iagraham

iTrader: (1)

So when its below -8c outside my '04 won't start. Its a no crank problem, my issue is that the ECU won't provide a ground for the starter relay. If I just keep turning the key it will eventually turn over and start as normal. The colder it is, the longer it will take. MY question is what conditions does the ECU need to see in order to provide the ground? Also if I eliminate the ECU and provide my own ground will that cause any other problems? An answer to first question will likely provide the answer to the second, but its likely a question for a mazda tech or someone who's looked at the programming closely. Thanks for the help.

Jon316G

iTrader: (1)

I'm more curious on how you concluded it was the PCM not allowing the starter relay to energize.
Also... is the engine turning over and just not starting, or are you saying that it takes a few seconds for the starter to begin turning?
Is this an MT or AT?

iagraham

iTrader: (1)

Its a no crank issue, I turn the key and the engine will not turn over, even if i leave the key turned it wont start. I just have to keep turning until it starts. I found that the "PCM" controls the ground by looking at the wiring diagrams then by confirming when the car wouldn't start. I checked for power at the starter s terminal, then by checking at the next "junction" in the circuit which was the starter relay, where I was recieveing power from the ignition switch but not the ground from the PCM. I haven't checked resistance between PCM terminal 5A and the relay yet but I was interested in the PCMs "conditions" to see if it needs to see a certain temp (i.e. intake temp), that way if the wiring from the PCM is good then I could continue my checks through those "conditions". Then I could confirm that the PCM is getting accurate info. Also its a MT.

Jon316G

iTrader: (1)

Just to clarify... you ARE getting voltage when the key is turned between the starter interlock switch and the relay?
The interlock switch is actually a common issue with these symptoms where you turn the key and nothing happens (and knowing the battery isn't dead).
People usually have to pull out the "plunger" on the switch to reset the position.
I've had no issues starting my car with temps that low so I highly doubt that is your problem.

iagraham

iTrader: (1)

I have full battery voltage at the starter relay, just no ground. I've bypassed the interlock to eliminate it during the diagnostics.

Jon316G

iTrader: (1)

You can wire the relay directly to ground to help troubleshooting, just keep in mind that there is a reason the PCM is handling the ground.
I've had a theory as to why but have never validated it (for obvious reasons).
With the relay wired directly to ground, you are able to turn the key to 'START' while the engine is running and engage the starter... which would be bad.
With the car running, I think the PCM eliminates the chance of this occurring.
I could be wrong... but that would make sense as to why the PCM is controlling the ground.

iagraham

iTrader: (1)

Thats why I was looking for those conditions. Though not engaging the starter while the engine is running is a good thing, I suspect there are other reasons for having the PCM handle the ground.

Jon316G

iTrader: (1)

I also recall reading in one of the service manuals that the firing order for the ignition changes for starting as opposed to when its running.
So this and/or what I mentioned above is probably why the relay goes back to the PCM.