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View Full Version : Open loop / closed loop


Bart
03-21-2007, 04:14 PM
I am a bum at Maft Pro and Supra's compaired to some of the people on this network...so please be gentle with me.

I've been reading lots about closed and open loop.
I've installed a LC1 WB O2 in my 1989+ supra with a 1992 ECU.

Other mods are:
Maft Pro, Boost control, T3 turbo, piped turbo/exhaust manifold, 3" exhaust, electric fan, head studs and Kametic gasket, HKS waste gate and blowdown valve, cooleze inlet air piping, stock fuel system.

If I have understood what I read...With the original O2 sensor wired to the ECU, we can only tune for cold start and WOT. To force the ECU into some sort of emergency mode, I should disconnect the original O2 and wire the LC1 to the Maft Pro ( as noted in other posts ). I would then be running in open loop (AF Tracking) all the time.

If the above is true, my questions are:
1 - When the ECU is in open loop, does it still self adjust to hold emergency mode settings? In other words, how often will I have to re-tune?
2 - I have plans on setting boost at 8 psi and aux boost to 15 psi. Will the stock fuel system allow this? Anyone guess at what boost levels I will be able to reach?
3 - I read about a 22 Kohm resister to be installed to make the ECU believe that there is still an O2 sensor hooked up. Can someone expand on this for me.
4 - What is the ultimate AF ratio we are all trying to achieve?

All answers are welcome,
Thanks in advance.
Brad

drjonez
03-22-2007, 10:12 AM
I am a bum at Maft Pro and Supra's compaired to some of the people on this network...so please be gentle with me.

not a problem. a willingness to learn is the key!


I've been reading lots about closed and open loop.
I've installed a LC1 WB O2 in my 1989+ supra with a 1992 ECU.

Other mods are:
Maft Pro, Boost control, T3 turbo, piped turbo/exhaust manifold, 3" exhaust, electric fan, head studs and Kametic gasket, HKS waste gate and blowdown valve, cooleze inlet air piping, stock fuel system.

If I have understood what I read...With the original O2 sensor wired to the ECU, we can only tune for cold start and WOT...

yes and no.

closed loop, the ECU will do whatever is necessary to maintain stoich....to a point. as you add mods, you may need to add corrections in the low and medium throttle tables to keep the ECU happy. here's some info on the ECU's feedback voltage, Vf:

http://www.mkiiitech.com/forums/viewtopic.php?t=593


To force the ECU into some sort of emergency mode, I should disconnect the original O2 and wire the LC1 to the Maft Pro ( as noted in other posts ). I would then be running in open loop (AF Tracking) all the time.

disconnecting the ECU causes it to default to a more rich map. if you disconnect the O2 sensor, you should use the MAFT pro to do part throttle AFR tracking.


If the above is true, my questions are:
1 - When the ECU is in open loop, does it still self adjust to hold emergency mode settings? In other words, how often will I have to re-tune?

when you allow the ECU to run as normal, it will apply learned closed loop corrections @ WOT....causing you to have to tune and retune....IF you have not satisfied Vf. the key to tuning the MKIII is making sure Vf is satisfied. once you've done that, there won't be any retuning...


2 - I have plans on setting boost at 8 psi and aux boost to 15 psi. Will the stock fuel system allow this? Anyone guess at what boost levels I will be able to reach?

no mention of ANY fueling mods in your list....upgraded turbo and NO fueling mods, that's scary.

the stock injectors are 440s, which in theory should support 400rwhp or so....the problem is your stock injectors are 20 yrs old. cheapest solution is to send them out to be cleaned and flowed.

likewise, your fuel pump is 20 yrs old. that should be replaced ASAP.

boost pressure is irrelevant, airflow is what matters. what compressor is in your turbo?


3 - I read about a 22 Kohm resister to be installed to make the ECU believe that there is still an O2 sensor hooked up. Can someone expand on this for me.

sounds like you've mixed up the resistor value to get rid of the air temp code with the O2 sensor.

since you've got a later ECU you will need a higher power resistor on the O2 sensor heater circuit...if you're going to remove the stock O2 sensor. i'll have to dig up specs...


4 - What is the ultimate AF ratio we are all trying to achieve?

All answers are welcome,
Thanks in advance.
Brad

"ultimate"? no idea what that is supposed to be....

stoich for gasoline is 14.7, that's a std cruise AFR.

"safe" WOT AFR for a forced induction engine is 12.0 or so....probably a bit more rich, depends on fuel quality.

HTH...

Bart
03-22-2007, 12:06 PM
Thanks DrJonez.

I think I should wire things up to keep my ECU in closed loop as much as pos.
One day when my knowledge level is stronger, I can always change to open loop.

no mention of ANY fueling mods in your list....upgraded turbo and NO fueling mods, that's scary


What type of scary things may happen??
I am hoping to avoid fuel system mods till after this summer.

Brad

Rick87gn
03-22-2007, 05:48 PM
Thanks DrJonez.

I think I should wire things up to keep my ECU in closed loop as much as pos.
One day when my knowledge level is stronger, I can always change to open loop.


What type of scary things may happen??
I am hoping to avoid fuel system mods till after this summer.

Brad

Brad
Always remember when moving more air through any motor you need more fuel. You can blow your motor without proper fueling. Don't mess around, upgrade your pump. Just some friendly advice. :usa:

drjonez
03-23-2007, 03:35 AM
Thanks DrJonez.

np.


I think I should wire things up to keep my ECU in closed loop as much as pos.
One day when my knowledge level is stronger, I can always change to open loop.

i tend to agree- try to keep the ECU doing as much as it can, since that was what it was designed to do. this will also keep the tuning on a more basic level....


What type of scary things may happen??
I am hoping to avoid fuel system mods till after this summer.

Brad

blowing you engine.

as rick implied, you cannot just upgrade one side of the fuel/air equation....especially on a 20 yr old car. either pay a little now for a pump and perhaps some gauges or pay for a new engine in the near future...

Bart
05-01-2007, 11:59 AM
I took your advice and replaced fuel pump, drilled out J tube, installed new 550 cc injectors.
Now I just have to tune. Waiting for better weather.
Still looking for the resistor specs for O2 sensor (engine light is pissing me off)