Mileage Switch / Mileage Sensor
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From: Virginia Beach, VA
Mileage Switch / Mileage Sensor
I thought I knew a lot about the RX-7 but I am perplexed about one thing: the mileage switch. This switch affects the car when the odometer reaches 20,000mi (34,000km). I noticed this in the wiring diagram manual for the ECU. No other thread previously addressed this topic specifically. Could someone explain its importance?
My FD reference can be found on the Wiring Diagram Manual Pg Z-36, Diagram B-1, Terminal 1N & Pg Z-30, Diagram B-1b. It has 2 input values:
1) Steering Pressure Sensor - when P/S OFF at idle the value would be B+ (12-14v); when P/S ON at idle the value would be < 1v.
2) Mileage Switch - when mileage is under 20,000mi the value would be B+ (12-14v); when mileage is over 20,000 the value would be < 1v.
This type of switch is not peculiar to the FD. It also appears on the FC's ECU as the Mileage Sensor. Unlike the shared input on the FD version, the FC's version is an output that is sent to a switch inside the instrument cluster. The voltage values are identical between the FC and FD.
My reference for the FC wiring diagram can be found on Pg Z-34, Diagram B-1, Terminal 1M & Pg Z-30, Diagram B-1b (for Non-Turbo) and Pg Z-42, Diagram B-2, Terminal 1M & Pg Z-38, Diagram B-2b (for Turbo). There is also a cautionary note about the Mileage Sensor in Section T, Pg T-52.
As a side note, there is a remark for the FC's Power Steering Pressure Switch that did not transfer to the FD's remarks. It states:
P/S ON: Turning
P/S OFF: Straight ahead
The manuals used for this research are from the 1991 and 1994 workshop manuals.
Thank you in advance for the knowledge.
Cheers,
George
My FD reference can be found on the Wiring Diagram Manual Pg Z-36, Diagram B-1, Terminal 1N & Pg Z-30, Diagram B-1b. It has 2 input values:
1) Steering Pressure Sensor - when P/S OFF at idle the value would be B+ (12-14v); when P/S ON at idle the value would be < 1v.
2) Mileage Switch - when mileage is under 20,000mi the value would be B+ (12-14v); when mileage is over 20,000 the value would be < 1v.
This type of switch is not peculiar to the FD. It also appears on the FC's ECU as the Mileage Sensor. Unlike the shared input on the FD version, the FC's version is an output that is sent to a switch inside the instrument cluster. The voltage values are identical between the FC and FD.
My reference for the FC wiring diagram can be found on Pg Z-34, Diagram B-1, Terminal 1M & Pg Z-30, Diagram B-1b (for Non-Turbo) and Pg Z-42, Diagram B-2, Terminal 1M & Pg Z-38, Diagram B-2b (for Turbo). There is also a cautionary note about the Mileage Sensor in Section T, Pg T-52.
As a side note, there is a remark for the FC's Power Steering Pressure Switch that did not transfer to the FD's remarks. It states:
P/S ON: Turning
P/S OFF: Straight ahead
The manuals used for this research are from the 1991 and 1994 workshop manuals.
Thank you in advance for the knowledge.
Cheers,
George
Back when I had an FC the going thought was it changed the ECU map or something somehow for an extended break-in procedure. Never saw the bit about the power steering. Maybe the PS system has to break in to some extent?
Dale
Dale
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From: San Diego
I thought I knew a lot about the RX-7 but I am perplexed about one thing: the mileage switch. This switch affects the car when the odometer reaches 20,000mi (34,000km). I noticed this in the wiring diagram manual for the ECU. No other thread previously addressed this topic specifically. Could someone explain its importance?
Cheers,
George
Cheers,
George
We actually discussed this waaaaaay back in time during the big list days. In '94 most people began to notice a 3,500 rpm hesitation in their 1993 RX-7s. We all wondered what the heck was going on when we noticed that this hesitation for most people seemed to crop up after 20,000 miles! A couple of service technicians told us that the mileage switch flipped the ECU from engine "break-in" mode to "normal operation" mode. One of the effects of this switch over was a slight decrease in idle speed (How'd they do that?). Obviously, other things were changed, maybe the fuel injector timing and/or some section of the fuel maps. What ever was change it made the hesitation go from a few isolated new cars in the beginning, to almost everyone's car after 20k. No one at Mazda has spilled the beans as to what the exact changes to the ECU operation are. Since we can reprogram the mileage chip (a big no no folks). Some enterprising individual could conceivably change their car back to 10,000 miles, eliminate the hesitation, and document the changes. Or we can just live with it as one of life's little mysteries.
