P3191 Engine takes a long time to start when cold after head gasket replacement

After the car sits for a while it takes an unusually long time for the engine to start. For example this morning after having it sit overnight for maybe 18 hours or so, it took three attempts to start the engine. First start (lightly depressing pedal to start immediately), engine cranked for 10 seconds, timed out and threw P3191 ("CHECK HYBRID SYSTEM" on dash); had to power off and restart, timed out again, only third time engine eventually starts running. If it sits for a few minutes then it'll start up relatively fine although it doesnt sound as good as it used to. If it sits for a few hours it may fail the first time but work the second time like I experienced yesterday. Also the first time I started it up after putting the engine back together IIRC it took four attempts to start the engine; then it started running but not on all cylinders and knocking loudly, but ran fine after a short while. I did put new spark plugs in so maybe that had something to do with the initial knocking.

Could air in the fuel rail have something to do with it?

I also have a P0118 which I don't think is related, however it does cause the engine to run in a failsafe mode where the fans always run when the engine is running, and also once the engine starts in Park, it never stops, and when the system is to stop charging the battery where it would normally shut down the engine, instead it just disconnects the engine and the engine spins faster (well the rpm it spins at seems to vary but first time it span unusually fast when it stopped charging). So i'm not sure if/how this fail-safe mode might affect this cold-start issue.

 

Battery seems fine; 12.7 volts; obviously it is able to energize the HV contactors to start the hybrid system, which then powers the low voltage system at which point I don't think the battery would do anything anymore besides be charged.

 

don't have techstream but will consider getting soon if I still need to debug things.

 

hmm how can I test fuel pressure on gen3?

 

Ok turns out this was just a symptom of my other issue; since I plugged the correct sensor in it starts up normally now. I guess that makes sense, because according to the repair manual, when P0118 is set, "the engine coolant temperature is estimated to be 80°C (176°F)". Which probably means the parameters are always tuned for that temperature, which isn't suitable when the engine is actually cold.