V8 Compression Test

[Bully]

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]

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]

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]

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

[barney]

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

[Nigger]

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]

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]

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

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

huh?

[PhilipA]

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

[Bully]

Thanks guys
Ill try Your idea's tomorrow.

Ill let You's know how things go regardless

[Bully]

The mis fires happen at all revs..so far no difficulty in starting whether hot or cold.
I checked the battery and it holds 12.44 when the engine isnt running.

I also double checked my readings and they vary from 120psi to 137psi.(I havent worked out the % as yet...I thinks its just over the 10% mark)

This coolant temp sensor'theres just the one on the engine?

[Bully]

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..


Usually you get smoke from start up when the engine hasnt been start for a feew hours.
The oil seeps thru the valves and sit in the pot,so when you start the engine it burns that on start up and clears up after a few minutes....

[MacMan]

START SIMPLE! Start with a replacement rotor - even if it is a borrowed one just to try. I was stunned at how badly my 3.9 ran with a non-genuine rotor after only 5000km.

"What can be done with fewer assumptions is done in vain with more."

[Rayngie]

On a similar theme, can someone tell me what the spark plug gap should be for a 3.9?, my Haynes manual makes no mention of it..

Cheers,

[4bee]

W/M Manual says: 0.84 - 0.96 mm.

[Bully]

not sure where the mention of the rotor came in to it,I havent mentioned the rotor.(rotor is the orginal)
What I did do is check the destributer cap for cracks to ellimunate tracking within the cap....

But very usefull info to say the least.

Ill be trying all these fresh ideas this weekend when I have a chance.(damn work require my body:p )

[DEFENDERZOOK]

did these engines run the cold start injector.....?
if it has a cold start injector...simply unplug it and see if it fixes the problem......





you could also try.........pulling the engine fuse.....
(if its in limp mode...it richens the mixture up something drastic.....
to avoid burning the engine due to lean running......)
pulling the fuse or disconnecting the battery may reset any faults present.....

[101RRS]

not sure where the mention of the rotor came in to it,I havent mentioned the rotor.(rotor is the orginal)
What I did do is check the destributer cap for cracks to ellimunate tracking within the cap....

But very usefull info to say the least.

Ill be trying all these fresh ideas this weekend when I have a chance.(damn work require my body:p )

I raised the rotor button - the aftermarket versions develop cracks in them causing shorts or lack of constant spark that result in sysmptoms very similar to what you originally mentioned. On cranking can show up as HT to the distributor but no spark to the plugs - however the engine may still fire and run at higher revs and the spark jumps around inside the distributer.

It is only the aftermarket rotors that have the problem - they usual last about 3-6 months before they pack it in - it doesn't kill the engine but makes it run like **** - something like the symptoms you suggested.

Gazz:D

Just something to check - do the easy things first.

[Bully]

okkk
Ive cleaned and rechecked the plugs again all ok
Cleaned the airflow sensor
Checked the rotor(well I checked it for resistance)(rotor is a lucas ,is that the after market brand?)
Cleaned the coolant sensor plug with contact cleaner.

But still runns like crap,still missing and getting worse.

One thing I did notice was when its running and I unplug the airflow sensor there is no difference in performance(I started it with it unplug,forgot to plug her in)...could this be the cause??? my guess is if the airflow sensor should work when u unplug it it should be a difference in engine performance on idle and on revs(just my thoughts as I have no idea)

What do u guys think?

[101RRS]

Lucas is the genuine rotor

There is one other possibility - the ignition module on the side of the dirtibutor - when it starts to fail it can cause misfiring etc - it mostly happens when thye car and temps are hot (the mod cooks in its location) however in my case it was the opposite - started to breakdown on minus temp mornings in Canberra and went on that for 5 years until it started playing up all the time irrespective of temperature - they are about $120 to replace.

Given the testing that you have done maybe it is time to take the car to a specialist :o

Garry

[Bully]

GOOD NEWS

I played around with the timing by ear(Iknow this is a no no to some ,but Im desperate)and found I got it to run and sound better.

Two things
1.I now need to buy a timing light for the fine adjustment.
2.Why would the timing go out if I have never touched it and the distributer wasnt loose?


Garry,I like the blokes at the LandRover dealership but there knowledge isnt quite the same as most others.The 2/3 guys there,there is only one tradesman and the others are apprentices and both havent been there that long around landies.

Ive asked them for help ,which they have given but I have gotten more help from the people in this web site in 1 week then what I have in 1 year from them.


So a big thanks to all that tried to help me


Thanks

Bully

[DEFENDERZOOK]

check the vaccuum advance unit on the side of the dizzy.....
if the diaphragm has a hole in it it wont advance properly.....

[barney]

the motor will often idle smoother if the timing is out, but it rears it's ugly head at revs and under load.
get yourself a timing light and like any other landy V8 owner, keep it in the car. mine lives in the under-seat box on the drivers side with my dwell meter.
they do wander a bit, don't know why, they shouldn't but they just do.
26deg BTDC.
have fun and don't get your 9/16 spanner caught in the fan

[101RRS]

they do wander a bit, don't know why, they shouldn't but they just do.


They most certainly do - Landrover specialists were trying to sell me new distributors from when my disco was 20,000 km old to when I sold it at 100,000 km - when on the tune up machine the distributor was all over the shop - yet I was always able to time it with a light without any problem so it ran OK - at least with a new ignition module.

Gazzz

[MacMan]

Another thought. You might have one or both of the mechanical advance springs broken or detached if changing the timing made a difference. I had a bugger of a time with the dizzy on my Disco after whomever the previous owner used to service the thing failed to put oil on the dizzy shaft prior to fitting the rotor. It was jammed solid, I pulled on it the two parts of the shaft seperated. This unhooked the weights and springs and allowed a massive amount of play. I had to remove, strip and rebuild the dizzy. After that experience I too carry a timing light in the car. Always!

[Bully]

Ok I need to get a timing light ,will do tomorrow.

But I have another question for ya's
Im getting a constant spray of water/moisture coming from my exhaust.With finding this I took the plug out of the radiator and noticed I get bubbles when I bring the revs up a little bit.(*note the radiator tank was not completely full about 1/2inche from the top and I get no bubbles on idlethat I can see)


Ill be booking my Disco into a workshop asap but just wanted ur thoughts