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Changed Parts. Still Misfiring!! Help Please!

YakAttack
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YakAttack Enthusiast

YakAttack

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I have a 2012 GMC Sierra with 5.3L V8. I started to get a misfire while idling. I plugged in a code reader and got a p0305 code. Misfire on Cylinder 5. I changed plug wires, plugs, coil pack #5, injector #5. When I pulled the connector for each injector I got a difference except for #5. No change. I have swapped coils & injectors and still get the same reaction from only Cylinder 5. Checked for fire and it’s definitely getting fire. Checked the wire connectors with a light and it’s getting current. Just don’t understand why pulling that  wire connector makes no difference and the others do. Also pulled valve cover and rocker arms operating just fine. Everything seems to be in great working order. What could it be? Is it grounding out somewhere before or after the ECM? I’m confused on this one. Any help would be greatly appreciated. TIA

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diyer2
diyer2

It will make a mess but run it with the valve cover off and observe rocker arm movement.  

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AUPlainsman New Member

AUPlainsman

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I had a similar issue with the #1 cylinder. P0301 code. Changed coil, wire, plug. Nothing worked. I took it into the dealership. They found that one of the DOD lifters collapsed. Had all four DOD lifters on that side of the engine replaced. It’s likely the same thing is happening to you. Sorry.  

Edited by AUPlainsman
YakAttack Enthusiast

YakAttack

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6 hours ago, AUPlainsman said:

I had a similar issue with the #1 cylinder. P0301 code. Changed coil, wire, plug. Nothing worked. I took it into the dealership. They found that one of the DOD lifters collapsed. Had all four DOD lifters on that side of the engine replaced. It’s likely the same thing is happening to you. Sorry.  

This model truck has the AFM lifters. But anyways we pulled the valve cover and checked the rocker arms and all seems to be functioning fine. All of them are tight and when pushed down on do not go down with the cam flat. Is it still possible the lifter could be collapsed without any telling signs from the rocker arms? Would a collapsed lifter cause no change in sound when pulling the injector connector plug like the others do? 

YakAttack Enthusiast

YakAttack

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4 hours ago, sefiroxx said:

Did you check the wire with a timing light?

We checked the wire with a test light and everything seems to be getting voltage. Even used a jumper wire and have voltage. 

diyer2 Senior Enthusiast

diyer2

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It will make a mess but run it with the valve cover off and observe rocker arm movement.

 

:)

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YakAttack Enthusiast

YakAttack

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39 minutes ago, diyer2 said:

It will make a mess but run it with the valve cover off and observe rocker arm movement.

 

:)

I done that and had someone with mechanic experience check it out and he said everything was moving as normal. Also while off he had me click the ignition whereas the cam was in the flat position. He checked all the rocker arms for any play and also pushed down on them to see if a lifter was collapsed and none of them had any play or issues. Cylinder 5 which is what the code pointed to has a new coil (getting current), new plug & wire(getting fire) and new injector (which we thought it could be) and still throwing the code for that particular cylinder. We unplugged every connector at each injector and clearly heard a difference in the engine except for 5 which made no diffference in sound. We checked for current at that connector and it’s getting voltage. So we are stumped. I mean if the lifter were to be collapsed at the cylinder wouldn’t there be a sign of it with the rocker arms. Also why would that be the only connector plug when pulled make no difference in engine sound. Could still get something even with a collapsed lifter right? Would pulling the head be the only soulution at checking it? That’s basically a $500 kit for nothing if it isn’t the lifter but I’m not sure what else to do or try or think at this point. Like I said we are stumped. Also the traction control light comes on when sitting in idle. Once it gets rolling it goes off. I put a pic of the valve cover off. 

A3C009E8-C663-4DAC-AA48-C842A128DF1A.jpeg

diyer2 Senior Enthusiast

diyer2

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Posted

Compression check of #5?

Traction control light on at idle is a red flag to me.

If nothing mechanical is found then electrical issue?

 

Regular oil and filter changes?

Mileage?

Are you the only owner?

Second owner?

Point is maybe something in the past is now showing up.

 

:)

Black02Silverado Senior Enthusiast

Black02Silverado

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Compression test/leak down would be the next step.  The cylinder might not have compression so a firing plug will not do anything.

YakAttack Enthusiast

YakAttack

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14 minutes ago, diyer2 said:

Compression check of #5?

Traction control light on at idle is a red flag to me.

If nothing mechanical is found then electrical issue?

 

Regular oil and filter changes?

Mileage?

Are you the only owner?

Second owner?

Point is maybe something in the past is now showing up.

 

:)

Check compression: 110 at cyl 5 and held

Regular Oil & Filter Change

127,000 miles

Second Owner

Never had an issue for the 5 years I’ve owned it. 

Was coming back from TN to Louisiana when about 4 hours into the drive the check engine light came on. Put on code reader. Threw code P0305 & P0300.  Changed plug wires, plugs, injector & coil at Cyl 5. Put back on reader and got same codes. Took it to my father in law who has had mechanic shop in the past and we ran through all things I wrote up above and still has us puzzled. I assume only way to check for collapsed lifter would be to buy a $500 lifter kit and open it up. Not sure where else to turn. Reason I say electrical is that When I pull connector on injector I get no apparent sound difference but I’m getting current in the connector. 

 

diyer2 Senior Enthusiast

diyer2

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Posted

Before a tear down maybe a scan with a Tech 2 scanner?

Dealer or?

May help.

 

:)

YakAttack Enthusiast

YakAttack

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2 minutes ago, diyer2 said:

Before a tear down maybe a scan with a Tech 2 scanner?

Dealer or?

May help.

 

:)

I’m not sure which scanner was used. 3 different times with 3 different people. Got same codes each time. Did a reset and of course check engine light came back and the stabilitrak lights also. Hadn’t brought it to dealer but did bring it to shop and was told collapsed lifter. Wasn’t too confident from the symptoms so that’s why I brought it to someone I trusted who doesn’t think it’s a lifter because of the checks he and I did plus don’t have the ticking noises typically associated with a lifter issue.  

diyer2 Senior Enthusiast

diyer2

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It's my understanding a Tech 2 will do a more detailed diagnosis. 

It will tell if the control modules are having a problem I believe.

 

:)

:)

 

mjm-1957 Enthusiast

mjm-1957

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Posted

Did you check the injector connector with a noid light? The connector has 12 volts on one leg and the ecm grounds the other to fire the injector. The noid light plugs into where the injector would go and shows if the ECM is providing power and ground.

 

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