GM 6.0l Advice: Read my spark plugs please

[Markk]

Worked on one of our older commercial vehicles today. Replaced the spark plugs, wires and coil packs.

My question is related to reading the plugs I pulled out. Plugs from driver side collectively looked very different than passenger side. Also notable, plugs from passenger site on cylinders 6 and 8 smelled of gas.

With the plug groups looking so different I’m concerned I may have a problem prior to the coil packs. If only 1-2 would have been different I’d have dismissed it as just a bad wire or coil pack.

The truck ran much better after new parts. Only concern is that it stumbles occasionally when applying gas quick from stop. After takeoff engine runs very strong and smooth. I’m considering replacing alternator, based on hunch that it may be losing current at low idle. Seems to stumble more when all lights and AC are on.

Engine is 15 years old with 97,000 miles. I’d welcome any insight or suggestions for what other parts to check out. I plan to pull a new plug from each side in about 1000miles to see if there is any notable difference.

 

[Dixie Highway]

LS engines are notorious for intake manifold leaks (plastic intake), especially in a van with nowhere for the heat to go. I’d be willing to bet there is unmetered air getting in the engine from the passenger side. Carb cleaner sprayed around the manifold while idling should give away the location of the leak.

 

[Markk]

LS engines are notorious for intake manifold leaks (plastic intake), especially in a van with nowhere for the heat to go. I’d be willing to bet there is unmetered air getting in the engine from the passenger side. Carb cleaner sprayed around the manifold while idling should give away the location of the leak.

Do you normally see leaks at the manifold gasket or middle plastic? Gasket replacement sounds manageable. A leak mid plastic seems like it would require manifold replacement?

 

[Neutron]

I would think if you had an intake leak you would get a lean code p0171 or p0172.
Unless GM systems dont recognize lean vacuum leaks

 

[Dixie Highway]

Usually gasket leaks. It’s possible to have a leak and not throw a code, especially if it’s small. Often times the leak isn’t even a factor except for idle/just off idle condition, then the open throttle body negates it. Other times it only leaks while cold.

 

[2kwik4u]

I would pull the valve cover on the "dirty" side and check for valve seal leaks. They aren't common, but those plugs look dirtier than I would expect from a 97k engine. Does the truck puff smoke at startup at all, usually a good indicator of valve seals leaking down into the chamber overnight, or after long periods (day or so) of sitting.

Might also consider a cheap catch can on that truck to help with the PCV valve drainage into the intake tract. The 5.3 in my '03 Yukon, and 6.0 in my '06 TBSS both had oil residue ALL OVER the inside of the intake when I had them off. Put a catch can on the 6.0 and it stayed clean for the short time I had it. Would drain about a cup of oil every 3-5k miles from the PCV system.

The 5.3 required intake gaskets around 120k miles. Took about 2hrs in my buddies driveway with basic hand tools. Helped with driveability a good bit, and the lean codes went away. I'm not sure I would make a special trip on yours based on your reports, but maybe schedule some time in to get it done with the next oil change. They're pretty cheap if I remember right, $30 maybe?

Took me a second to realize it's in a van. I was seriously scratching my head trying to figure out why the firewall looked like that, and why the coils were pointed "backwards".

 

[Sbrown]

Take a look at the driver's side valve cover. The PCV valve is in the back of the valve cover. If it has an actual PCV valve mounted into a grommet in the valve cover, you need to replace the valve cover with an updated unit that uses a fixed orifice type setup. There is a service bulletin about this. It lets too much oil into the intake manifold, which can end up causing excessive oil consumption and fouled plugs along with some driveability issues.

A quick check of the fuel trim PIDS with a scan tool will tell you if you have an intake vacuum leak or not, even if the leak isn't bad enough to set a lean code. GM runs a MASS AIR fuel injection system on most of their vehicles, which are usually pretty sensitive to any lean or rich situations.

The intake leak most of the early LS motors experienced was due to a faulty gasket design which has since been remedied. The earlier gaskets had orange colored elastomer seals set in a rigid plastic frame, the upgraded gasket has green seals. The seals on the earlier version would separate from the frame and get pulled out of shape, thus losing it's sealing ability. Only way to tell which one you have is to take it apart.

