mike73
Newbie
Not a big expert, but I'l give you my .02.
Sounds internal, could be rod or lifter. You could drop the oil pan and check for play in the rods and you could remove the valve covers and check for anything unusual looking. Might also be helpful to use a dial indicator to measure lift- if one valve is less than the others, that tells you something is going on.
I had a '92 with a 4.3 that sounded somewhat like this- I dropped the oil pan and looked in the valve covers (didn't measure lift though). Couldn't see anything unusual. It did tend to go away under load, which is typically a rod knock symptom, but the rods felt tight. I ended up selling the truck, so I never figured out what was wrong.
Other possible (but less likely) causes could be a loose harmonic balancer, loose flexplate bolts, etc.
Another possibility is that it could be knocking due to low oil pressure (would need some wear in the rods to do that too, but maybe not enough to need a full rebuild if you catch this soon enough and change out the shells and the oil pump)- that would explain why it goes away while driving but comes back at idle. You could check this by using a manual oil pressure gage- I don't think the factory oil pressure sensors are always trustworthy on these trucks- some leak internally and then give a false reading.
Sounds internal, could be rod or lifter. You could drop the oil pan and check for play in the rods and you could remove the valve covers and check for anything unusual looking. Might also be helpful to use a dial indicator to measure lift- if one valve is less than the others, that tells you something is going on.
I had a '92 with a 4.3 that sounded somewhat like this- I dropped the oil pan and looked in the valve covers (didn't measure lift though). Couldn't see anything unusual. It did tend to go away under load, which is typically a rod knock symptom, but the rods felt tight. I ended up selling the truck, so I never figured out what was wrong.
Other possible (but less likely) causes could be a loose harmonic balancer, loose flexplate bolts, etc.
Another possibility is that it could be knocking due to low oil pressure (would need some wear in the rods to do that too, but maybe not enough to need a full rebuild if you catch this soon enough and change out the shells and the oil pump)- that would explain why it goes away while driving but comes back at idle. You could check this by using a manual oil pressure gage- I don't think the factory oil pressure sensors are always trustworthy on these trucks- some leak internally and then give a false reading.
