V8 Compression Test

**Bully** · 28th June 2006, 04:56 PM

My Series 1 disc is playing up,running really rough(missfiring).So I've got the injectors cleaned put new HT leads on ,new plugs ,checked the distributer cap for cracks and the coil is all ok and its still misfiring.
I did a compression test this morning and the results were from 124psi to 137psi.
I read that there is two readings
Low compression engine 150psi min
High compression engine 170psi min

So with my highest reading is way lower then the minimun pressure for the Low compression engine.

The engine doesnt burn any oil or blow any smoke but the plugs get sooted upreally quick...so im buggered if I know what is wrong with my Disco.

So the out come at the moment is I have a engine that miss fires ,the plugs get sooted up quickly and my compression test shows that either the valves are not sealing.And on top of all that someone told me I could need a new airflow sensor unit.

Specs:series 1 3.9lt Disco

Please help because I cant afford the $95 per hour labour costs at the local Landy Dealer

**rangieman** · 28th June 2006, 05:16 PM

try and squirt some oil down the plug hole and redo the commpression check (it could be a valve) if the reading goes up its rings if it doesnt it will be a valve

**101RRS** · 28th June 2006, 05:33 PM

After market rotor buttons fail after a few months and can cause the problems you describe. Put in a genuine rotor button and see how you go.

garry

Rovernaut · 28th June 2006, 06:01 PM

Try the compression test with a warm engine. Also check your timimg, when mine was way out the plugs sooted up badly

**barney** · 28th June 2006, 06:02 PM

Check Your Valves Are Opening Properly, Ie Your Camshaft Isn't Worn.
sorry i didn't realise i was yelling

**Nigger** · 28th June 2006, 06:10 PM

could be valve stem seals. I'm going through it at the moment, no noticeable oile usage and no smoke but burned out plugs and sooted up to buggery. All this with only 34k on the clock.....
Maybe try some heavy duty engine cleaner and see if it helps? May be a low cost winner..

**Bully** · 28th June 2006, 06:19 PM

The engine was warm when I did the compression test.

I will try the oil when I do it again...

I have been thinking alot in the last few hours and came up with ........
The engine has been playing up for a few weeks but the wife needed the car because of the brand new baby and the other ratbags.
So I can=me up with if the airflow sensor is stuffed it would be giving me a rich mixture and after a little while it would foul up the plugs and maybe the valves....What does anyone think....could be on the right track?

**Pedro_The_Swift** · 28th June 2006, 06:26 PM

When my air flowmeter broke it stuck on full rich,, car would only run properly on full throttle (

), otherwise foul plugs etc.

if its not using oil, and the compression is nearly even,, V8's will run ok down to around 100psi.

**101RRS** · 28th June 2006, 07:11 PM

Originally Posted by barney

wouldn't you need a distributor to fit a new rotor button?

huh?

**PhilipA** · 28th June 2006, 07:19 PM

Why not try to clean the MAF with electronic contact cleaner from Jaycar. Take it off and spray lots through the little hole. When clean you will see 2 little wires inside. AND then clean the electrical contacts on the plug.
Its a small easy job and may fix it.
Also clean the contacts on the temperature sensor plug which is the one on the right front of the inlet manifold with an injector type plug just behind the thermostat housing.
Regards Philip A

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