Hi all,

as always when I have a problem with my Jag I turn to you! I'm hoping someone can help identify the cause of what's happening at the moment.

Just for background, I have recently had entirely new coils & spark plugs fitted, just thought I'd mention that.

So basically, the exhaust is popping on idle, there is only about half the power there should be, and the whole car sounds and feels extremely rough. An engine warning light did come on, but by the time I got it back home it had stopped flashing and no fault code could be read by the AA man (that's AAA for any Americans here who might get the wrong idea!). He looked at a few readings on his diagnostic reader and suggested it might be a problem with the fuel or air feed, but couldn't pinpoint it better than that.

I have uploaded a short video so you can hear the sound; listen especially when I kill the engine, I have never heard my car make this noise before - it's like a low gravelly rumble!


So... does anyone have any suggestions as to what it might be? I should mention that the engine is not misfiring (the AA guy checked this) even when the exhaust pops.

Any thoughts would - as always - be much appreciated.

Thanks,

Joe

 

sounds like a misfire to me, that flashing light was telling you the misfires were causing damage to the cats.

chances are that with all the rain, water has got past the wiper cowl / bottom windscreen seal and which then drips into the plug / coil recess, damaging the coils.

i'd remove the coil / plug cover and check for contamination.

you can have cat destroying misfires with no codes

 

Thank you for the advice re the misfire; this was certainly the first thing we checked and at the 'business end', the engine itself is running smooth as anything, even when the exhaust pops (which is very confusing!)

The coils and sparks are brand new and we removed and checked all of them in both banks.

With this in mind, do you have any thoughts on alternative causes?

 

Sounds like an exhaust leak to me.

 

in your first post you say "the whole car sounds and feels extremely rough" and "there is only about half the power there should be"

but in your second post you say "engine itself is running smooth as anything"

so when stationary everything is fine its just when moving ?

has it had an lpg conversion ?

 

Hi,

sorry for the confusion about the running.

When it is idling and the bonnet is open, you listen to the engine itself and it sounds absolutely fine. It doesn't misfire, and runs smoothly.

You then go round to the back of the car and the exhaust is sounding awful, and is popping (I didn't catch a pop in the video, but they are quite loud but not backfires.

Driving it, it feels rough and you can hear the gravelly loud exhaust sound and the power is very much reduced. It is slow to respond when you put your foot down.

However, pull up and leave it running, pop the hood and the engine itself still sounds smooth, not missing a beat... even though the exhaust note is terrible...

Hope that makes a bit more sense! Thank you for taking the time to answer.

 

Oh - and no to the lpg conversion, it is as standard.

 

ok, i still think its misfiring but we'll see what others think.

the flashing light you mention, was it the orange engine light in the shape of an engine ?

 

I also believe it is one or more intermittent misfiring coils.

An exhaust leak could easily be ruled out by getting the car on a lift and checking out the entire exhaust system paying close attention to the resonators. If the exhaust checks out - the engine up front can sound "smooth" as you mention and still have coils intermittently misfiring.

That "popping" sound is evident of a misfiring coil(s) - if the CEL was flashing then you are essentially damaging your cats as police666 already mentioned. Also, if the popping sound is coming out of the driver's side exhaust only - then you just narrowed it down to the driver's side coil bank. (seperate exhaust from the exhaust manifolds through the rear mufflers)

 

Install an OBDII code reader and drive the car when the engine light flashes check your codes.

 

You are fairly likely not to hear the misfires at the engine end. Everything so far points to very bad (cat-damaging) misfires. Wrong coils? Wrong plugs? Contamination? Don't know - keep looking and fast as cats are expensive.

 

Are you aware of the timing chain tensioner problems on the 4.0L?
Have you changed them?
If not have you inspected them?
Your engine could have jumped a tooth and now is out of time?

Just a thought and you know the car's history better than us.
.
.
.

 

+1 that could be it

 

Thank you all for your thoughts, all of this is very much appreciated.

It's going into the garage on Thursday; I think that's the best solution considering my limited extent of expertise! I'll pass on the thoughts to check for the misfires as a top priority and of course the exhaust leak and the timing chain and hopefully my mechanic can use the info to identify the problem.

Once again, cheers for all the advice and I'll keep things posted up to date to help anyone else with similar problems - if we ever find the cause!

Thanks again,

Joe

 

OK, so here's the update. My mechanic reckons it has blown the head gasket. Not good as that means it's not worth repairing.

Sadly then I think that's the end for this jag. Thank you for all your help everyone, I hope to be back one day!

Cheers,

Joe