119K mi 08 Chevy Suburban 5.3 L P0300

[Witsend]

Basically a dead miss on Cylinder 1 with ridiculous misfire history count. Cylinder cranking amps test showed a compression deficit on #1. Engine vacuum test with vacuum transducer showed fairly decent engine vacuum but missing a vacuum hump for #1. Checked actual #1 compression only 30 psi. Put shop air to cylinder and feel some blow happening from crankcase , but nothing ridiculous, and intake and exhaust valves don't seem to leak much. Don't hear any loud tappet sound from top end either.Possibly got a Piston not coming up as high as the others from a bent rod from going through water or an intake valve that isn't opening? Will pull left valve cover tomorrow and take a look, I guess. From looking at vacuum display, Any body know what I should likely expect to find? #1 is the 5th row over

[Matt]

Is this an AFM engine? Camshaft lobes probably wasted or collapsed lifter.

[Matt]

Cracked or broken valve spring maybe.

[Witsend]

I did a little internet searching and believe it it could have an AFM lifter issue along with possible worn , washed , or stuck piston rings. (due to amount of air getting past #1 rings) Also has a code for the oil pressure sensor.

[BRIAN617]

Running compression test, or pull valve cover and watch rocker arms to diagnose failed afm lifter.

[Matt]

Oil pressure sender failure is common on this one. Also there should be a screen below oil pressure sender that plugs up with sludge. Remove screen and throw away IMO.

[Witsend]

I removed the left front valve cover (not to bad looking inside )and verified that the #1 intake valve was not being opened I took the rocker off and verified the push rod was straight. I put the push rod back in place and shot some carburetor cleaner down the pushrod to the top of lifter with the straw of the spray can and let it soak awhile while I changed the oil pressure sensor and filter screen (only a little gunk was at the bottom half of the screen. I took the #1 intake push rod out and put the valve cover back on , disconnected #1 fuel injector drained off a little engine oil and added a quart of synthetic transmission fluid and ran the engine till hot and changed the oil and filter with fresh 5W -30 full synthetic oil and ran it hot again (#1 fuel injector is still unplugged the whole time). I pull the valve cover and install The #1 pushrod and rocker arm and put the valve cover back on (but leave #1 injector still unplugged) I go to crank over the engine and it is hydro locked. I pull #1 plug and pressure releases and gasoline comes out, I put the plug back in and the engine starts up but still missing. Still Need to make sure I'm not getting fuel pressure leak down from #1 injector. Just figured there was a puddle of gas accumulated from when the injector was working behind a non opening intake valve ,and when I torqued down the rocker, the valve opened a little and the puddle of fuel ran in the cylinder .

[snapon20r]

I spent a year at a Chevrolet dealership only to see tons of this style engine go through camshafts, lifters and piston rings being stuck to piston grooves. May be time for an engine. Great thread !! Keep us updated.

[Witsend]

Fuel rail pressure is holding fine and noid light pulses normally when plugged into injector connector, so nothing to indicate excessive fueling or leaking fuel injector. Engine runs quiet with no tapping Can't see any movement of the #1 intake rocker arm though to open the intake valve ,so the fuel is puddling up inside the intake so if you get a dead miss on any of those 4 cylinders with the 8 DOD lifters you might want to unplug the fuel injector of misfiring cylinder immediately to reduce possible ring damage from cylinder wash. Tomorrow I will pull the intake and valley cover and try to see if I can see the cam lobes. Cant imagine I should need a new cam unless the roller on the lifter failed. Cylinder leakage past rings on #1 seemed reduced after the oil change and running it with the fuel injector disconnected for awhile. Think the cylinder had just got washed from the fuel. Hope the cylinder wall looks ok and the piston comes up as high as the others at TDC.

[Matt]

I don't think removing valley cover, AKA valve lifter actuator manifold, is going to grant you access to cam lobe inspection. If I remember correctly there are only a few oil drain back holes cast in block that you can peak through. I have seen internal collapsed lifter cause your symptoms and requires head removal to replace lifter. I have also seen lifter roller failure which takes the cam shaft with it. If the cam is gone it's cheaper to replace engine in an AFM situation.