I had my blazer in shop having an intake gasket replaced that I just purchased. Ran great before but was leaking antifreeze into engine from intake. Had it replaced and oil changed. Very bad oil came out. Went to pick car up and I now have a Knock and a miss. Thought at first it threw a baring. After listening to it closely it was more like a carbon knock. Checked the compression on missing cylinder and it is changing compression on me. One time good another time bad.

1)First of all did the mechanic do something wrong when he took it apart?
2)second of all What the heck is going on?

This place that did the work doesnt look all that bright. I have refrained from loosing my cool with them until I get more info. It could of been a fluke.

 

Let's see. You could drop a couple of cups of oil out in the morning and see how it looks.
When it's hot you could pull the coil wire and crank it and see if it diesels.
Compression results seem odd. Do it a couple more times and post what they are. Also what cylinder.
What if any codes?

 

I agree with sbays,but if you had an internal manifold leak as opposed to an external one,it is quite possible bearing damage was done prior to the gasket replacement.I seem to think it would have been audible at that time,however.How long did you drive it before diagnosis was made?Was it driven to the shop or towed? Too many variables to assess.If the shop is questionable:losing one's cool is never a good thing...just find another shop familiar with these motors! I hope for your sake no serious damage was done,175K is a young 4.3! Let us know. All the best!

 

It's possible the shop did something, but I wouldn't jump to conclusions.

As others have said, put some oil in and retry compression test. That will let you know if its valves or rings. It sounds like messed up rings to me.

 

Drove it quite a bit with no knock. I went back to car which is still at shop and it is missing on one cylinder. The miss maybe the knock. Spark is there. I put some mystry oil in oil hoping to unstick a valve if that is what it is. Also sucked some sea foam into intake. May of helped alittle. The miss is a lot of the problem I think. Thanks guys for your help. Ill get some oil into cylinder to see what happens to compression. I do know it would read good one time and bad another with 2 different guages. That why I think sticky valve. I hope to save it over new engine.