'91 Blazer not starting when it's REALLY cold out.

[Mickey_D]

A coworker of mine has a (I think) '91 blazer with the 4.3L Vortec V-6 in it. He says that last winter whenever the temps dropped below about -25 to -30 that his truck would turn over fine, but it wouldn't fire. Is there an ignition or fuel pump cutout related to oil pressure on these? If so, is it the sender by the exhaust manifold (driver's side) or is it the pressure gauge sender up by the distributor?

[Zoomad75]

IIRC there is a oil pressure related fuel pump shut off feature. If the pressue drops to zero (like in event of a roll over) the fuel pump gets it's power shut off. However, in really cold temps I'd expect cold starting oil pressure to be really really high as the oil is thicker in colder temps (even multiwieght oil)

I'd venture to guess that the fuel pumo is running, but at 60 degrees below freezing I don't know what the fuel will do. That's friggen cold. You might want to make sure the injectors are not fouled/clogged. I know I went through some cold nights with some of my stuff and a lot of things happen when its that cold. Cranking speed is slow, battery charge level is low. Oil is thick (engine, trans and p/s system). If you have any moisture in the fuel system it would have froze at -30. Since water is heavier than fuel it could have collected at the base of the fuel pump where it picks up the fuel and froze inside the tank. Moisture in the fuel filter could have froze it up solid too. either way the pump can't move fuel if the inlet is frozen or you have frozen filter.

I'd suggest a block heater for the engine if he doesn't already have it and run a couple of cans of Sta-bil through a couple of tanks of fuel to try and eliminate most of the moisture in the tank before it gets that cold.

[screwballl]

some years back my dad had a 86 Blazer with 350 TBI in SD that had the same problem... after years of troubleshooting never did get it fixed... the only thing they figured was that the fuel pump was frozen enough to not pump anything. It only seemed to happen if the air temp dropped below -20... and since gas takes much colder temps to freeze, it was holding onto that temp which was transferring it tot he pump and freezing the parts...
this was just a theory though.
A block heater and a antifreeze heater never helped at these temperatures. Someone mentioned a gas tank heating blanket but I heard they are more trouble then it is worth...

[Mickey_D]

After talking to my coworker more, I'm leaning towards it being his starter.

He says that if he plugs the block heater in and lets it warm the engine up a bit, it'll fire up. But of course that doesn't do a damn bit of good if he needs it for work (because Walmart being the cheapskates they are don't supply outdoor plugins for our block heaters).

I used to have a similar problem with my old '81 in that if it got too cold the original starter would draw SO much power trying to turn the cold engine over it wouldn't leave any for anything else. As soon as I changed the starter out for a new one, I can now start my truck unassisted all the way to -40 (it would cut out on me anything below -10 with the old starter).

So he's going to give that a try first. Do the easy / cheap fixes first.