overheated 4.3, now rough idle

[timothyhampton]

Mom blew the water pump in her 98 Blazer and overheated the 4.3 engine. It always had a bit of a rough idle but now it's even worse. The guy who replaced the pump ran the codes on it and it came up with cyl #4 misfire. She had someone else replace the plugs, cap, rotor and wires. It still idles pretty bad. He said maybe a blown head gasket. I had a quick look at it today and checked the compression on the #4 cyl and it seemed fine with no leak down. The plug is gapped correctly and is the correct AC delco replacement. What should I check next? I'm hoping she didn't cook the intake manifold gaskets and cause a vacuum leak! Thanks Guys

[OverBoardProject]

Please take the time to do a full compression test and get back to us.

Also look for any vaccum hoses that aren't hooked up while your at it.
I hope that it's a vaccum leak.

[BlazerLT]

Might also be the #4 injector.

Reset the computer by pulling the negative battery terminal overnight and see if things come back.

It could be the computer.

[timothyhampton]

Thanks Guys, I'll reset the computer and do a full compression test of all the cylinders as well check out the vacuum hoses. Tim

[wolfox]

These engines do not take overheating well. I have heard stories ranging from blown head gaskets, to totally bent up valvetrains not to mention what happens when what remaining coolant mixes through gaskets into engine oil...

I am with the other guys, do a compression test and a leakdown test if possible. If you haven't already change oil and filter like, yesterday. Change oil and filter again in 500 miles. You might have a valve stem contaminated with coolant that turned into a blob at one end, not letting it open fully or close for that matter. SO many things can go wrong after overheat. I wish you luck.