'm going to add a couple of snips from the GUFB. I was going to post this earlier, but the site keeps going down for hours/days at a time!

Chris Mureen · Post by **Chris Mureen** » Fri Feb 22, 2008 9:49 pm

sailorbob wrote:Relative TP is not set at key on, the eec constantly adjusts the closed TP position downwards so that the various thresholds are not affected by the closed throttle value varying thought out the run.

Are you saying that you can adjust the throttle opening and thereby increase or decrease TPS voltage and not have to cycle the ignition switch? I realize it is always montoring but I always thought that the base point was set at KO.

Chris

Adam McLaughlin · Post by **Adam McLaughlin** » Sat Feb 23, 2008 12:52 am

It appears as though you can adjust the throttle sensor's closed position to a lower reading, without cycling the EEC, but to go higher would make the EEC think that the throttle was being opened.

I am going to have to go out to the garage tonight and experiment...

Adam

sailorbob · Post by **sailorbob** » Sat Feb 23, 2008 5:46 am

Adam McLaughlin wrote:you can adjust the throttle sensor's closed position to a lower reading, without cycling the EEC, but to go higher would make the EEC think that the throttle was being opened.

Yes, to a point anyway :D Later eec's have a self test mode called 'Throttle Adjust Mode' where the closed TP value (aka RATCH) is constantly readjusted to the current TPS value rather than being only adjusted downwards.

Post by **cgrey8** » Sat Feb 23, 2008 9:10 am

To make up for slop, there are some deadband scalars that define voltage above the RATCH voltage to still consider as Closed Throttle (CT). If the throttle was .95v, then .94, then .93, it could very easily go back to being .94v again at some point during the drive. Since the EEC controls CT differently than Partial Throttle (PT), then it's important that the EEC understand that the voltage can vary a little. I don't remember the exact amount allowed, but it seems the scalar is somewhere around .3v. So as long as the TPS reports CT within .3v of RATCH, the EEC will treat that as CT. Otherwise what you'll notice is the ISC controller would hold open, run the engine RPMs higher, and the spark would be drive-values (mid to high 20s), not idle values (mid teens to low 20s). If you are datalogging Throttle Status, you'd also notice the EEC believes everything is still at PT. I had this very problem when my throttle plate was sticking. Sometimes the throttle plate would get lower, other times gunk and buildup kept it from closing all the way and it wouldn't meet that .3v range. So the EEC would hold the spark and RPMs higher than what they should've been for sitting still at a light. Tapping the throttle would sometimes fix it. But ultimately cleaning the throttle body got rid of the problem. Unfortunately, my Explorer throttle body sticks fairly easily and has to be cleaned often. I should probably put some sand paper to it so the edges of the TB don't come so close to the butterfly and cause actual contact with the butterfly.

tvrfan · Post by **tvrfan** » Sat May 14, 2011 11:58 pm

Hey Guys, (I'm new to forum, but not EEC stuff).

My understanding of RATCH is that it is the MINIMUM voltage ever reached by the TPS
sensor. Because of manufacturing tolerances, and real life wear etc. This value probably stays pretty stable for a particular vehicle, but not across multiple vehicles.

If you look at A9L family it checks - if TPS voltage is less than ratch, then ratch = TPS.

It doesn't go up, only down.

This value (RATCH) is then used to decide if throttle is closed...... which then determines a range of strategies (accel pump, decel shut off etc.)

Simple, when you think about it.

Andy.

Re:

Who is online