2nd Generation Specific 1986-1992 Discussion

High Idle dut to ECU openign BAC

Old 04-23-2014, 06:03 PM
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Default High Idle dut to ECU openign BAC

Hi, I just registered here, so first post, feel free to move it if its not in the correct forum.

Anyway, I just installed a 1986 13B non turbo in my 93 B2200 which had factory EFI, the motor runs and seems to be operating correctly, however, my BAC is opening all the way as soon as I turn the ignition on, I can hear is buzzing. The BAC is working, it closes if I unplug it, or turn off the ignition, and it is getting an AC signal from the ECM (not a 12V DC indicating a crossed wire), but even when the engine is fully warmed up, I have an idle speed of about 3,000RPM or higher. If I unplug the BAC or jumper the test port thing to set idle, my idle is steady at 750 like the service manual says. My throttle body thermopellet is working correctly, and the TPS is set according to the manual. What could be causing the ECM to want the BAC wide open? I have tried 2 different ECU's, 2 different BAC valves, I have tested all wiring to the computer for the sensors, and they are correct, all sensors are putting out the correct resistance too.

Some background, I bought this motor and car as a running car, it ran fine before, was bone stock. I have removed the emissions stuff under the intake, EGR is removed, air pump removed, oil injection removed (using premix), had injectors flow tested and cleaned, using the B2200 EFI fuel pump and radiator (no radiator temp switch), also using the B2200 gauge cluster, I installed a pacesetter header, and until I can figure out a 5/6 port activation method, I have the ports wired open. I am using an intake manifold and throttle body off of a parts motor I bought of the same year.

I am thinking for right now to just remove the BAC and run it without, but I would like it operational since I am from Canada and it gets cold here, and I would like to be able to drive it year round.

Oh, I will post pics of my project when I am not at work lol.
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Old 04-24-2014, 12:47 AM
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Default Re: High Idle dut to ECU openign BAC

Wow, I failed at typing the title to this thread...anyway.

I unplugged the BAC and the motor starts and holds an idle, I temporarily installed a tach, and I was idling at 500RPM on a warm engine lol, so I fixed that and I am at around 800RPM on a warm engine. I will leave it like this for now. I would like to run an aftermarket ECU on this thing in the near future, so I will get the idle motor working with that.

What does the stock Mazda ECU use to control fuel ratio on these motors? The coolant temp sensor, air flow sensor (all wires), intake air temp (on intake), vac sensor, and ambient pressure sensor all have 0 ohms to the correct terminal on the ECU and all of the sensors are working, so I would think I am not running in some enriched fuel mode.
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