I,m posting for a friend that needs help on his 97 blazer 4.3.
He had the intake gasket replaced and now it has a loud knocking coming form the front of the engine thats consistant with rpm's and the engine runs very rough. He also put a new alternator on and it does not seem to be charging.
The engine ran fine when he brought it into the garage but the mechanic told him that it has nothing to do with what they did. They tried to pull the codes but cant. He was told that it was missing and that a piece of carbon was screwing it up.
I checked the distrubitor, the plug wires and the as many connections as i could but i cant find anyhting wrong. Any suggestions on where to look?Could they have fried the computer when they did the intake manifold?

Thanks for any help

 

repairing the intake manifold wouldn't damage the computer. ive done mine about a year ago, its time consuming but really not that bad. as far as the charging issue check belt tensioner make sure it isnt real loose if you can pull it without a lot of effort chances are it needs replacment. the knocking could be a lifter if the intake manifold has been leaking coolant into the engine for a while internal damage could occur. it could also be the flywheel knocking on the bell housing cover, or numerous other things idk. what i do know is i have a similar problem currently. its been a year since ive done my intake manifold gasket without any knocking i caught the leak early on. my oil pressure at idle is below 20. at a stop foot on brake in drive i noticed oil pressure dropeed below 20 then fell to zero then died. i think its the oil pump knocking but havnt had a chance to remove oil pan and inspect. as far as being unable to read codes check fuses obd2 fuse could be blown making connection from scanner to vehicle impossible. the rough idle can come from carbon build up in the egr and egr passages, the idle air control valve,purge valve and purge line going from evap canister to purge valve filled with carbon which comes from g fuel tank being over filled a lot breaking down the charcoal in the canister and filling purge line. also the engine coolant temp sensor located next to the egr can cause rough idle if it is dirty and coolant is dirty causing a poor reading. the temp sensor helps control fuel injector operation based on engine temp. all the things ive mentioned ive experienced personally and have fixed minus the recent knocking issue i have. the rough idle could come from the throttle position sensor as well. mine had 218,000 miles on it i just replaced it along with cleaning egr and ports, cleaned idle air control valve and cleaned throttle body now it runs fine minus oil pressure issue.hopefully his helps, sorry for being long and drawn out but the more info the better when trying to diag a proble such as yours there are a lot of variables.