UnVMySS

iTrader: (31)

Hello everyone,

I am having issues with my 2004 5.3 Silverado... It is not a flex fuel model. To start, it runs and drives fine mostly, there MAY be a slight miss at idle, but not really noticeable if at all. The MIL light is on, and occasionally flashes random numbers of times. I have read codes and came up with p0303 Cylinder 3 misfire.
The truck has, within the last year, had plugs/wires changed to AC Delco Rapidfires, and OmniSpark plug wires from O'Reilly's.
What I have tried thus far, and mind you I am no expert on the 5.3, is the following...First, I checked the coils by changing them around to see if the misfire moved with the coil to try to rule it out. It did not move with the coil to say the least.
Next, I changed AGAIN the plugs and wires. No difference.
Then I tried changing around injectors and at first I thought that it had fixed it, but then it came back.

I *think* I hear a vacuum leak...but I cannot locate one for sure. I attempted to 'smoke' the intake manifold to see if any smoke would leak out of a leaky area and it did not leak anywhere that I could notice; and the intake was slightly pressurized.

Although I doubt this would cause this issue, I looked at all of the oxygen sensors briefly, and they appeared to be original units. I am thinking an O2 sensor wouldn't cause this anyway, but considered it.

Does anybody have any suggestions or ideas? This is my daily so you know how that goes... Thanks a ton for any help in advance.

transaminator99

iTrader: (3)

Check injector pulse , listen to the injectors to see if number 3 is clicking , leak down test , clean maf

transaminator99

iTrader: (3)

Those are the simple things I can think of doing anyways , could be a bent push rod , compression , weak spark ... get it hooked up to a good scanner , do a cylinder contribution test , it will tell you how often the cylinder is misfiring then you can look at your fuel trims ,o2s etc ...just start with the easy stuff first thenstart digging

UnVMySS

iTrader: (31)

I borrowed a compression gauge from O'Reilly's today, and checked cylinders 2,3,5. I think I did it right, never used one before, but couldn't get any compression to show for cylinder 3. Cylinder 5 had 150+... But zero on 3? I pulled the valve cover to check for damage on drivetrain, and didn 't see anything. I even pulled the pushrods out of 3 and they looked good.

Any input or suggestions? Or is it looking like I need an engine?

Jontall

Detonation destroyed #3 piston. See if O'reilly's has a "digital inspection camera" and pull the spark plug on #3; inspect inside.

miker2

iTrader: (1)

you could get an air hose hooked up to a spark plug adapter and learn a bunch.

Becker

iTrader: (4)

I would be boroscoping cylinder 3, as long as your positive cylinder 3 is at zero compression.. If you are positive you might as well pull the heads and or motor, cuz it is time for a rebuild or a new one.

transaminator99

iTrader: (3)

Get a leak down tester and test cylinder 3 find where the air is coming out , redneck version pour a table spoon of oil in the cylinder and see if the compression shoots up that would mean you're rings are done

1998TransAmWS6.

Very curious about this so let us know wat you find. I agree cylinder leak down test is the best place to go next. 0 compression I'm thinking intake valve isn't actually opening or piston is scrapped