“Lethargic” engine/transmission?

[le33sw]

I hope this is the right place to ask this question.

Car - 1999, 4.0 OHV, 112,000 miles.

I wonder if anyone can shed some light on this.

If I accelerate gently (never exceeding 2000rpm), the gears change up. At around 40mph or so, the revs drop to 1500. Thereafter, it will keep on accelerating, but there is a distinct jerkiness – as if the engine is struggling to get enough petrol. At 60-65mph, this ‘struggle’ disappears.

If I do accelerate rapidly, this problem does not arise.

Am I imagining things or is this normal?

The fuel filter, the plugs, and the air filter were all changed during the last 1000 miles. The autobox oil is not brown nor is it burnt.

I have another problem, discussed here: http://www.explorerforum.com/forums/showthread.php?t=219768 – don’t know whether the two are related.

Thanks in advance.

 

[BrooklynBay]

Did you ever check the fuel pressure?

 

[le33sw]

No, I am afraid not. Can a drop in fuel pressure cause symptoms of this nature? could this also explain the 'check engine' warning?

 

[BrooklynBay]

You have to pull the codes from the PCM to know exactly what is wrong.

 

[le33sw]

Happy to report that the problem is now sorted.
The cylinder 4 plug (which was not replaced earlier, as it was 'stuck' according to the garage) had its head partially disintegrated. The misfire is now gone, engine running smoothly. Thanks everyone for their contributions.

 

[BrooklynBay]

Thanks for the update!