Diagnosing my LQ4 issue
03-08-2015, 01:55 PM
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Diagnosing my LQ4 issue I've read through countless threads trying to determine what could be causing my problem, but haven't been sold on what it actually might be. So hopefully someone can help.
I bought a high mileage 2000 Gmc sierra truck with an iron head 6.0L that had 191k on it. Ran perfect. No weird noises, idled great. It's connected to a 4L80E.
The reason I bought the truck is to swap the engine/trans into my Toyota rock buggy. I pulled everything out, and cut down the harness and had the computer re-flashed including deleting all emissions and egr. I also pulled the pan and replaced the pick-up tube o-ring just as a precautionary measure. Everything checked out in the bottom end. After a few months of fab, I was able to get everything in and wired up. Fired right up, with no codes. Ran great.
Now to the issue. The truck can be sitting for days on end, and it fires right off with zero blue smoke. Even at high revs, not even the slightest bit. I drive it around and get it nice and warm. If I let it just idle for a few minutes it will start puffing out a little blue oil smoke. If I rev on it hard a few times, it will clear out, but will eventually return after a few minutes of idling. After it's warm, I can kill it and re-start it in 10 mins and it will puff smoke at start-up.
After doing a bunch of reading, I changed the pcv to a fixed orifice style. It still didn't fix the issue. People behind me on the trails say it puffs a little out each time I take off.
Could this be a valve seal/guide issue? I'd rather not do a full rebuild if I don't have to.
I bought a high mileage 2000 Gmc sierra truck with an iron head 6.0L that had 191k on it. Ran perfect. No weird noises, idled great. It's connected to a 4L80E.
The reason I bought the truck is to swap the engine/trans into my Toyota rock buggy. I pulled everything out, and cut down the harness and had the computer re-flashed including deleting all emissions and egr. I also pulled the pan and replaced the pick-up tube o-ring just as a precautionary measure. Everything checked out in the bottom end. After a few months of fab, I was able to get everything in and wired up. Fired right up, with no codes. Ran great.
Now to the issue. The truck can be sitting for days on end, and it fires right off with zero blue smoke. Even at high revs, not even the slightest bit. I drive it around and get it nice and warm. If I let it just idle for a few minutes it will start puffing out a little blue oil smoke. If I rev on it hard a few times, it will clear out, but will eventually return after a few minutes of idling. After it's warm, I can kill it and re-start it in 10 mins and it will puff smoke at start-up.
After doing a bunch of reading, I changed the pcv to a fixed orifice style. It still didn't fix the issue. People behind me on the trails say it puffs a little out each time I take off.
Could this be a valve seal/guide issue? I'd rather not do a full rebuild if I don't have to.
03-12-2015, 10:42 AM
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Thanks for the response. I'm thinking that at initial cold startup, the oil is too thick to leak through. Once it warms and thins, it leaks through. I put my thumb over the dipstick while it's running and I'm not getting any pressure, so I'm hoping the rings are fine.
03-12-2015, 11:42 AM
#4
Well actually what happens is when you shut it off hot and don't restart it the oil that leaks past the seals gets vaporized from the engine heat soak and deposits form in the intake manifold, injectors and cylinder heads. The reason it smokes if you restart it after 10 mins is the oil is still liquid on the valve stems. If it were mine I'd either change the seals or use a seal sweller product like TransX or high mileage oil.
If you use a seal swelling product go easy, few ozs at most.
If you use a seal swelling product go easy, few ozs at most.
03-12-2015, 11:54 AM
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Well actually what happens is when you shut it off hot and don't restart it the oil that leaks past the seals gets vaporized from the engine heat soak and deposits form in the intake manifold, injectors and cylinder heads. The reason it smokes if you restart it after 10 mins is the oil is still liquid on the valve stems. If it were mine I'd either change the seals or use a seal sweller product like TransX or high mileage oil.
If you use a seal swelling product go easy, few ozs at most.
If you use a seal swelling product go easy, few ozs at most.