Mazda 3 ECU swap question

[newguy90]

..and here is the pic with the 'old' ECU's EEPROM 93C56:

[narkeleptk]

I was really only interested in the pcb for the bad unit but your "new" unit has no zener installed and looks to be left off by design, that is pretty odd they chose to do away with the over voltage protection even tho the footprint was already there..

[newguy90]

Yes, no limitation for the voltage... That's why the diagram shows B+ for the voltage, otherwise they would have put the a fixed value of 12V., don't you agree? Likewise, in Autodata 3.45 the B+ has a value of 11-14 V... So again that means it's not a fixed value of 12 V.

[narkeleptk]

I'm sorry its actually referred to as a TVS diode and really nothing to do with your current issue, I was just pointing it out because I thought it was a bit odd. If you look at your old ecu you will see it has one, yet the replacement ecu does not. The ecu will function as normal with out it but you run higher risk of transient voltages ravaging the ecu.

TVS Diodes only blocks voltages if they go to high from coming in. Around 19-26V's is typical on 12V systems. This prevents the higher voltage's from outside the ecu coming in and blowing up the lower rated components, like those 35V caps which would be on the B+ line and even those 10V caps on the mcu power supply side if things went really bad. I would install one myself personally, Maybe this one SM8S22A. It has a working voltage of 22V and breakdown around 25V.

B+ is just what ever your battery/alternator is putting out so yes it will range from 11-15V but people tend to just refer to these things as 12V for simplicity.

[newguy90]

I don't know that much about electrical components, just the basics... that's why I prefer to do "software mod" instead of a hardware mod.. .
Did you take a look at the specs for the two EEPROMs mentioned before? ( A93c56 and S93A56) As far as I see, both of them have the same pin structure /functions , so I think that (with a bit of luck) the cloning of the IMMO data can be susccesful. I hope.

[narkeleptk]

Yes they have the same pinout

[Meat-Head]

Not going to argue as the pcb images not clear enough to me, be have found that some cars the ecu is used as a junction point

power in/out.

sounds to me, but won’t argue the pcm relay is bad, or one of them fuses is missing?

if it has been ok for a year more likely something gone open circuit

can you swap fuel and pcm relays over

[newguy90]

@Meat-head:
By PCM relay, do you mean MAIN RELAY? Swapping the main relay with the pump relay was one of the first things I did. Also, as I previously said, I cheked every single ECU harness wires for open circuit / short to mass / short to Batt+. I didn't find anything wrong.

[Meat-Head]

Remove the main relay, feed airflow meter, start indain and see what voltage you got on all pins.

[kiszka]

Remove the main relay, feed airflow meter, start indain and see what voltage you got on all pins.

there will definitely be bad tension

@Meat-head:
By PCM relay, do you mean MAIN RELAY? Swapping the main relay with the pump relay was one of the first things I did. Also, as I previously said, I cheked every single ECU harness wires for open circuit / short to mass / short to Batt+. I didn't find anything wrong.

from fuse F34 (on output)
or F69 20A engine compartment
if it catches the air flow meter error on F34
make a bypass with a wire to the flow meter
use the correct thickness of wire, for the length of the wire
and believe me you'll forget about the fault forever

[newguy90]

Remove the main relay, feed airflow meter, start indain and see what voltage you got on all pins.

Sorry, but I can't figure it out what do you mean by "start indain"

[newguy90]

@kiszka:
At first I did something similar (I fed B+ from F34 not only to the MAF but to the CKP also (to avoid overloading of the ECU's circuitry) and the result was : engine died in a winter night on the way home ... not very pleasant ... Luckly, I was only a few miles away from home, so I called a friend to tow my car home. Only the next day I discovered the culprit: F69 fuse (20A) from the PJB (Passenger Junction Box) was blown! I replaced the fuse and the car started without any issues. To avoid this kind of problems, I decided to make a separate power source, so I used a relay which when is triggerd by the ignition it feeds the MAF sensor and the CKP sensor with B+ directly from the battery through a 10A fuse. No more blown up fuses from that moment.
... But still... I can't just "forget about the fault forever" . Sometimes on occasion, the engine cuts when I rev it above 4000 rpms (not all the time , though) , and strangely just today I felt a brief engine cut just after I passed over some bump with my rear wheels at low speed!
So that's why I can't just ignore this problem... I need to get to the bottom of this, somehow.

[Meat-Head]

Indian, as in engine.

reading that, somewhere, is a tiny tiny chaffed wire, which has blown away.

find the nearest bumpy road, hit it fast see if fuse blows.

chances are something silly like injector loom rubbing when engine cover moved?

[newguy90]

Indian, as in engine.
reading that, somewhere, is a tiny tiny chaffed wire, which has blown away.
find the nearest bumpy road, hit it fast see if fuse blows.
chances are something silly like injector loom rubbing when engine cover moved?

No fuses blow whatever bumpy road I'm on. Only yesterday I felt an engine brief "hiccup" when I passed with the rear wheels over some bump at low speed.

[electronico]

I'm planning to do just that... I'm awaiting on my EEPROM programmer to arrive ( I ordered a cheap clip on EEPROM Programmer from china, so it takes a couple of weeks until arrival).
The issue is the following: The car died while coasting downhill and refused to start ever since. I pulled over and I plugged in the cars OBD a code reader and discovered 5 DTCs:
P0031
P0037
P0102
P0403
P0443
I've cleared them all, and then I tried to start the car. The engine cranks, but doesn't start. I took it to a Mazda dealer and after testing it for almost a day, dealer said that ECU is the problem... A new ECU is 2000 US dolars, so I took it home and I start investigating the problem myself. With the workshop the workshop manual and Autodata by my side, I checked fuses, wires, sensors resistance, voltages, checked for shorts to ground and batt+... almost everything I could think of!
What I found was: The ECU doesn't provide 12 volts to the following : Lambda sondes (1 and 2),EVAP, CMP, CKP, EGR, MAF and all 4 fuel injectors. All these sensors are wired to the ECU (ports 2T and 2BG) It only provides 12 Volts to the Ignition coils. As I said I checked all the inputs of the ECU (it receives 12V from Battery and Ignition) and all grounds are good also. If I take a live feed from battery and hook it to the MAF power wire the car starts and runs just fine, no DTCs at all! In fact I'm using the car hacked like this for almost a year now!
But I'm not comfortable knowing that something is wrong so that's why I want to try a new ECU to see if the car will be fixed, so that I will not need to drive a 'hacked' car ...
Any help will be appreciated! Thanks!

Hello,
(sorry for thread hijacking)
I have the same issue with the same ECU on the same car.
Trying to put hand on some wiring diagrams, especially ECU pinouts (as I only have the ECU for repair right now).
Thanks a lot if you can help.
Be sure I'll keep you informed if I solve the problem.

EDIT : Mazda dealer service told : "no power to fuel pump => ECU"
I'm not aware of any DTC he might have found