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!