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Old March 6th, 2013, 04:46 PM   #1
welderboyjk
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Default Poor mileage '05 silverado 4.8 2wd

Spec's. 2005 silverado, std. cab, long box, 2wd, 4.8 liter, 170k miles.
Not sure what it really should get but I'm getting 16 mpg. 80% of my driving is highway and I limit myself to 65-70 most of the time. Round trip to work and back is about 70 miles a day and it's drinking a nice chunk of change every week LOL
Check light was on so I had my BIL check it.
Low output from MAF sensor
Random misfire
Evap leak
Well the evap shouldn't hurt mileage but the purge solenoid seems good. I haven't checked the vent solenoid on the tank yet. From what I've googled the vent solenoid is a common problem.
If it does misfire, it is not noticeable.
I changed the MAF with a "new" reman and mileage did not change a bit.

Anyone have any ideas or pointers????
I wouldn't be worrying too much but a co-worker has the same truck but extended cab, short box, 4wd and he get's waaayyy better mileage than I do
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Old March 6th, 2013, 05:09 PM   #2
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Random misfire can mean its ready for a tune up or bad coil plugged fuel filter or air filter bad o2 sensor plugged converters and ues the vent solenoid is a common issue on those the replacement part is pretty pricey

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Old March 6th, 2013, 06:12 PM   #3
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You should have just tried cleaning the MAF before replacing it.

And 16 MPG is not that bad especially for winter. But it could be better if those things need to be fixed.
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Old March 6th, 2013, 09:18 PM   #4
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Well I changed the plugs once with oem's about, hell, I dunno...60k ago
Air filter changed 3 oil changed ago.
BIL told me o2 sensors looked ok on the 'puter.
Coils are individual for every cylinder. Never have changed the wires though.
Haven't ever changed the fuel filter...yet.
It's not "poochey" nor can I hear the hiss of plugged convertors (kinda hard to hear anyway when you're the one driving). Is there an easy way to check them?

I know mileage drops a little in the winter but.....I want my '97 back. Low mid 20's. That was nice

I sprayed off the MAF with contact cleaner but mileage didn't change at all so I replaced it.
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Old March 6th, 2013, 09:21 PM   #5
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Well i would start with changing the wires and fuel filter u can check the converters by banging on them and see if the rattle

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Old March 6th, 2013, 09:21 PM   #6
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My 08 with 5.3 gets 14. It's a truck, quit complaining
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Old March 6th, 2013, 09:30 PM   #7
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change the fuel filter then reset the KAM (Keep alive memory) it will reset the fuell adaptive and relearn after the repair. More than likely its your fuel filter kiling you and its Most imperative to reset the adaptive and enjoy your 20-23 mpg thats closer to what it should be.
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Old March 7th, 2013, 07:31 AM   #8
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Marshall, if it was a 3/4 or 1 ton 4x4 then I wouldn't complain but it's a half ton 2x.
I like pigfat's idea of what the mileage should be
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Old March 7th, 2013, 07:53 AM   #9
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I have a 99 ex cab short box 4wd. 5.3, 3.73 gears, 285s and get 14.5. You are really close to what you should be getting IMHO. Good luck.
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Old March 7th, 2013, 07:59 AM   #10
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I have an 05 crew cab 4x4 with the 5.3l I consistently get 16+ on a recent trip to mount Pleasant the computer said 19.3

What gears does ours have? That could make a difference. Mine has 3.42s all of my friends with similar trucks have 3.73s and experience significantly worse mileage. Larger tires don't help them either.

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Old March 7th, 2013, 09:14 AM   #11
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An 05 may or may not have a fuel filter. The factory did away with those areound that time. A fuel filter will likley not improve you fuel mileage, unless you are experencing a loss of power at high load/high rpm- like trying to pass up hill going 80 mph. Did your random misfire go away with the MAF replacement? You said that you replaced the plugs with the factory type, so I assume you used the ac delco platniums. If not I have seen a lot of gm engine that dont like anything besides the delco, and cause random misfires. You can check for vacuum leaks around the intake, which is real common with those ls motors in trucks. The lean condtion will cause a random mis, and poor fuel mileage.
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Old March 7th, 2013, 07:50 PM   #12
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If it has a fuel filter I have no idea where it is. Crawled under it tonight and couldn't see one anywhere.
The plugs are ac delcos' I'm sure they are the platinums because I can remember squeaking when I bought them. I pulled a boot and tried to get a number but they're buried too deep to see.
No idea if the random misfire went away with MAF replacement. Haven't got it back on a 'puter yet to see. Maybe tomorrow.......I know mileage still sux though LOL
I crawled all over the top of the engine tonight trying to listen for a vacuum leak. I heard a little hissing at the rear drivers side. Popped the plastic cover off of the top and crawled back up. Hissing appears to be the pcv hose plugged into the back of the tappet cover. Popped the hose off (she didn't like that at all) and put my finger over the end of the hose. Hissing stopped.
Hope I can get the BIL to check it again tomorrow on my lunch break.
Not sure on the gearing. It spins close to 1800 at 70 mph.
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Old March 7th, 2013, 08:20 PM   #13
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Mine runs about 1800 at 70 too. I also have the CEL for the evap solenoid so I doubt that is the reason for poor mileage. Mine has about 190k miles. What weight oil do you use? I currently have Mobil 1 5w-30 I doubt a thicker oil would change that much but it's possible.

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Old March 7th, 2013, 08:33 PM   #14
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Valvoline 5w-30. Just like it says on the fill cap and the owners manual.
My google fu has turned up everything from clogged injectors, broken valve springs, bent pushrods, wiped cam lobes, low fuel pressure clogged cats..... and on and on and on LOL.
It's gonna be a week or two until I have time to do much of anything like a compression or vacuum check.
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Old March 8th, 2013, 06:10 AM   #15
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http://www.fueleconomy.gov/feg/Find....n=sbs&id=21085
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Old March 9th, 2013, 01:22 PM   #16
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You need to check for vac. leaks with spray carb clenaer or brake parts cleaner by spraying around the intake and listening for the engine rpm to change or start to stall. You will probablly not be able to hear the vacuum leak by ear unless its really big.
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Old March 9th, 2013, 02:07 PM   #17
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Quote:
Originally Posted by IFS SUCKS View Post
And do they ever get what they say they are supposed to?
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Old March 9th, 2013, 02:51 PM   #18
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I had 4.8 in a 2003 4x4 and it was the worst mpg truck I have owned. It was about 15 average from new thru 150k miles
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Old June 3rd, 2013, 10:40 PM   #19
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Checked it again now that the weather has warmed up a bit.
The last 10.75 gallons got me 19.2 MPG.
I'll be checking it again when I remember to write down my miles and gallons I put in it.
Think I'm going to have to figure out how to pull an old school heat riser off of the exhaust manifold and plumb in it upstream of the MAF sensor before next winter.
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