So here's some history and the problem

New LIM AND UIM gaskets, fuel pressure regulator, fuel filter, maf sensor, plugs, wires, cap, rotor, ignition switch, synthetic oil.

The engine runs flawlessly after running, accelerates, idles, and starts after shut down without skipping a beat. When it does start, it idles up like normal, and once warm, the idle drops to the normal range.

The problem is in sub zero temperatures it will not start. This progressively got worse. At the start of winter in -35c I could start it in the morning with no block heater easily. Now at merely -10c it wont start. The battery is good, it cranks like a monster. After plugging the block heater in for 45 minutes, the engine starts. What is causing this problem?!

Thanks in advance,
Andrew.

 

Have you checked your fuel pressures at the service port on the engine & at the outlet of the fuel filter? Here is a link on how to do this:
https://blazerforum.com/forum/2nd-ge...eakdown-88305/

 

You have something that is running right on the edge of specification, some things can be out of spec yet be functional at normal operating temperature or once the engine starts initially, 2 major parts that cause a lot of "tail chasing" during diagnosis are the fuel pump and the battery, just because the engine runs it doesnt mean the pump is supplying pressure to specification and just because the engine cranks normally it doesnt mean that the battery is supplying the specified voltage and amperage. You can have a battery with a bad cell or low cranking amps and it will still crank the engine seemingly well, but if the voltage drops below about 9 volts while cranking there may not be enough power left for the PCM to supply voltage all of the sensors, fire the injectors, ignition coil and run the fuel pump. I suggest having the battery tested or at least do a cranking voltage check. Using extra power to crank is normal as temps fall, as your battery fails the lowest temp it can crank the engine at rises, so if you warm the engine up 10 or 20 degrees it frees up enough juice to run the rest of the electronics and the engine starts.
On the pump side, if your pressure is low or just on the edge of low and the starter is demanding extra amperage to crank a freezing cold engine it may not leave the extra amperage that the weak pump needs to supply the required fuel pressure needed on cold startup.

 

I agree with both posts! Good job.

 

Wonder if the fuel line is freezing and the block heater is just enough to thaw it out so that the engine starts...??
Could try adding some water absorber to the fuel to see if this helps.

Been a long time since I have seen -10°C.

 

We have seen 10 F in New Jersey this year and that is colder than -10C and have not had any of those issues. Unlikely the fuel lines are freezing. Block heater would not be close enough to any to even have an impact. Problem is something related to answers from previous posters.