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Discussion Starter · #1 ·
Hey everyone, I have an 03 1500 Z71 5.3/LM7 with 3.73 gears in it. Up until about a year ago, the truck could get 14mpg in town and 17 on the highway. Even after the leveling kit and tires it would still get that. One fill up, I have been getting 12 City/ 13 highway in it and nothing has changed that should cause it. I have already changed the plugs in it. It has 153k miles on it and runs great. I thought maybe the fuel filter was clogged but the truck seems to be running rich because it will haze black smoke under WOT. Anyone experienced this and or know what's wrong?
 

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Yah, we seem to see a lot of these kinds of threads each fall when they start introducing the Winter Blend gas and the weather gets colder so we warm up our trucks a little longer before taking off and the truck runs less efficient for the first 4 or 5 miles until it does get up to optimal running temps.

The only thing different this year is that we haven't seen the corresponding jump in gas prices when the fuel companies use the change in seasonal blends as a reason to bump pump prices.
 

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esox07 said:
.....The only thing different this year is that we haven't seen the corresponding jump in gas prices when the fuel companies use the change in seasonal blends as a reason to bump pump prices.
Do you have backup information that pricing is ever manipulated in that way? Seems more likely that pricing is due to supply and demand.
 

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Wild: Yah, probably so. But we do typically get a lot of those kinds of thread posts this time of year. But the change in gas blends shouldn't amount to more than about a 5% drop in mileage. I know my mileage goes down in the winter. Probably mostly due to a bit more idling and the truck running cold longer.
 

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May be a number of issues. Id check the plugs if you've been running them a while even if new. If its not burning clean they will suffer and just get worse. I take it that it didn't store any codes. Should show something. Check fuel pressure regulator see if its full of gas in vacuum line, fuel pressure a vacuum leak, intake tube and spray a bottle of water through it.

Id try some MMO in the gas also. Or something to clean the injectors.
 

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Discussion Starter · #9 ·
Yeah I have tried all different kinds of fuel injector cleaners and octane boosters. This is the 2nd new set of plugs in the last 40k miles from trying to figure out the problem. I'll check into the regulator
 

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Alright so I just replaced my fuel pressure regulator after seeing what symptoms of a bad one would be. Truck used to blow black smoke under wot and would really lack power once hitting second gear and every once in a while it would crank for a while before firing. Truck seems much happier now. Fires on 2nd crank and runs much stronger. It is raining right now but on 305's it broke free at 60. Hopefully my mileage will come around.
 
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