2003 GMC Sierra 4.8L Vortec Engine - Gas

I'm having an issue with low compression on one side of my block, on cylinders 1,3,5, and 7.

It happened suddenly driving home, I took it to be seen and they said i need a valve job and it was gonna run me $2,500. Now i know thats bull ****, i can get it done cheaper, but my question is what could have caused the low compression other than sticky valves? It seems too odd to me that all four would start sticking only on one side, at low miles.
I'm guessing it's a bent cam shaft, or bad cam gear, other than that i have no clue, anyone have any clue?
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Aaron C Michaud
Easy Car Forum Creator / Michaud Projects
2105635177 Call/Text

 

On a cam in block engine, a bent camshaft would effect the other bank of cylinders too, would it not? So low (evenly low compression? or different compression on each?) compression on 1,3,5,7 would probably be something involving the head. Either way, valve job or not, I'd suggest pulling the head off and inspecting the head and block for warping.

Before we get ahead of ourselves though, put 1tsp (Or just a little splash) of engine oil into each cylinder on that side of the engine, 1,3,5,7, and redo the compression check. If your compression numbers go up, then your rings are leaky. If the compression numbers stay about the same, them the issue is not likely your rings. A leak down test would also tell you if it is the valves or not.

 

How do i do a leak down test and if it if valves would a good soaking in sea form sorta help the issue? And thank you for your reply.

 

Here's a great video on leakdown tests:
[youtube]QNf0IOIvIcY[/youtube]

You might not be able to do a leakdown test at home, but a dealer or independent mechanic shop should be able to do it for you. You need a decent air compressor to do it.

As far as seafoam goes, if you have a problem on your intake valves, then I don't think it would hurt. If the issue isn't on the intake valves though, then it wont do much good.