2007 Denali Rough Idle and Stall After Running Long

[General Stalin]

Have done a search and found a handful of threads for this similar issue but nothing all too conclusive on a solution, but I have a hunch and wondering if anyone else has had this issue and fixed it.

I have a high mileage 07 Denali (195k) and about 3 months ago at the tail end of a long day of driving it bogged down and stalled while on on the highway. I was able to pull it off the road and tried to restart but it would not stay running. Would fire up, idle rough for about 5 seconds, then stall. I thought it might be an oil pressure issue as the piston rings are worn and it burns a lot of oil. Called a buddy to bring me a couple quarts to see if that would get her running. After waiting for about 45 minutes my buddy showed up, I dumped some oil in it, and it it fired it up and ran fine. Drove it back home and hadn't experienced the problem again until a couple months later. Was driving back from an event and same thing - this time it stalled while in stop and go heavy traffic on the highway. Was able to limp it off the road and into a gas station. I put a bunch of oil in it again right away but that did not fix it this time. Still rough idle when starting then stalls soon after. Had it towed home and replaced the battery as it was old. Next day it started fine and had been running fine since the other day.

Had the same issue just a few days ago sitting in a parking lot letting it idle for a while. Was waiting for someone in a grocery store and wanted to have the AC on because it was hot so I was sitting with it running for a while. Started to bog down just sitting in the parking lot so I shut it off. Had the exact same issue... rough idle/stalling at low RPM didn't want to stay running. Let it sit overnight and next day drove it home fine.

Now here's the nuts and bolts:

It has two relevant codes - Fuel pump relay, and Catalytic Converter. The fuel relay I'm actually pretty sure is NOT the issue as this popped up only because I removed the relay when doing a wet and dry compression test on the motor. I bought a new fuel pump but have NOT installed it yet as I don't think that is the issue - as the problem is not consistent with a bad pump. Wouldn't make sense that the pump would only have issue when running for a long time, and would magically work after it sits for a while.

Here's my big question: could the cats be causing this?

As I mentioned my truck burns a LOT of oil. This has likely ruined the catalytic converters (which is why they are throwing codes) and since this rough idle/stalling issue only happens when the truck has been running for an extended period of time, I'm wondering if the cats are clogging up the exhaust when they get hot. Thoughts? Anyone else experience these same symptoms?

 

[Jedig33k]

Have done a search and found a handful of threads for this similar issue but nothing all too conclusive on a solution, but I have a hunch and wondering if anyone else has had this issue and fixed it.

I have a high mileage 07 Denali (195k) and about 3 months ago at the tail end of a long day of driving it bogged down and stalled while on on the highway. I was able to pull it off the road and tried to restart but it would not stay running. Would fire up, idle rough for about 5 seconds, then stall. I thought it might be an oil pressure issue as the piston rings are worn and it burns a lot of oil. Called a buddy to bring me a couple quarts to see if that would get her running. After waiting for about 45 minutes my buddy showed up, I dumped some oil in it, and it it fired it up and ran fine. Drove it back home and hadn't experienced the problem again until a couple months later. Was driving back from an event and same thing - this time it stalled while in stop and go heavy traffic on the highway. Was able to limp it off the road and into a gas station. I put a bunch of oil in it again right away but that did not fix it this time. Still rough idle when starting then stalls soon after. Had it towed home and replaced the battery as it was old. Next day it started fine and had been running fine since the other day.

Had the same issue just a few days ago sitting in a parking lot letting it idle for a while. Was waiting for someone in a grocery store and wanted to have the AC on because it was hot so I was sitting with it running for a while. Started to bog down just sitting in the parking lot so I shut it off. Had the exact same issue... rough idle/stalling at low RPM didn't want to stay running. Let it sit overnight and next day drove it home fine.