Joined: Mar 2001
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From: https://www2.mazda.com/en/100th/
the FC Ps switch turns on the Air Supply Valve, which is a US thing.
the mileage switch is also a US thing, it disables some part of the ACV, i forget, its buried in the FSM's somewhere
the mileage switch is also a US thing, it disables some part of the ACV, i forget, its buried in the FSM's somewhere
Thread Starter
Joined: Jun 2004
Posts: 2,770
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From: Virginia Beach, VA
Dale & mdp,
Thanks for the background and insight to some very old posts. I found one unusual fossil while reading the "archives"...the argument over Zenki or Kouki styled cars. Admittedly, I had to look it up.
Back to the switch, I don't understand why Terminal 1N shares the same input from 2 different sources on the FD. It doesn't make any sense - when the car is in a turn (P/S on) or when the odo is over 20k then the ECU input is the same. Does that mean the fuel map changes when the car is in a turn vice going straight? At least Mazda had sense on the FC to keep each signal separated from one another.
Perhaps it's best to press the "I Believe" button and carry on?
Mdp, I'm with you...this is one of life's little mysteries that make our cars unique.
Cheers,
George
Thanks for the background and insight to some very old posts. I found one unusual fossil while reading the "archives"...the argument over Zenki or Kouki styled cars. Admittedly, I had to look it up.
Back to the switch, I don't understand why Terminal 1N shares the same input from 2 different sources on the FD. It doesn't make any sense - when the car is in a turn (P/S on) or when the odo is over 20k then the ECU input is the same. Does that mean the fuel map changes when the car is in a turn vice going straight? At least Mazda had sense on the FC to keep each signal separated from one another.
Perhaps it's best to press the "I Believe" button and carry on?
Mdp, I'm with you...this is one of life's little mysteries that make our cars unique.
Cheers,
George
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From: https://www2.mazda.com/en/100th/
Thread Starter
Joined: Jun 2004
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From: Virginia Beach, VA
j9fd3s,
Are you referring to the difference between the 8-bit and 16-bit ECUs? Unless mistaken, the 16-bit ECUs were used on 96+ JDM cars; they also use the black box instead of the rats nest. Am I correct?
When j9fd3s talked about the Air Supply Valve, that got me thinking more about the car's emissions control system. I found a few interesting notes about the ECU terminals and the need to make one correction. First, the correction: the FC's Mileage Sensor at ECU Terminal 1M is an input. I mistakenly said it was an output. The FC's FSM confirmed this in Section F, Pg F1-80. Second, I read the entire ECU terminal listing in Section F and discovered an additional reference to mileage above or below 20k. The FC's ECU Terminal 2N is an output that controls the Port Air Solenoid Valve. The output varies between N/A and Turbo models so here's the skinny:
1. N/A (Pg F1-81) Terminal 2N
---Test Condition: Except idle (below 20,000mi); Value: 12v (approx)
---Test Condition: Idle or above 20,000mi; Value: Below 2v
2. Turbo (Pg F2-79) Terminal 2N
---Test Condition: Idle (Below 20,000mi); Value: 12v (approx)
---Test Condition: Idle (Above 20,000mi); Value: Below 2v
---Test Condition: Engine Speed above 3,500RPM; Value: 12v (approx)
3. Unfortunately for the FD's ECU terminal listing, there is no explicit output that references mileage. The ECU terminal list begins on Pg F-152 in the FD FSM.
I believe this next section may answer the relevance of the Mileage Switch! And there is a little bonus too. There is a relationship chart between Input and Output Devices that exists in the FC and FD FSMs. One of the input devices happens to be the Mileage Sensor (FC) or Mileage Switch (FD).
A. Reference FC FSM Relationship Chart on Pg F1-76 (N/A):
Mileage Sensor Affects: Fuel Injection Amount, Port Air Solenoid Valve, Solenoid Valve (Switch) [unknown solenoid], Igniter (Trailing & Leading Ignition Timing).
B. Reference FC FSM Relationship Chart on Pg F2-74 (Turbo):
Mileage Sensor #1 Affects: Fuel Injection Amount, Port Air Solenoid Valve, Igniter (Trailing & Leading Ignition Timing).
Mileage Sensor #2 Affects: Fuel Injection Amount, Duty Solenoid Valve (Turbo Boost Pressure), Igniter (Trailing & Leading Ignition Timing). *
* - Mileage Sensor #2 active for the first 600mi (1,000km). Bonus find!
C. Reference FD FSM Relationship Chart on Pg F-182:
Mileage Switch Affects: Secondary Air Bypass, Split Air Bypass, Port Air Bypass, and Relief2 Solenoid Valves
Ultimately, it looks like the mileage switch/sensor affects the car's fuel & emissions in an obscure and minuscule way. Whatever magic happens inside the ECU will still remain a mystery for the uninitiated. It does make you wonder why it exists in the first place! Maybe VW used this example for their infamous emissions test bypass scandal, aka "Diesel Gate"?
Like the X-Files [que outro music], "The truth is out there!" And for now, "I believe."
Cheers,
George
Are you referring to the difference between the 8-bit and 16-bit ECUs? Unless mistaken, the 16-bit ECUs were used on 96+ JDM cars; they also use the black box instead of the rats nest. Am I correct?
