cylinder misfire diagnosing

2010 Chevrolet 5.3L
Recent AFM/DOD delete cam,lifters,trays,gears,oil pump. Stock non-dod and non vvt camshaft replacement.

Bought truck 'as is', from gentleman, with rough idle after doing the delete. The ECU delete was done with supplied Diablosport Predator2

After getting the truck home,it does have zero compression on cyl 5. Cyl 5 is leaking through intake valve. All other cylinders have 160 psi. Leak down on all cyls were less than 5%. The gentleman said the truck run fine before two lifters collapsed so he went with the AFM complete delete kit.

What is a puzzler is cyl 7,checking with temp gun on exhaust manifold is producing no heat. Changed coil,wire,spark plug from hot cylinder to this 'cold cylinder' and still the same,,no heat,,and checking with low end scanner is constant misfire but not as fast as cyl 5.
So,,, changed fuel injector from cylinder 5 to cylinder 7,,,and still missing a lot and no heat building on exhaust manifold. Pulled valve cover and it appears intake and exhaust are traveling the same as all other rockers. Didn't put a dial indicator on valve stem though.

Done a running compression test,on cyl 7 ,,and is right at 160 psi. Going to tear it apart in couple days,,,but just curious with good compression, different ignition components ,,,and different injector its not producing any heat. With stethescope it does sound like injector is pulsing correctly.
Don't have a high end scanner to really get down to business.


The old truck once off of idle,,actually runs nice,,, and decent power,,it just idles very crappy. No odd sounds.At first start up high ideleit actually sounds very smooth as well..oddly enough,,when comes off high idle,,it starts stumbling.

TIA

For your #7 misfire, I'd suggesting backing up your thermometer readings by doing a simple balance test. Engine idling, disconnect the #7 injector or coil and see if the engine runs worse. If it does, #7 was doing something. If it doesn't, then #7 truly is dead. You can always compare #7 to another cylinder (other than #5) for reference.

#5 & #7 are adjacent cylinders and #5 starts it's exhaust stroke when #7 is halfways thru' its intake pull. Exhaust gas might be getting into the intake thru' the bad #5 intake valve and sucked into #7.

Matt T wrote:

#5 & #7 are adjacent cylinders and ...

There's an idea, too. Is it possible to swap the #5 and #7 coil or injector connectors? :blink: It wouldn't do anything about the leaking #5 intake valve, but it might bring #7 back to life.

Thank You for replies,,,,everyone,,I wondered if may be a correlation,,,between the dead hole cyl #5, and cyl#7
My main concern is when i take off cyl head,,,am going to do the alcohol in each cyl,,see if leaking,, Am going to replace intake valve pretty sure,,,lap in,,and retest leakage with alcohol heads sitting level...Kind of shad tree way but should work,,,Just trying to learn why cyl #7 is producing no heat at all,, with temp gun on exhaust as it is.