Now here's the nuts and bolts:

It has two relevant codes - Fuel pump relay, and Catalytic Converter. The fuel relay I'm actually pretty sure is NOT the issue as this popped up only because I removed the relay when doing a wet and dry compression test on the motor. I bought a new fuel pump but have NOT installed it yet as I don't think that is the issue - as the problem is not consistent with a bad pump. Wouldn't make sense that the pump would only have issue when running for a long time, and would magically work after it sits for a while.

Here's my big question: could the cats be causing this?

As I mentioned my truck burns a LOT of oil. This has likely ruined the catalytic converters (which is why they are throwing codes) and since this rough idle/stalling issue only happens when the truck has been running for an extended period of time, I'm wondering if the cats are clogging up the exhaust when they get hot. Thoughts? Anyone else experience these same symptoms?

Nothing like that, but they should be able to test you CAT for free at a muffler shop. I had similar codes, but my stalls were when hauling a trailer in hot weather. Also, besides adding oil, have you changed the oil plus all the other fluids that need to be changed due to mileage?

 

[Rocket Man]

At 195 k ifthose are the original cats I'm sure they're gone. And yes if they're plugged it will cause those issues and get worse the hotter they get. And if you shut it off and let it cool down they can open up again until they get hot. Have a shop check them.

 

[swathdiver]

Probably the cats Uncle Joe. What codes are you getting? How long does it take her to burn a quart of oil?

 

[General Stalin]

Thanks for the tips and info guys, especially Rocket Man. I have an update, but first to answer questions:

Probably the cats Uncle Joe. What codes are you getting? How long does it take her to burn a quart of oil?

Tell-tale p0420 code. Banks 1 and 2. Had 6 of them sitting on my ECM. Also had a bank 1 lean code and some other irrelevant stuff (suspension compressor exhaust error).

I probably burn a quart every couple tanks of gas at this point.

Now onto the nitty gritty
---------------------------

I used an infared thermo to check the cats at operating temperature and they were about the same temperature on the inlet and outlet which was telling me they weren't doing their job so I made the decision to pursue replacing the cats. I returned the fuel pump and bought 2 new Magnaflow universal catalytic converts and planned to weld them onto my Y-pipe.

Long store short - this fixed the issue.

New cats are in the truck right now and the CEL is off and it seems to be running fine. In fact I went for a 50 mile drive today and back and it had zero issues. I did not replace any of my O2 sensors either.

----------------------------

Now the next issue is that the motor still burns oil, and if I don't address this in the near future then my new cats will surely get ruined too. Also sweats/seeps oil from someplace(s) as well that I can't seem to pinpoint. It's not the oilpan as I replaced the oilpan gasket last year and it seems fine there. I don't think it's the head gaskets or intake gasket as I have had zero heat issues or coolant loss/leakage. Maybe valve covers/cover gaskets? I'm pretty sure that the oil burning issue is due to worn out piston rings though, which will basically require an engine rebuilt/replacement. I did do dry/wet compression test and did not see an higher compression in the wet test which tells me I'm not getting a good oil seal around the pistons.

 

[General Stalin]

UPDATE::::

Good new and bad news.

Bad news is that replacing the cats apparently did NOT fix the problem despite the fact I have taken the truck on two 2+ hour-long drives since then with zero issues - today I drove about 120 miles roundtrip with no problems then parked my truck at my house for a few minutes before heading into my office. Get back in the truck and it started real ******. Long sputtery crank, but it fires up. Drove about 5 minutes and it died waiting at a red light. The exact same way it died in the past. Sputtery and bogging at low rpm then stall. Put it in park and sat until light turned green then fired it back up and drive back home. Parked in front of my house and it stalled as I was parking it.

Not sure what the problem is here anymore. No engine light came on. I haven't checked if it threw any codes yet but will run to oreilly and check in just a bit.

But now the good news:

Found a junkyard right in town that just got a truck in that has my same motor. Going to pull it tomorrow. Depending on what kind of shape it is in I might just clean it up a bit and swap it directly into my truck, but that is TBD. If it needs work I'll rebuild it then swap it in when ready. If it doesn't then I'll swap it in right away and rebuild my current motor.

