2009 Tahoe 5.3 2X4 Cylinder #4 not firing. Low compression.

[TexasTahoe2025]

2009 Tahoe LT 2X4



I am getting the P0304 error code. I have a DOD ODB2 chip. Took intake off the intake and valve covers and the rockers are working on that #4 cylinder were moving. So I do not think it’s the DOD issue.. The #4 injector was bad and the spark plug (intake was dry as a bone) was dry.



Replaced the fuel injector and the spark plug is now the plug is wet but still not getting any fire on that cylinder. The plug is wet with fuel now. Spark plug was firing



Ran a compression test on the #4 and it has only 60PSI.



Do you have any suggestions on how to repair the #4 Cylinder? I looked at using Restore oil treatment and I have mixed feelings on using it. I have read some scary results about using it. What has your experience been using it?



Thank you for your input.

 

[PPK_]

Well... i would do a leak-down test to see if is a valve.. they can leak and you end up with lousy compression. could be if it was this way a long time.. maybe you have coked up the rings. i might try to fill the cylinder up with solvent.. i have used a lot of wd40 - for some time.. then drain it with the plug out.. you might get some compression back that way...

not good.

 

[SpareParts]

Did you only compression test #4? If so maybe the gauge is not reading right.

 

[TexasTahoe2025]

Thanks for the replies!

We tried two different gauges.

I have seen putting marvel mystery fluid and leave it over night.

 

[strutaeng]

Run a compression test on the other cylinders.

Based on what you see, do a leak-down to see if you can determine where the air is leaking. If other cylinders are okay and only that one cylinder is leaking through the intake or exhaust valve, a head removal/replacement won't be horrible. If most cylinders area also low on compression (or air is leaking thru the piston rings into the crankcase), that changes things.

 

[TexasTahoe2025]

Thank you for your input. I'll try the wd 40 idea.

 

[Fless]

After your compression and leakdown tests (if you do them, and you should) rotate the engine to the spot that the valves should be fully closed. Pump compressed air into the spark plug hole and check exhaust and throttle body to determine if the exhaust valves or intake valves are leaking.

 

[j91z28d1]

you don't really need to buy a leak down tester if you have compression tester in hand. remove the valve core so it becomes just a hose. screw it in, rotate the engine till both valves are closed and connector it to your air compressor.

then listen to where the air is blowing out. it could be anything from a broken ring land to a valve that's stuck open.