Misfire on 1/3/5/7 - XJR S/C

[Lordgaz]

Hi all -
As an ongoing saga with my XJR continues, I have had all vacuum leaks fixed on the car, fitted new MAP sensor (the one on the throttle body), had new spark plugs, and swapped over the coil packs from one side to the other, but I have a fault remaining which is a misfire all down the one bank, affecting Cylinders 1,3,5,7)
The garage also swapped over the lambda sensors to see if anthing changed but it did not

The garage is unsure where to go now -

Injectors? Cat? Camshaft Position Sensor (Could anyone point out where these are on the 4.2S/C - I guess there are 2, which could be swapped over)
Any experience of this type of fault ?

[J44EAG]

Not had to dig that deep on mine yet so I too also have to refer to manuals to find various parts locations. Have a look on this link for the correct manual. I recall they are a free download.

http://www.jagrepair.com/JaguarSTypeEle ... Icodes.htm

You might drop David Marks an email. You seem to have gone through a solid deduction and diagnosis procedure and certainly have an issue which I don`t think many of us here will have experienced. Watch for additional posts from members over the weekend. Someone might have had a similar problem. The fact that the fault appears to be on just one bank is curious but it is also something of a pointer. You appear to have isolated any potential plug and coil issues as part of your process of elimination. It has me a bit perplexed.

If you are not already using an independent Jaguar garage (has to be better than a general garage) I would suggest that a move to such a specialist might be helpful. In depth training and knowledge is worth so much when the gremlins come out to play.

Mike

[Lordgaz]

Thanks for the input on this problem - It is now solved -

All the air leaks have been fixed, and supercharger bearings changed, along with valley pipe and other bits and bobs - For the misfires, I asked my garage to check the backpressure on the exhausts as I suspected CAT damage due to the previous air leaks - Found that both of them were blocked, (when we removed the lambda sensor to pressure test on one side, it was glowing cherry red inside) - Cats have been removed for now, and my god it goes like the clappers - Must have been like it for a while (or even since I bought it about a year ago)

[J44EAG]

A classic cause, effect and solution scenario of a type.

Standard cats have an open cross sectional area which broadly equates to about 55% of the exhaust pipe size. So that is quite a blockage out of the factory! Tom Lenthall put me straight with this figure and also said the inlet side of the engine was somewhat constricted as well. Both "blockages" constrain and contain potential engine power production and rob a motor of its true potential.

To help with this issue I opened up and ported and polished the plenum above the throttle body, the throttle throat, removed the constricting metal shelf below the throttle, reworked and opened up the throttle body elbow and dropped the floor of both the elbow and the entry into the supercharger. A severe restriction on the right hand rotor inlet was removed, the narrow end of the V-shaped charger outlet was reworked, the upper charger case and cowhorn joint area was matched to avoid steps, the cow-horn chamber and charger case above the pressure plate polished, open up and smoothed, The by-pass duct turn was de-constricted and flowed and the outlet ports from the cowhorn manifold and entry to the inter-cooler bricks were opened, balanced and polished. Various other mods on the inlet side occurred which included a Mina Gallery cold air induction pipe rather than thye standard plastic abomination which has noise attenuater flutes which reduce induction roar but at the expense of power and torque.

Standard cats were removed in favour of sports cats with approximately a 65% open cross section. These allow an improved exhaust flow together with deletion of the large central resonator box complete with internal H balance pipe. In its place went a purpose built X-pipe arrangement without a resonator box around it. Yes, that is a little noisier. That was expected. Junking the old cats and inserting the new sports media proved highly effective at de-restricting the exhaust system. A very noticeable improvement in punch was immediately evident. That however comes at a cost at MOT time. The car whilst sitting at idle on the MOT ramp quickly looses cat heat and emissions can rocket. at that point I ask for a fast idle test which means the engine is revd for a couple of minutes to put heat back into the cats and allow the Lambda sensors to regain control of emissions. The procedure is a pain but necessary to pass the test. Cats are still present within the old cases which were cut open, old media cut out and sports media inserted before being re-welded. I make this point for the following reason.

As I understand it and please correct me if I`m wrong, I thought it was now illegal to remove cats or DPF filters from a car if previously fitted by a vehicle maker. As I understand it, cats may be removed from a car running solely as a gas conversion but if petrol is still fitted, then cats must always be present.

I can well understand you saying the car goes like stink with cats removed. Essentially you have got rid of a huge exhaust constriction but at the cost of cats removal. One has to ask where your the emissions currently stand as regards future MOT gas testing and whether the car is in fact still legal?

I`m intrigued!

Mike

[Lordgaz]

Hi Mike

The caveat was in "cats have been removed for now"
I am currently sourcing some more (whether it be sports cats (any links to where you obtained yours) or some from the catman.co.uk)


You are correct about removing CATs, as having owned an S55 AMG Merc with Cats removed, but running on LPG, I needed to get DVSA letter to prove to the MOT testing station that it was in fact legal for an LPG presented car to have cats removed, but anything else will cause problems at MOT time (or if stopped and emissions tested on the side of the road - (though that is unlikely) )

Would definitely be interested to know more about your sports cats.