08' Chevy Avalanche check engine light on with decreased gas milage

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#1
I have an 08' Avalanche that during the past month or so has had the check engine light come on and then go off again. . . . only to come back on a week later. About 5 months ago I replaced the gas cap because the light had come on and it came back with a faulty seal. I can't imagine that the cap is bad again in such a short period of time. I've noticed that my gas milage has gone down and it's rough and slow when I accelerate. Any ideas what may be causing this issue? Thank you in advance :)
 
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#2
Go to Advance auto or Autozone for a free scan, then tell us what the code is (e.g. P0420).
 
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#3
Two codes came back. One was p0449. . . a purge/vent solenoid??? And the other was p1174. My truck is a V8 5. 3L. The man said it had to do with the fuel vapors or something. Sorry, I don't know much about vehicles :). When I replaced the gas cap I originally bought the 08 yellow flex fuel cap that Autozone said was for my truck. I noticed it didn't fit right and returned it. He looked at an 07 non flex fuel cap and it fit so that is what I am using now. Four months after replacing the cap I started getting the light on, then off again. Could the problem have anything to do with the gas cap?
 
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#4
How many miles on this thing? Regardless of what they say, that center electrode insulator builds up with carbon that shunts out the spark about every 20-30 miles. With double platinum plugs, pull those and clean with ground walnut shell, then regap them. Typically to 0.035, don't and never have believed in those larger gaps.

This can cause your P1174 code accompanied by reduce fuel economy and hesitation in starting and acceleration. Also your heated O2 sensor can be getting slow causing this code. New Cruze fuel economy dropped from 40 mpg down to 33, that's because of this rotten winter gas we have to use, paying four bucks a gallon for oxygen, nitrogen, and MBTE's. But doesn't affect acceleration, just my pocket book.

P0449 is a generic code dealing with the fuel evaporative system. GM has been mounting the carbon canister and vent valve way back by the fuel tank. Wasn't much of a problem when the canister was mounted high under the hood. But some idiot bean counter is trying to save a buck on those long hoses.

Normally that vent valve has to be opened with the vehicle sitting, if not, your gas tank would explode as the temperature rises. When the gas expands, suppose to be collected by that way overpriced carbon canister. When you run the vehicle a test is made. the vent valve is open, solenoid activate and purge valve, normally on the engine opens to draw those fumes back into the engine. But this also sucks in road debris and moisture getting that vent valve filthy.

When the fuel evaporative test is made, vent valve can't fully close and therefore a slight vacuum cannot be built up in the tank as detected by a pressure sensor. If the vacuum does not increase, sets a code.

Generally, a good cleaning is all that is required. If excessive carbon is found, canister is going to pot and has to be replaced. If driving in salted snow with puddles all over the place, that fuel evaporative system can suck water back in the tank causing more fuel system problems. Whoever that idiot is that elected to save a buck, caused the rest of us a lot of misery.

Also 99% of the idiots on the web blame the gas cap where it is mounted high, over the years, only found one leak by the gas cap. And wasn't even the cap, but a crack in that cheap piece of plastic they used for the fuel filler.
 
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#6
P1174 looks like a camshaft sensor fault. This might affect fuel mileage. Maybe also make it run rough, but seems more likely you are due for tuneup parts; fresh spark plugs and maybe spark plug wires.
 

Gus

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#7
Found this on internet:


Got this off of wiki answers: Hope it helps

P1174 indicates fuel trim cylinder balance malfunction. This means that your cylinder-to-cylinder air to fuel ratio is not balanced properly. Usually caused by a faulty heated oxygen sensor located on the exhaust or a simple vacuum leak. It will not harm your vehicle but it will lower your fuel mileage and the engine light will remain on until the issue is fixed, which will fail an emissions test for some states. This may be repaired free under your emissions warranty. Check with your dealer.
 
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#8
More detailed information...

DTC P1174 or P1175

Diagnostic Instructions

- Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
- Review Strategy Based Diagnosis for an overview of the diagnostic approach.
- Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P1174: Fuel Trim Cylinder Balance Bank 1.
DTC P1175: Fuel Trim Cylinder Balance Bank 2.

Circuit/System Description

The Fuel Trim Cylinder Balance diagnostic detects a rich or lean cylinder to cylinder air/fuel ratio imbalance in each bank. The diagnostic monitors the pre-catalyst heated oxygen sensor (HO2S) signal's frequency and amplitude characteristics by calculating an accumulated voltage over a predetermined sample period. An imbalance is indicated when multiple samples of the accumulated voltage are consistently higher than the desired value.

