'05 XLT V6, P0303 & no compression -- head gasket? valve? piston?-- pls help diagnose (video)

[pkn]

'05 XLT V6, ~85k. Truck was suffering from P0430 (Catalyst system efficiency below threshold (Bank 2)) and moderately uneven idle for few years, but yesterday -- peaceful local driving, stopped at intersection, when started moving (no noticeable "pop" or "clang" or whatever) -- engine shaking, big loss of power, barely made it to parking lot on other side. Towed home, now trying to figure out what happened. Severe shaking at idle, suspicious sound (see video), full throttle revs to 2500-3000 RPMs not more. New code appeared -- the infamous P0303. From basic (not thorough) looking -- no broken/hanging vacuum or other lines .

My diagnosis is -- blown head gasket :-((( I've rented cylinder compression tester from Autozone and right now I'm preparing to do compression test on all cylinders.

However I would greatly appreciate any considerations/suggestions/pointings to what I might be missing.

Video (~80MB) here
20190820_095654.mp4
attached does not work for some reason

 

[Drewmcg]

Does not seem like a blown head gasket to me. Is your coolant low? Is there water in your tail pipe exhaust? Is it overheating? Why do you suspect blown head gasket?

Could be anything from bad cat to clogged fuel filter to vacuum leak to bad coil pack, to ? Have you ever changed the spark plugs? Not much to go on here.

 

[pkn]

One of main reasons I suspect head gasket is sound (see video) when idle -- harsh "chuff-chuff-chuff" with frequency close to one cylinder sparks.

It happened instantly, so I don't think it's clogged fuel filter. Overheating, low coolant, water in exhaust -- I could not tell because after the "happenning" the engine was run maybe 5-7 minutes total, in short chunks. And I don't want to run it longer because if it is the head gasket then I don't want to damage the matching surfaces where gases are escaping the chumber. Before the "happenning" it was OK -- no overheating even in heavy traffic in 100-deg heat, coolant level OK, water in exhaust as normal condensate.

Vacuum leak -- I don't see any broken/lose vacuum lines. Bad coil pack is another possibility (for which I'm secretly hoping), the cylinder compression test should tell. Funny thing is that to do cylinders compression test I must move the truck inside the garage, and to do so I have to move a lot of "stuff" out... still moving, hope to finish tomorrow. I will report my findings.

 

[pkn]

Ah, and yes, I've replaced spark plugs less than year ago.

 

[pkn]

Well, here are the cylinder compression test results:
#1 - 180 psi
#2 - 182
#3 - 0 (manometer needle did not even move, tested many times with two different manometers)
#4 - 175
#5 - 180
#6 - 173

I think this points to blown head gasket, however I am not sure. If it was cracked piston or something, then the pressure would push out the oil stick, right? What else could it be?

 

[miker104]

Bad valve is possible. If you can borrow a cylinder leak down tester you can isolate intake or exhaust valve or rings by listening to where the air leaks out under test.

 

[Leftysrepsol]

There is a coolant pressure tester you can rent to see if it's a head gasket. The fact that your not building any pressure in that cylinder sounds like either a hole in your piston or you dropped a valve. Bad rings usually give you some sort of pressure reading.

 

[pkn]

Bad valve is possible. If you can borrow a cylinder leak down tester you can isolate intake or exhaust valve or rings by listening to where the air leaks out under test.

Thanks. Looks like Autozone/Advanced/OReylly don't have it for rent, I'll keep looking

Question: given the cylinder does not have any pressure at all, if it is a bad valve -- will I be able to verify it after opening just the valve cover?

 

[pkn]

There is a coolant pressure tester you can rent to see if it's a head gasket. The fact that your not building any pressure in that cylinder sounds like either a hole in your piston or you dropped a valve. Bad rings usually give you some sort of pressure reading.

Thanks. Coolant pressure tester I can rent at Autozone, will do.

Hole in piston -- should not it produce noticeable gases escaping thru PCV valve and/or oil dipstick pipe?

 

[Littleant]

Miker 104 is correct. Cylinder leak down tester will show you just where the issue is. If you find one cyl 3 piston has to be at TDC to test.

 

[Drewmcg]

Its not a head gasket with those numbers. Pull the valve cover and see if you can fix the valve/camshaft problem w/o removing the head.