The BAC, A/C and HEADLIGHTS
06-05-02, 02:15 PM
#26
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I think you are right on the initial set coupler.
It must prevent the BAC from getting anything other than its "light" duty cycle (idle with no load).
So if you disconnect the BAC plug, obviously the rpm will drop since you are then only relying on throttle gap for air.
Some more thoughts:
There's a procedure to check if TPS signal makes it to the ECU, that says to hold the throttle at around 2000 rpm, then push the TPS plunger, the rpm should change.
What makes the engine speed change ? Does the ECU sense a TP reading not corresponding to engine speed and it adjusts. But how ?? What intake circuit does that ? The BAC ?? (is it still active when not at idle ?)
If you push the TPS plunger a tad while at idle,
is it like putting a load on the engine (engine speed lower than what it is supposed to be).
just wondering,
Hugues -
It must prevent the BAC from getting anything other than its "light" duty cycle (idle with no load).
So if you disconnect the BAC plug, obviously the rpm will drop since you are then only relying on throttle gap for air.
Some more thoughts:
There's a procedure to check if TPS signal makes it to the ECU, that says to hold the throttle at around 2000 rpm, then push the TPS plunger, the rpm should change.
What makes the engine speed change ? Does the ECU sense a TP reading not corresponding to engine speed and it adjusts. But how ?? What intake circuit does that ? The BAC ?? (is it still active when not at idle ?)
If you push the TPS plunger a tad while at idle,
is it like putting a load on the engine (engine speed lower than what it is supposed to be).
just wondering,
Hugues -
06-05-02, 06:10 PM
#27
HAILERS
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HUGUES...... Shoving the tps plunger in while at 2000 is a test of sorts for the deceleration system. See this old thread, *at the bottom*, and the reply by Six Rotors. You'd do good to ask him about just what is happening. He's read things that I don't have privy to, therefore a better understanding.
I did get off my duff and put the initial set coupler in my car and then turn the a/c on. Sure enought the bac did not make any corrections keep the idle up, so the thing came close to dying on me.
Just a thought. If you get bummed out and don't get your problem resolved, you might try *playing* with your variable resistor and deliberatly make your idle mixture a touch richer than needed and see if this will make an improvement. Its just a thought with no procedure to be found in the book. Something to try if you get bored. Oh, the thread: https://www.rx7club.com/forum/showth...threadid=35204
I did get off my duff and put the initial set coupler in my car and then turn the a/c on. Sure enought the bac did not make any corrections keep the idle up, so the thing came close to dying on me.
Just a thought. If you get bummed out and don't get your problem resolved, you might try *playing* with your variable resistor and deliberatly make your idle mixture a touch richer than needed and see if this will make an improvement. Its just a thought with no procedure to be found in the book. Something to try if you get bored. Oh, the thread: https://www.rx7club.com/forum/showth...threadid=35204
Last edited by HAILERS; 06-05-02 at 06:12 PM.
06-06-02, 10:39 AM
#28
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Thank you HAILERS for your suggestions. I have sent Six Rotors a mail explaining my problem. Hopefully, he will be able to enlighten me on the ECU's secrets.
Otherwise,
I'll just have to raise my idle speed and play with the mixture screw to minimize the rpm drop. What bogs me is that I still don't know if the BAC should be involved or not. One day, I think yes, the other, I think not.
Hugues -
Otherwise,
I'll just have to raise my idle speed and play with the mixture screw to minimize the rpm drop. What bogs me is that I still don't know if the BAC should be involved or not. One day, I think yes, the other, I think not.
Hugues -
06-15-02, 02:48 PM
#29
HAILERS
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I got off my duff and did the following:
Bought a Fluke 88 automotive meter at: http://www.toolsource.com
Reread what Paul Stoakes wrote at:http://www.teamfc3s.org/info/articles/idle.html If it wasn't for that article I'd know less than nothing about the workings of the BAC.
