First off,

1986 22re, auto Truck 4x4
32" tires
Other than a lift, all stock except K&N.
Replaced 02 sensor about 6 months ago
Plugs/wires/cap/rotor 6 months ago
exhaust is leaky, cat was plugged and was replaced.

Here in Minnesota it's getting cold, down to the zero degree range and suddenly my freeway power and mileage is crap. I used to be able to cruise at 60mph in overdrive, now I have to kick it out of overdrive to maintain speed even after it warms up completely, even going with the wind I have to knock it out of overdrive. Mileage has also been down from about 18-19mpg to around 14mpg. I would expect this while using the 4wd or while in snow, but not on dry pavement!

Tires all are at ~32psi, no engine lights or anything.

Any ideas?

Pic of truck (not that it matters), btw bed is a 1992. Windsheild has been replaced (not in pic)

 

Is your cold start injector still operating when the engine is warmed up? That could cause excess fuel consumption.

 

Is your engine getting up to temp( whats your temp gauge read)? Is it running rich( hows your exhast smell) Why did you replace your o2 sensor?

 

What do the plugs look like? (Keep track of what plug from what cyl)

Any codes?

 

its not the weather....cold should help it perform better as the lower air temp helps the combustion in many ways.
first Check your cold start inj.,
try holding a white cloth over the tailpipe for a few seconds to check mixture for color?...smell?
the cold air temp. makes for mixture problems sometimes if it is already set too lean or rich....check your cloth and adjust accordingly.
lean it out if the cloth stains and reeks of fuel..

 

ya know...Ive got 33x12.50 mud terrains and now that i think about it, mine has dropped to...
I usually get right at 17 to the gallon on a good week and this past week was 14.5.
And its been down in the 20's here in sc...

 

My carbed truck has this problem.
i blame it entirely on the higher humidity when snowing, and the winter fuel. Which has a tendency to have a little more water in it..

 

Winter fuel in many areas also has more ethanol in it, which kills power & gas mileage.

 

Hmmm I think this is going to take a little bit of figuring out.

I warmed up the engine and then disconnected the inlet from the throttle body and sprayed it with throttle body cleaner....No change in the way it drives.

After the warm up I disconnected the cold start connector and drove to work, there was no change. I left it disconnected and the engine wouldn't start this evening when I went to go home. Plugged it back in and I had immediate ignition like always, so I don't think that's the problem.

I have a terrible sense of smell, but my boss was leaving behind me the other day (cold engine) and he said it smelled pretty rich. Not sure if that's normal for a cold truck.

I replaced the O2 sensor just because I didn't know when it was last replaced. It looked pretty damn old and beat up on the inside.

I'll try to pull my plugs tomorrow when I get home from work.

Engine has been getting up to operating temperature (always runs in the middle, to slightly below middle of temp gauge).

There's some stations near me that sell non ethyl gas, (not sure the price) so I may try going that route.

 

I'd almost guarantee it's the winter gas.

 

X2. It pisses me off when they switch around here. I go from getting 23+ mpg to 18 if I'm lucky and my "power" on the highway suffers also.

 

these would be my thoughts. I still think you rig isn't warming up all the way. I found that even though the gauge doesn't show it, the temp gets way low when it drops down to 25 and below. it just won't warm up all the way. at 0 out side i was warming my truck up and noticed my lower radiator hose leaking, so i tightened up. What i noticed was the radiator was cold on the bottom, i mean really cold. top was hotter than hell, bottom was cold. thermostat was open i could feel the water flowing but since it was pulling 0 degree air across the radiator it was over cooling the engine. I cut a piece of cardboard and slipped in between the radiator and the radiator support. covered about a third of the radiator. Took care of it! warms up faster (obviously, less radiator) and runs better around town.

One thing that always kills my mileage in the winter is warm up time and cold thick oil. I put on a oil pan heater from wolverine heater and holy crap what a difference. Combine that with a battery heater for 32 and below it started like it was 75 degrees outside. the little oil pan heater is only 125 watts but it heats the oil up and it radiates up through the engine and while it doesn't heat the water much the engine is definitely happier and warms quite a bit quicker than without it. if you size the heater right it won't burn the oil. on a properly size pad, it will heat the oil from 0 to 75 degrees in an hour, up to 135 in two hours, and then it starts to plateau at around 160-170 degrees. I have left it plugged in over night and it nice and warm in the morning, felt the cylinder heads under the manifold and it was nice and warm. great product.

http://www.wolverineheater.com/index.shtml

 

That's why it's so important to use an appropriate winter oil, since oil DOES thicken up to cold honey/molasses in cold temps, and becomes too thick to pump, too thick to go through the oil filter, and too thick to make it into the bearings. To get oil that will flow well - not just ooze - in very cold temps, use a synthetic 5W-30 or 5W-40 (both have the same cold performance, they are different only when motor is at op temp. If you run 10W-30 in the summer, use the 5W-30; if you run 10W-40, use the 5W-40 (like Shell Rotella T6). Or in temps that get below -5 deg F, use a 0W-30 (like Castrol Syntec or Amsoil) or 0W-40. The Syntec 0W-30, aka "German Castrol", is almost a 40 weight at operating temp. Unlike the rest of the Syntec line, it's a group IV PAO true synthetic.

0W-40 is hard to come by in the U.S. Red Line makes one, but it's almost a 50 weight at op temp. John Deere sells what looks to be a very good diesel 0W-40 that would work great for our motors except that it has more zddp than most modern oils which, if your motor burns oil, would eventually damage your cat. But it has a gasoline SL and SJ rating, which are the oil ratings originally specified for our trucks. And the zddp is great for the motor.
http://www.deere.com/en_US/parts/par.../oil_0w40.html
http://www.bobistheoilguy.com/forums...Number=1062417
http://www.greenpartstore.com/John-D...s-TY24349.html
http://www.tractorforum.com/f183/who...licensed-1394/
http://forums.tdiclub.com/showthread.php?t=271176

But getting back to the OP, you are going to check the plugs, but have you checked for codes?? There might be a reason besides pissy winter gas that accounts for the poor running, and it's worth checking to see if the computer can give a clue.

 

Once I lock in my hubs for winter (even if iam not in 4x4) my mileage drops significantly. I am running full synthetics in all my drive train now but before when I used conventional oil in my old truck it would thicken in cold weather and bog right down until warm. Your problem sounds different but thats my experance.

 

As mentioned, I know the gas blend makes a different. I ride a motorcycle a lot and check the mileage every fill up. Mileages is worse in the winter by several miles a gallon.

Also, not to explain your mileage getting worse, but if you have oversize tires you have to account for the speedo error to get the true mileage.

 

Its a combination of the winter gas and the cold weather, that`s why your mileage has dropped, its normal. Once the weather starts warming up and they change over to the summer gas again you gas mileage will go back up.

 

Vote for rotella T6 5w-40. Been using shell rotella products for a while now and like them a lot. 15w-40 in the warmer months and the 5w-40 full syn in the winter time.