3.7l started with rocker for # 3 came off supposedly because of back pressure from blocked cats, I got the rocker put back on changed the converters, O2 sensor down line and air temp intake drove great for an hour engine light came on, Crank position sensor changed that ran good for 30 minutes threw a p2314, p305 checked plug on 5 black and dry, changed ran good for about 30 no low compression on driverside bank. Mechanic is telling me I need a new engine Any ideas???

 

You might need a new engine if that's what they are telling you.

 

just trying to figure out how the engine devolved so quickly

 

Blocked converters will wreak havoc on an engine,.

 

Do you know specifically which cylinder on the driver-side bank now has low compression (or all of them)?



...And did they have to remove the camshaft on that side to re-seat the rocker?

 

Cylinder 5 is the issue for low compression and they did not have to remove camshaft, since the lifter wasnt stuck is there a product I can use to restore compression

 

There is no miracle product to restore compression.
A leak down test could show the root cause of the low compression, such as rings, bad/scored cylinder wall, bent/stuck valve, blown gasket.

Now, I am not saying this will work on your engine, but I will tell you what I do on Outboard motors, is a small amount of oil in the trouble cylinder and do another compression test. If the compression increased with the oil, then you have a ring/cylinder wall issue. If the oil does not help, then it is probably a valve.

 

Ok, so after the engine was running good for 30 minutes and then threw two codes as sensed by the #5 coil, the spark plug was removed and checked, and now you have low compression in that cylinder?

Without making an accusatory statement, *hypothetically* if the spark plug was not reinstalled properly (for example, if under-tightened, or over-tightened and affecting the cylinder head threads), that could lead to low compression in that cylinder.

Another possibility is that, because the spark plugs in these trucks are of the crush-washer design, if you reinstalled the same plug with the same crush washer, it may no longer sufficiently be making an adequate seal upon subsequent installation(s).

A third possibility is that at some point while the plug was out, debris fell into the spark plug well, preventing an adequate seal.