Mint87RX7

ok i have been ******* with my idle for like 2 months trying to get it to idle like it did stock. i just got a new variable resistor because mine was messed up(turned infinatly instead of 3/4 turn from lean to rich) this helped stable the idle a lot because it used to be running insanely lean at idle. now im trying to figure out why my bac isnt kicking in. i connected the initial set coupler and got my idle to around 750 then disconnected it and the idle stayed at 750. I then turned the heater on and the idle dropped to about 550 and never went back up. i cleaned my bac last weak and when i give it power from the battery it opens and i can blow through it so there isnt anything wrong with the bac.
Is this an ecu problem?
what are some suggestions on things to test to see whats wrong?

Mint87RX7

bump, is there anything else that would effect whether or not the bac engages?

ddub

I had that same problem with my BAC, I would give it power from the battery and it'd click repeatedly so I knew it was working, but it didn't do anything when connected. Ended up never finding the problem and just took it out completely and blocked it off.

I'd check voltage, first, for the wires from the harness going to the plug that goes into the BAC. Check it under conditions when the BAC should/shouldn't be open and see if it changes. That should give you a start at finding the problem, it'll tell you if the BAC is even getting a signal through the plug.

Mint87RX7

good idea, thanks. anyone got anymore info on what it could be?

WAYNE88N/A

Whip out the FSM for your car, find the ECU pin that drives the BAC, put a meter set to voltage on it (other lead to ground), and see what she's doing with the car running. Should have about 13v at rpms above idle, and the voltage should drop as the BAC kicks in as the idle approaches and falls below 750 (the duty cycle affect). If it doesn't, either the driver circuit in the ECU is inop, or the wiring is bad (IF the valve is good)...

Mint87RX7

k thanks alot

J-Rat

iTrader: (2)

Are you sure about this? The BAC signal is a square wave that varies in amplitude with increased load. I wasnt aware that it changed duty cycle.

Sounds like this person has a broken wire or a bad drive circut on the ECU.

SpAm@FC

iTrader: (4)

connect your BAC to the wireing and DON'T instlal it on the motor...

then put your ignition on (don't start) and hear if your BAC is vibrating @ 50Hz

If not there are two possible reasons...

1.) your BAC is dead... take another BAC from a friend or so and try this with the other BAC... if the other BAC also don't work we come to point2

2.) a Transistor or something else is damaged in your Ecu!

edit:

can you tell me the corect resistance 4 the variable resistor? (Air/Fuel Mixture)

Mint87RX7

i dont know where the variable resistor is set stock, you are supposed to connect initial set coupler then using the variable resistor, adjust it little by little untill you have the highest idle possible then using the idle set screw you get it back down to 750

slvr7

iTrader: (1)

Check your BAC resistance as per the FSM, with the engine warm.
I had one that measured *just* within spec when cold, but resistance climbed out of spec when hot.
If the resistance is too high, the ECU cannot cycle it fast enough to pass the proper amount of air.

HAILERS

Do what the SPAM said. Remove the bac but leave its connector on. Turn the key to ON. The bac should be vibrating now. Now turn the key to START. While the key is to START the bac should be wide open.

If it did not do the above, then the transistor in the ECU is friied and needs replacement. Or possibly the bac is bad. Probably the ECU though.

WAYNE88N/A

Hey Rat, haven't seen ya around in a while

How can it vary in amplitude? You telling me that there is a variable voltage output from the ECU. In this case, that's what amplitude of any wave (square or sine) would correspond to- voltage...A square wave is nothing more than an on-off voltage, much like a digital signal. If you have a 12v source, and the signal is energized 50% of the time (same distance between wave transitions), an analog meter will show approx 6v...

Besides, I've done this on my car- she works just as advertised above. The thing that really tripped me out during observations is that the BAC is active (or energized) for far longer ranges than we give it credit for. For instance, it wasn't until a couple of minutes into highway cruise that she finally went to zero duty for good.

J-Rat

iTrader: (2)

Lets see.. Full time career, homeowner, going back to college, installing a haltech on an FC, fixing everyone elses car... No time for internet!!!...

You are assuming that the DMM you are using can actually trigger that fast (Hint: it cant). And we are also assuming that this fixed cycle is at 50%. Now I am not above dragging one of my O'scopes home from work, but my BAC is now controlled by a Haltech, so I would need a test subject. So how did I actually come to this crazy theory of mine?.... HERE COMES T3H SCIENCE!!11!!:

I listened to the BAC and held it in my hand while it was operated (back when I was stock). At no load it was triggering at a fixed rate (very quietly). At any increased load, the trigger speed (at least audibly), appeared to be the same but it got louder and the visible movement of the plunger increased, which leads me to believe that the amplitude of the square wave is increasing (think about it, it WOULD simplify the drive circut).

Admittedly not the most scientific approach, and maybe I will find someone around here that will let me probe thier BAC (sounds kinky)...

Rat