Misfiring Continues..No Solution

[YakAttack]

I have a 2012 GMC Sierra 5.3L SL. 

I will post all I have done up until this point. 

I brought to 2 different shops one being a GM service department. None of the shops have went into the engine any deeper than the top end. No head taken off.

 

*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

 

Not sure what could be causing these issues or what else to do. 

Any help or info would be highly appreciated 

TIA.

 

 

[tbarn]

Remove left valve cover. check for broken valve spring. If you are sure both on #5 are ok then reattach the coils so you can run it with the valve cover off. Loosen #5 intake and exhaust rockers slowly  one at a time and see if the miss goes away. Sometimes a lifter will stick in the "up" position as if a solid lifter.

Edited August 21, 2019 by tbarn

[riverbanks]

Had one on here, not to long ago,turned out to be a broken valve spring,not visible to the eye, machine shop caught it,scroll thru past threads,not long ago

[Jsdirt]

Yeah, those beehive springs are tough to find where they're broken.

 

Running compression check will sometimes show that. 

[YakAttack]

22 hours ago, Jsdirt said:

Yeah, those beehive springs are tough to find where they're broken.

 

Running compression check will sometimes show that. 

The compression test ran by dealer showed good on all cylinders. I’m going to pull valve cover on Saturday if I can and do a little more inspecting. Thanks for the info. 

[YakAttack]

I have video with the valve cover off and rocker arms moving but it’s too big to post here 

[Jsdirt]

Any tests done by the dealer, I'd do again myself. Just MHO. As far as the vid goes, upload it to YouTube or Vimeo and link it here.

[YakAttack]

 

[Jsdirt]

Hard to tell over the net, but I'm hearing something in the valvetrain that sounds broken. Sounds like it's in the cam or lifter area. I'm betting one of the lifters may have spun - that destroys the lifter and cam lobe.

 

I think the only easy way to find that out is to measure all the valve travel with a dial indicator, or check the drain plug magnet for excessive metal.

[YakAttack]

So basically pull the oil drain plug and check it. Would it show any metal even though I went through an oil change since it started? What steps would I take in order to measure valve travel. Is that something I could do myself? When the cover is on I don’t get any strange noises, not any loud ticking or anything. Seems I would here something when idling that sounds broken. 

[Jsdirt]

If a lifter spun, there would be quite a bit of fine, and some coarse metal stuck to it. If you didn't notice it during the last oil change, and nothing has changed sound-wise, then I'd move on to the next thing.

 

Measuring with a dial indicator is pretty easy. Good ones are pricey, but for this, it just needs to be consistent - the actual numbers won't matter much. A magnetic base is a must - you'll need to anchor it to the head so that it is SOLID, and will not move. Just stick the pointer on the edge of a valve retainer, zero the gauge, and bar the engine over by hand. It'll be a lot easier if you remove all the plugs, first. 

 

You'll just be looking for one or 2 oddballs of the 16. Since the misfire is only on one cylinder, you can just check the other 6 valves on the non-misfiring 3 cylinders on the bank you already have the cover off of, and not even bother with the passenger side bank. If there's a problem in the valve train, you'll get different numbers on either or both valves of the #5 cylinder.