Misfire on DOD cylinders

[Ceejkay]

Back with a new to me truck. Just got a 2010 Escalade with the 6.2 awd. 180k miles. Been about 8 years since ive owned a gm and little rusty in the troubleshooting.

Truck idles decent in park. A little miss, But when in gear at let's say a stop for a min or 2 it starts misfiring bad and the stablitrack lights up and flashing cel. But as soon as I go within a few seconds it clears. Doesn't feel low on power. And the lights clear. Ran the misfire log on my tech 2, cylinder 4 is the worst followed by 7, 1, and 6. I believe those are all dod cylinders. I bought it used and they did plugs, oil and a few other things and it has the dod obd dongle but the dod delete doesn't appear to be done.

I did check the gap on #4 spark plug and it's good and looks new, they are ac delco plugs. Swapped #2 and #4 coil pack and wire and the problem didn't follow. I don't hear a lifter tap at all. I haven't pulled the valve cover to check yet as it's a little sketchy to do it in gear as that's the only time I really get it. The dod delete with a cam and a few other goodies are going to happen in the future but wanted to get a decent baseline. Any suggestions?

 

[donjetman]

@Ceejkay
Add a catch can. There are hundreds of post here on the subject. Spend a little or a lot, your choice:
https://www.tahoeyukonforum.com/threads/get-a-catch-can-before-any-mods.49716/page-53#post-1288561

Has the the TSB about replacing the poorly designed driver side valve cover been replaced?
https://f01.justanswer.com/ebrock63...il+Consumption,+MIL+ON,+Engine+Runs+Rough.pdf

 

[Ceejkay]

@donjetman ill look into that, it's a new to me vehicle so who knows what's all been done. They did do a tb cleaning before I got it and it did take a couple drives to show up. But on the same hand I've only put about 15 miles on it and haven't really got on it.

 

[swathdiver]

Make sure the plugs are all gapped to .040 and while hard to tell, make sure they aren't the counterfeit 41-110s. Check the wires.

If you do a leakdown and the pistons are good, turn that L94 into an L9H. I say this because people buy those high performance trucks and feed them a steady diet of 87 octane fuel and over time that wrecks the pistons and rings.

Have you checked the trims too? Any exhaust leaks or broken manifold bolts?

 

[Ceejkay]

@swathdiver I did check the gaps and wires. And I couldn't tell you if they are fakes or not. I would be lying if I said I knew what I was looking at for fuel trims. No exhaust leaks that I can hear. And I'm a firm believer of 91/93, my other car is the new Ranger that has never seen a tank of lower octane other than what the dealer put in it when I bought it.

 

[swathdiver]

Well, make sure she has some Top Tier 93 from somewhere or even E85 and check the alcohol content in Fuel Trims with the Tech-2 to make sure it's not out of whack. Than have a look at those misfires again.

 

[Ceejkay]

@swathdiver went and put some chevron 93 in it, 27 gallons to be exact. So good gas. Only about a 5 mile run. Checked the alcohol content and it was sitting at 25%. Did a reset and it's reading more like 3% now. Ran decent with actual fuel trims and then it didn't and everything zeroed out.

 

[swathdiver]

@swathdiver went and put some chevron 93 in it, 27 gallons to be exact. So good gas. Only about a 5 mile run. Checked the alcohol content and it was sitting at 25%. Did a reset and it's reading more like 3% now. Ran decent with actual fuel trims and then it didn't and everything zeroed out.

So she's good now? Tell me about those oxygen sensors. Are they GM OE and have they been changed before?

I learned on these forums that aftermarket sensors don't play nice with the computer system, even Denso not in GM wrapper.

Also learned that factory sensors get lazy after about 100K miles and quit calculating the alcohol content correctly while otherwise working ok to keep trims in check.

If she is good now, check the alcohol content again in 20-50 miles and see if it stays between E0 and E10, trusting that the fuel is good. I got some Shell 93 that calculated to 11% in my tank right now.

 

[Ceejkay]

So she's good now? Tell me about those oxygen sensors. Are they GM OE and have they been changed before?

I learned on these forums that aftermarket sensors don't play nice with the computer system, even Denso not in GM wrapper.

