Rendom misfire

[ukrkoz]

Sorry for a bit of unclear question, I should have taken snap shot, but for now, I'll shoot blank.
I just bought auctioned 2007 Tahoe.
Engine runs a bit rough, not too bad, and there's random misfire code.
Truck is in my pal's shop, I know him since his age 11, he won't lie to me. So far, he replaced plugs and wires, that didn't help.
He showed me 2 chewed up plugs, one has wire inside really exposed. As I said, I should have taken snap shot of those 2 plugs... they are, facing engine, R hand side close to fuel rail, mid way on engine top. One is red and one is grey I believe. Grey is less chewed up, red one is wire fully exposed.
My gut tells me, that's cause of random misfire, but what do I know. I had Ridgeline once, it had very similar situation. Parked outside, rats got to it, started misfiring, dealer replaced some chewed up wires and problem went away.
It's 5.l Vortec engine.
OK, I found pic of same engine and marked grey plug. Red one is hidden deeper towards firewall, can't see in this pic but arrow points roughly where it's at.
Will those cause misfire?

 

[exp500]

Guessing Game? How many parts can you throw at it at one time? Then you still need to address codes. Start with scanner. We are willing to help if you are willing to do the work.

 

[ukrkoz]

P0300 randomly appearing and disappearing. So much for scanner. Rough idle. So much for symptoms. CEL randomly coming up and disappearing.

 

[wjburken]

As @exp500 stated, you need to start with the basics or you are going to just be throwing a bunch of parts at this hoping one of them actually fixes it.
Please keep in mind that we are not there to see, hear, smell, feel or experience what you are seeing, hearing, smelling, or experiencing so you need to be a little more specific in your descriptions if you are wanting us to help and do not get upset if we ask more questions.

Get a proper scan tool that allows you to see live data and see what's going on and post any and all DTC codes you are getting. The fact that you have chewed up wires going to things definitely needs to be addressed. Is your friend a mechanic or does he just have a large garage that you call his shop? If he is a mechanic, he should be able to tell you what the chewed up wires are going too. Can you get some better pictures of what you are referring too?

 

[gooffeyguy]

The random misfire and rough idle is more than likely a vacuum leak. Check all vacuum and intake hoses for brittleness and cracked or broken ends. Could also be a bad intake gasket. With engine running spray carb cleaner, starting fluid, or even WD 40 along the gasket edges and if the idle speeds up you've found the leak.

Sent from my SM-G930V using Tapatalk

 

[Fless]

Regardless, bare wires need to be fixed.

With your scanner take a look at your short- and long-term fuel trims cold, then warm at idle and 1500 rpm or so. Post those numbers up and let's see 'em.

 

[exp500]

And all your vehicle specifics, including any mods. And including condition of items like coolant tank clean?
Since you don't know the history (auction), My first would be a cooling pressure check, overnight or 4 hours minimum. 2nd, fuel pressure check including a drive (need a long hose to see guage).3rd pull valve covers, look for coolant leaks, maybe even dye check, see 1st. 4th- drive cycle live data, what cylinders misfireing, fuel trims.
Anything less than these and you will never know the condition, and could easily ruin engine from coolant.

 

[wsteele]

The wire bundle you pointed to, might be the one that contains the MAF sensor leads. If so, a fault in those could definitely lead to Random Misfires. As everyone has said, any wiring flaws need to be delt with right away, regardless to whether they do or don't address your specific issues.

 

[ukrkoz]

Thank you.
A bit of update.
It is 2007 Tahoe LTZ, I looked it up through VIN decoder.
Rear air shocks were completely torn, so we replaced them. That didn't help with engine run he he.
Vehicle drove - yes, it drives, just runs rough - a mile away from the original shop to car electrician shop. Spent a week there. He fixed all wires actually, found several more chewed up. Scanned system few more times - all electric checks out on his end.
If he does not determine the cause to random misfires by today, my guy takes it back into his hands today.
Thing is, I know this mechanic since his age 11, and he's closing on 40 soon. He's a very close friend. I do not believe he'll lie to me. Plus, he owned 3 Tahoes, his brother owned and owns several and he repaired numerous ones with similar issue. Which is the one and only left - driveable but rough running engine with now and then random misfire code and no other stored codes. He says, he had everything checked/scanned. Nothing. So he thinks, it's something mechanical thus, not throwing specific error codes.

 

[wsteele]

Thank you.
A bit of update.
It is 2007 Tahoe LTZ, I looked it up through VIN decoder.
Rear air shocks were completely torn, so we replaced them. That didn't help with engine run he he.
Vehicle drove - yes, it drives, just runs rough - a mile away from the original shop to car electrician shop. Spent a week there. He fixed all wires actually, found several more chewed up. Scanned system few more times - all electric checks out on his end.
If he does not determine the cause to random misfires by today, my guy takes it back into his hands today.
Thing is, I know this mechanic since his age 11, and he's closing on 40 soon. He's a very close friend. I do not believe he'll lie to me. Plus, he owned 3 Tahoes, his brother owned and owns several and he repaired numerous ones with similar issue. Which is the one and only left - driveable but rough running engine with now and then random misfire code and no other stored codes. He says, he had everything checked/scanned. Nothing. So he thinks, it's something mechanical thus, not throwing specific error codes.

It would be helpful to know if the misfires happen on both banks, or just one side. That will help with the diagnosis.