Subaru Forester 2010 crank but won't start

Oct 24, 2021
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I have a Subaru Forester 2010, standard. Since a couple of weeks, it had problems starting. I tried a couple of things but nothing worked.

The symptoms:

Every morning, the car can take a good 15 second cranking to start or not start at all. Usually during the day, it starts fine, with the exception of a couple of times here and there.

When I plug my jump starter on the car, it starts right away, even in the morning BUT it's really weird, as the jump starter doesn't use any of it's charge. Only the fact that the jump starter is plugged make the car start like a charm, but the battery of the car is not flat, and I would say full, since the jumper starter is always full of charge after use. What can cause the jumper starter to make a difference while not using it's charge? I just think if I figure that out, I can find the overall problem.

What I tried to do:

First, I changed the old battery for a new one, I cleaned the battery wires and the grounds from corrosion, and I added a new ground. Then, I changed the spark plugs, the coil and the wires are new.
I've also changed the crankshaft position sensor as one morning that the car didn't start, the check engine light when on afterwards with a code for a faulty crankshaft.

I ve removed the battery from the key knob, as maybe it was sending a faulty message to the car immobilizer. I didn't knew what to try at that point.

What I didn't do:

Change the fuel pump but it seems to work just fine. Starter seems fine since it's cranking no problem. Maybe a ECM problem?

Thank you, I don't know what to do anymore.
I'm in the almost exactly same situation....I read in another forum that 12.3V is considered low. Can the ECM cut power to the coil and cause a no spark at the plugs when voltage is 12.3V or lower ? Because I have no spark. Boost the car with another car, wait 10sec and the car start very well. Engine crank a lot but voltage was just below 12V (after a lot of try of starting). I've just bought the car and no start 3 days in a row.... Battery seem not so old.

Anyway: my really question is: can the ECM cut power to ignition coil when voltage drop below a certain thresold ?
Seems like more of a voltage problem then anything else. Have you checked to see if the alternator is providing enough voltage? The battery is honestly only there to power the starter at startup. After that the alternator pretty much does the rest. Id would check the output voltage on the alternator first. Most parts stores have a voltage tester they will hook up and run free of charge.
14.5v when engine running so, i don't think the alternator is the problem. Once the car is started, start very well for the rest of the day. It's just after 10-12 hours of "sleep" that the engine don't want to start, and if the temperature is cold (not so cold, talking here about minus 6°C, not talking about minus 30°C, just minus 6.....). And two days ago, i've checked the voltage at the battery before putting the key to ON position and have 12.4V at the battery and 12.3V in my DTC code reader. I don't think this is alarming... 11,7V ok but 12.4V ????? This is why I think that maybe the ECM have a parameter or programming that state that 12.3V (or another voltage near) is considered low and not sending power or signal to the ignition coil. Because remember that i have no spark at the plug and just jump start the car it start on the fly. And what bother me the most is that the engine crank a lot, easily and for a long time before the battery start loosing power....but no spark....... Very intriguing problem,,,,,,

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