Howdy guys,
My truck will not start when the temp falls below -10F, this started early this winter and I've been playing the game and troubleshooting to the best of my ability.
Battery is fully charged and has zero corrosion on terminals or starter connections. Turns truck over like normal.
Fuel, spark, air is where I started when it wouldn't start. Cleaned my airfilter (K&N aftermarket intake) and maf sensor, made sure all wire connectors were connected, [STILL NO START],
Pulled plug and checked for spark, had spark, plug was wet with fuel.
[STILL NO START]
Tested fuel pressure at -10F with key in the on position 0 fuel pressure. when the temp gets to -5 below fuel pressure hits 34psi truck starts and runs normal as soon as it get to -10F truck will not start.
Things I have changed 1) fuel filter 2) fuel pressure regulator 3) fuel pump 4) cht sensor 5) thermostat

Again any help would be greatly appreciated.

 

Get a better pump or purchase good fuel, - perhaps a fuel additive.

 

maybe a better pump ......its a Carter that had better specs than the motorcraft stock one. I only run premium in the winter with heet additive.

 

Try running regular, - it's usually fresher. Premium can stale if it sits to long as well. I wouldn't run it at all or recommend it. These trucks are tuned for a certain octane fuel, - unless you alter the tune for premium. Which plugs do you run w/premium? Anyway, that's not the problem here, not yet anyway lol.

Well, for some reason your pump isn't charging the lines at 10 below. When this happens again, - leave the key to run and bang on the tank. Chances are, that will wake up the pump, - you'll hear it when it does.

 

I cant remember what plugs I have right now. I have hit the tank and open the filler cap to hear the pump and I swear it turns on and acts like its priming. Ive even switched the relay thinking it didn't like the cold haha. if im not mistaken the PCM runs the fuel pump theres nothing in between them, when the PCM receives a signal it tells the fuel pump to prime correct. I appreciate the help man this gremlin has been driving me nuts.

 

You have checked everything I would have checked and you seem to know what you are doing. Bottom line it starts and runs above -10 but not at -10 or bleow. Perhaps the PCM or a sensor like the crank or cam sensor. I am thinking maybe those sensors are acting funny when it gets cold. changing them will only cost you about $50.

good luck

 

Have you changed the fuel filter?

 

Is there possibly water getting in the tank not a ton but just enough so that when the temp hits-10 it freezes up I know the freezing temp of water is above that and fuel is below that but maybe you got enough water for a mixture that freezes at that temp just an idea

 

They shouldn't be tho. The problem is pressure anyway right ? So either a blockage or failing pump. Thing is, - did the same thing after he changed the pump ? Is that right OP ? So, tuff one. Well if its low on fuel and water being heavier than fuel, the more water you can have cycling thru the pump. - Which can screw it up as well.
Water can gel and slush, specially when low of fuel. Fuel additives like "Heet" are really just alcohol which is soluble in both water and gasoline. This solubilized water is then able to work its way out of the tank along with the gas. So, is it topped off with fuel ? If it's low enough, that could be screwing things up.

BTW, there's a circuit breaker for the fuel pump. Called the inertia reset. Its behind the p[passenger side kick-panel. But if that were to trip, it wouldn't start at all until manually reset again.

Wait a minute, - when you changed the fuel pump, did you replace the sock ? That may be freezing up as well.

 

Yes, after changing the pump, fuel pump gasket, the fuel pump sock, fuel filter, everything was the same no fuel pressure. I try to never go below a half tank not saying it doesn't happen on occasion, but its been full when it wont start.
If it starts at -5f and not -10f how much can really change if the water is freezing in the fuel and causing a blockage? anybody now a better product then heet? I always thought it was the best on out there, should I just buy some straight isopropyl alcohol and dump in the same amount as a heet bottle?
(KRACK499)The option of water getting in the tank could happen, there definitely is a lot of salt and snow on the road, so to get some inside the tank I guess wouldn't be out of the question.
I have also activated and then reset the inertia switch and unplugged the switch to see if the plug had corrosion, no luck looked brand new. maybe I should meter it out when it gets could to see if operating correctly?