2010 Burb Misfire

[solli5pack]

Hey everyone. I've been chasing an intermittent misfire on my 5.3 Suburban that I think I figured out but looking for some advice to confirm. So the truck only misfires first thing in the morning after sitting all night setting off the engine light and the stabilitrack/traction control off messages with white smoke coming out of the tailpipe. After running for a few minutes it clears up and runs fine for the rest of the day. Using the Tech 2 I verified the misfire to cyl 4 only. I eliminated plugs, wires and coil by moving them around and misfire stayed on 4. I haven't been able to check fuel pressure when it's running bad but later in the day it idles at 43psi which I believe is good for a flex engine and all the injectors passed the leakdown test with the scanner. Fuel trims also look fine. I took a shot in the dark and replaced the intake gaskets and thought I got lucky after pulling the intake and had oil pouring out of it which led me to install the new style valve cover. I ran great for a couple of days but the misfire returned. So noticing that I've been losing coolant slowly with no sign of a leak anywhere I decided to pull the plug on 4 first thing in the a.m. before running and I found coolant on it. As far as I know only way for coolant to get into the cyl is a failed head gasket or cracked head. Never really had any engine issues in the past and the truck never overheated so I just find it weird the gasket/head would go bad. I did a quick compression test on cyl 4 and it came in at 150 which I believe is good. So my next steps is going to be a proper compression test on all the cylinders and a leakdown test on 4 and see if I get bubbles in the overflow tank. I guess then I'll know for sure. Just don't understand why it happens only on first start up in the morning. Maybe it's a small leak and when the engine warms up it seals? and only cyl 4? Oil looks clean by eye but I did find sludge under the oil cap, picture below. Engine has 168,000 miles and not sure if it matters but I've been using a Range Tech AFM disabler since November. What do you guys think?

 

[Geotrash]

Hey everyone. I've been chasing an intermittent misfire on my 5.3 Suburban that I think I figured out but looking for some advice to confirm. So the truck only misfires first thing in the morning after sitting all night setting off the engine light and the stabilitrack/traction control off messages with white smoke coming out of the tailpipe. After running for a few minutes it clears up and runs fine for the rest of the day. Using the Tech 2 I verified the misfire to cyl 4 only. I eliminated plugs, wires and coil by moving them around and misfire stayed on 4. I haven't been able to check fuel pressure when it's running bad but later in the day it idles at 43psi which I believe is good for a flex engine and all the injectors passed the leakdown test with the scanner. Fuel trims also look fine. I took a shot in the dark and replaced the intake gaskets and thought I got lucky after pulling the intake and had oil pouring out of it which led me to install the new style valve cover. I ran great for a couple of days but the misfire returned. So noticing that I've been losing coolant slowly with no sign of a leak anywhere I decided to pull the plug on 4 first thing in the a.m. before running and I found coolant on it. As far as I know only way for coolant to get into the cyl is a failed head gasket or cracked head. Never really had any engine issues in the past and the truck never overheated so I just find it weird the gasket/head would go bad. I did a quick compression test on cyl 4 and it came in at 150 which I believe is good. So my next steps is going to be a proper compression test on all the cylinders and a leakdown test on 4 and see if I get bubbles in the overflow tank. I guess then I'll know for sure. Just don't understand why it happens only on first start up in the morning. Maybe it's a small leak and when the engine warms up it seals? and only cyl 4? Oil looks clean by eye but I did find sludge under the oil cap, picture below. Engine has 168,000 miles and not sure if it matters but I've been using a Range Tech AFM disabler since November. What do you guys think?


View attachment 402140

You're doing/planning to do all of the things I would to narrow it down. That cap looks like it's showing signs of dark coolant foaming deposits, so there's that. How does the oil look on the dipstick? There are rare cases of cylinder heads cracking on these - more on the 823 heads on 6.2's between the valve seats than on the 5.3 heads. Head gasket leaks are also rare but not impossible - especially if it's been overheated with doesn't seem to be the case here.

Let us know what the leakdown test reveals. You might be sending the heads out for inspection afterwards. :-(

 

[solli5pack]

You're doing/planning to do all of the things I would to narrow it down. That cap looks like it's showing signs of dark coolant foaming deposits, so there's that. How does the oil look on the dipstick? There are rare cases of cylinder heads cracking on these - more on the 823 heads on 6.2's between the valve seats than on the 5.3 heads. Head gasket leaks are also rare but not impossible - especially if it's been overheated with doesn't seem to be the case here.

