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Chevy Fuel mileage help

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#21 ·
H8tank said:
Run a clean K&N air filter
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Big mistake. Great way to ruin your MAF.

Fact, not theory.

I see this all the time on many vehicles, especially these trucks since the area I live in is mostly these trucks.

FYI: I am a big K&N fan, but not on most/every MAF equipped vehicle. Also, do not re-oil the K&N as you'll not do it correctly. No one does. Not me, nor you, nor anyone.
 
#22 ·
cfm said:
Big mistake. Great way to ruin your MAF.

Fact, not theory.

I see this all the time on many vehicles, especially these trucks since the area I live in is mostly these trucks.

FYI: I am a big K&N fan, but not on most/every MAF equipped vehicle. Also, do not re-oil the K&N as you'll not do it correctly. No one does. Not me, nor you, nor anyone.
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Are you referring to the drop in OEM style, or cold air intake style?

So what, never oil it?

Also keep track of the filter, they can, and do come apart. I've read of a few on the diesel forum I frequent that have come apart, and ruined turbos. Mine is comming apart at the seem, reminds me to get it replaced.
 
#23 ·
The filter itself. It's the oil that is the problem. It get's on the MAF wire.

If you just have to use a K&N and are in need of cleaning/re-oiling then I suggest you buy a new one.

Oiled from K&N, your chances of MAF failure is pretty high, but will take a bunch of mileage.

Oiled from you, me, whomever, that mileage before failure is usually much less.
 
#24 ·
H8tank said:
If it was bad o2 sensor, it would be bad all the time right, but the mileage is fine when non-stop driving.

I'll print out this thread and give him a read, see what he thinks.

Any other ideas are appreciated. I need this truck to last a couple more years. :(
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It is not as simiple as bad or not bad, works or doesn't work and on or off. The 02 sensor input is a variable in a logarithm that is constantly changing. The demands of driving change fuel management through adaptive capabilities and different modes of driving have different profiles in fuel curves. All this to say the 02 can satisfy one profile and mess up another profile and never set a code.
The light only comes on if a parameter is violated and in trucks that parameter is a mile wide. ;)
 
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#25 ·
The timing chain is designed for a 150K mile durability cycle. The pin-apperture wear at that high mileage (not counting all the idle time) causes the camshaft to retard from base timing. When that happens, you lose power and efficiency. Combine that with the loss in compression from normal engine wear, and you have an old tired engine that is in need of a rebuild. The question you must ask yourself: Is it worth is to start replacing parts in a futile effort to get back 2mpg? With those kind of miles on the ticker, be happy it runs and is paid off!
 
#26 ·
Everyone has some good thoughts listed...let me add one more to the mix. Have the fuel pressure regulator checked. Hook up a psi gauge to the fuel rail....energize the electrical without starting the engine so the pump primes the system and turn it off and see if it holds the psi...if it starts leaking down then it may be a simple as changing that out....and if you do go through route and have the intake split then go with the upgraded injector spider. It has injectors on the ends instead of the crappy popets they install stcok. :)
Oh and a can of seafoam through the engine does good too :D
 
Discussion starter · #27 ·
Wally said:
Everyone has some good thoughts listed...let me add one more to the mix. Have the fuel pressure regulator checked. Hook up a psi gauge to the fuel rail....energize the electrical without starting the engine so the pump primes the system and turn it off and see if it holds the psi...if it starts leaking down then it may be a simple as changing that out....and if you do go through route and have the intake split then go with the upgraded injector spider. It has injectors on the ends instead of the crappy popets they install stcok. :)
Oh and a can of seafoam through the engine does good too :D
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This is very interesting, a little while ago it started needing me to crank the engine over for a few seconds to start, (before it always started instantly) I was told that it was the fuel pressure regulator (or something) not keeping the fuel right at the intake. Could this, and how could this affect my mileage? You may be on to something.

It's freezing cold out right now, and it seems the mileage is even WORSE.
 
#28 ·
H8tank said:
This is very interesting, a little while ago it started needing me to crank the engine over for a few seconds to start, (before it always started instantly) I was told that it was the fuel pressure regulator (or something) not keeping the fuel right at the intake. Could this, and how could this affect my mileage? You may be on to something.

It's freezing cold out right now, and it seems the mileage is even WORSE.
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That is an interesting piece of new info. There are only three ways that fuel pressure can be lost; regulator, fuel pump and nozzles.

The regulator would let pressure off when the truck is shut off to give long crank time or the check valve in the fuel pump would leak pressure off giving long crank times. Fuel pressure should hold nearly 2 hours after shut off and if not then there is cause for long crank times. No mileage would be lost from pressure loss through regulator or pump check valve but long crank times would result.
The regulator could leak externally but that is not so common.
Here is the one that could leak off pressure, cause fuel mileage loss and give long crank times.....NOZZLES. If you have a nozzle leaking fuel then not only would fuel delivery not be precise but mileage lost also. A leaking nozzle could loose pressure and cause long crank times. If a nozzle is leaking, a spark plug should show the extra fuel burn. Anytime I remove spark plugs I read them all in prespective to the cylinders they are in. Volumes of info for diagnosis is in the spark plugs and they would show the culprit cylinder if a nozzle is leaking.
 
