Crank but no Start (Intermittent)

[ysKn]

Hey guys,
I’m currently having a crank but no start issue. It’s really weird as when I go to start the car, it will crank for a few seconds, then automatically stop (and can hear a blower sound spin down), even if I’m still turning the key fully.
However, if I disconnect the battery and reconnect it, it will let me continuously crank but won’t start.
The non start issue is intermittent, on the odd occasion the car will actually start fine, and run fine the whole time without stalling, I have driven it for over 20 minutes fine when it did start.

This all started after I replaced the heater hoses (very fine crack on one of them). So I’m thinking I may have accidently knocked something or maybe some coolant leaked onto/into something it shouldn’t?
However, after I changed the hoses, I also did a coolant flush, and the car did start immediately after as I was burping it. It wasn’t until next morning that I ran into the problem.
I did remove the intercooler when doing that job. I have since removed the intercooler and try to spot for any loose connections, but couldn’t, but I don’t think I have the expertise to really check that thoroughly.

I’m thinking it has something to do with the immobiliser, as, when I put my key in (without turning), I would get a solid red key light on the dash. I’ve noticed once, when car was able to start, the solid key light was not lit up when just inserted.
Spare key has also been tested and same results.
I’ve also replaced the crankshaft position sensor already, and there was no difference.

Anybody have any idea what this could be or what I can try? Maybe a grounding issue? It’s got me really stumped. Any help would be appreciated!

Thanks!

[Ric]

My first thought would have been crank position sensor.
Maybe it's a problem with the CPS wiring, not the sensor itself.

Otherwise the immobiliser is the next most obvious culprit. I assume it's an after market one.
How does it normally operate when immobilising? i.e. does it interrupt the start signal, or just kill the fuel pump or ignition?

[ysKn]

My first thought would have been crank position sensor.
Maybe it's a problem with the CPS wiring, not the sensor itself.

Yeah, since I replaced the crank position sensor, it could be the wiring, any idea where the other end actually terminates to?

Otherwise the immobiliser is the next most obvious culprit. I assume it's an after market one.
How does it normally operate when immobilising? i.e. does it interrupt the start signal, or just kill the fuel pump or ignition?

Completely stock 07 GTB immobiliser.
This is where I'm really thinking the issue is.
Sometimes, I would simply put the key into the ignition without turning, and the solid red key light would light up, this is when I know it would crank but not start, even without trying.
Other times, I would put the key in, and the solid red key light won't light up, and it would start as per normal.
Seems as though the immobiliser recognises my key only sometimes.

This is the same light I'm talking about when I put the key in (not flashing)
https://www.reddit.com/r/subaru/comment ... key_on_my/