Checked the car out using a breakout plug that has the bac signal to the ECU plus others, and another meter in the bac circuit to read the amps.
With the car at idle, fully warm, no accessories on the following: Pulls .24amps, Duty cycle in milliseconds .24ms pulse width, percentage of duty cycle 39.2%
The above with the lights on: .28amps, 3.7ms, 45%.
The above plus full a/c: .34amps, 4.5ms, 54.1%
The above with the a/c fan at minimun: .32amp, 4.2ms, 51.4%
I know there is no input to the ECU for the headlights, so I'm assuming the ECU is looking at voltage drop and compensating for it. You can look at the pulse width of the primary injectors at idle and see the pulse width increase some when the lights or the a/c is turned on, further proof that there is more going on than meets the eye.
I also think that Mazda found this 1987 setup inadequate, thats why on the 89 fsm they show the light input to the ECU and the diagram I mentioned in the 89 fsm that shows what all goes into influencing the bac.
Far as I'm concerned the bac on the 86-88 is influenced by the headlights. I noticed a change when the brake pedal was stepped on also.
My figures are different that P. Stoakes's. The only time I see 2.4ms is when the engine is over 3,300rpm. Seems there is a switching action there of some sort.
It aint no voltage drop causing the above figures to change, in my honest opinion.
Bought a Fluke 88 automotive meter at: http://www.toolsource.com
Reread what Paul Stoakes wrote at:http://www.teamfc3s.org/info/articles/idle.html If it wasn't for that article I'd know less than nothing about the workings of the BAC.
Checked the car out using a breakout plug that has the bac signal to the ECU plus others, and another meter in the bac circuit to read the amps.
With the car at idle, fully warm, no accessories on the following: Pulls .24amps, Duty cycle in milliseconds .24ms pulse width, percentage of duty cycle 39.2%
The above with the lights on: .28amps, 3.7ms, 45%.
The above plus full a/c: .34amps, 4.5ms, 54.1%
The above with the a/c fan at minimun: .32amp, 4.2ms, 51.4%
I know there is no input to the ECU for the headlights, so I'm assuming the ECU is looking at voltage drop and compensating for it. You can look at the pulse width of the primary injectors at idle and see the pulse width increase some when the lights or the a/c is turned on, further proof that there is more going on than meets the eye.
I also think that Mazda found this 1987 setup inadequate, thats why on the 89 fsm they show the light input to the ECU and the diagram I mentioned in the 89 fsm that shows what all goes into influencing the bac.
Far as I'm concerned the bac on the 86-88 is influenced by the headlights. I noticed a change when the brake pedal was stepped on also.
My figures are different that P. Stoakes's. The only time I see 2.4ms is when the engine is over 3,300rpm. Seems there is a switching action there of some sort.
It aint no voltage drop causing the above figures to change, in my honest opinion.
06-18-02, 04:12 PM
#31
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OK, so Hailers has proven that the S4 ECU does use the BAC valve to compensate for loads other than the A/C. Yesterday I found out it works very well!
I had a meeting in the middle of the city and got stuck in traffic getting out afterwards. It was a lovely Auckland winter day; 18ºC (64ºF), pissing with rain, high humidity and foggy windows! I had the fog lights, windscreen wipers, rear demister, interior fan and A/C all switched on together and the idle sat beautifully at 750rpm! When I pushed the clutch in it would sometimes dip to ~600rpm but quickly recover to 750. The engine sounded loaded up, but was always smooth.
So the ECU is obviously doing something right!
I had a meeting in the middle of the city and got stuck in traffic getting out afterwards. It was a lovely Auckland winter day; 18ºC (64ºF), pissing with rain, high humidity and foggy windows! I had the fog lights, windscreen wipers, rear demister, interior fan and A/C all switched on together and the idle sat beautifully at 750rpm! When I pushed the clutch in it would sometimes dip to ~600rpm but quickly recover to 750. The engine sounded loaded up, but was always smooth.
So the ECU is obviously doing something right!
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