2005 Silverado stumbling on accelaration, run lean

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Nov 14, 2005
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Ive got a 2005 silverado that has me stumped. The truck has been stumbling on accelaration. But runs fine at wide open throttle. It just seems to hesitate when it is in the 2000 to 3000 rpm. I pulled the plugs today, and they are all white. Replaced plugs and wires today. Pulled the codes today and coded lean bank 1 and and bank 2. Any ideas what is wrong
 
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Possible vacuum or intake leak. Check all vacuum hoses as well as the brake booster hose for any leaks.
 
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White plugs aren't good. I agree with checking for vacuum leaks since it said both banks are lean. Also a possible chance of a bad upstrem O2 sensor or 2.
 
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I'd check out the fuel filter if possible...and/or put a good dose or two of Chevron Techron Fuel System Cleaner through it. Since it's lean, it could be an issue with the FIs or filter(s).
 
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I would clean the throttle body and plate. When carbon and varnish builds up around the plate(s), it can stick and cause a stumble. Once you get past the sticky varnish-as at WOT- the stumble goes away. Don't use Carb cleaner. It is too harsh. Use a 3M product made to clean throttle bodies. This is caused by the PCV system recycling the vapors from the engine to be burned. Therefore you should clean the TB and plate routinely.
 
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 Originally Posted By: Jim Spahr
I would clean the throttle body and plate. When carbon and varnish builds up around the plate(s), it can stick and cause a stumble. Once you get past the sticky varnish-as at WOT- the stumble goes away. Don't use Carb cleaner. It is too harsh. Use a 3M product made to clean throttle bodies. This is caused by the PCV system recycling the vapors from the engine to be burned. Therefore you should clean the TB and plate routinely.
Usually gummed up throttle bodys just effect idle and cause stalling. But, I agree it's a good maintenance plan and I do it every oil change or so.
 
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Vaccuum leak is tops on the list but don't rule out the MAF sensor either. And check the ductwork from the MAF to the engine to be sure there are no tears or leaks. When you go WOT the PCM ignores most sensors, riches the mixture and gives you all its got. When you are getting your stumble at 2-3k RPM it could very well be a leak somewhere and that air was not monitored by the MAF so therefore the wrong info is given to the PCM and that's why it is leaning out. It doesn't know about the extra air.
 

rmattingley

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Ok, did some more testing, vacumm seems to be ok, checked with vacumm gauge. However, checked fuel pressure. Sits at 38, when reved, it spikes to 60 and drops to 30 really fast up down up down up down. It never stays constant. Is the fuel pump starving for fuel (in tank fuel filter) or would this be the pressure regulator?
 
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Buy CRC MAF cleaner and clean your MAF. Do not use any other cleaner on MAF. Most lean codes are thrown by bad dirty or broken MAF sensor. Google MAF cleaning and you might get exact procedure for your truck. - Vikas
 

rmattingley

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Cleaned maf sensor and throttle body. No change, but did idle better. Connected the Fuel pressure gauge up and strung it so I could watch when I was driving. The fuel pressure varied from 35 to 62, when it dropped it corrisponded to the low pressure. When I gave it full throttle, the pressure stayed at 60 psi.
 
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 Originally Posted By: rmattingley
Ok, did some more testing, vacumm seems to be ok, checked with vacumm gauge. However, checked fuel pressure. Sits at 38, when reved, it spikes to 60 and drops to 30 really fast up down up down up down. It never stays constant. Is the fuel pump starving for fuel (in tank fuel filter) or would this be the pressure regulator?
Something definitely wrong with the fuel pressure. Vortec engines need a minimum fuel pressure of 55psi. It looks like a fuel pressure regulator problem. Do you have a engine-mounted regulator or do you have a returnless system with the regulator in the tank? BTW we still do not know which engine you have.
 

rmattingley

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5.3 gm with the return less system. The pump comes as a whole assemble. I pulled the pump today and have a new one coming tomorrow. Hope this is it. Why is it every time some one in washington decides to make things more efficient, the gas mileage goes up less than one mile per gallon and the price goes up exponentially.
 
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 Originally Posted By: rmattingley
5.3 gm with the return less system. The pump comes as a whole assemble. I pulled the pump today and have a new one coming tomorrow. Hope this is it. Why is it every time some one in washington decides to make things more efficient, the gas mileage goes up less than one mile per gallon and the price goes up exponentially.
The returnless fuel module also means that the OEM can spend less time installing the stuff, lowering assembly cost... But 9/10 times this makes repair more difficult.
 
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 Originally Posted By: rmattingley
5.3 gm with the return less system. The pump comes as a whole assemble. I pulled the pump today and have a new one coming tomorrow. Hope this is it. Why is it every time some one in washington decides to make things more efficient, the gas mileage goes up less than one mile per gallon and the price goes up exponentially.
How did you access the pump? Did you drop the tank or lift the bed or cut an access hole on the floor of the bed? Keep us posted on the results of the pump swap. I hope you got a Delco, the aftermarket pumps don't have a good reliablity record.
 

rmattingley

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I went ahead and dropped the gas tank. I have a topper on box and I really didn't want to take it off. Plus, I wanted to clean the inside of the tank and check for any debre. Taking the tank off was actually pretty easy. 1: Emptied the tank. I had about 10 gallons in there, so I took my pressure gauge and clamped the pressure release valve. Then I jumped the relay to the fuel pump at the fuse box. Filled up 2 5 gallon jugs. 2: Crawled under the truck and disconnected the hoses. 3: Unhooked the retaining straps to the tank 4: Pulled it out and rinsed with clean gas. Quite alot of sand in there. Now it is sitting in my drive way waiting for my new pump. Should be here tomorrow by 2:00.
 
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So the 2005 Silverado is one of the trucks that now come without an external, ie: servicable ,fuel filter? I like GM but disagree with them on this decision. Gasoline quality across the USA is not good enough to go unfiltered-except maybe in the GM lab. Yes, I understand they have a 'filter' in the tank. If I am correct, this is really a strainer afixed to the bottom of the fuel pump. That strainer is not a proper fuel filter at all. If R Mattingly will take a second to look at the fuel filter attached to the new fuel pump and let us know, I would be very greatful. Also look at the condition of the FP wire harness and see if it is overheated. My 1994 RWD Impala SS had fuel pump replaced and the wire harness was burned. I am a big GM fan and would like to purchase a new Chevy Silverado or GMC Sierra.
 

rmattingley

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Ill take some pictures. I don't see any burnt wires. I plan on tearing the pump assemble apart once I get the new one in. Curious to see what type of filter is in there.
 
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