Hi,

I am feeling the car is on it's last miles but I would like to push it some more...
Two days ago the car suddenly stopped during drive, there was the "burned electronics" smell.
I had to get the car dragged to home and then troubleshooting started.
When trying to start the car the engine cranks but never fires up.

In the description below I reference the green "FS 02" fuel pump relay in the engine room, I call the pins 1, 2, 3 and 4. Pin 1 and 2 closest to driver, and pin 1 & 3 closest to engine and air inlet (away from wheel on driver's side).

What I have checked:
1. Fuses are OK, both inside car and in engine room.
2. Battery power is OK (I recharged it to approx. 12.5-12.7 V).
3. Pin 1 and 3 of the "FS 02" relay reads 75 ohm (the coil?) and when putting 12 V on them there's a click and the resistance between the other two pins drop from "infinite" to "0" ohm. I think that should mean it is OK?
4. Feels like an unlikely reason, but I changed fuel filter - I think it has never been done to this car. It did not look too bad but it is impossible to know what is inside.
5. The resistance between the "FS 02" relay pin 4 and the white/yellow cable under back seat hatch (same contact as for the fuel level sensor) is close to 0 ohm - no broken cable.
6. Before reinstalling fuel filter I tried to fire the engine up, fuel was pumped from the pipe running from the tank. However I do not know if it has adequate pressure...
7. The resistance of the fuel pump (measured from the back seat hatch) is very low, 1 ohm?
8. I removed the PCM below the radio compartment. I cannot spot any burned black spots on the board.
9. The "FS 02" pin 2 reads 11.6 V compared to ground. Shouldn't it be higher?
10. The spark plugs looks reasonable.

My best guess is that the PCM might be broken (due to the smell) or that the fuel pump is too weak. Or that something is wrong with ignition (should it smell gasoline from the spark plug holes then?). Is there some test or thing I have missed? Changing fuel pump is not that fun, tank is almost full...
A second hand PCM would be easy to exchange but the question is if this is the issue.

 

Update:
- Gas gets to the cylinders as tried to start and removed spark plug to check.
- The distributor is fairly new and the rotor arm sits firm.
- I cannot get error codes from the "DIAGNOSIS" box. Followed Hayne's manual advice and jumpered pins STI and GND (called TEN and GND on the box lid). Then added 12V lamp to the STO and battery positive. No blinkings at all.

Ignition problem due to electrical wiring or PCM problem?

 

Ferret:
I think you are on the right track. But I readily admit that electronics are not my forte.
You could try if you can get a used one from the junk yard or send it in to a company that fixes broken electronics. Sometimes it is a bad solder point.
This is one of those companies:
Automotive Scientific Inc. Your #1 Source for ECU, TCU, ABS, EBCM, Climate Control and Speedometer Repairs

 

You state the rotor arm sits firm? Does that mean it turns when you crank it, but there is no slop? With hei the voltage is not battery voltage when running, it is full battery when cranking. Do you have a trouble light? If so, I'd suggest take the distributor cap off, cover the light with the cap, you should not see any light from the cap. in other words you are looking for a crack in the cap. i think you posted it trys to start? Pull the coil wire from the cap, thats to single one on top, then try to start it, does it do the same thing, or dosen't try to start at all?

 

This will be a non-issue soon as I just checked out another Mazda 626 2.0i from the same year which has been running for only 45 000 miles (compared to mine which is almost 200 000 miles). No visible rust, engine runs smoothly. Only one previous owner who have now passed the safe driving age. For $2 000 this is a quick and convenient solution to the problem.
I will strip the current car of useful parts such as the stainless steel exhaust pipes and catalytic converter.

But I hate to give up on this, of pure interest I will troubleshoot it some more this week. I will have another go at the distributor, I had the cap and rotor replaced 1 000 miles ago but could there be a broken sensor somewhere stopping the ignition? Crankshaft position sensor? Should be one in the distributor according to this pic: http://www.justanswer.com/uploads/RI...NT_LOCATOR.jpg

 

...and the answer is... broken distributor! Probably the crankshaft position sensor, but according to Hayne's manual it is not possible to replace as a separate unit.

I purchased a igniter lamp to place between the spark plug and the igniter coil.
No spark when trying to start the engine.
Got a second hand replacement unit for $60, engine started immediately. :-)

Well now I have two working Mazda 626, will try to sell this one for $600-$700...