 

[Markk]

Take a look at the driver's side valve cover. The PCV valve is in the back of the valve cover. If it has an actual PCV valve mounted into a grommet in the valve cover, you need to replace the valve cover with an updated unit that uses a fixed orifice type setup. There is a service bulletin about this. It lets too much oil into the intake manifold, which can end up causing excessive oil consumption and fouled plugs along with some driveability issues.

A quick check of the fuel trim PIDS with a scan tool will tell you if you have an intake vacuum leak or not, even if the leak isn't bad enough to set a lean code. GM runs a MASS AIR fuel injection system on most of their vehicles, which are usually pretty sensitive to any lean or rich situations.

The intake leak most of the early LS motors experienced was due to a faulty gasket design which has since been remedied. The earlier gaskets had orange colored elastomer seals set in a rigid plastic frame, the upgraded gasket has green seals. The seals on the earlier version would separate from the frame and get pulled out of shape, thus losing it's sealing ability. Only way to tell which one you have is to take it apart.

Here is driver side valve cover. Can you tell if it is the older generation.

 

[Sbrown]

Here is driver side valve cover. Can you tell if it is the older generation.

Looks like it might be, but I need you to pull the hose off to be sure.

 

[Sbrown]

Is there any reason why there is a bolt missing from the No. 8 coil bracket?

 

[Markk]

Is there any reason why there is a bolt missing from the No. 8 coil bracket?

I dropped it and couldn’t find it. Gonna replace it before use.

 

[Markk]

I sprayed carb cleaner all over intake manifold today. Took my time spraying along gasket line then also in the upper parts. Couldn’t get rpms to change no matter where I sprayed. Thinking there’s not a leak?

I also watched for white oil smoke at tail pipe on startup after sitting over a day. No white smoke and no rich fuel smell either. Makes me think PCV valve does not need changing?

Any suggestions on scan tools that are good? Id like to next look and see what the codes can tell me.

 

[Sbrown]

I sprayed carb cleaner all over intake manifold today. Took my time spraying along gasket line then also in the upper parts. Couldn’t get rpms to change no matter where I sprayed. Thinking there’s not a leak?

I also watched for white oil smoke at tail pipe on startup after sitting over a day. No white smoke and no rich fuel smell either. Makes me think PCV valve does not need changing
Any suggestions on scan tools that are good? Id like to next look and see what the codes can tell me.

Probably not, but on modern fuel injected cars, the engine control system is more than capable of making adjustments for some small air leaks in the intake system, so spraying the area with carb cleaner or anything else and just listening for an RPM change is not as reliable a test as it used to be unless the leak is really big, which you would most likely be able hear anyway. To diagnose it accurately, you really need to connect a scan tool and watch the short term fuel trim. If there is a leak, the trim will have gone positive some amount (added fuel). When you find the leak with the choke cleaner, the fuel trim will start dropping back down toward zero, then when you take the carb cleaner away, it'll start climbing again.

The lack of white smoke on startup indicates nothing as far as the condition of the PCV valve is concerned. It's not a PCV valve issue per say, it's more a valve cover baffling issue that allows the PCV system to draw oil into the intake.

As for a scan tool, any of the Launch Millennium series would do what you need. Just pick your price point or the features you want, but any of them will read the codes and reset them if necessary.

 

[2kwik4u]

I sprayed carb cleaner all over intake manifold today. Took my time spraying along gasket line then also in the upper parts. Couldn’t get rpms to change no matter where I sprayed. Thinking there’s not a leak?

I also watched for white oil smoke at tail pipe on startup after sitting over a day. No white smoke and no rich fuel smell either. Makes me think PCV valve does not need changing?

Any suggestions on scan tools that are good? Id like to next look and see what the codes can tell me.

I have been using a cheap ELM327 reader and the Torque App (android only) for many years. It will read and clear codes, as well as read your fuel trims for you. Has some other neat datalogging features as well if you want to dive further into that world in the future.

Best feature is the video camera with GPS and OBD2 data overlay. Makes some interesting videos. I made this video with the Torque App (no OBD2 data, but GPS data used).

 

[Markk]

Finally got around to changing intake manifold gasket today. Also replaced knock sensors, throttle body gasket and O2 sensor. Cleaned throttle body and Mass Air flow. Shocked at how smooth it runs now.

Old knock sensors had no corrosion and read correct at 99 ohms, however since I had new parts I went ahead and swapped.

Working on paint next.