You'll need to do a leak down test to see if it's valves or rings. Was the compression test done dry or did you put a little oil in the cylinders? My guess with that many miles, it's a bit of both valves and rings. Some of you numbers seem quite high for a stock engine with roughly 10:1 compression. You may also have some significant carbon build up. Run a tank full of fuel through it with a can of BG44K and re do the test. See if the high numbers come down some. Might even smooth you idle out.
What did the back of the intake valves look like when you replaced the manifold gaskets? Did you find any oil in the intake manifold or the intake tubing? I take it you did not replace all those parts at the same time, how many tanks of fuel have you gone through? Do you always get fuel at the same place? Any chance you have bad or watered gas?
I've been doing all my maintenance items on all our vehicles. Fixing leaks, noises, new brakes etc. Your truck looks good. If this stay at home stuff lasts too much longer, I'll probably start some more as well.
So far so good. The new tensioner and the slightly longer belt seems to be working. No noise so far, but it's not that cold today, mid 40's. I'll fire it up tomorrow morning and see what happens.
This engine does not have AFM. Stethoscope does not pick up the noise anywhere on the valve covers, heads, timing cover, valley cover or block. I picked up another tensioner and a new belt just to try. I found out there are 2 belt lengths depending on which alternator you have. The current belt is the shorter one, so I picked up the longer one just to try. It's only about 3/4" difference in length. I'll post back if either item fixes it.
Ok, with the belt off, none of the pulleys seem like to have any issues. At least none yet I can see or feel. The stethoscope only seems to pick up the tapping sound when I put it on the tensioner housing. The tension seems to be about tight according to the markings, it about in the middle. Again, no noise with the belt off and engine on. Turning the a\c on or off makes no difference. It's definitely a tapping noise and not a squeak or squeel of any kind. I'm at a bit of a lose. I've replaced the tensioner based on where the stethoscope picked up the noise, but no change. The weirdest part is the temperature dependence. Why would it only happen when cold?
I'm trying to diagnose a tapping noise. I strongly believe it is in the belt drive somewhere. When I remove the belt, the noise goes away. The noise also goes away when it's warm outside and once the engine warms up some. The sound seems like a metal to metal tapping noise. It's loud and is not rythmic but more random. I thought I had it nailed down to the belt tensioner, but the replacement seems to be making the same noise. Any ideas?
I noticed today that my AC compressor is cycling in and off. It runs for about 3-4 seconds every 30 seconds or so. The AC is off on the dash and the HVAC is set to dash with the fan on low, but not off. Turning the AC on made no difference. It was about 45 degrees out, dry and sunny. 2000 GMC Sierra 1500 SLT. My question is, is this normal, or do I have an issue? I found this while trying to diagnose a noise. This doesn't appear to be the cause of the noise, but it has me scratching my head. Any help would be appreciated.
If it's making noise, you likely have more damage than just the locker. Unless you cracked the housing, plan on new diff, gears, bearings and seals. The true Trac is what I'm planning as well. My G80 is also toast, but I have no noises and it operates normally as an open diff.
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