1994 K2500 Strange Knock

[clevernickname]

I purchased a 94 k2500 a couple weeks ago. Runs fine, all that needed to be done was have a new clutch put in it. Put the clutch in and it runs fine... Except the knock.

 

Cold engine dosnt knock, it has 166xxx miles on it. After it warms up to operating temp it starts knocking. So i started pulling plug wires.. found that knock was coming from #2 cylinder. So i changed the #1,#2 main and rod bearings, which looked pretty typical for the mileage, Knock still there. Put 5w-20 oil and a couple bottles of stp in it to boost the oil pressure and the knock sounds the same.

 

It seems like if i put the truck under load, imagine putting it in 2nd gear rolling slow then hammering it, the knock will go away. IE: more vacuum less knock.

 

The only other problem i am having is with the idle, More frequiently than not it will idle irratically, usually stays around 1500-2000 rpms. But sometimes it will idle at a perfect 650 and the knock is not noticeable unless you feather the gas a little.

 

NO Exhaust leaks

Dist looks ok

no smoke

no loss of performance.

No vacuum leaks

 

I tried testing out the knock sensor, unplugged the whole KS Module harness and the sound didnt change. But when i hit the right manifold the Ohm resistance increases from the sensor!

 

I AM STUMPED!!!! WHAT THE HECK IS GOING ON?

[ride65]

wrist pin? , but I imagined you checked that when you put in the bearings or did you just pull the Pan? Did You plastigage the bearings? maybe restricted oil passage to #2? just throwing a few possibilities out there.

[GMstrong]

I was alos thinking wrist pin.5-20 is very thin for that much mileage.Whats the timing at?