Conditions for Running the DTC

- DTCs P0030, P0036, P0050, P0053, P0059, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0128, P0131, P0132, P0133, P0134, P0135, P0151, P0152, P0153, P0154, P0155, P0201-P0206, P0300, P0301-P0306, P0411, P0412, P0418, P0442, P0443, P0446, P0449, P0452, P0453, P0454, P0455, P0496, P1133, P1153, P1516, P2101, P2119, P2120, P2125, P2135, P2138, P2176, P2431, P2432, P2433, P2440, P2A00, P2A03 are not set.
- The device control is not active.
- The intrusive diagnostics are not active.
- The engine overspeed protection is not active.
- The power take-off (PTO) is not active.
- The traction control is not active.
- The fuel control is in air-fuel Closed Loop.
- The system voltage is more than 10 volts, or less than 18 volts.
- The engine run time is greater than 100 seconds.
- The engine coolant temperature (ECT) is greater than -20C (-4F).
- The engine speed is greater than 425 RPM, but less than 6,000 RPM.
- The mass air flow is greater than 25 g/s, but less than 510 g/s.

Conditions for Setting the DTC

Multiple samples of the pre-catalyst HO2S accumulated voltage are consistently greater than the desired value.

Action Taken When the DTC Sets

DTCs P1174 and P1175 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P1174 and P1175 are Type B DTCs.

Diagnostic Aids

- The fuel trim cylinder balance diagnostic is very sensitive to heated oxygen sensor (HO2S) design. A non-OE sensor or an incorrect part number may set a false DTC.
- Monitoring the misfire current counters, or misfire graph, may help to isolate the cylinder that is causing the condition.

Circuit/System Testing

1. Read and record the Freeze Frame/Failure Records data taking note of the speed and load at which the DTC set.
2. Diagnose any other DTCs that are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
3. With the engine idling and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19-42 kPa.
->If the MAP sensor parameter is not between 19-42 kPa, refer to DTC P0106 or DTC P0107 or P0108.
4. Inspect the air induction system for modified, damaged, leaking, or restricted components.
5. Inspect the crankcase ventilation system for improper operation.
6. Inspect the vacuum hoses for splits, kinks, and improper connections.
7. Inspect for vacuum leaks at the intake manifold, the throttle body, and the injector O-rings.
8. Test for a restricted, damaged, leaking, or modified exhaust system from the catalytic converter forward. Refer to Symptoms - Engine Exhaust.
9. Test the fuel injectors for improper operation. Refer to Fuel Injector Diagnosis.
10. Test for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
11. Test for fuel composition error, FlexFuel/E85, only. Refer to Fuel Composition Diagnosis.
12. Test for excessive fuel in the crankcase due to leaking injectors.
13. Test the ignition system for improper operation. Refer to Electronic Ignition System Diagnosis.
14. Test the engine for any mechanical conditions such as sticking valves, lifters, etc., which could alter the flow into the combustion chamber. Refer to Symptoms - Engine Mechanical.
 
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#9
A Technical Service Bulletin that may apply...

TECHNICAL

Bulletin No.: 03-06-04-030G

Date: April 22, 2009

Subject:
Various Driveability Symptoms Due to Clogged Fuel Injectors, MIL/SES DTCs P0171, P0172, P0174, P0300, P1174, P1175 (Clean Fuel Injectors and/or Perform Injector Test With AFIT CH-47976)

Models:
2005-2009 GM Passenger Cars and Light Duty Trucks
2005-2009 HUMMER H2
2006-2009 HUMMER H3
2005-2009 Saab 9-7X

Zoom and Print Options
46_03-06-04-030G_tbl-001.png


Equipped with Engine RPOs listed in the Table above and MULTEC(R) 2 Fuel Injectors

Attention:
GM does not support cleaning injectors on any engines that are not listed in this bulletin. Engines other than the ones listed in this bulletin that diagnosis indicates having restricted injectors should have those injectors replaced.

Supercede:
This bulletin is being revised to update the model year to 2009 and to provide applicable engine RPO table. Please discard Corporate Bulletin Number 03-06-04-030F (Section 06 - Engine/Propulsion System).

Condition

Some customers may comment on any of the following various driveability symptoms:

- Extended Crank Time

- Hard to Start

- MIL/SES Illuminated with DTCs

- Hesitation

- Lack of Power

- Surge or Chuggle

- Rough Idle

- Light or Intermittent Misfire

Cause

Due to various factors, the fuel injectors may become restricted. Extensive testing has demonstrated that fuel related issues are the cause of clogged injectors. At this point, no specific fuel, fuel constituent, or engine condition has been identified as causing the restriction. The restriction causes the engine to operate at a lean air fuel ratio. This may either trigger the MIL to illuminate or the engine to develop various driveability symptoms.

