LLT diagnostic questions

[RandomCamaroDriver]

Full disclosure, I do own a 2010 Camaro, with the LLT V6 and 6spd MT, but this LLT is not in a Camaro. I've been looking for info elsewhere, but not finding people that know this engine, so hopefully I can get some answers here.

After a long saga and failed in tank fuel pump, I'm checking compression on this new to me LLT, and the even bank cylinders are popping back into the intake runner on the cylinder with the compression gauge attached. Odd bank doesn't do this. Does this mean for certain that the even bank intake cam has jumped timing? Or could the VVT system allow this to happen? Something else I should check?

The vehicle is a 2009 GMC Acadia AWD with 142K miles on it, and Carfax shows the timing chains were replaced at 75K miles in 12/2014.

Since this engine is transverse mounted, inspecting the timing chains is not an easy thing to do. I'm looking for a little more conformation before I resort to pulling the engine. Any help would be appreciated.


--
Rob.

[RandomCamaroDriver]

Lots of views, but no comments? Is it because it's not in a Camaro, or because no one knows if a failure in the VVT can cause the intake valves to be open when the compression cycle starts?

[cawengr]

Could you have a cam phaser that is not returning to the released position ?

[RandomCamaroDriver]

Originally Posted by cawengr

Could you have a cam phaser that is not returning to the released position ?

That's what I'm wondering, but not sure how to tell. I was hoping someone would chime in that knows more about that aspect, and say it's possible, or no way, it has to be a chain jumped a tooth.

When I brought it home, it was low on fuel, so I filled it. When I backed it out of the trailer, it ran very smooth. I let it run for a good 15 minutes, and still idling smooth when I shut it off. The next morning, it wouldn't start, and after some diagnostics, found the in tank fuel pump wasn't putting out pressure. I replaced that pump, and although now pressure is within spec, still won't start. Also, it still shows low rail pressure when trying to start (78PSI per scanner), so I replaced the HPFP. Still no pressure, so I started to check the injectors for leaking (a couple plugs were wet), and figured I damaged one or more trying to remove them, so just put in 6 new ones.

Same issue, so I decided to check compression just as a sanity test. With the intake manifold off (required to access the even bank spark plugs), I'm seeing the even bank blast back up the intake runners when the compression gauge is connected. I'm still getting numbers 10% to 15% less than the odd bank, so I'm guessing the intake valves haven't fully closed when the compression cycle starts. As to why, that's why I'm here.

[RandomCamaroDriver]

One other detail, after trying to start it, codes P0302, P0304, P0306, and P0191 are all it showed. Those are even bank cylinder misfires, and fuel rail performance. The first 3 indicate a problem with the even bank, and the last a hint there's low fuel pressure, but why not a low fuel pressure code? There are / were no timing related codes.

[PaulsSS]

Could have bent intake valves if the chain jumped. Probably the easiest way to proceed is pull the valve covers turn the engine over by hand and see where the timing marks are on the phazers compared to the flats on the rear of the cams. If you can't line up the marks or the flats at the rear of the cams you will need to remove the frt cover and probably remove the head to repair the bent valves.

[RandomCamaroDriver]

Originally Posted by PaulsSS

Could have bent intake valves if the chain jumped. Probably the easiest way to proceed is pull the valve covers turn the engine over by hand and see where the timing marks are on the phazers compared to the flats on the rear of the cams. If you can't line up the marks or the flats at the rear of the cams you will need to remove the frt cover and probably remove the head to repair the bent valves.

I'm concerned about bent valves too. I was considering pouring a little bit of carbon cleaner in to see if it runs down into the cylinders, which it should if they're bent. If not, I have a small hand operated vacuum pump to siphon any liquid back out.

I already started pulling the valve cover, but there's a power steering reservoir mounting bracket wrapped over the front of the valve cover, and the bolts holding it are not easily accessible. I'll be working on getting that bracket out of the way next so I can pull the valve cover and have a look inside.

One more thing, I did peek down into the even bank cylinders with a borescope camera, and didn't see any indications of contact on the tops of the pistons by the intake valves. Not sure if it would make a dent, but I would expect some kind of marks.

[RandomCamaroDriver]

Update : Got the even bank valve cover off (what a PITA!). There is some minor sludge build up, but not horrendous (I've seen a lot worse). The timing chain in between the two cam gears has a lot of vertical play, as in up and down, like an inch. Very little side to side. Don't know what's normal, or acceptable, but this seems excessive.

When I put a wrench on the intake cam, I gently tried moving it, and it moved easily towards the center of the motor (CCW) only. I watched the chain on the teeth of the cam gear, to make sure it wasn't jumping a tooth. It felt like I was pushing against a spring, and moved a lot, like 15 or 20 degrees, then clicked, and seemed to lock there. After that, it wouldn't move back, and had just a little bit of play in either direction. I have no idea how much movement the VVT system should have, or why it seemed to lock once it got to a certain point. Anyone know more about this system?

I then tried the same thing on the exhaust cam, and it almost immediately jumped a tooth, then another. I've got a Cloyes timing chain set on the way (should have been here today), so that will be going in next. The Camaro would be WAY easier to work on than this transverse mounted thing. Looks like my weekend will be messy.