Camshaft failure??

Sergio Quiroz · August 21, 2019

I need help confirming a camshaft failure a 07 5.3 with DOD and flex fuel before I start tearing into the engine. I've been chasing a #5 dead misfire, gone through all the diag. and everything seems to be fine. Good plug, wire, coil, injector.. swapped all of those to #3 and misfire still on #5. No abnormal noise to speak of really, normal LS noise. Can disconnect #5 coil while running and can't notice a difference in sound like I do on all the other cylinders. HPTumers scanner shows #5 cylinder misfire counter going up steady.

Now following some advice I've read from searching.. with the engine running (misfiring) and watching the misfire counter, I can back off #5 intake rocker about half turn and the misfire goes away. Tighten it back up and you can feel the engine misfire and watch the misfire counter go up immediately. I read this is the sign of a flat lobe on the camshaft. Can somebody confirm?

I don't see a broken valve spring and the rocker seems to be moving fine just like the others. All rockers are tight and sound pretty normal. I know #5 is not a DOD cylinder but could still have a bad cam lobe / lifter I guess.

Could an intake vacuum leak just on that cylinder cause this? I've sprayed brake clean around the area and didn't notice a change in rpm at all.

DeePa · August 21, 2019

If the valve is indeed opening and closing like the other cylinders I would think it’s something else.

Any way for you to measure lift on the valve? It seems to me that backing off on the preload would cause a worn cam to not open the valve as much. If you pulled the rocker, you could look in at the lifter with a scope or watch how far the pushrod moves. If one is bent, you may not be getting full valve travel.

Are you sure injector 5 is firing? Need to rule out that too...broken wire or something ecm related.

Did you do a compression test yet? How about a leak down test? That would be my next step before tearing down further.

When HP tuners stops counting Misfires, can you pull the plug boot and see if they start happening again?

Edited August 21, 2019 by DeePa

newdude · August 21, 2019

Do you hear any metallic squeaking? We had a 6.0 non DOD in an HD spin a lifter in the lifter guide and made a squeaking noise, you'd think it was a belt or belt tensioner on its way out. That cam was beat, so was the lifter.

I'd compression test and leakdown that cylinder. Also, try swapping a fuel injector and see if the miss follows or stays.

Edited August 21, 2019 by newdude

Sergio Quiroz · August 21, 2019

I don't have any way of measuring valve lift with any sort of accuracy. I will check the pushrod to see if it's bent.

Injector 5 is definitely firing.. I have constant 12v and ECU ground signal to it. Tested with noid light and flickers while engine is running, swapped injectors, can hear it clicking with stethoscope. Wiring looks fine without tearing the harness apart.

Haven't done compression test yet. I'll need to rent or buy a tester.

I'll have to try unplugging the coil while the rocker is backed off to see if misfires come back. Good idea.

I can't wrap my head around why the misfire stops when backing off the rocker... Could the lifter plunger be stuck all the way at the top essentially making it longer and causing that valve to open more than it should? I can see oil squirting out of that pushrod so that tells me the plunger/lifter is doing its job right? I'm still not 100% sure about my intake leak test... I may try that again or take it off to check the gasket. Could a vacuum leak explain the misfire stopping by backing out the rocker?

Thanks for replying by the way. Bouncing ideas definitely helps more than people think.

Sergio Quiroz · August 21, 2019

5 minutes ago, newdude said:

Do you hear any metallic squeaking? We had a 6.0 non DOD in an HD spin a lifter in the lifter guide and made a squeaking noise, you'd think it was a belt or belt tensioner on its way out. That cam was beat, so was the lifter.

I'd compression test and leakdown that cylinder. Also, try swapping a fuel injector and see if the miss follows or stays.

No abnormal noises. If anything I think it's quieter than the valvetrain in my LS3 Camaro.

DeePa · August 21, 2019

Any blowby coming out of the dipstick or pcv system?

Sergio Quiroz · August 21, 2019

45 minutes ago, DeePa said:

Any blowby coming out of the dipstick or pcv system?

No blowby noticed.

I'm buying a leak down tester tomorrow and checking that. Spark plug looked fine so I don't think the head gasket is leaking coolant either. On second thought, since both valves have to be on the base of the lobe for the leak down test would a leak down test even help diagnose anything if the cam lobe is messed up?

DeePa · August 21, 2019

You can always remove rockers as they are just a torque value if I recall right.

When a piston is TDC on compression stroke both valves are closed, so it can be done. Just need to watch both valves.

YakAttack · August 22, 2019

I am going through exact same thing with same cylinder. Done a compression and leak down test and both came back fine.

YakAttack · August 22, 2019

*Check engine light on
*Service Stabiltrak lights on
*RPM fluctuations and surges
*Feel the engine miss inside truck
*Computer reads code of PO305 misfire cylinder 5 , PO300 random misfire and PO171 System to lean bank 1
*Fire to coil
*Fire to plug from wire
*Fire from plug
*Current going to injector (check with noid light)
*Tried swapping coils but still get same misfire on cylinder 5 code
*Compression good at all cylinders as per GM Dealer
*
*All injector orings changed
*Intake gasket changed
*oil pressure sender & filter changed
*Throttle position sensor changed
*Valve cover removed, ran engine and all rocker arms seem to be moving normally (have video on both sides)with engine running *didnt check for any play in rocker arms with engine not running

My next move Saturday will be to remove valve cover and inspect the spring on 5 up and down. Loosen the rocker to see if I can get miss to stop

Sergio Quiroz · August 22, 2019

2 hours ago, YakAttack said:

*Check engine light on
*Service Stabiltrak lights on
*RPM fluctuations and surges
*Feel the engine miss inside truck
*Computer reads code of PO305 misfire cylinder 5 , PO300 random misfire and PO171 System to lean bank 1
*Fire to coil
*Fire to plug from wire
*Fire from plug
*Current going to injector (check with noid light)
*Tried swapping coils but still get same misfire on cylinder 5 code
*Compression good at all cylinders as per GM Dealer
*
*All injector orings changed
*Intake gasket changed
*oil pressure sender & filter changed
*Throttle position sensor changed
*Valve cover removed, ran engine and all rocker arms seem to be moving normally (have video on both sides)with engine running *didnt check for any play in rocker arms with engine not running

My next move Saturday will be to remove valve cover and inspect the spring on 5 up and down. Loosen the rocker to see if I can get miss to stop

Well aren't we lucky! Lol

I've checked play on the rockers and have very little side to side and none up/down which I believe is all normal. I'm guessing my compression test is gonna come out fine too. I can't imagine the lobe having a flat spot affecting compression.

Do you have any noise?

I'm thinking I'm going to put my stethoscope on that rocker bolt and compare to an other one just for the giggles.

Gonna check that pushrod too and make sure it's still straight.

Edited August 22, 2019 by Sergio Quiroz

YakAttack · August 22, 2019

19 hours ago, Sergio Quiroz said:

Well aren't we lucky! Lol

I've checked play on the rockers and have very little side to side and none up/down which I believe is all normal. I'm guessing my compression test is gonna come out fine too. I can't imagine the lobe having a flat spot affecting compression.

Do you have any noise?

I'm thinking I'm going to put my stethoscope on that rocker bolt and compare to an other one just for the giggles.

Gonna check that pushrod too and make sure it's still straight.

So if you remove the rocker you can pull the pushrod out?

Sergio Quiroz · August 22, 2019

Yes, just make sure you're on the base of the lobe. If you're removing the intake side, you can spin the engine til the exhaust valve is open and vice versa. Make sure to torque to 22ft lbs when putting the rocker back on.