As a recap...

A 2004 4.6 V8 Disco2. ~144k miles on the dial. I have driven this max 100 miles in this condition, and in total, just to MOT and for welding.

Plenty of misfires on cylinder #6 except on idle, occasionally on #4 if I recall right, smog tests fail, exhaust gets very hot all the way, enought to melt the rear bumper plastic.
New coils, plugs and leads have not helped.

Worst case, cracked block, slipping sleeves, bad HG etc etc.

Well, started yesterday to do the HG job and finished the taking all apart today.

Did not find any huge disasters.

Head gaskets seemed good.
Plugs seemed good, except the cylinder #6 that has black gunk.
Definately not the steam cleaned look I was afraid of.

Overall pics of the cylinders and heads.
I do have larger individual pics of them all if anyone want's to see.






I'd say, no sleeve slipping has occurred, or if, the sleeves felt like perfectly flat to the block.
Phew!

So, what are we looking at here?
Coloring of the valves etc tell things I do not know/remember?
I tried not to wipe any dirt off the pistons and heads, only the gasket surfaces I wiped. Just stuffed rags in the cylinders to remove the coolant from them after they got flooded when removing the heads.

Could the timing be off or whats the dealio?

Ohh, does anyone know anything about the engine number thats next to the dipstick, or the block number?
Mine has XM50M107A5 and no compression ratio marked.
Block number? is M02520

Tried googling around for that XM50.. but no luck.

 

The block number is likely from a rebuilder, as to #6 that looks like oil to me could be as simple as really bad valve seal it looks "wet" over fueling doe not generally present that way

 

I think I might have started with compression /leak down test. all new injectors, spark plugs, and MAF probably needed, and possibly knock sensors....also, do a light valve job.....If HG's are good, just check surfaces for flatness, don't machine anything unnecessarily....you may not have much block deck or head thickness left....

and maybe go with ARP or similar studs.....I use them for all my rebuilds..work great

edit: and new O2 sensors....

 

Cylinder 1 valve colors tell a story, but I'm not sure what it means, maybe too lean? Cylinder 6 looks like burning some oil, like RG mentioned above.

Like Xrad mentioned, a compression check would have helped assess the condition of the piston rings. Compression is the first thing my mechanic asks about for motor issues, including when checking out a used vehicle to buy.

 

Is #6 oily? You are either burning too much oil or fuel on #6 and #4. Let's see the plugs. If it is oil, likely a broken oil ring. If it is fuel, I would say leaking injectors. If the plug is white/tan at the tip and black on the insulator it is oil, if it black on both it is fuel

 

Yeaaaah... compression and leak tests.. mm.. Now that might have beeen a wise thing to do.. first.. dangit..

I'm taking the heads somewhere to be checked for flatness, and the valves seating.

I will be replacing the injector o rings, have ordered new ones from rockauto.
Plugs are already new.

Will look into gettin the MAF and knock sensor.
I will neeed a new airbox lid also as almost all the retaining clips are shot/broken off.

For now I will use new genuine tty bolts, maybe next time upgrade to arp studs. Budget just did not allow studs now.

 

#6 plug is all black. Others looked fine enough so I didn't pay that much attention to them and just set them aside.
The black on it is not wet, it's just.. gunk built up.

Did take a photo of it, but seems to be completely out of focus so it's not really showing anything.

 

Forgot to say..
O2 sensors are also new as is the exhaust.

 

So if #6 is all black, dry, it is running rich, leaking injector.

 

Well thats a bit of a relief.

Looked at rockauto, they have new injectors from ultra-power, bosch and smp.
Are they all a good choice?
There is a significant difference in price from ultra-powers 20 to smp almost 50 each.

Also checked local pricing for testing and remanufacturing injectors.. with those prices for new ones, not worth it.