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94 Mazda b4000 no power from ecm


Ttownmedia

New Member
U.S. Military - Veteran
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Location
Tacoma
Vehicle Year
1994
Make / Model
Mazda b4000
Transmission
Automatic
Ok brain trust, I have a Mazda b4000. 4.0 V-6 automatic. Took it into the shop to have a valve job done. Afterwards the shop states it fired right up then quit. They started throwing parts at it.. new fuel pump, fuel filter, all new fuel injectors, m airflow sensor, crankshaft position sensor and a host of other sensors and all relays, then replace twice the ECM, no luck so they ordered a specially programmed ECM programmed to the serial number. After four months in the shop I had it towed home. When I put my code reader on it the reader gets no signal or power to come to life , the reader is getting no power. This explains the no spark issue. Fuses are good, relays are new, diode is good, I am not good and going nuts. Please throw some ideas my way. The no power to the code reader when everything is hot makes no sense.
 

lil_Blue_Ford

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Location
Butler, PA, USSA
Vehicle Year
00
Make / Model
Ford
Engine Type
V8
Engine Size
5.0l
Transmission
Automatic
Total Drop
4”
I’m gonna move this over to the 4.0 section…
 

SenorNoob

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Location
Middle Tennessee
Vehicle Year
1988
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Total Lift
1.5" Front + 4" Rear
Tire Size
245-70-R16
My OBD1 code reader isn't powered by the truck. It requires batteries to power on. It only connects to the signal wires to/from the PCM.
 

Ttownmedia

New Member
U.S. Military - Veteran
Ham Radio Operator
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Messages
4
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Location
Tacoma
Vehicle Year
1994
Make / Model
Mazda b4000
Transmission
Automatic
My OBD 1 reader works off the truck. Plug it it and when you turn the key on it powers up with the control module…normally
 

SenorNoob

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Location
Middle Tennessee
Vehicle Year
1988
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Total Lift
1.5" Front + 4" Rear
Tire Size
245-70-R16
So it draws power from the fuel pump circuit? That'd be best thing to check 1st then. That and the PCM relay. I think power for the fuel pump relay actually comes from the PCM relay.
 

Ttownmedia

New Member
U.S. Military - Veteran
Ham Radio Operator
Joined
Oct 23, 2023
Messages
4
Reaction score
3
Location
Tacoma
Vehicle Year
1994
Make / Model
Mazda b4000
Transmission
Automatic
Turns out that the oxygen pressure sensor on the exhaust manifold had a low power voltage. Should read 5 volts but only read 3 volts. I unplugged it and the engine fired right up. Replaced the sensor and it runs great. Go figure
 

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