Let us know what the leakdown test reveals. You might be sending the heads out for inspection afterwards. :-(

Oil on the dipstick actually looks pretty good. Definitely not a milkshake. The stores near me don't rent the leakdown tester so I'm gonna have to buy one. Any suggestions? Harbour Freight has one for $80 and Amazon has one for $25. I don't usually like buying cheap tools though.

 

[swathdiver]

It's a blown head gasket or cracked head. Probably the former since it goes away as the motor heats up. Either way, not a terrible repair.

 

[solli5pack]

It's a blown head gasket or cracked head. Probably the former since it goes away as the motor heats up. Either way, not a terrible repair.

Agreed. Once I verify with the leakdown tester I'm going to tear into it end of week/weekend.

 

[solli5pack]

So I did the leakdown test last night and the Cyl passed. I put 70lbs of air on it and it only leaked down to 66lbs. Is 70lbs enough? I didnt want to push it. So now I have more questions than answers. Since the issue only seems to happen with a completely cold motor I might redo the test first thing in the morning and see what happens. Also I'm thinking about renting a coolant system pressure tester and pulling the valve cover to see if anything shows up. I saw a video where the heads get hairline cracks around the head bolts and coolant can seep up through there. I'm 99% positive that there's coolant on the plug when I pull it first thing in the morning so it's gotta be something around there. I did another compression test on bank 2 with cyl 2 @ 155lbs, cyl 4 143lbs, cyl 6 150lbs and cyl 8 I have no idea how I would ever get the tester hose to screw into the sparkplug port so I didn't read that one. And of course this morning it ran great. I'm thinking because I had all the plugs out and cleaned out the cyl with air. I'm sure the issue is going to come back shortly.

 

[solli5pack]

So I did the leakdown test last night and the Cyl passed. I put 70lbs of air on it and it only leaked down to 66lbs. Is 70lbs enough? I didnt want to push it. So now I have more questions than answers. Since the issue only seems to happen with a completely cold motor I might redo the test first thing in the morning and see what happens. Also I'm thinking about renting a coolant system pressure tester and pulling the valve cover to see if anything shows up. I saw a video where the heads get hairline cracks around the head bolts and coolant can seep up through there. I'm 99% positive that there's coolant on the plug when I pull it first thing in the morning so it's gotta be something around there. I did another compression test on bank 2 with cyl 2 @ 155lbs, cyl 4 143lbs, cyl 6 150lbs and cyl 8 I have no idea how I would ever get the tester hose to screw into the sparkplug port so I didn't read that one. And of course this morning it ran great. I'm thinking because I had all the plugs out and cleaned out the cyl with air. I'm sure the issue is going to come back shortly.

So I rented the coolant system pressure tester and of course the system stayed solid @ 17lbs with no loss for 2hrs so far. I'm going to leave it on all night and see what happens. I did the test on a cold motor. I pulled the valve cover and found more evidence of coolant in the oil with some white sludge under the cover and in the oil fill tube. Also I'm noticing that oil pressure is up which I was told is also another indicator of coolant in the oil. I know there is coolant in cyl 4 so I'm going to move forward with the idea that the leak is only occurring under a certain condition that I haven been able to recreate but either way the head needs to come off. I'm gonna start tearing it down tomorrow and get the head to the machine shop on monday.

 

[Geotrash]

So I rented the coolant system pressure tester and of course the system stayed solid @ 17lbs with no loss for 2hrs so far. I'm going to leave it on all night and see what happens. I did the test on a cold motor. I pulled the valve cover and found more evidence of coolant in the oil with some white sludge under the cover and in the oil fill tube. Also I'm noticing that oil pressure is up which I was told is also another indicator of coolant in the oil. I know there is coolant in cyl 4 so I'm going to move forward with the idea that the leak is only occurring under a certain condition that I haven been able to recreate but either way the head needs to come off. I'm gonna start tearing it down tomorrow and get the head to the machine shop on monday.

Solid plan. Thanks for the update.

 

[solli5pack]

Anyone have any advice dealing with the exhaust manifold bolts? I haven't tried them yet but the look rusty and I'm thinking they're gonna be a pain. I was going to use some kind of penetrating fluid but not sure how it can work itself down to the threads.

 

[donjetman]

Heat/propane torch
or PB Blaster
smack it with a hammer wo/damaging it
When turning the head/bolt go back and fourth