Cg86

Posting to hopefully help someone else. About 10 months ago I noticed a whistle coming from the engine bay. It would only present while in gear and driving, I could not get it to happen while in park, so I had a very hard time determining the exact location of the culprit. I started replacing belts, pullies, CAI, vacuum lines ect... to no avail. Soon after the truck started to idle rough and would occasionally misfire. Changed all the plugs, wires, coils, injectors, intake gaskets with no success. I took the truck to the shop and was told it was an AFM lifter, but at that point I had already had the valve covers off and was fairly confident that was not the case. Well about a week ago I took my go pro and zip tied it in different locations in the engine bay to see where the sound got louder, and it seemed that it was coming from the passenger side, aft part of the engine. Well lo and behold after pulling the heat shield off there was clear evidence of an exhaust leak from the aft manifold (I do not recall it being there when I was changing the plugs). A quick visual inspection showed no broke bolts or obvious evidence, but when I went to check the torque of the aft most bolt, it immediately snaped off with no force. I used a drill and extractor and was easily able to remove the sheared threads left in the head. So after months of stress, hours of labor, and thousands in unnecessary parts, it was an $8 exhaust manifold bolt. Afterwards, no more whistle, engine idles smooth, and I seem to be getting better mpg. Hope this can help someone else.

Follow up: First thanks for the replys. I was finally able to run down the issue, so I'll give a full recap incase it might help someone else. There will be some assumptions in this, as I have no way yo prove parts of my theory. Initial issue (whistle, occasional rough running and CEL) was a bad seal on the # 4 injector, hence the misfire and CEL prior to the initial injector change. Latest issue (barley running at all) was in part my own fault (first time attempting this). Durring the injector swap I somehow managed to completely destroy the # 6 HP Teflon seal. It was very apparent that there was blow by when I pulled them again. I'm not sure how I managed this, as I thought I was being careful, but alas that's what happened. After pulling all 8 injectors and replacing the HP seal, she seems to be back up and running (for the time being, at least). So, what I learned. Be very careful and deliberate when placing and tightening the fuel rail. When tightening make sure you do all 4 bolts at the same time (tighten a little, move to the next until at desired torque) Lube the seals with a small amount of engine oil before installing. Make sure your seals are properly seated on the injector. If you don't have the tool to install them you can use 3/8 ID rubber hose and a hose clamp. 4.5in of extension and a stubby 1/4" air ratchet is perfect for getting the last bolt on passanger side out. Be sure to tape the intake openings as soon as you get the manifold off, as all the plastic wire sheathing is very brittle and will fly everywhere. Hopeful this will help someone.

Incase anyone else needs it - 89 imch pounds in 3 steps (30in/lb 60in/lb 89 in/lb), and the pattern is the same as the intake manifold, which is easily found.

Hello, I have been trying to chase this down for months, with no luck. A lot has gone on so please forgive the long post. 2 months ago - noticed a whine/whistle during acceleration, only when engine was under load, and seemed to be realitive to throttle position vs RPM. Replaced, bekts, plugs, wires, alternator, CAI When that didn't work, I took it to my mechanic who told me it was due to a spark plug wire being not seated. This month - things have gotten much worse. On a road trip, while cruising @ 75 mph the truck shttered (while accelating mostly), CEL came on (flashing), Traction control light. When I got to the next town I pulled over at a gas station. As soon as I stopped the lights went out. After restarting the truck it ran fine, but I had the codes pulled which showed a cylinder 4 misfire. Replaced - All 8 fuel injectors Yesterday - while running around in town I noticed the truck start to shtter when slowing to a stop. By the time I got home the engine was running VERY rough, and the CEL (solid) came on. The traction control light did come on also, but would estinguish as soon as RMPs were increased, then turn back on when stopped. Code was fuel trim, Cylinder 6 misfire. I pulled the valve cover to check the lifters (check for slop in the rocker by hand), which all checked out. I did notice a small leak from the valve cover gasket over the # 8 cylinder. I also swapped some of the ignition coils which yielded no results. So, anyone have any ideas? I'm just about to witts end, and I have no idea where to go from here. Again, if you made it this far thank you. Please if you have any ideas or even a guess I'd love to hear it.

Pulled my valve cover to check if I had a bad lifter (misfires, whine, and over all poor running). I don't, but can not for the life of me find the bolt pattern or torque specs. Appreciate any help

Hello all, First let say thank you for anyone who can possibly help. I'm pretty frustrated as of right now, trying to run this down. 2014 Sierra 1500 5.3L All Terrain 125,000 miles Noticed a whistle/whine coming from the engine bay, but only when under load (won't do it in park), and accelating (stops as soon as I let off the throttle). I first noticed it when I was towing, but now does it everyday. It seemed to go away after the engine got warm. However, it seems to now be staying regardless of temp. So far I've: Changed all 3 belts, replaced the alternator, used a mechanics stethoscope with no luck. So my questions beyond what do you all think. 1. Could this be coming from the PCV tube being worn? 2. Where else should I look for a vaccume leak? 3. Literally anything else you may feel as pertinent, please let me know. Thanks Again, CG