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#30 ·
The problem is the CSI fuel injection, its not very good at delivering fuel, and it only gets worse with high mileage. You can spend a few hundred dollars to upgrade a new 'spider' assembly complete with new injectors and fuel return valve, but your better off dumping a bottle of seafoam additive into your gas tank. You can get it from autozone, advance etc. It worked for my 2500HD. Mileage went from 11 to 14 and it has 172k on the clock.
 
#31 ·
BabyScarab said:
The timing chain is designed for a 150K mile durability cycle. The pin-apperture wear at that high mileage (not counting all the idle time) causes the camshaft to retard from base timing. When that happens, you lose power and efficiency. Combine that with the loss in compression from normal engine wear, and you have an old tired engine that is in need of a rebuild. The question you must ask yourself: Is it worth is to start replacing parts in a futile effort to get back 2mpg? With those kind of miles on the ticker, be happy it runs and is paid off!
Click to expand...
The CPU will throw a code if timing is off. If the check engine light is off this is not your problem.
 
#32 ·
Wally said:
Everyone has some good thoughts listed...let me add one more to the mix. Have the fuel pressure regulator checked. Hook up a psi gauge to the fuel rail....energize the electrical without starting the engine so the pump primes the system and turn it off and see if it holds the psi...if it starts leaking down then it may be a simple as changing that out....and if you do go through route and have the intake split then go with the upgraded injector spider. It has injectors on the ends instead of the crappy popets they install stcok. :)
Oh and a can of seafoam through the engine does good too :D
Click to expand...
Should've read this before posting. I completely agree. Happened to my truck. Get the new spider if you have to tear into the intake.
 
#34 ·
RSCHAP1 said:
Leaky injectors/nozzles should probably show a rich-stagnant fuel condition at start up right? Puddles of fuel laying on piston domes? Smoke at start up or HARD starting with wet plug tips...
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Maybe/maybe not...would depend on how quickly you drive after shutting it off....like it was mentioned the regulator should hold psi for set amount of time. If lets say it starts dropping off right away after you shut the truck off then the heat of the engine could just vaporize the fuel and you wouldnt see any rich condition on startup next time. But it may show up rich if the engine cooled off fast enough not to vapor the fuel. As far as longer cranking goes, try this next time you get in the truck and see if it makes any difference.....turn the ignition on but dont start the truck...you should be able to hear the fuel pump turn on and prime the fuel system (its easier to hear with the drivers door/window open. fuel pump is in the tank) Then when the pump turns off try starting the truck...if its back to its normal starting times then i would start testing the regulator. If its not a normal cranking time as you had in the past then do the ignintion on thing twice in a row...turn it on (dont crank or start) let it prime....turn it off then do it again and try starting...if it takes twice to get you back to normal cranking id lean to the fuel pump going out.
 
Discussion starter · #35 ·
Where is a good place to buy a 'spider' injection assembly?


Thanks for the tip on checking the regulator. When cold it takes 1-2 secs to start, when warm it starts right up. I still don't understand how this could affect the mileage so drastically.
 
#36 ·
I'd start by putting a locking gas cap on her. Maybe you have a neighbor trying to improve their own gas mileage while you are asleep. That would explain why you got good gas mileage running 80mph non-stop for 300 miles.:D
 
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Discussion starter · #37 ·
I'd start by putting a locking gas cap on her. Maybe you have a neighbor trying to improve their own gas mileage
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1. I live half a mile from anyone or pavement

2. The dogs wouldn't like that...

3. My truck is parked right outside my bedroom window and this is right under the bed and arms length away. :D

Image
 
#38 · (Edited)
H8tank said:
aqua, would that behavior regarding nozzles also repeat on long, non-stop drives where the mileage is within what one would expect?
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On long durations of fuel demand, such as highway travel for long periods of time, the duty cycle is high and continued so a small leak would almost be insignificant since the little leak is spread out over such a long distance and the high duration of fuel delivery would nearly mask any leak.
As injector duty cycles move up and down the leak would be more significant because when fuel needs to trim down the leak is still delivering.


If I understand your question right, this is how I would apply a nozzle leak to your mileage loss scenario.

A lazy 02 doesn't work the same in fuel management but the result would be the same.
A test drive watching a scanner on the 02 data lines could show rich activity, low crosscounts and more time at .5V or more. A rich condition for regular driving would be an indicator of leaking nozzles and still not be excessively rich to set a code.
 
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#39 ·
RSCHAP1 said:
Leaky injectors/nozzles should probably show a rich-stagnant fuel condition at start up right? Puddles of fuel laying on piston domes? Smoke at start up or HARD starting with wet plug tips...
Click to expand...

This is an extreme leak senario. I have seen this level of leaks but the ones that are hard to pinpoint are the small leaks that are noticed by a discerning driver. :)
 
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#40 ·
H8tank said:
Where is a good place to buy a 'spider' injection assembly?


Thanks for the tip on checking the regulator. When cold it takes 1-2 secs to start, when warm it starts right up. I still don't understand how this could affect the mileage so drastically.
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Check this site out. Its saved me tons of time and money.

www.fullsizechevy.com

If you can't find the answer to your questions on that site you might as well just sell your truck cuz it can't be fixed :laugher:
 
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