Cylinder3 misfire. 20% loss of compression. What now?

My engine (2.7) has been shaking like crazy for a while. It is really only noticeable when I am at a stop. I replaced the plugs and wired thinking that was the problem but it did not help.



I recently had a P0303 code (cylinder #3 misfire) pop up and I thought that might be an indication of what was wrong with the engine so I took it to my mechanic to see if they could tell what the problem was.

The mechanic indicated that I only had 80% compression on cylinder #3. What do I do now? The mechanic did not really offer any suggestions, he just diagnosed the problem (which I guess is all that I asked him to do).

Do I need to budget for replacing the entire cylinder head?

If I need a new cylinder head, does the cylinder head come already assembled ready to bolt on or are there other parts needed?



Where is a good place to purchase one (if I actually need one)?

 

How much oil are you burning in an oil change? Is it significant? Have you noticed a change since the motor started shaking?

 

Do a compression check, and if one cylinder has low compression put some oil in it and measure again. That's how you check the rings. Otherwise it may be a valve.

 

did the mechanic test all 4 cylinders?

 

I am not sure if the mechanic tested all four cylinders. I would assume that he only tested one since the code was referencing only one cylinder. He referenced a 20% leakage on cylinder #3 on the printout he gave me so I assume he only did one cylinder. I will check and see if I can have all four cylinders tested for comparison.

 

For anyone that is following this thread and is unsure what a compression test is, I found a really informative video that explains it.
http://www.youtube.com/embed/X_tbksFYhl4

 

testing only one cylinder is pretty pointless. It's the difference in pressure between cylinders that matters most unless you have like 100 PSI across the board.

 

I think I am going to purchase (or rent) a compression tester and check it out myself this weekend. I am going to do a dry and a wet test to see what totals I come up with and will report back once I have some more data.

 

hold the throttle wide open during cranking.

 

Ok I finally did a wet and dry compression test. The figures did not make any sense to me. Can anyone help me make sense of these figures.

Cylinder #1: Dry: 200, Wet: 270
Cylinder #2: Dry: 170, Wet: 220
Cylinder #3: Dry: 185, Wet: 240
Cylinder #4: Dry: 190, Wet: 210

Does these figures make any sense?????

 

Not horrible but not good either. Cylinder 2 being 30 PSI lower than the highest is a bad sign. Next step would be a leakdown test on that cylinder to see if it's the rings or the valves.

 

What gets me is that my vehicle is throwing a P0303 code which is a cylinder #3 misfire. The cylinder #3 seems to be ok while cylinder #2 seems to have the lowest compression.

 

cylinder 3 is not okay, it is too low in comparison to cyl 1. It is weird that it doesn't throw a code for cyl 2 though. Hopefully someone with more knowledge than I will chime in.

 

my brother has an '02 2.7L and went through a similar issue about a year ago. it turned out to be a burnt valve.