2000 Mazda 626 - Losing Injector Pulse as engine fires

Maintenance/Repairs
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1

I am in dire need fro ideas and assistance.

My niece has a 2000 Mazda 626 2.0L that cut out while she was driving. To cut a long story short here is a summary of the problem and what has been checked and changed.

PROBLEM:

  • When you attempt to start the car, it fires initially before it continues to crank, firing on an off but will not continue to run.

PARTS REPLACED:

  • Fuel Pump
  • Cam Angle Sensor

ACTIONS PERFORMED:

  • Injectors Cleaned

OTHER VALUABLE INFORMATION:

  • Using Injector Pulse Checkers it is obvious that the injectors stop firing when the engine fires.

  • The engine will continue run if I squirt gasoline into the air box. (Eliminates spark plugs, ignition timing, timing belt in my books)

  • Fuel pressure is high enough to squirt out of the hose when the return is blocked when the pump is running

  • Pump primes when pressure is low at initial start up

Does anyone know what sends the injector pulse to the injectors once the engine is in a running state?

Please help me maintain my sanity!! :slight_smile:

2

I am not intimately familiar with the details of the 626 system. (Do you have a factory service manual? That would help).

But in generic terms, injectors are usually pulsed by the PCM, and on the ground side. So injectors are usually supplied constant 12V on the + side and the PCM supplies ground to pulse them. For some systems, I know that one thing that will cause the injectors to shut down immediately upon firing up is anti theft systems. I don’t know what Mazda does for anti theft or how it works. But what you are describing sounds like that. The PCM isn’t getting the right security info from the key so it is disabling the car. Perhaps try another key if these are chipped keys.

Either way, I would look into how the security system works and if you eliminate that you might start tracing out ground connections all the way back to the PCM.

In addition to thinking about that, I wonder if you’ve checked the crank sensor. I doubt it would be related, but it would be a good idea to put an actual fuel pressure gauge on it. The squirting fuel only tells you that there is some getting to the rail - not getting to the rail at the correct pressure spec.