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Eric, Master Technician/shop foreman
Category: Chevy
Satisfied Customers: 846
Experience:  ASE Master Technician, 25 years experience, Over400 General Motors certifications
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2005 Chevy: 125,000 miles, #1 cylinder not firing..oxygen sensor

Resolved Question:

2005 Chevy 5.3 liter 125,000 miles, #1 cylinder not firing at idle.
What do I need to replace to fix. Replaced spark plugs and oxygen sensor and this did not fix the problem.
Submitted: 4 years ago.
Category: Chevy
Expert:  Eric replied 4 years ago.
Hi, is it just at idle that it is missing? Is the check engine light on? Any codes? Let me know and i will try to help you out. Thanks, Eric
Customer: replied 4 years ago.
Here is alot more information.

I have a problem with my 2005 Chevy 1500 Silverado 5.3 liter engine with an automatic transmission and the truck has 125,000 miles. I had the transmission fluid and transmission filter changed and the first time I started the engine the truck idle was low and I thought the engine was going to die. It appears to idle at 400 rpm. I drove two or three miles and after stopping at a few stop signs the rough idle continued and the check engine light came on. As soon as I accelerate the truck runs with fine and when I push the accelerator down hard acceleration is strong. I do not think the transmission service and the rough idle are related. The mechanic that worked on my truck has repaired my mother’s and brother’s pickup trucks for years. The next morning I put a can of Sea Foam in the gas tank that was 80% full and drove 15 miles and the rough idle continued. I was hoping an injector that was partially blocked.

I talked to the mechanic and approved changing the spark plugs. The spark plugs were original. The low idle problem remained. He checked the oxygen sensor and the senor reading was 600 and then the reading dropped to is 13. The mechanic thought the problem was the oxygen sensor so I okay replacing the senor. When he changed the spark plugs I also had him change the fuel filter, oil and filter and belts.

Changing the oxygen sensor did not correct the problem. He stated the reading on the new oxygen sensor gave the same readings as before, starting at 600 and then dropping to a reading of 13. He looked deeper and hooked up the truck to his diagnostic machine and determined the number one cylinder was misfiring only at idle. He stated the only cylinder that as missing was the number 1 cylinder. He listened to the fuel injector on the #1 and he can hear is clicking. He checked fuel pressure and the fuel pressure was good. I think he said the fuel pressure was at 60 lbs.

He thinks I have a head gasket issue and this is why the number 1 cylinder is missing. The mechanic stated these Chev’s have weak head gaskets. The mechanic was informed I had added Sea Foam to the gas.

Normally I have the oil changed at 3,000 miles and I do not need to add oil so it does not burn oil excessively. A couple of times I when over 4,000 miles between changes and I did had oil to the engine.

After the spark plug and oxygen sensor were changed the check engine light was off and after a few miles of driving the check engine light came back on. Friday night I drove to 196 miles to my home. At above idle it ran normal. At my first stop at 53 miles, the truck idled smoothly while at the gas station. I was still hoping I have a partially blocked injector I added another can if Sea Foam 90 miles into the drive. Unfortunately at my next stop and while I ran errands Saturday, the rough idle continued.

I stopped at an Autozone Saturday morning and they gave me the errors codes. P0300, P0131 and P0171.

I would like another opinion and after reading the details of the codes I will not have the mechanic change the head gaskets.

Expert:  Eric replied 4 years ago.
Okay, assuming he put a factory sensor in the car and not an aftermarket, i would have the engine vacuum checked at idle and see what it is. GM has had problems with the intake manifold gasket leaking underneath. Alot of times it cant be detected in the old way of spraying carb clean or brake clean around the ports. They have a new design gasket for the intake. Also try driving it with the o2 sensor unplugged and see what happens. It will obviously set a code but it will tell us if anything is changing. Let me know what you find. Thanks, Eric
Customer: replied 4 years ago.
I am not sure if the O2 sensor is GM. He told me the spark plugs are OEM. The mechanic does use Carquest parts. If the O2 sensor is from Carquest, what do you suggest?
Expert:  Eric replied 4 years ago.
First i would disconnect it and see if the condition changes. If so, put in a factory sensor. If not then we need vacuum readings off the intake @idle, @1500 rpm and @2500 rpm. and we need to know if the vacuum holds steady or if the needle on the gauge jumps around. Let me know, Thanks Eric
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