1988 - 350 Problem

I have a 1988 Chevy Suburban with a 350 engine. It has almost 250,000 miles on it. Up until a few weeks ago, it ran great. Recently, it has been having problems after it has been running for 15 or 20 minutes. It beings making a louder than normal firing noise from the engine and does not maintain the same power that it normally has had. It is especially weak going up hills, after the noise starts. I am no expert mechanic, but I do enjoy working on vehicles when I have the time. Does anyone have any ideas what could be causing the problem? If so, is it something that I could tackle myself, take to a mechanic, or should I get rid of the vehicle? Thanks in advance for you response.

Nathan

That could be a tough one. One thought may be after so many miles you have some carbon buildup on the valves or pistons and as the engine warms up, the carbon starts to retain heat and causes detonation or pre-ignition. You could try running some fuel system cleaner through your tank (probably several times after 250,000 miles worth!). Sea-foam is a good product or anything similar (dealers choice when it comes to automotive products!).
You could also perform a compression check on your cylinders to see if you have a burned valve or stuck ring. This seems less likely to me but it's an easy test to perform.
Just some suggestions, good luck. Either way, at 250,000 it seems to me you may have got your moneys worth!

If you like the vehicle and its in good condition i wouldnt get rid of it for an engine problem. Worst you may have to do is a engine rebuild or swap. More details about the noise you hear may gain you more insight from the forum also.

ever had a timing chain and gears installed at anytime? check your rocker arms i have seen them crack from time to time.