Alright, I’m helping my bro-in-law out with a dud truck he bought. 2001 Dodge Ram 1500 SLT Laramie with ~175,000. Has CEL P0308. Tries to get it registered in Utah but is told he has a hole/crack in a piston that is preventing it from passing emissions.

This is where I got involved. He’s a poor college student living in my basement and I decided to help him out. Started reading and figured he has a plenum gasket leak that had lead to some failure in cylinder 8 (not sure what).

compression test >145 in all cylinders but 8 and 6 which are 70 and 80 respectively. Figured I would pull the intake and fix the plenum and then pull the heads and figure out this hole/crack.

well, definitely had a plenum gasket leak (see pictures), but when I got the head off the other night, there is no crack/hole. Actually looks ok. No obvious damage. Nothing really. Head definitely looks like 8 hasn’t been running right (quite a bit of carbon deposits) but no obvious valve problem either.

my question is now where to go. I’m thinking I’ll take the head to a matching shop to check out. What’s causing the low compression in 8 and 6? I’ve read a bunch of plenum threads and I can’t quite seem to get my mind around what the real problem is here.

just trying to cheaply get this truck back together so it can pass emissions. Any help is much appreciated. You guys are an awesome resource for me so far!

Cylinder 8

Cylinder 6

Passenger head. 8 has some more carbon buildup.

 

I know people like to see this from the posts I’ve read. Mine was obvious.

 

Could just be there pictures but is a chunk missing from cylinder 6? Did you do a leak down test? Could be rings.

 

No obvious chunk from 6 on my first inspection. Might clean them up later to better see. Sorry, pictures aren’t great. Didn’t do a leak down test because I foolishly thought I already knew there was just a hole/crack.

ive never had a shop check valves before. Can they do a leak test?

 

They can check the heads for cracks and see if the valves are seating, but to check the rings the heads have to be on the motor. In your pics #6 looks like there is a hole towards the intake.

 

I’ll have to look again at cylinder 6 for this hole. It was late. I took the pictures and went to bed.

maybe I’ll have them look at the heads for cracks and check the valves.

Could I just changed the rings while the head is off and hope for the best? Stupid of me not to do a leakdown.

thanks you guys for the help!

 

Would need to unbolt the connecting rod from the crank. So the oil pan would need to come off. You can rent a run compressor. Would have to check the cylinder walls to see if they still have crosshatching. Overall not a bad job just a little time consuming. I would rate it a 4/10 for difficulty. If you had to hone the cylinder walls you can rent that tool to. I would recommend it if the heads checked out ok.
EDIT: I do believe this is a piece of the piston missing but could be the photo.

 

Is that a chunk missing from the piston, or just fluid sitting in the cylinder?

Generally, low compression on adjacent cylinders means a bad head gasket.

Excessive carbon in number 8 is likely due to the plenum gasket sucking oil. I would be tempted to test the cat converter to see if it is partially/completely clogged as well. A frequent result of a blown plenum gasket.

With your heads laying on a table, combustion chambers facing up, and level, pour some water into them, and see if it runs out the ports..... Might be able to just lap the valves, but, having the heads gone thru is a better plan. Replacing them would be even better. But, being a poor college student, my guess is he can't afford that. So, get 'em checked, take it from there.

 

That’s just a little WD-40 and oil, not a chunk. Thanks everyone for your help. I’ll try the water trick to quickly see if the valves are the cause.

is there any good way to check the cat now that the engine isn’t running?

i will probably change rings and hone. Can I hone with the engine still in the truck? From what I’m reading you’ve got to meticulously clean after.

like you said, not looking to spend a bunch of money on this truck.

 

I would have been money that was a hole, glad it wasn't! I honed a buddies truck with it was inside the vehicle I used a cleaner to clean the walls (ended up in the oil, which he was going to replace anyhow). You could do that and might not have to hone anything if the crosshatching is still visible. Usually what happens on these motors is the rings freeze to the piston from sludge or sitting.

I don't know anyway to test the cat but you should also replace the front O2 sensor, as oil it cause it to read slower. NTK or Sensor if you buy one.