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I have a 2002 Tahoe with the flex fuel 5.3. Mileage is 104,000.

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I have had no engine...
I have a 2002 Tahoe with the flex fuel 5.3. Mileage is 104,000. I have had no engine issues until recently. The engine starts spuddering, backfires if you push the gas. It is very intermittent...it will run perfectly for days, then do the spuddering routine. It has given me the following codes; P0171/174. I changed the fuel filter, spark plugs, spark plug wires, and cleaned the MAF. After this maintenance, it ran perfectly for 200 miles over 3 days, then had a major episode. What else could this be?
Submitted: 8 years ago.Category: Chevy
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5/20/2009
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago
goodwrench9124
goodwrench9124, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,432
Experience: Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer, Hybrid certified
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Hello, and welcome. does the truck seem to start ok?
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Customer reply replied 8 years ago
Usually, yes. Although tonight, the problem happened as soon as it started. By the way, the truck had been driven 40-50 miles, then sat for approx 1 hr, then the spuddering.
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago

Ok, the codes P0171 and P0174 are a indication of a lean condition on both banks. the two most common problems for this is a weak fuel pump or a intake gasket leaking vacuum. normally with a weak fuel pump you will have a hard to start condition also, but still would be a good idea to make sure the fuel pressure is ok. if the fuel pressure is ok, then more than likely the intake gasket is leaking vacuum causing a lean condition. which is real common on these trucks. you can check the intake gasket for a vac. leak, by spraying some carb cleaner around the intake where it meets the head. if the rpm changes, then the intake gasket is leaking.

 

your engine code is the 8 digit from the left on your vin number. being flex fuel vehicle yours should be a Z engine.

(55-62 psi) VIN: (V, T,U)

335-375 (48-54 psi) VIN: Z

 

 

If there is anything you dont understand, please feel free to ask me to explain

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Customer reply replied 8 years ago
Vin # XXXXX it is flex fuel. I don't have a fuel pressure gauge, assume I can rent one from AutoZone.I will have to get some carb cleaner to run that check as well.

Would it be normal for the problem to be so intermittent? What is the typical cost to replace the intake manifold gaskets?
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago

yes, you can get one at autozone. being that it is a intermittent problem, the computer can make some adjustments for a lean condition, but when the computer trips codes P0171 and P0174 it is at max. the engine is just to lean to run properly. the intake gasket is a fairly easy job on this truck, depending on the shop rate in your area is, 150.00 to 250.00 in labor and the intake gasket runs

Manifold gasket, all models, 4.8l, 5.3l, 6.0l
99-06 $106.19

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Customer reply replied 8 years ago
The spot to check the fuel pressure is right above the intake manifold, correct?
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago
yes correct. on the fuel rail on the passenger side. looks like a tire stem
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Customer reply replied 8 years ago
I tried the carb cleaner trick and got no change in the idle speed. The local Autozone already loaned out their gauge, so I will have to try later or buy one. Would a bad fuel pump really create an intermittent problem like what I am having?
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago
a fuel pump relay, wont cause the problem you are having. a fuel pump relay would cause a no start or a stalling problem
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Customer reply replied 8 years ago
What about the fuel pump itself?
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago
Yes, for sure the fuel pump could be the problem. a fuel pump can have low pressure at times, causing your problems. that is why a fuel pressure test is so important. have you tested the fuel pressure yet?
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Customer reply replied 8 years ago
I tested it today on cold start-up - 42-43 psi. Reason enough to replace the fuel pump? Should I try to test it when it goes through one of its episodes (which will be a little difficult as it is likely on the road at the time)?
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago

pressure is low for sure. these trucks are real critical. yes a fuel pump replacement is in order. the pump just doesnt have enough pressure to maintain proper fuel trims, causing the codes P0171 and P0174

 

 

 

 

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Customer reply replied 8 years ago
From what I have been reading, the only way to change the fuel pump is to drop the gas tank. Is this correct? Also, seems like a big job for a DIY. What would the approx cost be at the dealer?
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago
yes, the tank has to be dropped for replacement of fuel pump. the factory pumps are quite pricey. the pump list for 549.00 which is a lifetime warranty part if installed at the dealer. it is about a three hour job. dpending on what the labor rate is at your local dealer you will be somewhere around 250.00 to 350.00 in labor
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Customer reply replied 8 years ago
Do they offer rebuilt pumps? If so, how much cheaper and is it worth the difference in price?
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago

there are some cheaper aftermarket pumps out there. but they just done seem to work as well. have seen some of these go out shortly after replacing. if you plan on keeping the vehicle long term, then the GM pump is the way to go. if you think a trade is in the near future, then a aftermarket pump would be ok and normally are half the cost

goodwrench9124
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Customer reply replied 8 years ago
Thanks for your help
Chevy Mechanic: goodwrench9124, ASE Certified Technician replied 8 years ago

your are very welcome!!!!

 

Thanks for using JA!! your questions are always appreciated!!!

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