Correction

Fuel injector restrictions, deposits can be cleaned on the vehicle using the following procedure. Under NO circumstances should this procedure be modified, changed or shortened. As a long term solution, and to prevent reoccurrence, customers should be encouraged to use Top Tier Detergent Gasoline. For further information on Top Tier detergent gasoline and fuel retailers, please refer to the following Corporate Bulletin Numbers:

- 04-06-04-047G (U.S. Only)
- 05-06-04-022D (Canada ONLY)

Notice
GM UPPER ENGINE AND FUEL INJECTOR CLEANER is the only injector cleaning agent approved for use with General Motors fuel system components. Other injector cleaners may cause damage to plastics, plated metals or bearings. General Motors has completed extensive laboratory testing of GM Upper Engine and Fuel Injector Cleaner, and can assure its compatibility with General Motors fuel system components, as long as the cleaning procedure is followed correctly.
 
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#10
Cruze manual states explicitly to only use top tier gasoline. Only pumps in my neck of the woods that state top tier is 91 octane ethanol free gas. Was only costing 20 cents per gallon more, now more like 45 cents a gallon more. But sure worth the price in terms of superior fuel economy and costly fuel system problems.

In my experience, using a simple formula, dividing the price per gallon by the miles per gallon you accurately calculate, the price for driving a mile is cheaper by using top tier gasoline is cheaper than buying that lesser crap.

Now I am curious about this:



Would that work in my 88 Supra with fuel injector problems?

"Other injector cleaners may cause damage to plastics, plated metals or bearings."

And what is the difference of top tier gas, is it the fact that it doesn't contain ethanol? Not only a problem in automotive, but also in marine, RV, and small engine applications. Volvo I/O is the only vehicle that I own that has a big sign on it. "Do Not Use Ethanol Based Fuels"

Can we somehow sue the government that is not controlling what they put in fuels? Major difference in an E-85 vehicle, uses far superior materials also at a much higher initial cost. But what difference does 10 or 85% ethanol make, just a question of time before your fuel system rots or corrodes away.
 

Gus

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#11
Anyone see the E85(flex fuel that can contain up to 85% ethanol) or E15(contains 15% ethanol, where regular gas only has 10%) gas added to their pumps?

E85 should only be used in flex fuel vehicles(usually have a yellow cap).....and while it is cheaper, the octane rating is lower, so in effect, your gas mile will be lower, so how much will you save?

Fox news is warning about the use of E15......basically, Fox was saying the higher % of ethanol causes separation and the higher concentration of it goes to the bottom of the tank and is pumped out first, rather than as a blend, which can be corrosive to metals and gaskets....


Also found this on the internet:

Local Mechanics Say E15 Fuel Will Damage Cars


December 4, 2012

The federal government is changing the chemical makeup of gasoline by adding more ethanol. The move is supposed to help protect the environment, but local mechanics warn that it may be hurting cars.

Ethanol is supposed to burn cleaner and help America become less dependent on foreign oil.

"We need a movement towards making the environment better, cleaner, more sustainable for the future," said University of Virginia student Ankit Gupta.

Currently ten percent of the fuel we put in our cars comes from corn-based ethanol. The Environmental Protection Agency has now approved raising the blend to 15 percent, called E15.

However, AAA is warning this may damage vehicles, especially older models.

"The government requiring manufacturers to blend their fuels at that high of a rate will cause those new vehicles to deteriorate at a faster rate," said Paul Jaderborg, a mechanic at Settle Tire in Charlottesville. "Therefore the manufacturers of those vehicles will not honor their warranties anymore."

A dozen auto companies, including giants like Honda, Toyota, and Ford, have said that their warranties would not cover damage caused by E15. Jaderborg says during the past five years, he has already seen more cars with problems because of the current level of ethanol in gas. He says a higher ethanol blend will only mean more repairs for his customers.

"It's unfortunate that the consumer is going to have to pay more to maintain their vehicle and I am going to see a lot more of that work here," said Jaderborg. "For my financial well being, it is going to help me a bit."

So take this advice with a grain of salt....
 
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#12
What does "Ankit Gupta" know about vehicle's? Could also add the EPA is demanding the commonality of materials used in vehicles to make recycling at lot easier. Can't use the best material for the job anymore.

We could easily use natural gas or methane to power our vehicles, all domestically available, just a question of doing it. Both these fuels emit far fewer emissions than gasoline. We also have a known at least 10,000 year supply between the both.

One way to solve the alcohol gasoline won't mix problem is to install a motor driven paddle wheel in our vehicle's.

Burning our food supply is not a good idea to run our way over sized pickup trucks and SUV's. You may have noticed that at the grocery store.
 
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#13
Well, I have gotten the light to go off and stay off. . . . for now :). After reading the comments and getting some information from a local Chevy dealer, I decided to take a look at the purge vent solenoid. Not knowing too much about any vehicles I wasn't sure what I was looking at but noticed a loose hose that was connected to the canister that was coming from the gas tank. I cleaned the connection to the solenoid and tightened the hose. I was also told to try some fuel injector cleaner, so I put some in and am on my second tank of gas since the light has gone off. I've put about 500 miles on since and haven't noticed any of the hesitation when I accelerate and my mileage seems to have gotten somewhat better.

Thank you all for your responses and help! :)