Q about bac/ vacuum /load
06-08-11, 02:42 AM
#1
Q about bac/ vacuum /load
I'm having issues with the BAC when there is load (a/c).
Just a thought...would the BAC have difficultly raising idle on a ported motor?
Maybe a dumb thought.
The BAC is set per FSM.
I just can't keep the idle at 800 or so when the AC is turned on. It will bump up idle for a few seconds then slowly drop down and stall. The BAC does click when 12v is applied. And it's been cleaned.
Another thing I found out is when idle is set higher using the throttle screw, the idle still drops to 800 or so when AC is turned on then slowly drops as same as setting idle via the BAC.
I thought I could bump the idle when AC is turned on...I guess not.
Just a thought...would the BAC have difficultly raising idle on a ported motor?
Maybe a dumb thought.
The BAC is set per FSM.
I just can't keep the idle at 800 or so when the AC is turned on. It will bump up idle for a few seconds then slowly drop down and stall. The BAC does click when 12v is applied. And it's been cleaned.
Another thing I found out is when idle is set higher using the throttle screw, the idle still drops to 800 or so when AC is turned on then slowly drops as same as setting idle via the BAC.
I thought I could bump the idle when AC is turned on...I guess not.
06-08-11, 10:57 AM
#2
I never could figure out why mine wouldn't idle with the ac on either. I just chalked it up to an old BAC that cleaning just can't fix.
It kind of makes sense though. All the BAC is, is a solenoid operated valve that the ECU pulses a waveform signal to it sort of like the ecu does to injectors. It's open over a given period of time only X%. If that plunger inside the coil becomes magnetic, it'll probably have losses associated with pulsing. Sure it'll open fully with 12v fully applied, but if it has some residual magnetism on it, it could resist the changes, thereby not opening enough, or fast enough.
Just my theory.
It kind of makes sense though. All the BAC is, is a solenoid operated valve that the ECU pulses a waveform signal to it sort of like the ecu does to injectors. It's open over a given period of time only X%. If that plunger inside the coil becomes magnetic, it'll probably have losses associated with pulsing. Sure it'll open fully with 12v fully applied, but if it has some residual magnetism on it, it could resist the changes, thereby not opening enough, or fast enough.
Just my theory.
06-08-11, 06:59 PM
#3
I never could figure out why mine wouldn't idle with the ac on either. I just chalked it up to an old BAC that cleaning just can't fix.
It kind of makes sense though. All the BAC is, is a solenoid operated valve that the ECU pulses a waveform signal to it sort of like the ecu does to injectors. It's open over a given period of time only X%. If that plunger inside the coil becomes magnetic, it'll probably have losses associated with pulsing. Sure it'll open fully with 12v fully applied, but if it has some residual magnetism on it, it could resist the changes, thereby not opening enough, or fast enough.
Just my theory.
It kind of makes sense though. All the BAC is, is a solenoid operated valve that the ECU pulses a waveform signal to it sort of like the ecu does to injectors. It's open over a given period of time only X%. If that plunger inside the coil becomes magnetic, it'll probably have losses associated with pulsing. Sure it'll open fully with 12v fully applied, but if it has some residual magnetism on it, it could resist the changes, thereby not opening enough, or fast enough.
Just my theory.
I'm not sure if having a large ported motor makes any difference since idling would be difficult at 750 and the BAC can't compensate for it.
Just a dumb thought.
06-08-11, 08:06 PM
#4
Rotary Freak
Get the engine fully hot then remove the BAC but leave the elect plug on it. Turn the key to ON and see if the guts vibrate or not. Most times it will which will more than less prove the transitor inside the ECU that drives it is...............good. But if you don't have a vibrating BAC doing the above..........start wondering if the transsitor is bad inside the ECU.
If you had a meter with a Duty Cycle on it you could back probe the BAC wire at the ECU and see if the duty cycle changes when the lights are turned on or the brakes are put on. It would change on a normal car that has an idle around seven fifty or so........but not on a car that has a real high idle of say nine hundred plus rpm.
Or maye idle the car fully hot and then jumper the initial set coupler and the idle should drop down a bit on a normal car that isn't idling real high. Say in the nine hundred range plus.
Or put a common meter on the output wire from the ECU to the BAC and watch the voltage drop as the headlights are turned on or brake pedal applied. IF I remember right you can see the voltage drop from say ten volts at a steady idle down to ??? seven or so. It's been awhile since I did that with a common digital meter. The drop in voltage would indicate the BAC is upping it's duty cycle.......but there are hazards with doing this depending on how good the alternator is. Like if the alt is just a so so one, then lowering the rpms would cause the output of the alt to drop down and confusing the issue.
OR if you have a spare BAC like I do............I can idle the car hot and then connect the spare bac to the harness and see the sucker vibrate its little heart out......proving the BAC is working.
OR I think this is a valid check of the BAC..........................pull the BAC off the engnine and leave its plug on the bac. Watch the guts of the thing while someone HOLDS the key to START. The BACs piston should move all the way aft and stay there if the key is HELD to Start. I think this would also prove the transistor in the ECU for the BAC is ...good. IF the piston does not move aft when the key is HELD to START...............bad BAC transistor in the ECU.
If you had a meter with a Duty Cycle on it you could back probe the BAC wire at the ECU and see if the duty cycle changes when the lights are turned on or the brakes are put on. It would change on a normal car that has an idle around seven fifty or so........but not on a car that has a real high idle of say nine hundred plus rpm.
Or maye idle the car fully hot and then jumper the initial set coupler and the idle should drop down a bit on a normal car that isn't idling real high. Say in the nine hundred range plus.
Or put a common meter on the output wire from the ECU to the BAC and watch the voltage drop as the headlights are turned on or brake pedal applied. IF I remember right you can see the voltage drop from say ten volts at a steady idle down to ??? seven or so. It's been awhile since I did that with a common digital meter. The drop in voltage would indicate the BAC is upping it's duty cycle.......but there are hazards with doing this depending on how good the alternator is. Like if the alt is just a so so one, then lowering the rpms would cause the output of the alt to drop down and confusing the issue.
OR if you have a spare BAC like I do............I can idle the car hot and then connect the spare bac to the harness and see the sucker vibrate its little heart out......proving the BAC is working.
OR I think this is a valid check of the BAC..........................pull the BAC off the engnine and leave its plug on the bac. Watch the guts of the thing while someone HOLDS the key to START. The BACs piston should move all the way aft and stay there if the key is HELD to Start. I think this would also prove the transistor in the ECU for the BAC is ...good. IF the piston does not move aft when the key is HELD to START...............bad BAC transistor in the ECU.
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