Hello everyone,
I have just bought an XJ40 with te 3.6 litre engine and have a problem. The problem is that the car idles in a very "lumpy" way and misfires consistantly on number 5 cylinder. The exhaust is also a bit fumy but it passed the MOT test yesterday and didn't fail on emissions.

I have done the following: Replaced the plugs (when I got the car, the plug in number 5 had faild completely, with the porcelain section loose and bouncing up and down as the engine ran).

Switched around the ignition leads to prove that they are not faulty.

Switched around the injector connectors to 5 and 6 to prove the injector supply.

Removed the injector rail and swapped injectors 1 and 5. Proved the injectors but connecting to a battery and blowing through them - worked ok.

Removed and cleaned the crank sensor.

Carried out a compression test - all pots about the same reading.

Now I'm out of ideas! Cylinder 5 still seems to do nothing - when you pull the plug lead, you can hear the spark, and when I disconnect it, there is no difference to the engine.

Any ideas?

Thanks.

 

How and why are you sure it is #5 that is causing the misfiring...BTW what was you compression reading across the board?

Start with the basics..wire leads in proper firing order....Plugs gaped to the right spec..Cap and rotor :NEW: use only geniune OEM replacment parts...not the cheapies from you local Auto Parts...XJ40's are tough on the Rotors and caps..buy only the best....has if it were me i would...of course had i checked all the basics "first" then i would remove the Cam cover and do a visual....Check all shims....Alignment...ETC

How many miles you have on the AJ6?

There is a lot to just go thru and check...when you first get a Jag..Now is the Time get a book.... Clean all replace what needs done....check all Specks....Just go thru the baby...and she will treat you right...they like to be pampered...

Good Luck....

 

Thanks for the reply Don. The problem turned out to be a spectacular inlet manifold gasket failure betwee the inlet for cylinder 5 and the bakellite seperator - the gasket had completely exited the gap causing a huge air leak to that pot. Common fault apparently and not really visible until I had removed the inlet manifold. Due to their poor performance, these gaskets are now unavailable so I've ordered some compatible gasket paper and I'll make one using the other intact gasket as a template. Until then, I've reassembled the engine using Hylomar Blue as a stop-gap - not perfect but better. As for the rest - getting through it - biggest current problem is that my rear exhaust manifold is cracked and - again - replacements for an early car like this are hard to find.
Cheers.

 

Try sngbarrat.com. I've clipped this from their site. Worth a try ;-)

Part No: EBC2781*
XJ40 3.6

2 required for full kit
Original part available part code EBC2781

 

Thanks Oddman, but the problem is now sorted. I went onto the internet and bought two sheets of 0.8mm gasket paper 10"x10" for £2. I then drew around the intact gasket and cut it out - a good dose of Hylomar blue on both sides and refitted the inlet manifold and it is now leak-free. I had to fabricate the gasket in two halves due to it's sheer length and I had to punch out the stud/bolt holes with the top half of a Parker "Jotter" ballpoint pen - just the right diameter and sharp as well. Now to address that annoying cracked rear exhaust manifold.