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Hi all, brand new member here! Go easy on me...

I drove my 2008 Escalade ESV about a couple weeks ago down the street, and the check engine light comes on (flashing), followed by the dreaded Stabilitrak error. The engine is very choppy and shaky, especially at low RPMs. My OBD2 shows code P0300 - engine misfire, multiple/random cylinders. OBD2 data shows misfires on cylinders 2 and 4.
In the meantime, I've done quite a bit of research on this. I'm not a mechanic, but I'm also not afraid to get my hands dirty, and have done some of my own car repairs.
So that being said, this is what I've done so far:

1. Replaced all 8 spark plugs and spark plug wires with AC Delco. Cleared codes. Started engine - same code P0300 returns, with misfires on 2/4.
2. Swapped 2/4 coils with 1/3. Cleared codes. Started engine - same code returns, misfires on 2/4.
3. Checked positive electrical signal to fuel injectors. When key is in ON position, there is a constant signal. Seems good to me.
4. Checked negative electrical signal to fuel injectors from ECM. When engine is started and running, I do see a fast "flashing" signal, which is what I would expect.
5. Removed fuel rail and all fuel injectors. Cleaned injectors by soaking them in fuel injector cleaner, and also blowing carb cleaner through them under charge. Although the cleaner was quite dark in color after I was done, they now appear to be very clean with no problems. Swapped injectors on 2/4 with 1/3 to be sure. Cleared codes, started engine - same code P0300 returns, with misfires on 2/4.
6. Removed passenger side valve cover. Rocker arms look good. I removed the arms and pulled out the push pins. Straight as an arrow. I have not yet put the rocker arms and push pins back in and tested, but am expecting the problem is still there.

So what else should I try? The only other things I can think of that it could be are:
1. Bad electrical connection somewhere.
2. Bad ECM.

Am I missing anything? Thank you so much for your help!
 

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Looks like you have been busy!! Maybe carbon on the valve stems causing your misfire , I would do a running compression test on all cylinders. Get a can of top engine Cleaner at auto zone and drive it hard this may help.
 

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Welcome. My apologies to others whom I’ve not said that to recently.

I’ll use your initial post to refer others for misfire situations. Nice job, very thorough. Good advice on fuel system clean. Spray the mass air flow sensor with your favorite recommended cleaner too. That should do it.

FYI just saw a post where a guy left his truck at a quickie lube and they cleaned his fuel system with a pressurized delivery system through the intake, started the motor and walked away. Long story short they claimed the delivery system malfunctioned and delivered the cleaner all at once.

The motor hydro locked because the technician didn’t know to monitor the cleaning process. It was allowed to sputter until the motor lost compression in two cylinders.

I also watched another tech in a situation similar to yours who verified compression was ok and moved on to completing the above suggestion and what you’ve already done. The pressurized fuel system cleaner & MAF clean cured the misfire.

I’ll bet your close.


Sent from my iPhone using Tapatalk Pro
 

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Sounds like all electrical connections and fuel has been gone through. That's a lot of good troubleshooting and a lot of swapping.

After looking at the pushrod, next thing is the bumpstick. If you wanted to get super technical, you could set up a dial indicator and rotate the motor by hand to see if you get similar lift readings from valve to valve. Wouldn't be the first time a soft cam lobe was worn down..

But, before that, a leak down test is warranted. Who knows.. motor could've been overheated in the past or a beer cap could've been sucked thru from a prior owner drunken K&N filter installation.. you just never know..
 

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Yea, but, he already swapped coils around and the problem stayed with the cylinder
 
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