There's something in there...

2005 Prerunner, 2.7L 2TR-FE

I was getting a misfire in Cylinder 4. When I pulled the spark plug, the ground strap and electrode were gone. Just gone. The ceramic was not broken, and there wasn't damage to any other part of the plug. I used a video probe and looked around the cylinder, and couldn't see any foreign material (such as parts of a spark plug..), so I hoped the debris shot out of the exhaust, put in a new plug, and sent it. It worked for a short time, before again getting a misfire in Cylinder 4, with a sound like static, or something bouncing around in my engine... I pulled the plug again, and it showed damage, small impact marks on all sides of the ground strap and face.

At this point, I pulled the head. I didn't find anything in the cylinder(s), but I did see impact marks in the head and on the pistons for cylinders 3 and 4. The valves were all seated, there was no apparent damage to the seats that I could see. I cleaned everything out, and put it back together. It ran fine again for a short period, and started the same again. Cylinder 4 plug shows the same type of impact marks. I don't think it's a rod bearing, because the plug would be smashed flat, not getting dings from all angles.

I'm at a loss at this point. Could a piece of a spark plug be hiding from me, jumping in my cylinder(s) to wreak havoc, then hiding from me again? Bouncing between cylinders?

I'm about to pull my manifolds and video probe to all of the valves and into the manifolds, as well as into each cylinder, but I'm hoping someone (anyone) has some idea of what could be going on.

Notes,
It was an NGK Iridium spark plug that fell apart.
Compression test was good.
I'm going to do a full rebuild (including a new head..) on this before I give it to my son when he's old enough to drive in a few years, I just need it to last me until then.
Cylinders 1 and 2 are clean, no damage. Some carbon but no damage.
All cylinder walls were clean.
No broken pistons or missing pieces.
I rotated the engine until piston 4 was halfway down the cylinder on the downstroke, and tapped the top of the piston, there was no movement at all, it was rock solid.
There is no forbidden glitter in my oil or anywhere at all when I took it all apart.

Original spark plugs:


Plug 4:


Second Plug 4. Notice the dings and dents all over, not a crushed ground strap, I don't think it's from contact with the piston:


Pistons 2 (carbon but no dings) and 3 (no carbon and dinged up):


Pistons 3 and 4, both dinged up.


Head of Cylinder 3:


Head of Cylinder 4:

 

Welcome to Tacoma World. That is a wild problem, never seen that before. Did some amateur Googl'ing for ideas because I got curious and the best theory I read somewhere else is that something hard (likely your chunk of grenaded spark plug) bounced around inside causing the dents. How it traveled from one cylinder to another is the big mystery but theory would be that it could be getting sucked back through the intake valves and due to the way that the intake flows it jumps over to the next bank and vice versa. Still quite a wild theory but only one that made sense to me. I'd to a very thourough check of the valves and intake and see if you can find your missing invader. Or it may have finally been blown out after wreaking havoc on the heads. You can try to smooth out the dents a little bit and run it again, else you might be looking at some machining or a new head later. Good luck, post back if you figure it out since this one is super weird.

 

Sorry for your predicament but if you cant find the scrub spark plug electrode, I suspect that its nestled right on top of your cat. Pull your O2 sensor and scope the top of your cats.

-J

 

Pulled the intake and scoped the intake valves. 3 cylinders (6 valves) were all nicely closed, 1 cylinder (2 valves) were open equal amounts. I don't think this piece of metal is pinched in a valve seat, at least not an intake.

Last time it ran it sounded consistent, not like the piece was bouncing around anymore.

I've decided I'm pulling the head again. If this little piece bounced around and hid from me last time, but is stuck in the head or piston now, I'll have to pull the head again anyway.

It should be faster, easier, and smoother this time, right? I'll update with pictures if or when I find anything.

 

I am so curious as to what is going on here. That seems absolutely insane. Let’s say a piece of grenaded spark plug is bouncing around… what caused it to grenade in the first place?

 

Are you using the wrong length spark plugs?

 

bad rod bearings, excessive play, piston to spark plug contact.

A single piece of metal isnt going to bounce around between difference cylinders.

 

If there were piston to spark plug contact wouldn't that be in all cylinders?

 

Nope. Not all main rod bearings will go at the same time.

 

I don’t think so. Same plug had been in it for a couple years, identical to the other 3.

 

Rod bearing would put forbidden glitter in my oil, and when the piston was on the downstroke it wouldn’t be rock solid when I tap on it with a hammer handle. Also, all of the piston vs. spark plug fights I’ve seen have had much more trauma to the spark plug. Other than missing the electrode itself and the grounding arm, it was pristine, not a single chip in the ceramic.

 

Any chance the plugs are Amazon counterfeits?

It certainly looks like something got in there. My guess is a nail or nails. Look at the top of the picture titled head of cylinder 3. Look very closely, kinda looks like the imprint of a nail.

If you think it’ll help, boroscopes have become affordable and in comparison to the one I bought over 20 years ago for over $2k, they work way better too.

 

A bad rod bearing would have to be knocking too

This is a weird one

 

Where did you buy the spark plugs?

 

How many miles on those plugs?

 

I thought that might have been the electrode from the electrode itself, which seems to have just fallen out of the center of the plug.

I have a small borescope, but it doesn't have the flexibility to go in through the spark plug hole and look back up at the head anyway. I can look around at the face of the piston, that's about it. It came with mirror attachments, but I'm about 90% sure that the first time I use one of them, it'll fall off and I'll have to pull the head to retrieve it anyway.

 

The plugs were NGK Iridium, I got them from one of the local auto parts stores. Decent number of miles on them, I don't remember exactly how many. Probably too many, but I would never have expected one to fall apart.

I got this truck used, there's a chance that some or all of the damage is from something in the past. The plug that came out of cylinder 3 was perfect, so unless this piece bounced between cylinders, up the intake from 4 and back into 3, then again and back into 4 again, I don't know.

Last time I had the head off, I compared the height of the pistons, they were all consistent. That doesn't account for the extra height from centrifugal force, but if the rod bearing was shot, it would normally show as not going as high in the bore as well.

Spent a couple hours last night, pulled everything off, again, so I can play executioner tonight after work .. Off with it's head! (after valve cover, timing cover, timing chain, and cams..)

More pictures coming tonight or tomorrow morning. Either for comparison for changes to the past posted pictures, or a picture of the little [Redacted, I don't know recall the policy for profanity..] if I find it.

 

Strange indeed.

Watching for a good outcome.

 

Based on the impact marks whatever is (was) in there is pretty decent sized. Cant imagine it can hide too many places.

Like J said, Id be curious to know if anything is sitting in the cat

 

Ah gotcha I see what you're saying.

One would think.