 

[General Stalin]

Brought it to oreilly and code reader found zero codes. Also that junkyard motor was yanked before I could get to it. These 6.2's don't last long in pick yards.

So the only mildly good news is that after talking to a fellow gearhead buddy of mine he impressed upon me that my oil burning issue likely is not the piston rings but rather the cylinder heads. Probably losing oil through the valves. If that is the case I can just pull the top end of the motor apart and have the heads machined for WAY less work and money than replacing the motor.

This still likely doesn't explain this stalling issues though. I'm pretty stumped.

I replaced the air filter and cleaned up the TB with some CRC throttle body cleaner.

 

[Rocket Man]

Brought it to oreilly and code reader found zero codes. Also that junkyard motor was yanked before I could get to it. These 6.2's don't last long in pick yards.

So the only mildly good news is that after talking to a fellow gearhead buddy of mine he impressed upon me that my oil burning issue likely is not the piston rings but rather the cylinder heads. Probably losing oil through the valves. If that is the case I can just pull the top end of the motor apart and have the heads machined for WAY less work and money than replacing the motor.

This still likely doesn't explain this stalling issues though. I'm pretty stumped.

I replaced the air filter and cleaned up the TB with some CRC throttle body cleaner.

How about cleaning the MAF? I had stalling issues before and it turned out to be a MAF that was failing so you could always try a new one.

 

[kbuskill]

I would start by cleaning the MAF as @Rocket Man suggested to try and see if that helps your stalling issue... although I would investigate the possibility of your fuel rails getting super heated and causing a vapor lock situation. This seams to be a somewhat common issue with the 6.2L. The next time it stalls try bleeding some fuel off at the Schrader valve on the fuel rail and see if it makes any difference. If it does wrap your fuel rails and lines in a decent heat shield like the foil backed fiberglass wrap they use for starters.

As for the oil consumption...

I am confused about how you can lose oil through the valves. The only way oil, or anything else, could pass beyond the valves when they are closed would be if there was a leak... like a burnt valve, which would be obvious from the miss it would create.

The more likely culprit is gummed up piston rings caused by oil ingestion via the PCV system.

Once the engine starts ingesting oil through the intake from the PCV it only gets worse unless you stop the oil from getting into the intake and then do a good cleaning.

I would install a catch can and then do a good deep cleaning with water to decarbonize the combustion chambers and pistons and maybe even a good top end cleaning by soaking the pistons with Kreen.

 

[Rocket Man]

Oil can be lost through bad valve seals but the telltale sign of that is a large amount of smoke at startup after sitting for awhile.

 

[kbuskill]

Oil can be lost through bad valve seals but the telltale sign of that is a large amount of smoke at startup after sitting for awhile.

Valve seals yes.... but that isn't the way it sounded to me in his post.

 

[General Stalin]

Valve guide seals is what I was referring to.

Will try cleaning the MAF and go from there. If I chase the potential valve seal issue then I may as well strip the top of the motor down anyway, clean and replace parts as I go along.

 

[Rocket Man]

Valve guide seals is what I was referring to.

Will try cleaning the MAF and go from there. If I chase the potential valve seal issue then I may as well strip the top of the motor down anyway, clean and replace parts as I go along.

Valve seals are pretty easy to replace; pull the valve covers and rocker arms, get a compression tester and hook it up to a compressor so you can pressurize a cylinder and keep the valves from falling down. Then it's just a matter of using an LS valve spring compressor and a pick tool to pull the keepers out. Remove the spring, pull the seal and replace it. You can do them all in an afternoon. I did mine but replaced the springs with duals for my cam and the only real hard part was installing the dual springs but the singles are easy.

 

[Warriorpluto]

Ever find out the problem?

 

[General Stalin]

Haven't had the time to get into my heads but did clean my MAF sensor. No good or bad news to report. Tough to test if anything I do works because as it's been shown, this issue is intermittent and only happens after I've run the engine for an extended period of time (hours, it seems).

