In light of some of the headgasket and overheating threads here on DF lately, I figured we could have a little discussion on what is going on with the LLY's in general that causes some of the failures we are seeing.
Turbo issues and turbo vanes "sticking" seem to be a problem. I can't count how many issues I've become aware of with problems with the vane sensor going crazy and over-boost or under-boost codes being set. GM really needed to have a drive pressure sensor monitoring drive pressure versus vane position. Drive pressure can hurt a motor fast. If the turbo vanes stay in a higher position than desired, exhaust air is trapped in the cylinder and causes the motor to loose power fast and it holds in a lot of exhaust heat! The turbo vanes in a lly are not very functional below 30%. 100% vane position equals closed, 0% equals open. A closed vane allows faster spool, but creates drive pressure. An open vane allows air to flow through the exhaust side of the turbo easier, but creates slower spool up.
An LBZ will make boost and maintain boost at sea level and 0% vane position. An LLY will not. As I stated above, the LLY needs 30% or more vane position to build boost or maintain boost. In general, the operating range of the vane in a LBZ is from 0% to 95%. 95% and above don't aid in spool up and only increases drive pressure. The range of a LLY is 30% to 95%. 0%-29% vane postion will loose boost on a LLY at sea level.
For efficient operation, the vane position typically is used between 30% and 75% for daily driving and towing on an LLY. Low load and low rpm usage of the vanes above 75% is okay, but there is a drastic increase in drive pressure vs. boost pressure when going above 75%. The same can be said for a LBZ when speaking of high vane position operating characteristics. The difference is that an LBZ can go as low as 0% to maintain boost. So now when comparing efficient vane position operation between an LBZ and an LLY you can see that the LLY uses 60% less of the vane position tables when compared to the LBZ. Because of this, there is less room for error on an LLY when choosing the correct vane position value to get the proper boost value, even in stock form.
The most important thing to realize if you own an LLY, is not all those technical aspects about how you turbo works, but that it was all designed to work with proper maintenance. You can see that a LLY turbo is at a disadvantage to a LBZ turbo right out of the box when it comes down to efficient operating characteristics. Drive pressure kills motors and vane position creates drive pressure.
A clogged or iced up air filter causes a restriction on the amount of air the turbo can suck in to make a desired boost number. Guess what happens when it don't get enough air to make the desired boost number? ECM calls for more vane position to get the boost up! Fail!
A bad MAF or MAP reading makes the truck think it's not getting enough air, guess what? ECM calls for more vane position to get the boost up. Fail
Fuel pressure bleeds off because your fuel pressure relief valve is weak(known problem). Truck has low power and don't make proper boost, so guess what? ECM calls for more vane position to get the boost up. Fail
You have a leaking intercooler or a torn intercooler boot that bleeds off your boost to atmosphere, so guess what? ECM calls for more vane position to get more boost. Fail
Your EGR is struck open and bleeding of boost pressure into the exhaust or sucking in hot exhaust air. Boost readings seem low so guess what? ECM calls for more vane position to get more boost. Fail
Your vane position sensor reads lower than the actual vane postion. The truck thinks it's at 70% vane position but it is actualy at 90%. The ECM don't know there is a problem so you have more boost and drive pressure than you need. Fail
You can see that this is not a perfect system. Your LLY truck doesn't always code or protect itself from self destruction. Your LLY was not designed perfect from the get go, so do yourself a favor and properly maintain it. If you have the means to go above and beyond the proper maintenance, get some gauges and monitor boost and drive pressure. Find a way to watch the vane position desired and actual values and get used to how it changes your boost and drive pressure readings. Stop driving the truck when you see a problem.
The 04.5 LLY and 05 LLY are known to have weak rail pressure relief valves in them. Watch your rail pressure if you don't have yours shimmed or plugged. [Can be tested by "Bottle test"]
The 04.5 LLY and 05 LLY are known to have an extremely restrictive factory turbo inlet mouthpiece and most owners upgrade this piece. If you do an intake upgrade, don't leave the stock mouthpiece on the turbo.
Clean your engine bay and keep an eye on your intercooler, boots, and clamps. Try to eliminate any boost leaks by removing and cleaning the silicone boots when you check them for cracks or holes. When in doubt, replace them with new boots and clamps.
WATCH YOUR COOLANT TEMP WHILE TOWING! Yes, LLY's overheat. Do whatever you can to prevent this. Pay attention to your coolant temp at all times while towing. It's not your fault your truck overheats, but you are the only one that can stop it from happening. You are the one paying to fix it when it overheats, so try to prevent it. Assume it is going to overheat all the time. Better safe than sorry.
Water pumps are known to fail. A big problem has been the impeller falling off the shaft of the pump. If you have a high mileage truck, replace the water pump with one that has been upgraded to keep this from happening. If you are having your head gaskets fixed and your water pump is old or high mileage, replace it with an upgraded one.
It's easy to point fingers at your EGR, a weak factory gasket, your tuner of choice, weak factory studs, or GM when you have a headgasket problem on your LLY. I think the finger pointing should start with the owner/driver of the truck before it ever gets pointed in any other direction. I'm not saying there are things GM could or should have done better. I'm only stating that we know of a lot of these problems already, and you should be informed enough to prevent them before they happen to your LLY.
I also think its important to keep an open discussion of what is failing and under what circumstances. If you have a failure or an opinion/finding on how you could have prevented a failure, let us know! I think we can all help each other make these last longer. I'm sure the info people have shared over the years has extended the life of these trucks a lot already.