Hey guys,

I recently picked up a 2006 v8 4wd with 160,000 miles on it. It was being sold as is for engine trouble so I picked it up for a steal. The dealer was quoting the poor lady 14k to replace the engine so of course decided to just part ways with it. When I went to get it towed from the dealer, the battery was dead, but I figured I already bought it under the stipulation that it had a bad motor.

Finally got it home and charged the battery and turned it over. It fired up, but rough and misfiring and wanting to die. Holding some throttle to keep it alive, I finally heard some rattling/knocking, but it would come and go. Yesterday, I finally had a helper start and hold the throttle on the car while I listened near the engine bay. The noise seemed to be coming from the top end. My brother recently had a spark plug break off in the cylinder on his BMW and it sounded a lot like that so I decided to pull all the plugs. Funny enough, the second plug ended up being smashed up. Pic is attached. this is plug 2 on the driver side from front to back.





I've come to terms with the idea of pulling the engine, no issue there. But now my engineering bug is coming out and I want to troubleshoot it for fun.

symptoms: random rattle, knock in the top end. Spark plug smashed in driver cylinder 2. No apparent metal particulate in the oil(oil looks really clean).

Anybody want to guess or throw suggestions for me to try and diagnose? Again, this whole project is for fun since I already have a 2006 v8 4wd with full long travel.

Something in there that smashed that plug, maybe a dropped valve?

Got a borescope or something similar you can feed into the spark plug hole before doing anything else? That way you can see what the issue is, maybe just pull the head instead of the engine.

As for the idle, make sure the throttle body is clean. Spray a rag with brake cleaner and clean it up as best you can, opening the butterfly by hand. I had the same issue after just disconnecting the battery for a bit while I cleaned the terminals and it wouldn't idle again. Cleaned the TB up as described and it was able to idle again. No problems since.

+1 for scoping the bores. A leakdown test isn't a bad idea either. Or even a simple compression test to see if the cylinders are holding pressure at all.

You could pull the valve covers to see the valve situation from above.

Also, an oil analysis would tell you about bearing condition.

Keep us updated!

In looking at this the other way. As we all know some dealers are crooks. I have seen it first hand personally and with my job.

Its "possible" that the dealer wrecked the plug to give it the issue you see to take advantage of the prior owner. These 4.7s are pretty bulletproof so is it possible it grenaded, sure, but unlikely. I would just go buy a new plug and coil and see what happens.

I’m going to get an inspection camera to check what’s going on. Keep you all posted on that.

I bought the cheapest spark plug autozone had and installed it, fired it up. Same thing. Pulled it and it was starting to get marked up, but didn’t get smashed like the last one.

This is the second vvti v8 I buy with a motor issue. My LT rig had a seized motor. I opened the oil pan after removal and the piston had broken apart. Only 230,000 miles on that one.

Meanwhile the 03 trd SC v8 I sold my dad with 370k miles is still pulling like a train. Go figure

I wish there was a way to easily check rod bearing play. Only way I can think of is to spin the motor by hand, and on the way down, try to push on the piston with a long, thin rod. In theory, if there was a lot of play, the crank journal would be pulling on the cap, leaving a gap on the rod side.

Anybody know if the spark plug goes past the plane of the cylinder head that mates to the block? I guess I can pull the head of my other bad motor to check if nobody knows.

Makes me think there is something pretty small in there then. Hopefully you can see it with the inspection camera and maybe get it out and be good to go. Worth a shot at least. Again, if it doesn't look too bad in there, short of pulling the motor, pull the head first and see if it's repairable. Once you have the head off, then you will know for sure if the motor needs to come out.

My 03 V8 is running great still with 282k on it.

I was thinking rod bearing too, but if oil drain was clean, probably not. In cylinder inspection with bore-o-scope if possible sounds like the best first option before pulling anything major.

cant you just drop the pan and inspect that way?

V8 thoughts.
Remove the small lower pan and inspect for sludge. Check the oil pump pick up to make sure it’s clear.
160,000 miles check to see if timing belt has been changed. A stretched belt or one that has jumped time would be suspect too.
If there is sludge in the lower pan, remove valve covers and look for more problems. The front cams bearings are protected by a screen in the head. Sludge or carbon can block the bearing or the oil passages that feed the vvti cams.
The plugs don’t go past the plane of the head.

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This is awesome!! So this confirms that piston slap would not destroy the spark plug unless it caused serious damage to the head first. I am definitely leaning on it being a valve train issue.

The timing belt has been changed once. The sticker is on the valve cover. Still it was about 70k miles ago. highly possible a guide/retainer/belt gave way or skipped a tooth and the valves have kissed the piston.

I get the borescope from amazon today. We will see what happens.

The only thing I can think of that would be hitting the spark plug is a piece of a broken valve or broken piston, I'll bet on a dropped valve.

Just an FYI, if when the timing belt was replaced and they didn't also replace the water pump and it started leaking the coolant has been known to degrade the rubber the timing belt is made of leading to either the teeth of the belt breaking off or the belt breaking.

One member here had his break from this happening which destroyed the engine.

from experience with my other bad engine, you cant really get to the rod bearing caps by just removing the small pan. you have to remove the larger pan and I don't believe I can do that with the engine still in the bay. I could probably pull the engine faster than trying to pull the pan with the engine in.

Survey says.... It dropped a valve. Looks like ill be pulling the head off. Piston looks nicked up but I didn't see any significant damage. I will document some more as I pull the head and see what caused it.