GMC Acadia, Crank But No Start.
Here we have a GMC Acadia with a crank but no start condition. No matter how long you try to crank the engine, the most you may get is a sputter if you're lucky. After running a few diagnostic tests, our technician Jay was able to prove that the SUV has spark and fuel, which leaves only one thing left to test for, compression. After compression testing the cylinders and also adding compressed air into the spark plug holes, (also known as a cylinder leak down test) he was able to confirm that the engine does not have good compression and is also leaking air into the intake and exhaust manifolds. Digging a little deeper proves the engine is out of time, this is a very common issue with these engines as the timing chain stretches and the guides wear down past the point the tensioner can keep the engine in time. Timing in an engine simply put is the synchronization of the top half of the engine (camshafts pushing the valves open and closed) and the lower half of the engine (pistons going up and down driving the crankshaft) making sure the valves and the pistons move up and down in the exact moments needed for optimal intake, compression, combustion, and exhaust.
Normally if caught quick enough, this can be remedied with new timing chains guides and tensioners, but unfortunately in this case we determined that even with the valves closed completely they still were not able to keep a good seal. This happens when a valve makes contact with a piston and bends the valve making it unable to seal (timing issue). Another way this may happen is when the engine gets a "burnt valve" which is when the valve becomes so hot it gets distorted to the point it can no longer seal. This happens from a few different things like running lean (not enough fuel) which creates much more heat, an exhaust manifold leak, or simply exhaust/combustion gases escaping past the valve seal due to the valve not being closed all the way at the right time (there's that time word again).
The customer went with our recommendation of replacing the engine with a brand new engine with a 3-year unlimited mile warranty. This doesn't only cover the price of the engine but also the price of labor and even towing and rental in the event of engine failure. We hope this information gives you another reason to bring your car in for recommended maintenance and our complimentary "health inspection" in order to avoid larger-than-needed repair bills. With vehicle maintenance, a small amount invested into preventative maintenance and routine "checkups" will always more than pay for themselves in preventing much more costly repairs.