2000 - 3000 rpm

[NeilB]

Hi Folks,

So what happens in the above rev range?

I have a '92 Disco 1 with a 3.5V8. It accelerates fine until I get just over 2k revs. Then it acts as if someone is turning the ignition off and on very quickly. It surges and stops, surges and stops. If I keep my foot down when it gets to 3k revs it all goes back to being smooth again.
When cold it is not so noticable.
It is the same in all gears - happens at the same rev range.

I think when I changed my spark plugs a while ago it all went better for a short time.

My thoughts were.....

If it was throttle position sensor (if it has one) why is it all gears - it's not the same place on the throttle.

If it was fuel why does it get better when you get over 3k revs.

If it was timing why does it get better over 3k revs. I have just changed my vacuum advance and that made the engine smoother but did not affect the problem.

If it was ignition, again, why better over 3k revs.

Your thoughts please........

Neil

[TEMPL4R]

Change the plug leads. Check inside the distributor cap and the rotor arm.

Chris

[NeilB]

So, I swapped my distributer cap and plug leads - no difference.

I went to the dealer and bought some new plugs.

Then I took my Dodge to the garage to have the AC fixed. While I was there I noticed the Disco dripping water. Drove it home quickly and found that the top radiator hose has a pin hole in it.
It was squirting steam over my new distributer cap!

Could this be the cause of my missfire?

I will let you know when I get a new pipe today!

Neil

[TEMPL4R]

Water will make the spark track out, so yes, it could be the problem.

Chris

[NeilB]

OK, not the water on the distributer cap. Changed the spark plugs last night - no difference.
My symptoms seem to be getting worse.

The spark plugs were black and sooty.
If I rev in neutral the engine revs fine to 3k but then coughs and spluts and generaly runs rough.

Could I have a dodgy coil?
Or is the sooty spark plugs a sign of poor fueling - air filter is OK.

[NeilB]

Right....I have tracked down the problem. It's my A/C!

My son was out one night and as it was cool (32degC!) he opened the windows and turned off the A/C - kangaroo petrol gone!

For the last couple of days I have been playing with this and he is right. If I accelerate to 2.5k and then turn the A/C on the car jumps and bucks. If I turn it off the problem instantly goes away.

I may be imagining it but I think if I turn the fan speed down the problem gets less severe ie. Speed III - kangaroo petrol, speed II - a few bumps, speed I - one bump then ok.

So what could make the A/C or the fan cause the engine to spit and cough and not want to run between 2 - 3k revs ?

There are straws floating infront of me and I am grasping.......

[DeanV8]

Hi Neil

It sounds like the load from the A/C fan is causing a drop in available current to power the ignition. My old 3.5 RRC v8 was very sensitive to this.

It could be that the ignition amplifier is on it's way out (they're solid state, so should either work, or not - but in reality it doesn't happen that way). Or, you may have an issue with the charging system, or the battery.

I'd check the voltage out of the battery, at rest and with various loads - A/C off, A/C on, etc. That should give you an idea of the health of the battery and the charging circuit.

If both appear to be ok, then I'd be looking at the ignition amplifier on the distributor.

Hope this helps

Dean

[Satancom]

Could be that the alternator is getting tired and the extra drain put on by the air con is sapping all the power till rev's increase and the alternator can keep up..

(Satancom wildley stabbing about in the dark)

[NeilB]

....and yea though he walked in the darkness there came a light, and he saw that the light was good. A voice spoke to him 'fear not, but read from the good book.'
So the good book he did read from and there came to him a most marvelous sight. The book of electics, chapter AC.....

' Verily if there be an electric overload the computer of the engine will turneth off the AC clutch.'

He fell to his knees and did give praise while looking at the oval green badge of power.

Thus did he search and did find the movement of the air device wanting.

Thus did he come to an understanding of the weakness of all things Lucas.

Praise be to the good book......

Or for those that don't worship at the alter of Land Rover.

Yep my A/C fan was faulty....one of the ones infront of the condensor. Must be causing the ECU to turn off and on the clutch in the A/C, causing my kangaroo petrol.