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Discussion Starter #1
If you look in my signature you could see many potential reasons for my poor gas mileage but I swear its the truth that doing every single one of those things has not changed anything in my mileage it has remained the same...
i used to have just the throttle body spacer and cold air intake and flowmaster exhaust with stock tires no lift and still could never hit more than 15 mpg...
even with gears, lift, tires i still have the exact same mileage which usually varies from 13 to 15 mpg, this is a V6 btw...
my last 2 tanks however have been shockingly awful... ive been about 11.5-12 mpg and i dont know why!
i just replaced my fuel filter, i have recently replaced plugs, wires, cap, rotor, oil, oil filter (fully synthetic for years now), sprayed my throttle body, cleaned my k&n filter....
and i still cannot understand why my gas mileage is so poor i also recently seafoamed my gas tank and, a few times a year i am normally throwing in 44K (dads pick)
But i have noticed over the last few months a minimal (noticeable to me) loss in power overtime and i havent seemed to gain it back yet...
I really am going crazy with a 26 gallon tank that i have to refill after 320 miles.... do the math
does anyone have suggestion/help/comments for me?
I am wayyy past my high school gunnin the gas years and hardly ever beat the pedal unless necessary...
but i am fed up with this mileage.
 

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I'll probably upset a few people with this post but IMO the reason for your poor fuel mileage is the 4.3.
It's never been a great fuel mileage engine, even in the S series trucks it didnt get much better than what your seeing.
I really think deleting the two cylinders killed the performance of that engine and I've always felt it was underpowered for a full size truck which causes it to work harder and consume more fuel.
As to why your suddenly experiencing even worse performance and mileage? Good question it appears youve done everything to ensure the maintenance is up to date.
Have you checked the compression lately? Maybe the engine's getting ready for a rebuild/replacement.
 

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Discussion Starter #3
not upsetting at all i have heard from multiple people and assuming basic physics i agree that smaller engine = more work especially for a full size truck.
i can see how a v8 would not have to work as hard to get the momentum going etc.
but why would this truck be rated 16 city 20 highway if it could never reach it especially if it was stock and had intake exhaust and tb spacer??? (all mpg/power boosters)
and i have heard alot about checking compression? where can i do that though i would not want to do it myself is it cheap to get done? and where at?
 

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The reason the trucks rated at those figures is because GM was under a mandate to produce fuel mileage numbers in a certain categorie.
After a lot of work they got a truck on a test track under perfect conditions to perform those numbers.
So they got their CAFE rating and sold trucks and everyone was happy.
Except the purchasers of those trucks that never got them to perform nearly as good as GM's claims. But to be fair every car manufacturer does this to meet their mandated numbers.
Compression testing is easily done in your driveway, most AutoZones will rent or loan a compression tester.
You'll need to get the appropriate section of the maintenance manual for your particular truck/engine to compare your readings and familiarize yourself with the safety precautions.
The short explanation of the task is remove the first spark plug, put in the compression testor adaptor, neutralize all the other spark plugs so the engine wont actually start, have someone turn the engine over while you record the readings on the compression testor gauge, then proceed to the next cylinder, repeat the proceedure until you've got a reading for every cylinder, compare the readings you have with the manual and see if you have any exceptionally low cylinders.
 

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How do you have the programer tuned? How do you drive? Do you use E-85 at all? Do you coast down hills? Have you checked out the rolling Resistance on those tires? How long ago did you put the bigger tires on?
 

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Like Avalanche says- if your station suddenly went from pure gasoline to Gasohol- up to 15% alcohol- your mpg could drop 1-2 mpg easily.
Check the pump at the station -see what it says.
Like TB implies- the 5.3 is hard to beat-the 4.3 and 4.8 usually can do no better than match it- and usually fall a bit short of the 5.3 in respect to mpg.
Charlie
PS But the sudden drop makes me think ethanol in gas- or you switched stations to one that has ethanol.
 

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Look for a gas station that sells non-ethanol. After about two tank fulls your mileage will pick up. I gained back 2mpg and mrs. silveradotrailblazer picked up 4mpg's on the highway.
 

