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  #1  
Old 11-02-2012, 12:47 PM
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Horrible Gas mileage

Hey Guys can someone give me some ideas?

Lately Since getting my rig back on the road I have been getting horrible gas mileage. A lot worse than before when she sat for 2 years. It's to a point where I almost can't afford to drive her to work. Can anyone help me figure this out? Getting around 12-14mpg highway

94- 7.3
3in down
3in straight pipe
Stock air box brand new filter
Tires good
Oil consumption somewhat normal nothing stands out.

Thanks!!


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  #2  
Old 11-02-2012, 01:47 PM
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Start looking at your HPOP to be weak (poor atomization of fuel) or a worn/cracked intake boots (exhaust trying to build good boost but the intake leaking it back out). Even a clogged air filter.
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Old 11-02-2012, 01:54 PM
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Thanks! Start checking tomorrow. Never looked at those things and no experience so ill have to do Sind research on these areas.


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Old 11-02-2012, 02:08 PM
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Did you check/change fluids, check the brakes to make sure they're not sticking, filters, etc.

Maybe the old boy just don't wanna move after sitting so long. It's good it's back on the road.

Out of curiosity, what'd you get before...MPG-wise?
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Old 11-02-2012, 02:11 PM
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Looks like your truck is pretty much stock. Your intake should only have three places that it will leak from. At the Y-adapter where it meets the turbo output there should be a rubber o-ring in there. At the base of the y-adapter are the two 2" boots that are the other place that leaks. to take the y-adapter off undo all five hose clamps, shimmy the boots up the y-adapter and remove. Shimmy the boots off the adapter and inspect. These are common places for leaks. The not so common places are all the way around the plenums (intakes attached to the heads) and the exhaust. It's fine if you have small exhaust leaks after the turbo but not before. Here the common leak spot is behind the motor there are two Up-pipes that feed the turbo from both sides of the engine. Where they meet the y-adapter for the turbine are two (one on each side) ceramic exhaust "doughnuts" (doughnut shaped exhaust gaskets). Our trucks do not meter the air going into them, only the fuel. With the PCM (and other things) saying that there is so much fuel going into the cylinder it assumes that the air is mathematically keeping up as well. All these little leaks in the system will have your engine fueling as normal by your foot pedal but the air won't be there in the quantity that is required. This causes you to push the system harder using up more fuel.

You said the truck was downed for two years? How long have you been driving it since putting it back on the road?
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Old 11-02-2012, 02:25 PM
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i agree with going through and checking brakes, all fluids, changing the oil/filter, fuel filter, etc. you may just need to work out the cobwebs.
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Old 11-03-2012, 06:37 AM
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Great help guys! Thank you. I think I have an exhaust leak. Big fuel you nailed it. I have an exhaust smell in the cab when I have the blower on. Also thinking maybe hpop too. The oil pressure gauge on the dash is on the low end of normal. Barely on the "n". Thanks guys. Ill keep you posted.


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Old 11-03-2012, 06:55 AM
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The gauge on the dash is for the lpop, it doesn't have anything to do with the hpop. If you want to know what the hpop is doing you need to use a scanner or hook a high pressure (3000 psi) gauge into a oil galley in one of the heads.
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Old 11-03-2012, 07:22 PM
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Not _entirely_ true. If you are just looking to check the rail pressure and ICP you can back-probe the Dark Blue / Light Green wire on the ICP (there are 3 wires, you need the one not in line with the other two. Back-probing a harness connector is easy with one simple custom tool, a staple. Bend one leg straight an insert it between the wire and the rubber weather jacket on the connector. Push it all the way in. More then half of the staple will go inside the connector. There will be no damage to the connector or harness with this setup.) and use a DVOM to see the HP oil in the rail. You are looking for these readings. Get all readings without going for a drive.


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Old 11-12-2012, 04:11 AM
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With mine, I was getting 13.2 mpg (mostly city/rural driving. Lots of stop & go, nothing mroe than 60 mpg).

I changed ALL fluids, aired up tires, went through my fuel system (forward of firewall), rebuild my fuel bowl, FPR Shim, and cleaned out that tiny screen (which was clogged almost solid-not sure how it ran).

Another trick (or so I've read in here) is to change out your fan blades with a 6.0 fan.

Checked my mileage yesterday. I'm getting 16.26 mpg. And still fighting a mysterious fuel leak.

Best part aboutdoing all this: you will KNOW the overall condition of your truck. Amazing the little things you find when youre slumped over your radiator for 6 hours!

Good luck. Let us know what you find.
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