2004 5.4L 3V w/ 185k miles. Oil changed every 3-5k w/ full synthetic. Truck developed the Triton ticking beginning about 60k. Changed the plugs shortly after with only 7 broken. Ticking became a tapping became a knocking. At 170k changed the plugs, injectors, coils, VCT solenoids, cam sensors, TPS, phasers, chains, guides, tensioners, lower gear, oil pump, water pump, followers and lash adjusters. Ran better than when I picked it up from the dealer with 8 miles on it. Couldn't feel it running at idle. Pulled like a tractor. I was so happy, I put on a BFN Flowmaster exhaust with stainless cats. It was like being on a first date again. Developed a slight exhaust tick a month later. Figured the new exhaust had worked it's way loose. I climbed under the truck and tightened the flanges on the flared pipes at the exhaust manifolds. Didn't fix the problem. Raised the vehicle on the lift while running, couldn't find a leak. Took it to the best muffler guy in the area. He said that there wasn't a leak. He thought it was internal. Over time, the ticking became a full blown exhaust leak sound almost as loud as when a plug is blown out. Seemed to be coming from the intake manifold. Truck ran smooth but slight miss at idle. No light and no code. Pulled the fairly new plugs. No signs of carbon or heat. All looked exactly the same with no broken or worn electrodes. Disconnected the injectors one at a time while running. All changed the idle slightly except that the driver side injectors seemed to not have as much of a change. Passenger side experienced a definite change in idle with each injector disconnected. Pulled the valve covers, no signs of wear, seized rollers or blueing from heat. Took it to a Ford shop. The tech said that he did a compression test and determined that the #5 cylinder was not holding compression. Dealer wanted another $657 to pull the driver side valve cover to investigate further. Since it takes me about 45 minutes to pull the valve cover, I thought that was a little steep. Driving the truck from the dealer to my office, the loud exhaust leak sound stopped completely with no warning or reason. I have no idea why but Jimmy cracked corn and I don't care. All that is left is the significant miss at idle. Engine is almost completely silent while running except for the miss and rough idle. Runs well, pulls like new. Still no light or codes. The scan tool shows no code but the Live Data stream at idle showed LTFT Bank1 (+25%), Bank2 (-18%). O2 were functioning, TPS functioning, IAT correct, MAF 5.79, RPM 620, Spark Advance 15deg, Fuel Pressure 40psi. I did a compression test. All cylinders Bank1 where 200-205psi dry. Bank2 were were all 150-155psi. No water/anti-freeze in oil. Not burning oil or any more fuel than usual. No vacuum leaks (used an entire can of brake cleaner all over engine). Still no light and no code. Could a piece of carbon have gotten stuck between an intake valve and seat in the #5 cylinder causing the valve to be held open, thus allowing exhaust to escape through the intake? What is causing my rough idle? Why is compression on driver's side consistently 50psi less?

 

You might want to try a differential compression tester. That tester puts air pressure to the cylinder with the piston at TDC. If you here air coming from the intake it's an intake leak, from the exhaust it's an exhaust leak, air escaping into the pan is ring blow by.

 

After exhaust noise stopped, all cylinders held pressure. No leaking at all. No hissing.