I have a 1978 Ford f150 with a 300. It has always started even when cold/below 32 degrees. But for some reason this year anytime it is below 40 to 45 it will not start. I live at 5,800 feet altitude so it does run a little rich but this has not been a problem before.


After it warms up to 45 or 50 degrees boom starts right up.


It appears to be getting gas. The choke seems to be working right.


It just cranks and cranks with no attempt to fire up.


Would there be something that would cause it to not get spark that is related to temperature?


Could it be flooding when cold?


But as I said when above 45 degrees starts right up with hardly turning over.


Appreciate any help solving this new mystery.

 

I assume you've checked for spark when it's cold?

 

When "cold,".....things tend to 'shrivel up' or contract to less than their relative 'normal' size. When warm, they'll reach their 'normal' size and mebbe surpass that expansion.

Suppose, when it's cold, you have a wire/connection that normally could be considered "iffy"......and slightly separates during a decline in ambient temperature.

Wams up, it expands and all is well with the cosmos.

Checking for spark when cold as dlburch suggests is a good start. Wiring connections at the coil, spade plug male/female connections, etc are next in line.

 

I know this is basic but you are giving it a couple pumps on the accelerator when it is cold ? Sometimes we forget we need to do this on carb'd engines after being spoiled with EFI.

 

When the choke is set up properly, you only need to pump it once.

 

Ya maybe for around freezing but that certainly is not case in sub freezing temps. 2 hits insures a one revolution start.

 

Interesting problem. How is the starting RPM when cold? There is a spec for that. Is it an old starter? As temperatures go down - oil thickens, engine is harder to turn over and consequently all this adds up, the starter current draw goes way up. At the same time in cold temperatures the ability of a battery to provide the current required goes way down. Double whammy! Might be interesting to measure voltage at the battery posts during cranking, when cold. In "normal" temperatures anything below 9.6 volts is cause to reject the battery. In cold temps it's adjusted down - at 0°F minimum voltage under load is 8.5, point being if battery is on its way out, it could be a factor.

It's possible .. just WAG thinking out loud .. the ignition is being "choked off" during start by a combination of those factors. Loose or corroded ground and start cables, weak or marginal battery, etc.

Shorter answer: check spark

 

That's crazy talk

 

What is the overall condition of the engine (meaning rings/compression)? If the engine is tired and the rings are not sealing good anymore it’s happened to me. When it the temperatures got colder it would not start unless I hit the carb with a shot of starting fluid. Got gas, got spark etc....wasn’t a Ford truck etc...was a ‘67 Olds 442. Pulled the engine eventually and rebuilt it and bingo....good to go!

 

My guess is that something is hanging up the choke plate, keeping it from closing all the way to its limit/setting.
Could a non-functioning pull-off cause this? If that is the case, I'd think that the truck would sound like it's firing and wanting to start for a split second.

Another possibility is that your plugs, wires, and cap & rotor, are worn out, (or any one of the four) and the extra cold temps are unmasking it for what it is.

 

I have a similar issue, won't start when it's cold. Narrowed it down to a no spark condition but don't know why yet, just sort of stumbled across it one morning by chance (it was unusually cool for that time of year). I've since replaced the battery but don't know if the issue is corrected.

Long story short and to parrot what everyone else said; check for spark.

 

This just happened to me. Threw a bunch of parts at the ignition because it was cold and dark and I didn't want to ride my motorcycle to work. A few days later I figured out what was actually wrong - the wires from the distributor pickup to the ignition coil had pretty much disintegrated.

 

I had this happen on an '84 Capri RS 5.0, but the problem was closer to the DuraSpark box. Chased that problem for a few months, until it popped up once again, right after an oil and filter change, where I knew I'd jostled those wires when changing the filter. The insulation cracked and fell off, exposing the conductors. This is a somewhat common malady on DuraSpark II equipped Fords.

 

You were right !
After checking out everything I decided to check the distributor cap. When I took it off the spring loaded center post fell out. It was worn out and not making contact when it was cold as suggested by FILTHY BEAST.


I replaced the Distributor cap and rotor and boom now it fires up every time even when it was 22 the other morning.


I put a new distributor on 20,000 miles or 3 years ago. A friend made sure I was adequately informed that I should have replace it at 10,000 miles.


In my defense I have not driven a vehicle with a distributor in a very long time!

 

Glad u figured it out. But as a side note I had a 500ci. Caddy that would do this from time to time. Ended up being the fly weights in the distributor not returning, leaving the timing too advanced to start.