Stutters and backfires - clogged cats?

[Rocket Man]

If it was me, I would buy a new one. They’re only $128 on RA. You shouldn’t need anything else, the gaskets are reusable and everything else just transfers over. https://www.rockauto.com/en/catalog/gmc,2007,yukon,5.3l+v8,1433252,engine,intake+manifold,5536

 

[RockGlock86]

So waiting for a intake to get here, and still considering that this somehow could be electrical aswell. Checked all my grounds on the coils and for chassis ground read 11.4 on cyl 1 and 10.7 on 3/5/7, for PCM ground they all 4 read at 12.04 volts. Checked Ohms on the chassis ground at 80ish, and 45ish on the pcm ground. The numbers were fluctuating to fast to get a good read, I'm not sure if that supposed to happen or not. All with key on engine off. Unless this is somehow a bad ecm. I'm not sure how you would check that. I just got it from black bear So I assume its good but who knows. The problem seems to intermittent to be ecm but I do not know alot about such things. Anyone know the signs or symptoms of a cracked intake? I assume it would lead to a lean code, but with the way these things throw rando codes for unrelated issues its hard to tell some times. From what I can tell all of my wiring is correct and operating correctly aswell. I also have a VXDiag on the way so hopefully that will help narrow things down. @iamdub I heard you know about wiring and such.

 

[OR VietVet]

Why would a cracked intake keep it from turning over, I read that in a previous post about 5-6 back. Or did I miss something?

 

[RockGlock86]

@PNW VietVet I think I am dealing with two seperate issues at the same time, The ongoing backfire and lack of power and 351/3/5/7 faults, and now this weird hesitation to turn over that just started happening. I am unsure if one is causing the other, or just happening at the same time.

 

[OR VietVet]

The Z71 that I just bought started and ran great when I first saw it. I then bought it about a week later. Drove home fine. I went to start it 3 days ago and the dash lights came on and when I went to crank the engine, the dash went black and I cycled the key and it would not light the dash and would not crank over. I popped the hood, checked battery cables and the negative cable was very loose. I got out my trusty 5/16" wrench and took off and inspected both cables and they were clean and no corrosion. I installed the cables and put my battery charger on it for 3-4 hours at a slow rate. Has not failed to start since then. Basics first ruled the day.

 

[Rocket Man]

Why would a cracked intake keep it from turning over, I read that in a previous post about 5-6 back. Or did I miss something?

I was only suggesting a possible cracked intake for the misfires on one bank, nothing more. I wasn’t referring to the latest issue with not turning over.

 

[Rocket Man]

The Z71 that I just bought started and ran great when I first saw it. I then bought it about a week later. Drove home fine. I went to start it 3 days ago and the dash lights came on and when I went to crank the engine, the dash went black and I cycled the key and it would not light the dash and would not crank over. I popped the hood, checked battery cables and the negative cable was very loose. I got out my trusty 5/16" wrench and took off and inspected both cables and they were clean and no corrosion. I installed the cables and put my battery charger on it for 3-4 hours at a slow rate. Has not failed to start since then. Basics first ruled the day.

Yessir.

 

[thompsoj22]

slow to turn over? im guessing that your timing/ecm is fubar. as long as you are sure it isnt a mechanical obstruction or low voltage than the timing beingadvanced will create the slow to turn as the cyls misfire on the upstroke. are the cyls misfiring the ones that the new lifters went into? i didnt go back and read but did compression test have good results?

 

[exp500]

Do you see the tach drop or fluctuate? I'm surprised no-one asked about crank position sensor.
Another way to test for manifold crack is spray can test- Use a flammable Brake cleaner, may not see an internal crack. Also, your Ohms test to ground are high. Try directly grounding ecm with alligator clips and retest.

 

[RockGlock86]

Tac does drop and fluctuate with the idle, it is representative of the actual idle and matches my torque pro. Vam position sensor is a month old and also did a cam relearn on it aswell after replacement. I will try out the brake cleaner, just spray some on the Intake while it is running? And for ecm ground just clip to the case of the ecm and to a ground location?

 

[exp500]

Thats correct. Ohms should be less than 1 on ground side, everywhere.
My question on tach is hard to describe properly, but I'll try to explain- usually noticed steady state cruising, like 60-75 or so, and noticing a quick bounce in rpm,usually down, without a noticed missfire. That is a very good indicator of a CPS problem, sensor/harness/system. Usually, on a failing CPS that will happen (if noticed) before missfires detected or felt.
Use your live data scanner and log everything you can think of on a 10 minute freeway run.then review logs.
Also, your injector voltages should be more consistant, varying only about 0.1-0.2 volts low-highest. Look at all grounds especially engine to body and check neg battery cable for failure.

