Here's the thing, my car wont start when its very cold. (-25 F) What is very weird was the first time it didnt start it was only 19 F. What i did was try the fuel pump relay trick bringing it inside at night, and for a few days that worked great, i got another used relay and installed it, all was good, in till it did it again, i switched back to my warm relay and got nothing. Anyway the fuel pump ALWAYS sounds normal when i "ON" the car. I went to see a mechanic he told me first thing to change was the temp sensor, so i did, again, that worked great in the freezing temp for 2 days (wasnt easy to start, but started firing right away at least)
Sometimes it turns and turns and turns no firing at all. Even after cranking so much the battery dies, i even killed my battery once, moved to a booster pack and killed that too.

When it doesnt start i normally get someone to tow start me, which works instantly..
My T stat is brand new OEM
The ETC (whatever it is temp sensor under t stat) is brand new OEM
Battery is brand new last year OEM ( tons of power turns over quickly)
All my ignition (except coil) is new last year (bosch)
Front O2 changed 3 months ago (bosch OEM replacement)
rear O2 hooked up, but not connected to DP, never changed no CEL

Now my spark plugs i changed last year, but ive boosted the crap out of them this year and think they need to be changed, i'm ordering OEM today and changing them ASAP.
I killed my starter cranking so much, now it grinds sometimes, but it still turns the motor pretty good, so don't think it could cause the problem.
I understand MAF sensor could cause this problem, it shall be cleaned tonight.
Could the coil get affected this way due to cold?
Could be the crank or cam sensor, but how do i diagnose that ( when it doesnt start, ive tried heating the cam sensor)
Anything i'm overlooking that may cause the problem?

 

If you are not getting spark it is likely the cam sensor. Check for spark.

 

i read that you can just pull out the plug and leave it connected and check, is there a better way?

im guessing you pull the fuel pump fuse too

 

also i'll add that even when it's warm outside, it starts rough

also how can you know if its the crank or cam sensor, i dont want to buy both new..

 

They are expensive. I never pull any fuel relay or anything. Heck, I was told that you don't even have to pull the plug, the plug wire will spark if it's near metal, like a motor bolt.

I don't know why it would start warm if not cold. Doesn't sound like a crank sensor if it will start warm. I'm a little stumped. But do check for spark. If you don't have spark you need to deal with that first.

 

Normally if you have a cam or crank sensor problem you will also have a check engine light and a code that would direct you toward one of those two sensors.
You might also have a bad temperature sensor as the computer will use it's reading to determine how much fuel to inject.

 

after this morning im leaning toward a fuel problem

It seems to start when it has gas, if the needle is anywhere near empty, no start..

That leaves fuel pump ( but it works) check valve ( the car's AWD, so i dont know where it's located) , or regulator..


In the morning i should still have full pressure at the fuel rail, im going to check for the heck of it tomorrow to see what the pressure is.

 

Sounds like you may have some tank condensation issues, if it is worse when the tank is near empty. Keep more fuel in it.

Also, if it's a NA model, make sure your air box thermostat is operational (that's the bit with the wax barrel and diverter door that pulls intake air off area of the exhaust manifold). At -25, fuel atomization is definitely an issue. Won't help for startup, but you said it still runs a bit rough when hot.

 

So i checked the pressure at the rail with a tire guage, (car running) and even though it was a tire guage read 32 psi, which is not bad... for a tire guage. I still need to get a real guage to test it, but my point is this morning i checked and it had 0 PSI, after i turned the key on "ON" once it still had almost no pressure, if any. But the car started.

 

I think you need that real gauge.

 

i think i found my problem....
I installed the fuel filter backwords, im an IDIOT!

i'm going to see tomorrow if i can get that fixed, and see how it goes.

 

As Homer Simpson would say...Doh!