Fuel Open Loop TP setting

[HPLouis]

Hi,
I'm working on this tune and I have a question about Fuel Open Loop Throttle Position. I read Fuel Open Loop TP is the throttle position that the car will go into open loop. I also read that on some vehicles, you may want to open WOT at a lower pedal position, 500 for a lower boost vehicle and 450 for a higher boost vehicle.

I've seen this done two ways, the modded way is on the left and stock 2003-2004 Cobra on the right

Fuel Open Loop TP

Modified.........................................Stock
7000.000...150.000....................16383.750...450.000
5000.000...150.000........................0.000.......450.000
4000.000...250.000........................0.000.......450.000
3000.000...350.000........................0.000.......450.000
2000.000...450.000........................0.000..........---
1000.000...450.000........................0.000..........---
0.000.........450.000...........................---...........---

I guess that 450 is about halfway on the throttle position. So, for stock, I'm guessing that whenever you press the gas more than half way, it'll go into open loop. The modified way, it looks like you have to press the gas more than halfway up until 2000rpms and then from 3000rpms and up, do you have to press the gas less or more? I'm trying to understand this. At 5000rpms, am I pressing the gas further to the floor to get into open loop, or am I entering open loop with less pedal effort?

I'm trying to understand which is better? Is it better with the TP going to 150 as the rpms go up (like the modded one) or is it better 450 all the way up (like the stock one)? Does anyone know the difference?

Thanks

 

[HPLouis]

Nevermind, someone gave me the answer. The numbers are a percentage, i.e. 450 is 45% throttle.

Thanks

 

[decipha]

No, that's incorrect

That value is TPREL in ad counts.

An a/d count is the analog to digital conversion used for integrated circuits.

On ecu power up the lowest throttle position voltage ad count becomes RATCH.
RATCH is the lowest throttle position voltage since ecu power up.

TPREL is relative throttle position.

TP Voltage - RATCH = TPREL

As you hit the throttle and tp voltage increases it is subtracted from RATCH to give you relative throttle position voltage.

There are roughly 200 ad counts in a volt.

If your at 1.125 volts on the tps at closed throttle then your at 225 ad counts.
(1.125*200==225) This becomes RATCH. So RATCH = 225 (closed throttle volts).

If you go WOT and the tps voltage climbs to 4.6 volts then-

4.6*200==920 ad counts
920-(RATCH==225)== 695 is your maximum TPREL at WOT.
THAT IS NOT 69% throttle its 100% throttle.

Some vehicles can reach 750 ad count TPREL at wot. Some can only reach in the 400s - typically common on modified cobras.

If you have a higher boosted engine then that needs to come down quite a bit. I've hit over 10 lbs of boost at only 200 TPREL before on 03-04 cobras.

Attached a screen shot of the base values I start with in all my 03/03 cobra tunes.

Also worth noting is that I have my own custom load/boost threshold code I use as well to force open loop power enrichment when in high boost regardless of this look up as well.