 

[iamdub]

So waiting for a intake to get here, and still considering that this somehow could be electrical aswell. Checked all my grounds on the coils and for chassis ground read 11.4 on cyl 1 and 10.7 on 3/5/7, for PCM ground they all 4 read at 12.04 volts. Checked Ohms on the chassis ground at 80ish, and 45ish on the pcm ground. The numbers were fluctuating to fast to get a good read, I'm not sure if that supposed to happen or not. All with key on engine off. Unless this is somehow a bad ecm. I'm not sure how you would check that. I just got it from black bear So I assume its good but who knows. The problem seems to intermittent to be ecm but I do not know alot about such things. Anyone know the signs or symptoms of a cracked intake? I assume it would lead to a lean code, but with the way these things throw rando codes for unrelated issues its hard to tell some times. From what I can tell all of my wiring is correct and operating correctly aswell. I also have a VXDiag on the way so hopefully that will help narrow things down. @iamdub I heard you know about wiring and such.

Eh. Kinda. Lol

It depends on what about wiring you're questioning. The varying voltages read on those coils could have just been the connection you were getting with your probes. I scratch or twist my probes until I get settled readings.

 

[BentleyArnage]

injector harness? are you sure it is ignition and not fuel related? although backfiring defines timing not necessarily no spark, no shop rags/paper towels left behind in the intake or head ports? if i read the post correctly, you initially replaced all lifters with AFM delete, than had to go back in and replace 4 of those? did you plug/cap the fuel rail during the R&R? If there were only 4 lifters replaced and they were on the drivers side i would guess lifter compatibility problem or debris in the valve port. ie valves staying open, this will backfire like a mother f'er do a compression test on the affected cyls and verify valves seated? im just guessing! hang in there!

You have to change the cam. It's ground differently on the AFM side. Will result in misfire codes.

 

[iamdub]

What if the problems ARE related? A intermittently failing battery (cells can fault internally) or a faulty circuit (loose ground, faulty circuit within the alternator, etc.) can make computers (PCM, BCM, etc.) do funky stuff. The PCM (or BCM) controls the starter relay, which could cause the weird key-crank-but-no-response issues.

 

[RockGlock86]

So to @exp500 the tach did do that and I didn't know the cause just thought a wonky ecu, when I did the AFM delete I smushed the CPS and replaced it and it didn't do it after that.

@iamdub yesterday I pulled all 4 terminals off and the passenger side battery had corrosion under the lugs, but not visible from the outside or without removing the terminal. I scrubbed everything clean, greased it and reassembled. I checked all my other grounds and removed them and wire brushed the contact points and everything got put back together.

I then started the truck again to see if cleaning all grounds and terminals and check voltages, the truck had been running for approx. 30 seconds, still idling very rough and soft backfires, I had my head under the hood looking at stuff and I noticed a huge cloud of white smoke. Turned it off as fast as I could get to it and checked the oil. Looks like chocolate milk and its FULL. I figure that's enough for the night and left it alone.

Today truck wont turn over by key, not at all. Try to rotate by hand, wont rotate at all. I figure I popped a head gasket somehow and pulled all the driver side plugs first seeing as that was the side with the issues and everything looked fine and all clear. Pulled the cyl 2 spark plug gushed coolant out, I guess it leaked down all night and filled the whole cyl.

So both gaskets were replaced when the AFM delete was done last week of July. The driver side was replaced again the third week or so of August when I replaced the lifters. I have a total of 500+ miles on the driver side since the AFM delete and didn't have any issues so not sure how or why it let go. Tomorrow I will replace the passenger side head gasket and go from there. This is getting a little ridiculous.

 

[iamdub]

So to @exp500...pulled the driver side and the cyl 2 spark plug gushed coolant out, I guess it leaked down all night and filled the whole cyl.

So both gaskets were replaced when the AFM delete was done last week of July. The driver side was replaced again the third week or so of August when I replaced the lifters. I have a total of 500+ miles on the driver side since the AFM delete and didn't have any issues so not sure how or why it let go. Tomorrow I will replace the passenger side head gasket and go from there. This is getting a little ridiculous.

Cylinder #2 is on the passenger side ("right side", "right hand side", "starboard side"...)

So, is it the same side that was opened up twice (driver side, left side, port side)?

 

[RockGlock86]

To clarify @iamdub , I pulled the driver side first, 1/3/5/7 and all clear, no issues. So I moved to the passenger side the 2/4/6/8 bank. I pulled cyl 2 first and thats where I got coolant from, only from cyl 2, nothing from 4/6/8. Not from the side opened twice. Sorry for the confusion

 

[Rocket Man]

Hoping it’s just a head gasket. Damn.

 

[iamdub]

To clarify @iamdub , I pulled the driver side first, 1/3/5/7 and all clear, no issues. So I moved to the passenger side the 2/4/6/8 bank. I pulled cyl 2 first and thats where I got coolant from, only from cyl 2, nothing from 4/6/8. Not from the side opened twice. Sorry for the confusion

Well, that kinda makes it a little better, but kinda not. lol

Hoping it's just a defective gasket.

 

[RockGlock86]

I'm not sure how or if this is causing the other issues, the backfire/misfire, the delayed crank. Unless it would leak coolant into the cyl and it was enough that it was trying to compress it rather than burn it and the delayed crank was it trying to turn over with coolant in the cyl and was working over the pressure.