Need some advice on next step. Have a slight tick noise for sometime now. Recently on A long trip the tick got louder and it threw a p0305,. I did a compression test today and got zero for cylinder # 5 , 100 psi for#7, 101 for#3,120 for#1, 120 for #2, 125 for#4, 121 for #6 and 125 for #8,
Engine is not overheating, rarely do I ever have to add antifreeze. It has been leaking oil quiet a bit lately. Mostly from the front seal (which I replaced last year.) Runs rough at idle but you would never know anything was wrong at highway speed. P.s. it is getting good spark and fuel injector is working as well. Checked both of those before I checked compression. (Wish I had done compression first) should have mentioned vehicle is a 2002 discovery 2 with 103,500 miles on it. Any thoughts would be appreciated.
Thanks, Jason

 

All those numbers are way low. Did you remove all the plugs, pull the fuel pump relay, wedge the t/body open and check them, if not those numbers are not good. Might also want to do a wet test on 5.

 

I did not know to wedge throttle body open. All plugs were out and fuel relay was pulled.
Forgive my ignorance but what is "wet test"? Thanks, Jason

 

You have got a blown headgasket at #5 cylinder. Check for pulled threads in the block before you reassemble it.
Ask me how I know.

 

Could l also be valve train problem holding valve on zero cylinder open. Take off valve cover and inspect before order head gaskets. Test with tablespoon of oil added to each cylinder to see if numbers rise due to worn rings.

 

A blown head gasket will not cause a cylinder to go to 0 PSI unless it is blown out the side of the block, and it will sound like a freight train.

 

Agreed. Do the compression test correctly first then confirm it to not be a ring/piston problem with a wet test. 0 psi is odd but If you want to find out if its a valve do a leak down test.

 

Mine was blown out on the intake side, sound must have been muffled by the double-decker intake assembly... cause it never made a sound I could hear above the running engine.
Put air pressure on the cylinder through the spark plug hole and then you will most likely be able to tell where you are losing compression.

If it is a valve train malfunction, isn't it very likely the head will have to be removed to repair it correctly anyway?

 

So I redid the compression test with throttle b/valve held open. Not much improvement.
maybe 10 more psi on cyl#1; no change for 3,5,&7.
took valve cover off and then did leak down test. Had air coming out exhaust and what appeared to be numerous other areas around the push rods. Valves were not stuck.

Pulled out the push rod on the left of cyl #5, found half way down the rod, 1/4 inch thick by 1 inch long build up of carbon /tar type of gunk. Then i noticed inregular shaped holes in the block next to the valve lifters which exposed the lifters for the other bank of cyl.s .
holes are over an inch in diameter and look like they were made something that wore them open. Removed valve cover on other side to side if holes were on that as well. Found no holes on that side. Question is: what made those holes? Is the engine block
any good? Thanks for any info you might have........ Jason

 

I have a HG leak on cylinder 3, out the side of the block just forward of the dipstick tube. Just did compression test (dry, TB open) and got 155 in cylinder 1 and 40 in cylinder 3. Not freight train, but certainly loud.

Pix of interal engine angles