Getting frustrated now!!!

Hi all, i have previously posted on here before regarding my 4.6 HSE and the misfire/loss of power at over 3000rpm.

Here's a few avenues explored,

New coil pack,
New NGK plugs,
New OE quality leads,
Replaced inlet gasket,

Maff sensor is showing 7 g/s on tickover and around 14-15 g/s @2500 rpm,

the car drives faultlessly at "normal" operating speeds smooth powerfull and doesn't miss a beat until i kickdown and she reaches over 3000 rpm then it hesitates and starts to loses power and starts to slow down almost as if it will grind to a halt, as soon as i back off the pedal it picks up and carries on without issue. Always starts first time hot or cold, i just get a rattle at cold start up from lifters until filled with oil.

It sounds like it is misfiring the revs go right up over 4000 rpm but with no increase in speed the revs hold but the car starts to slow down,

The whole thing is starting to confuse the hell out of me as i cannot find a certain solution to correcting the fault.

I get no warnig light and nothing is showing on the diagnostics except for a cam sensor circuit fault which has been reset and not shown again,

Left bank shows rich on long term trim
righ bank shows lean on long term trim

short term trims showing normal.

Coolant temp sensor well within limits etc, etc,

Is there any other explanation i.e mechanical (camshaft, hydraulic lifters or even exhaust) that may be causing this.

forgot to mention does all of the above on both LPG and Petrol (sequential multipoint LPG system which has just had new quick fire injectors)

All help would be much appreciated as i love the old girl to bits and don't want to part ways with her just yet, have always loved the Brand and know i will regret getting rid.

Not sure Bout LPG fuel filter clean ??plug gaps correct ...

Plug gaps are all correct and it has the problem on both fuels, forgot to mention car has same symptoms whether driving or in neutral whilst increasing the revs.

Could be faulty lead Arking under load listen for arking under hood

Have tried that and replaced the leads twice and coil pack as there were signs of corrosion on the original leads at the coil end, this is why it's all getting frustrating as all the usual culprits have been replaced but with no effect, i am at the point of stripping the top end to inspect cam wear, valve travel and even having the cat's off to look for restriction in them, with no fault codes showing and no othe obvious signs i.e cracked vacuum hoses seems the only route left.

robcad1972 said:

Have tried that and replaced the leads twice and coil pack as there were signs of corrosion on the original leads at the coil end, this is why it's all getting frustrating as all the usual culprits have been replaced but with no effect, i am at the point of stripping the top end to inspect cam wear, valve travel and even having the cat's off to look for restriction in them, with no fault codes showing and no othe obvious signs i.e cracked vacuum hoses seems the only route left.

Click to expand...

Are the leads the type that come with fixed / sealed caps ??

yes, the coil ends are "Moveable" but the plug ends are not when i put the second OE set on they did all "click" positively onto each plug and also made sure the leads were all in there holders and not crossed or touching, which in itself is an art form!

Ok I surrender only thing I can think of coil breaking down under load ????

The only thing I can think of is something iv come across in the past. Not on a lr though is a loose or knackered knock sensor. That was retarding the timing at certain times. Bit of a log shot but might be worth a look. Hope u get to the bottom of it.

robcad1972 said:

yes, the coil ends are "Moveable" but the plug ends are not when i put the second OE set on they did all "click" positively onto each plug and also made sure the leads were all in there holders and not crossed or touching, which in itself is an art form!

Click to expand...

Wait for a really dark night and run the engine, look for tracking around coils and leads.

defender300td1 said:

Ok I surrender only thing I can think of coil breaking down under load ????

Click to expand...

That's exactly how i feel, just can't work it out.

wammers said:

Wait for a really dark night and run the engine, look for tracking around coils and leads.

Click to expand...

Have tried that trick but nothing visible.

Took it to a local mechanic and he's arranging a priest!!!! had enough now,

Just a little update on my misfire under load problem, took it to be excorcised and a Camshaft/Crankshaft sensor fault came up put a silly scope on both sensors and was getting an identicle irregularity on the reading, whipped off the bellhousing cover to have a look at flywheel and hey presto 1 missing tab off the reluctor ring and a few twisted ones mechanic is confident that he may be able to repair damage without taking gearbox out so fingers crossed.

Nice bit of problem diagnostics there. Good luck.