I'm trying to chase down an increasingly persistent misfire on #6 (P0306) and an intermittent random misfire (P0300).

Vehicle info:
-99 Disco 2 currently w/ 131500 miles
-New head gaskets and cylinder head resurface at 90,000 miles
-No appreciable coolant leaks (checked daily - level stays the same)
-No appreciable oil leaks (checked daily - level stays the same)
-Occasional light wispy smoke from exhaust at start up but nothing especially remarkable
-No smoky exhaust
-No liquids from the exhaust pipe (whenever I've checked)
-No coolant smells (detected by me)
-Engine runs a little rougher than usual but not by much.
-Slightly less power than normal.
-Checking the serial number stamped on my engine shows that the compression ratio for my engine is 9:35:1
-Brand new fully charged battery

Compression Test Results (with brand new fully charged battery):
cylinder dry/wet

#8 82 / 90 **** #7 170 / -
#6 56 / 62 **** #5 170 / -
#4 152 / - **** #3 167 / -
#2 180 / - **** #1 174 / -

Considering the above info, which is most likely indicated?:

a) blown head gasket
and/or
b) broken camshaft
and/or
c) sticking or broken exhaust valve
and/or
d) piston rings
or
e) who the hell knows, go ask Who The Hell.

Other info:

500 miles ago, an independent Land Rover shop did a compression test, with the old battery that failed their load test; and they said, without a doubt, based soley on their compression test results, that I absolutely needed a $2500 (or more) valve job. Apparently, unlike most of their other customers, I lack enough faith to just take their word and blindly throw $2500 at a problem. I did my own compression test as soon as I got my truck home (with the same battery but letting the engine run for a minute or so between testing each cylinder). I got very different results:
Them with old batt / (Me with old batt)/ [Me with new batt + 500 miles]
#8 120 / (130) / [82] #7 125 /(136) / [170]
#6 90 / (100) / [56] #5 125 / (135) / [170]
#4 95 / (133) / [152] #3 125 / (125) / [167]
#2 125 / (137) / [180] #1 105 / (125) [174]

Should the differences between mine and the independent shop's compression test results make me wary of this independent shop's integrity and/or competence? (Especially when you consider that they insisted that I needed a $2500 valve job and "strongly recommend(ed) against just getting" the $1700 head gasket replacement job, and said that it could cost more once they remove the heads and take a look etc)?

I'll appreciate all considered and/or expert opinions, thoughts, comments, judgements, and guesses. (Irreverent but humorous responses are always welcome.)

Thanks,

Thomas

 

This is a SWAG, but my money is on the valves for #6 & #8 - obviously you'll do them all if you are doing them. Point is, if you have to pull the heads, have them rebuilt and change the gaskets (duh!). The block is probably fine, but you are going to have to pull the heads.

 

with all the plugs out? or one plug out at a time?

 

- I don't know the independent shop did their test with or without plugs.

- My first test is with individual plugs removed. (one plug out at a time)

- My last test (with new battery + 500) is with all plugs out, a warm engine, and accelerator floored during 10 cycle crank...

 

Take it to a different shop.
The battery will make no difference in the numbers. With a good battery the engine will turn over faster but that wont make any difference on the compression.

The only way to tell for 100% what is wrong is to pull the heads.

If the cam were broken it wouldnt run.
It could be a sludge problem and the sludge is making the valves stick.

 

highly doubt it's a ring problem, I would say valve's as well. The tests could very on the way it was done, and speed it cranked, and even the test equipment. My digital is tons more accurate than the old dial I've got.

 

Do a wet compression test next and depending on that a leak down test, then you will know for sure.

 

Thanks Fireman, Novadisco2, Spike555, and Disco Mike

I did a wet compression test on #8 and #6 cylinders.
Cylinder #8 dry = 82 wet = 90
Cylinder #6 dry = 56 wet = 62
There is a slight increase of 6 - 8 PSI. Is this increase "within normal limits? Or is that a significant enough of a PSI increase to suggest piston/ring/engine block problems?

How do I find the cylinders "top dead center" for the leak down test?

Thanks again..

Thomas

 

not significant enough for me to suspect thats the major issue, I'd say that your into valve/seat/cracked head issues. Pull them and head (no pun intended) the machine shop!

 

hopefully valve/seat issue and not cracked head issue... Am I right in my assumption that the only way to deal with a cracked head is to completely replace it with a new cylinder head? IE: The only use for a cracked head is as a door stop or scrap?

Can anyone tell me how to find "top dead center" for a lead down test?