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[Carlos Fandango]

My 4.0L XJ facelift, the proposed off roading project 

When I purchased this pos  the chap I bought it from said........ the head has been skimmed and a new gasket fitted, basically put back together bar a few items, he had run out of time and was selling as a non runner, so muggins here bought it, anyway, I have now put it back together fans, pipes radiator etc nothing too major and it runs sweet at tick over and low revs, starts on the button, doesnt over heat, pressurize or any water in the oil, but it wont rev past 3,000-3,500rpm and when it does it just dies and splutters, ease off and it returns to normal tick over, sweet. Have now swapped the throttle body & associated sensors and its still the same, the exhaust is off after the cat wouldnt have thought it would have caused this tho.
So any ideas chaps as I have run out of them???
Ive tried the codes but cant seem to get any sensible reading, unless I am not doing it right which wouldnt suprise me!!

Failing that I will scrap the lot and give up 

[isle of man]

What is the fuel line pressure?

Is the symptom the same hot or cold?

[Nosebolt]

from fault described I would first check the timing, ignition and cam, also vacuum pipes , also worth checking the coil, seem similar on an old coil that was breaking down (although that didn't start to well)

[Mike Pavelin]

Make sure the cat isn't blocked.

[Carlos Fandango]

Fuel line pressure.............good question, I assume its ok, I have no fuel leaks.

Its the same hot or cold

Timing could be a good one as well would need to check it any idea anyone what it should be?
Coil pack would be simple to swap to check to eliminate, but this does start straight away.

Cheers  keep em coming, 

my assumption is, it was ok till the head gasket was replaced but who knows or this fault developed and he did the head gasket thinking it was that and it wasnt so he gave up.

I will take the cat off and try that as well, good one

Thank you
Do you think it could be the ECU?

[isle of man]

It's NOT the PCM!!!!

If it was the cat the cold/hot would be noticeable "that is" the back pressure would be easily identified and it would HISSSS like a snake.

It's a fuel or ignition sensor for sure.

[Panic mechanic!]

try changing the rotor arm.I know some  vehicles have used  ones that limit rpm and t can also  happen when they are failing.

[Carlos Fandango]

ok so most likely candidate is lack of fuel / pressure.................most likely the fuel pump?
Ignition sensor, can be found where? sorry 
Rotor arm / coil pack / distributor / timing?

Thank you very much. 

[scrw]

I had a cat break up and flip over inside on our wrangler, no audible difference just no revs about 2k rpm.