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I agree with everyone here - the 4.3 is a bit of a pig because it just doesnt have the power to move a vehicle that heavy. Even in 2011, it still only has 195 horsepower and 260 ft.lbs of torque. I also agree that its possible that a change in the gas where you fuel up could cause your recent MPG drop. Also, like enkei said, you might be able to get 1-2 back just by adjusting your programmer a bit, depending on how it is set now.

One more suggestion I have is to clean your Mass Airflow sensor, especially since you have a K&N intake. Over time, the mass airflow sensor can get dirty and cause poor performance and fuel economy. The oil on K&N filters also has a tendency to coat the mass airflow sensor and cause problems with it - particularly if you might have over-oiled it at some point. To clean the sensor, you just need to pick up some mass airflow cleaner (safest to get this because other cleaners could damage the sensor) and give it a good spray. let it dry and then reinstall it.
 

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Big tires and lift kit are hurting your economy.

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The short explanation of the task is remove the first spark plug, put in the compression testor adaptor, neutralize all the other spark plugs so the engine wont actually start, have someone turn the engine over while you record the readings on the compression testor gauge, then proceed to the next cylinder, repeat the proceedure until you've got a reading for every cylinder, compare the readings you have with the manual and see if you have any exceptionally low cylinders.
When doing a compression test -

Remove all spark plugs. Hold the butterfly wide open. Pull the ECM fuse. Then do the test as described above. You need the butterfly open to get plenty of air in the cylinders. You also reduce load on the starter/battery because you're not pulling any vacuum. That's also why you pull all the plugs first.
 

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Discussion Starter #10
as far as tuning my hypertech programmer there isnt much to do its only actual "tune" function is to choose regular or premium fuel, then theres other little things like shifting and top speed limiter etc...
theres not many hills in corpus christi, and as far as rolling resistance im not sure, but my tires have a T speed rating so i would assume there wouldnt be too much resistance for an AT tire to have that high of a speed capability and i have had these tires since december 2008

ill need to look over that ethanol deal yall are talking about and definitely should check out my mass airflow sensor
 

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You could join the new fad of "hypermiling" and become a "hypermiler" - although you would probably be the first "hypermiler" in a full size truck. I'm sure all the Prius drivers would welcome you though! (Ha. Ha.)
 

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Nope
I hypermile my 1998 Suburban-when just I drive it- I get about 15 mpg city 21 mpg hy.
Wife however gets maybe 10 mpg city.
Many folks do hypermiling "lite" with 1/2 ton and even 3/4 ton trucks.
Mild hypermiling can improve your city mpg by 15-20%- it is basically just accelerating up to 35 mph-lifting off the gas and cruising down to 28mph- repeat repeat.
The GM truck transmissions GLIDE (ONCE YOU LIFT OFF THE GAS) in D just like they were in N.
1/2 Trucks and SUVs respond great to hypermiling- you save a lot more gas -and $$- hypermiling a 1/2 ton than you do hypermiling a Prius.
Charlie
 

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Discussion Starter #14 (Edited)
i cleaned my mass air flow sensor and still not too much difference
also i did find out valero down here is up to 10% ethanol and thats pretty much always where ive always filled up for a while now, time to switch rudys bbq sells ethanol free gas!
also if i started using premium or super gas whatever the higher one is (89 octane to 93 octane) and i also tune my programmer to it, would the extra price of gas be worth any mpg/performance increase?
 

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Just try to run the non-ethanol. I have my truck tuned for 87 and it runs better than with the 93 tune. It will take about 2 tankfulls of the non-ethanol to see a differance.
 

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Discussion Starter #16
alright i definitely wont be filling up with valero anymore ill see how that goes hopefully i can pick some mpgs up
 

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Discussion Starter #18
do these hypermilers go 35 on the highway too?
 

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35 hy- nah, I set my CC to65-68mph in 70 75 mph zones- but 58 mph in 60-65mph zones. I get 21 mpg on long trips, but that is because of all the 45mph road work zones and towns where you have to drop to 35mph or so.I would get about 19.5-20 mpg at a steady 65mph.
Our V-8s probably get best mpg at about 50 mph or so- just above where the converter locks up.
 

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Discussion Starter #20
so yall think that me goin from 10% ethanol to no ethanol that i should notice a difference in a few tanks?
 
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