Question, getting the CEL 13 CODE which is MAP Sensor;
does this mean the MAP sensor has gone bad? or is it indicative of some other issue related to vacuum pressure in the UIM?

Car cranks and will run for a few seconds and then stall out.
Will keep running if I give it some gas, but once I let off on the gas pedal the engine will stall out.

I've tried replacing the MAP Sensor with a used one, same issue.
Is it safe to assume the replacement sensor is bad as well?

 

Either the MAP sensor is bad, or its wiring is damaged (i.e., shorts, open circuits, intermittent poor connections). You'll need the FSM wiring diagram to troubleshoot further, but the gist of it is there are 3 terminals on the MAP sensor with 3 wires connecting the MAP sensor and the ECU. One terminal/wire will be for +5VDC power, one will be the ground return, and one will be the MAP output signal. First thing to do will be to verify that each MAP sensor terminal is reading the correct voltages with the key switched on/car not running.

 

thank you, i will test the wiring harness

 

if you've tried two sensors, and that didn't fix it, its probably not the sensor.

the code will set if the signal voltage is too high or too low.

 

I bought a used sensor, so i cant really confirm if the sensor is truly without fault.

 

I found the pin on the ecu that's connected to the MAP sensor (1O), do i just do a continuity test? to make sure the wire is not shorting out?

 

The ECU cares about the voltage at the sensor input wire. With the car off (key out of the ignition), I would check resistance between the ECU pin (1O) and the sensor connector (wire should be grey with yellow stripe for a 1994 car, according to the service manual). Your multimeter probes won't be long enough to do this check without adding an extra length of wire, and you might need something small and pointy to reach the pins inside the connector without damaging the plastic connector housing. Resistance between the ECU pin and the sensor connector should be very low, less than 10 ohms. If it's higher, that usually needs to be fixed. High resistance can be from connectors unplugged, or corroded metal pins/sockets not making a good electrical connection, or from wires that have been frayed or sliced or broken or pulled apart or burned.

If the resistance from the ECU input pin to the sensor signal pin is low, I would next check the resistance between the sensor's ground pin (center pin, black/green wire) and the ECU ground wire (pin 4D on the ECU). This should also be low, below 10 ohms. If the resistance is too high, I would double-check that connector X-05 is connected.

It's late here and this feels pretty long already, but hopefully that's enough to get you started. Good luck, sensor or wiring troubleshooting can be tricky. If it's hard to access the ECU, unplug the MAP sensor and measure voltage at each of the three MAP sensor pins. The negative (black) probe of the multimeter can go to the battery negative post for those measurements. Expected voltage is between 0.00V - 5.00V for each pin, but not all three pins should be the same. Keep careful track of the wire colors when you make those measurements, it's expected for two of the pins to measure about 5.0V with the sensor disconnected but it's important to know exactly which is which.

 

i took the car the the local mazda dealership, they tech was saying that the wires that feed the MAP sensor, all 3 pins were reading 5V, is this indicative of a short? i apologize my electrical knowledge is not up to par.

 

 

Gentlemen, I require assistance with reading the schematic for the Wiring Diagram, apologies for my limited knowledge in the field. My questions are the following:

Pertaining to the BR/W wire for the MAP Sensor, is it’s power source 3I on the ECU?
Can someone please explain to me what “SHIELD WIRE (SECTION B-1a)” means? and what the circled “14” means as well?

Thank You in Advanced

 

That will be an earth point/different ecu pin on the sensor shield wiring.

 

Yes, pin 3I (Brown/white wire) on the ECU is the 5V sensor reference power. It should always read about 4.9V - 5.0V when the ignition key is on.

Pin 4D (brown/black wire) is the sensor reference ground. It should always read about 0.0V - 0.1V when the ignition key is on. When measuring the voltage for this wire, the black (ground) probe of the multimeter goes to the battery ground and the red (positive) probe should 'tap' or 'backprobe' onto the brown/black wire at the back of the MAP sensor connector.

Pin 1O (green/yellow wire) is the MAP signal, that will probably measure about 5.0V if the MAP sensor is disconnected from the harness. When the MAP sensor is connected and you are backprobing the signal, the voltage should be between 2.3V - 2.8V with the engine off (not pulling vacuum).



I missed your previous post, but if pin 4D is measuring 5V then that is a problem. I would disconnect the MAP sensor and check resistance between that pin (with the Black/Light Green wire) and chassis ground. The resistance should be very low , below 10 ohms. If you measure high resistance I would check that Black/Light Green wire at connector X-05 (near the ECU) to make sure it is present and connected. Note that the wire will be a different color on the other side of the X-05 connector, it looks like it is Brown/Black in the harness that connects to the ECU. Connector X-05 will be different for an automatic-transmission car than a manual-transmission car, so if yours has been swapped it's possible someone didn't merge the harnesses correctly.


The circled '14' in the diagram means that the same line (or wire) is also connected to a circuit on another page of the wiring diagram (page B-1a). It goes to the shield wire in the ignition coil harness, between the ignition coils and the ignitor. Shield wires get connected to ground to prevent electrical energy from causing interference on other wires nearby. I wouldn't worry about it too much, focus on checking the voltage at each of the three pins on the MAP sensor connector.

 

I was able to test the MAP sensor wires with a multi-meter:

BR/W = 5.017V
B/LG (ground) = N/A
G/Y = 4.945V

when it tested it with the power probe 3:

BR/W = 5.0V
B/LG = no indication of ground
G/Y = 5.0V, but drops to 2.4V and i here some type of clicking noise

*I was able to confirm continuity between BR/W of the TPS and the MAP sensor.




I checked for continuity between BR/B (X-05 connector) and the B/LG (MAP Sensor), no continuity
I checked for continuity between B/LG (MAP Sensor) and B/LG (end of Front Harness by ECU), no continuity
I will double check again.

but if the results remain the same, its safe to assume the B/LG wire is severed between the MAP sensor and where the front harness runs to the passenger foot well?

As a temporary fix would it work if I ran a tap between the MAP sensor ground and the engine harness at 4D?
or should i run it between MAP sensor ground and the end of the B/LG by ECU?

 

I ended up running a tap from the MAP sensor ground wire B/LG to the end of the front harness near the ECU, and now CEL 13 went away. Thanks so much for your help scotty305!!!

 

Glad to hear it's working now. I haven't had my car's front harness apart, but I think some of the wires which are not connected on your car might run near the left side fenderwell, above the tire. That section of harness is known to get shredded by cars that are lowered or have wider tires. It would probably be wise to check it on your car, tuck it up in a safer location, and repair if needed. There's good photos and info in this thread: https://www.rx7club.com/3rd-generati...-well-1161975/