down to 4.5?thanx.

 

Easiest way is to use a potentiometer (adjustable resistor). It has three points of connection. Attach 12 volts and ground to the ends and your 4.5 volt output will be the middle. You'll need a voltmeter to adjust the output. I assume you want this to force your TPS up to a WOT voltage to run open loop all the time.

 

what are the advantages to running open loop?any disadvatanges?

 

a 2.66 ohm resistor would do it too I believe...I have a 4.5 volt LED and i used a 2.66 ohm resistor to reduce current.

12 divided by 4.5 = 2.66

 

do they have those at radio shack by chance,lol.

 

The reason you would want to force the ECU into open loop earlier is for boosting, you don't want to be in closed loop under boost.

A single resistor won't do it because you'll be putting it in series with the input resistance of the ECU which is essentially infinite (about 100 kohm I think, I measured the input resistance of the MAP sensor input once), therefore the current draw will be zero and your voltage will still be 12 volts. You need a voltage divider, with a sufficiently large resistance that it won't fry your TPS power supply circuit from too much current draw but smaller than the ECU input resistance by a factor of ten or so. Try a 10K pot.

 

well,the reason i was asking was because im going to be using my zex kit for spraying my intercooler,i was told not to put more than 5 volts to it to kick it on,so i was going to wire it to my washer fluid switch(i no longer have washer fluid),so i need to drop that 12 volts down to 4.5 to spray the intercooler.BUT>>>now that you have brought up the open loop thing im interested.is there a way to make it go into open loop before you boost,maybe using a boost switch(hobbs switch i think its called).when will my ecu autocmticaly go into open loop,at WOT?

 

Don't forget your current. Remember, V=IR (voltage = curent x resistance)

 

Usually people just hook the ZEX input up to there throttle position sensor which puts out 4.5 volts at WOT. Seems like that would work for your application too (intercooler chilling) except that it wouldn't work for partial throttle boosting.

You could use an op amp to amplify your TPS signal so you go into open loop earlier. I believe the stock setpoint is 75% throttle to go into open loop but I could be wrong about that.

You could also use a combination comparator plus adder circuit to peg your TPS voltage at 5 volts once a certain MAP sensor voltage is reached (i.e. once a certain boost level is reached).

A boost switch would work too.

 

so,what if i just adjust my tps so it thinks the throttle is open before it actaully is,i made it adjustabal with some hex head screws,if i just move it forward,sounds like a plan?it would move it into open loop sooner and trigger the zex right,plus ill wire it up to the washer switch with a diode so i can spray right before take off,using the diode so it wont interfear with the tps when using that switch,you see any problems with this?

 

Rotating the TPS may work but the ECU may use the closed throttle TPS voltage to do some kind of idle correction so it may screw up idle, not sure about that.

Actually now that I think about it, there are three wires going to the TPS and one is a constant +5 volts so you could just wire your windshield washer switch to that instead of 12 volts and use it to trigger the ZEX. Just don't try to drive your windshield washer pump with that 5 volts, you'll fry your ECU.

 

lol,i got rid of the washer bottle years ago,do you know the exact voltage for open loop?is closed loop anything under that,like i think what ill do is rotate it to a certain point,till the voltage is where i need it,and make sure that it is about 3/4 of the throttle,so in the last 1/4 it will go to open loop and spray at the same time,ill just use a relay on the zex then.

 

You're probably going to have a hard time adjusting the position of the TPS enough. The slots on the TPS don't allow for that much rotation. But it's worth a shot.

Don't know the exact voltage for closed loop. I'll guess 3.75 volts. How are you going to get the relay to close at that exact voltage?

 

ill be using the relay on the washer switch,using the 12 volts from that to trigger the relay to send the 4.5 volts to the zex(from the TPS wire),it should trigger the zex when i use the switch and when i hit WOT,ill put a diode in the mix so i dont go into open loop every time i hit the switch,id like to cool it down right before the run as much as possable.