2007 Denali Rough Idle and Stall After Running Long

[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.