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1991 B2200 EFI, high idle speed and excessive fuel consumption

653 Views 26 Replies 3 Participants Last post by  Bobmo
Hi, first I'd like to say thanks for any advice.

I have a 1991 Mazda b2200, EFI, manual transmission with 256k miles

I have changed:
- spark plugs - distributor cap and rotor - coil - plug wires - ignition module - fuel filter - fuel pump and strainer - water pump - timing belt - rear end swap -

I have cleaned the Mass Air flow sensor, throttle body butterfly valve, Idle Air Control passages(not the entire unit), Air intake Temp sensor. Used Seafoam intake cleaner while the engine was running, Lucas in tank fuel injector cleaner/conditioner occasionally.
Achieved a much smoother idle after

The truck has seen better days, but still runs strong. Trying to fix these issues before it gets any worse or prematurely wear more of the engine.

Blows blue and black smoke on start up, idles high and gets 10MPG lately. Occasionally misses a cylinder on start up.

Unplugging the IAC drops the rpm, unsure if this indicates it working correctly or not

I plan on doing valve guides, and cylinder compression tests in the near future to address the excessive blue smoking problem.

What could be causing the loss in mileage?
What could be causing the high idle?

What are the correct ohm readings for things like the IAC, air temperature sensor, barometric pressure sensor?

Any help or advice will be appreciated
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Thanks for the heads up bobmo, I have to check if the carb truck was a manual or auto, that'll affect the model again.
As Bobmo has said, the carbureted B2200 Mazda trucks have a totally different ECU and it won't even plug into your EFI B2200 harness. The carbed ECU is junk can get those cheap, but if you change out to a Weber carb, you can just eliminate the ECU in the carbed truck.

On the EFI B2200 trucks, you definitely need the ECU that came in those, as the engine won't start without it.
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After a few days fighting battery issues, I got the Mazda started and test drove 30 miles to the nearest station. Mileage seems to be fixed close to normal, although it still idles high rpm.

More driving around and keeping track of mileage will show how its really doing.
Thanks earl and bobmo for your help, directing me to that faulty capacitor was a great help.
This trucks got a bit more work ahead, but I'm plugging away at keeping her alive.
New phone, better pictures of the old defective ECU.
New phone, better pictures of the old defective ECU.
Great News!!
I hate to throw things away and these old Mazda's are to useful to be crushed because of a simple and common problem.
Enjoy your new truck and congratulations on keeping the B's humming
Enjoy the holiday
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