Loss of engine power

[piman]

Hello all,

my recently purchased 2.5 estate has suffered loss of power when accelerating, similar in action to a rev limiter (about 3,000 rpm) idle is fine with no warning lights showing. If I drive gently and keep the revs down it is smnooth again. This has happened a couple of times and then seems to clear and the engine will rev again.

I have a fuel filter to fit, but I would not expect that to give an intermittent fault.
Is there a particular likely culprit; it has new plugs by the way?

Alec

[Brakebuster]

I presume it petrol

the cam cover oil breather pipe breaks , this allows air in past the MAF sensor and throws the fueling all over the place,

this link pipe is a known issue and a revised pipe had been issued by Jaguar

by chance, and only if you need one, I bought a spare for my 2ltr, but it was for the 2.5 and is brand new and unused

but first thing to do is take off the engine cover and inspect this pipe from the cam cover to the induction pipe

BB

[piman]

Hello BB,


Thanks for the quick reply.
That pipe is new; I did wonder about various vacuum hoses etc but I would expect they to give a consistent fault? When I changed the plugs I looked at the MAF sensor but it was very clean.

Alec

[J44EAG]

My V8 S-type at one time had a similar issue. I changed the fuel filter and all came well again.

Even though a MAF sensor hot wire (which has to be shiny bright and clean all round to be up to standard} can give issues. I cleaned the unit on my X350R recently at 80k miles and performance improved somewhat. Not satisfied with the result, I fitted a new component. Result was a transformation especially at low revs. So the diagnosis in my mind is that whilst a MAF can still be functioning reasonably well and not cause faulting, the units are prone to "going off a little" with advanced age or mileage.

There are two small rubber air elbows under the inlet manifold on petrol V6 models which can split, crack or generally decay with age. The lower of the two elbows is only accessible with the inlet manifold removed as is done to gain access to three of the six spark plugs at service time. Often these items get neglected and not replaced. They are not expensive and for peace of mind should realy be replaced when spark plugs are changed.

Have a good look around the engine and ensure that any small bore rubber pipes are securely fitted to stub pipes on the appropriate units. Sometimes the rubber pipes expand with age and cause leaks. Snipping 20mm off a rubber pipe which is slack its metal stub pipe can do wonders for some of these issues.

Also take out the air filter and ensure it is clean. It is not uncommon to find that a filter has not been changed in years and looks like the inside of a vacuum cleaner! A dirty filter will seriously impair general performance.

Lastly check tightness of jubilee clips on the inlet pipe from the MAF sensor back to the throttle body body.

Mike K

[piman]

Hello Mike,

thanks for the advice I'll have a look around as you suggest. I know the air cleaner element is clean as I had it out to change the spark plugs. (Isn't that air cleaner box a fiddle to remove, getting the air inlets through the body and radiator?)

Alec

[Brakebuster]

ote="piman"]Hello Mike,

thanks for the advice I'll have a look around as you suggest. I know the air cleaner element is clean as I had it out to change the spark plugs. (Isn't that air cleaner box a fiddle to remove, getting the air inlets through the body and radiator?)

Alec[/quote]


there are two screws in the bottom of the air box to remove the main box from the twin flat ducts trapped between the radiator and top member , undo the screws and the box slides of the section that stays put

BB

[piman]

Hello BB,

thank you for that, I'll remember for the future.

Alec

[steve_m]

I had similar symptoms in my Subaru and it was one of the catalysts broken up inside the pipe causing a big restriction when revved.

[piman]

Hello Steve,

was that fault intermittent, it is only occasionally I experienced the fault.

I have replaced the fuel filter now so I'll see how it goes, ran well enough on a small test run but I I am not yet convinced that is the problem? Isn't there a fuel pressure sensor and if it is lack of fuel wouldn't that bring up an engine fault light?

Alec

[steve_m]

Alec, it was sudden and constant as soon as any revs were put on; resolved by removing the cat and welding a plate over the hole.

[piman]

Hello Steve,

I know my cat is sound, externally anyway since I was underneath the car yesterday.

Alec

[steve_m]

The problem is that you can't see if the cat has collapsed but you can compare the exhaust outlets from each pipe; if they are about the same pressure (just hold your hand very close) then the cats are ok.
I'm not saying that it is the cats but I had the same symptoms and that was the cause; we identified it by just shaking the exhaust and it sounded like gravel in the pipe.