When j9fd3s talked about the Air Supply Valve, that got me thinking more about the car's emissions control system. I found a few interesting notes about the ECU terminals and the need to make one correction. First, the correction: the FC's Mileage Sensor at ECU Terminal 1M is an input. I mistakenly said it was an output. The FC's FSM confirmed this in Section F, Pg F1-80. Second, I read the entire ECU terminal listing in Section F and discovered an additional reference to mileage above or below 20k. The FC's ECU Terminal 2N is an output that controls the Port Air Solenoid Valve. The output varies between N/A and Turbo models so here's the skinny:
1. N/A (Pg F1-81) Terminal 2N
---Test Condition: Except idle (below 20,000mi); Value: 12v (approx)
---Test Condition: Idle or above 20,000mi; Value: Below 2v
2. Turbo (Pg F2-79) Terminal 2N
---Test Condition: Idle (Below 20,000mi); Value: 12v (approx)
---Test Condition: Idle (Above 20,000mi); Value: Below 2v
---Test Condition: Engine Speed above 3,500RPM; Value: 12v (approx)
3. Unfortunately for the FD's ECU terminal listing, there is no explicit output that references mileage. The ECU terminal list begins on Pg F-152 in the FD FSM.
I believe this next section may answer the relevance of the Mileage Switch! And there is a little bonus too. There is a relationship chart between Input and Output Devices that exists in the FC and FD FSMs. One of the input devices happens to be the Mileage Sensor (FC) or Mileage Switch (FD).
A. Reference FC FSM Relationship Chart on Pg F1-76 (N/A):
Mileage Sensor Affects: Fuel Injection Amount, Port Air Solenoid Valve, Solenoid Valve (Switch) [unknown solenoid], Igniter (Trailing & Leading Ignition Timing).
B. Reference FC FSM Relationship Chart on Pg F2-74 (Turbo):
Mileage Sensor #1 Affects: Fuel Injection Amount, Port Air Solenoid Valve, Igniter (Trailing & Leading Ignition Timing).
Mileage Sensor #2 Affects: Fuel Injection Amount, Duty Solenoid Valve (Turbo Boost Pressure), Igniter (Trailing & Leading Ignition Timing). *
* - Mileage Sensor #2 active for the first 600mi (1,000km). Bonus find!
C. Reference FD FSM Relationship Chart on Pg F-182:
Mileage Switch Affects: Secondary Air Bypass, Split Air Bypass, Port Air Bypass, and Relief2 Solenoid Valves
Ultimately, it looks like the mileage switch/sensor affects the car's fuel & emissions in an obscure and minuscule way. Whatever magic happens inside the ECU will still remain a mystery for the uninitiated. It does make you wonder why it exists in the first place! Maybe VW used this example for their infamous emissions test bypass scandal, aka "Diesel Gate"?
Like the X-Files [que outro music], "The truth is out there!" And for now, "I believe."
Cheers,
George
Last edited by Gen2n3; Nov 16, 2017 at 10:37 AM. Reason: Correction to Item C.
Thread Starter
Joined: Jun 2004
Posts: 2,770
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From: Virginia Beach, VA
I failed to mention the Steering Pressure Sensor when comparing it to the Mileage Switch on yesterday's post. Here it is:
D. Reference FD FSM Relationship Chart on Pg F-182:
Steering Pressure Sensor Affects: Fuel Injection Amount, Igniter, Idle Air Control Solenoid Valve.
These output devices are entirely different from the ones affected by the Mileage Switch. I still find it amusing that the 2 different inputs on 1 ECU pin affect different output devices. In certain electronic circles, that is known as PFM!
Cheers,
George
D. Reference FD FSM Relationship Chart on Pg F-182:
Steering Pressure Sensor Affects: Fuel Injection Amount, Igniter, Idle Air Control Solenoid Valve.
These output devices are entirely different from the ones affected by the Mileage Switch. I still find it amusing that the 2 different inputs on 1 ECU pin affect different output devices. In certain electronic circles, that is known as PFM!
Cheers,
George
Joined: Mar 2001
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From: https://www2.mazda.com/en/100th/
the 96+ cars do use the 'black box' but its functions are the same, its just physically simpler.
Thread Starter
Joined: Jun 2004
Posts: 2,770
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From: Virginia Beach, VA
no, the 8bit US ecu and the 8 bit JDM ecu have slightly different pinouts. the JDM ecu has no aws/EGR/Mileage sensor, and e/l box. instead it has an exhaust overheat light, and a speed fuel cut. this then frees up a couple of pins and the things that the US ecu needs the e/l box for just have normal pinouts on the Japanese models.
the 96+ cars do use the 'black box' but its functions are the same, its just physically simpler.
the 96+ cars do use the 'black box' but its functions are the same, its just physically simpler.
Thanks for pointing out the differences between the 2 ECUs.
Cheers,
George