While it may be Overkill, I'm thinking of completely taking my heads off and sending them out to the shop for a valve job just to eliminate any other top end possibilities. This will also give me the opportunity to inspect the intake and gasket condition, as well as re-gasket everything.

 

[General Stalin]

It's been a while with little progress made as I've been busy with other things but here is an update: Cleaned my throttle body, replaced air filter, and cleaned MAF as stated in last post but issue still remains and is actually getting worse it seems. Its been really hot out and that seems to exacerbate the problem. It stalled multiple times over the weekend on relatively short trips driving in traffic. Symptoms are still the same:

After some time driving engine will sputter and bog down at idle then stall. When it is sputtering and RPMs are dropping I can pump the gas pedal and it does nothing - engine just chugs a bit then stalls. I can turn it off for a few seconds then turn it back on and it will start and drive as long as I keep the RPMs up.

With the hotter air temperature seemingly making the problem worse/more frequent, then this vapor lock issue that was brought up earlier by kbuskill seems to make some sense. Will start looking into that.

 

[General Stalin]

Sorry for the triple post but after doing just a little research the symptoms I'm having seem about 100% inline with a vapor lock issue. Engine starvations/backfiring/stalling at low RPM in hot weather and high elevation (I live up in the mountains).

So now looking at my next move. New higher-pressure fuel pump? Insulate my fuel rails?

It's odd that I did not have this problem at all last summer or the summer before that.

 

[swathdiver]

It's been a while with little progress made as I've been busy with other things but here is an update: Cleaned my throttle body, replaced air filter, and cleaned MAF as stated in last post but issue still remains and is actually getting worse it seems. Its been really hot out and that seems to exacerbate the problem. It stalled multiple times over the weekend on relatively short trips driving in traffic. Symptoms are still the same:

After some time driving engine will sputter and bog down at idle then stall. When it is sputtering and RPMs are dropping I can pump the gas pedal and it does nothing - engine just chugs a bit then stalls. I can turn it off for a few seconds then turn it back on and it will start and drive as long as I keep the RPMs up.

With the hotter air temperature seemingly making the problem worse/more frequent, then this vapor lock issue that was brought up earlier by kbuskill seems to make some sense. Will start looking into that.

If you have active contaminants leaking into your exhaust, they may have killed the new cats. Get a junkyard y-pipe, hollow out the old cats and see if your problem goes away. What kind of adhesive did you use on the new intake gaskets? The wrong adhesives can kill cats and O2 sensors.

Uncle Joe, this has been going on for three months plus now. If you had a Tech2, the problem would've been solved a long time ago. It would have paid for itself already.

 

[General Stalin]

I have access to a dealership technician's code reader. It is not throwing any cat/O2 codes. It is not throwing any codes at all actually. My motor burns oil, but there is no way some burnt oil killed these brand new cats in a matter of a couple months. For the gaskets: driver's side has a O-ring gasket that I sealed with high-temp RTV and the passenger side is just a donut that I reused.

 

[swathdiver]

I have access to a dealership technician's code reader. It is not throwing any cat/O2 codes. It is not throwing any codes at all actually. My motor burns oil, but there is no way some burnt oil killed these brand new cats in a matter of a couple months. For the gaskets: driver's side has a O-ring gasket that I sealed with high-temp RTV and the passenger side is just a donut that I reused.

The scan tool can see other things, its not just for codes. It can run a graph of your O2 sensors, check for misfires, see if the sensors are up to par even if they're not out of line enough to throw codes. If you motor just dies, there's got to be some indication within the computer system that will shed light on why.

As for the RTV, check to make sure it is cat and O2 sensor friendly. But something else might have killed them or maybe they're fine.

I use these to inspect barrels:

https://www.amazon.com/dp/B01CL1QUC...colid=5Z8RL5YK3XLO&psc=0&ref_=lv_ov_lig_dp_it

You could pop an O2 sensor out and stick this in there and have a look at both sides to check their condition. You could even pull a spark plug and see the combustion chamber with it. They also make a 3.5 mm camera for a dollar or two more.