Also learned that factory sensors get lazy after about 100K miles and quit calculating the alcohol content correctly while otherwise working ok to keep trims in check.

If she is good now, check the alcohol content again in 20-50 miles and see if it stays between E0 and E10, trusting that the fuel is good. I got some Shell 93 that calculated to 11% in my tank right now.

Nope she's not good at all. Misfires are still hitting and feel even worse. It's doing it even in neutral now. When it starts missing really hard the fuel trims all go to zero. Cylinder 4 is still the worst. I haven't looked at the O2 sensors yet but they seem to be reading around .700-.800.

 

[swathdiver]

Nope she's not good at all. Misfires are still hitting and feel even worse. It's doing it even in neutral now. When it starts missing really hard the fuel trims all go to zero. Cylinder 4 is still the worst. I haven't looked at the O2 sensors yet but they seem to be reading around .700-.800.

So the high alcohol content, even though wrong, was adding fuel. Trims at 0% is good. The upstream sensors ought to be moving up and down through their full range, those are the B1S1 and B2S1 sensors. The downstream sensors ought to remain pretty steady. If they are moving like the upstream sensors, you have a bad cat on that side. Don't think that's your issue.

From the shop manual:

The above is for a base engine misfire without internal engine noises.

Since you just got this, check that injector harness and make sure none of the plugs is on the wrong cylinder. My mechanic helper did that to me once! I was going crazy for a while trying to figure out why she was misfiring all of a sudden!

 

[j91z28d1]

if the trims lock to zero when it starts missing badly. it might be dropping out of closed loop.

 

[Ceejkay]

if the trims lock to zero when it starts missing badly. it might be dropping out of closed loop.

I figured that out shortly after posting. So right now I only get 2mins to look at stuff before it zeros out.
@swathdiver so next steps I was going to do was pull the injectors, do a bench test of #4. Then put it in the #2 hole and vise versa. Also make sure all the connectors are correct and plugged in. If that doesn't seem to rectify it or if it doesn't follow, I'll pull the pass side valve cover and see if the lifters are working as they are supposed to.

Also have a full BTR vvt/DOD delete with truck Norris cam on the way. I'd like to get this fixed so I can get a decent data log to black bear, but if the lifters are the problem it won't matter either way.

 

[Ceejkay]

So did some more troubleshooting I guess you would say. Ran a compression test, probably should have started there. All the afm cylinders were low like 125-140 low while the other 4 were about 180-185. Pulled the valve covers and rocker arms were not sloppy and moved as they should while running. Plus side I have the pre tsb driver valve cover and will address that once the engine comes apart.

I'm thinking the afm switch or sensor what ever it is that controls that system, is failing or the valves have some serious build up. None the less ran some seafoam in the vacuum line and now letting it sit for a bit. Doubt that will clear anything up but you never know.

 

[Fless]

Is that PCV hose cracked or just an illusion?

 

[Ceejkay]

@Fless i think it's an illusion. It's pretty caked.

 

[donjetman]

You might want to do a piston/combustion chamber soak. The bad pcv in the driver side valve cover can stick the piston rings in their groove. Doing this and a new rear main seal cured my oil consumption 6+ yrs and 68k miles ago. Today it has 198k miles and never needs any makeup oil between 5k mile changes.
https://www.tahoeyukonforum.com/threads/2007-denali-cylinder-6-oil-foul.115601/page-2#post-1394161

 

[Ceejkay]

@donjetman since it's all my dod cylinders I'm not 100% sure the full soak is needed. I will be curious how it looks when I pull it apart.

 

[donjetman]

@Ceejkay
My, and most all, 07&08 6.2L L92 engines did NOT come with AFM/DOD. But it was a mess when I bought it 6+ yrs and 68k miles ago w/130k. Immediately in 2018 I did the rear main seal, TSB = TSB# 10-06-01-008M , catch can, torque converter + seals, oil pan & o-ring.
This last June of 2024, for preventative mx, I changed the valley cover, cam position sensor, VVT magnetic pu, oil pump tube o-ring again, crank pulley & seal, oil pressure sender, all new gaskets, cleaned parts inside and out: https://www.tahoeyukonforum.com/threads/valley-cover-crank-pulley-etc.149036/