350 knock

Jeff H

Active Member
Joined
Nov 26, 2009
Location
harrisburg
I changed the intake gasket on my 1990 gmc with the 5.7 and 10 miles down the road I come to a stop light and the truck dies. When I started it back up there was a knock in it now, and if i didnt give it gas it would cut off, also truck didnt seem to lose power i drove it back home and changed the timing chain, harmonic balancer, oil pump and went ahead and changed the intake gasket again but knock is still there. Sounds like its coming from the front of the engine and if i rev it up the know seems to get quieter. After changing all this i think it could be a broke crank, is this possible? i have never had a crank break but have heard of it. anyone that can help?
 
could you have dropped anything down inside the motor when you had the intake off?
 
no i know nothing fell down there, it dosnt sound like that either a buddy of mine had that happen before and it sounded totally different from my knock, like it almost sounds like the knock is coming from the front of the block outside but nothing up there is vibrating abnormally
 
Check your timing. My guess is you dropped the dist. in a tooth or 2 off.. Causing the computer to try to compensate as best as it can..
 
if timing was off like that why did it run fine for 10 miles then have a knock, like this thing ran brand new after the first intake gasket change then just started acting up out of no where
 
Well, dono, its your gig not mine, so i'm just guessing tryng to help... 10min is usually about the time the CPU tries to go into closed loop or starts to try to make adjustments to idle etc.. until that time its usually running on hard settings in the ECM.

Possibly check for large vacuum leaks, could be brake booster line, TBI base gasket, etc.. Possibly IAC not hooked up or working, gasket etc.. any CELs?? Plug wires all on right? (I mean pull em all off, and redo em.. Not look at em again and think they are right)

Look at anything you touched during the intake gasket process, something is not right, broke, or different than before... Step through it one piece at a time..
 
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