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Not firing on two Cylinders

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Not firing on two Cylinders

Postby Koeschi » Mon May 14, 2018 11:03 am

Dear All, Ive been the owner of a lovely (in a dodgy way) XJ40 3.2 since July last year and despite a little bit of leaks into the boot and the gradual increase in rust over the year its been a great car which i was hoping to keep loving long into the future ! I had just been sprucing it up for its MOT yesterday changing a couple of bulbs and checking things over and when i went to move it in the evening it was obviously misfiring and low and behold when i remove the plugs in cylinders 4-5 (counting from the bulkhead) there is no change so i guess they are not firing. Now my worst fear is that the gasket between the cylinders has blown but i am not sure yet that this is the case There is no contamination of coolant that i can see and my oil looks goo. I will do a compression test tonight to see what those cylinders read at but while Im checking is there anything else i should be looking out for before i decide to either drive into a tree or replace the head gasket ?

Its done 77000 miles 1991 model and it had new plugs probably 2000 miles ago

Any advice would be much appreciated i would love to keep this car going

Many thanks


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Re: Not firing on two Cylinders

Postby stevemc » Mon May 14, 2018 11:38 am

check the cap for damage arcing and check the rotor arm is okay as well, check the ingition leads are okay and not broken down.
Also check the inlet manifold gasket as these can and do break down and let in air
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Re: Not firing on two Cylinders

Postby NMV 1E » Mon May 14, 2018 2:36 pm

............................and then do a compression test. "They" should be all the same reading, (roughly) :)
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Re: Not firing on two Cylinders

Postby Brake buster » Mon May 14, 2018 7:13 pm

in the XJ engines the cylinders are counted from the front, just so you don't confuse anyone

so your ' 4/5 ' cylinders are actually 2 and 3 ...... from the radiator end

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Re: Not firing on two Cylinders

Postby Jaguarxj40 » Fri May 18, 2018 8:51 am

Hi JP,
Is your car a daily driver Or has it been standing for a while?

Personally if this was me I would check that I was getting a spark first at both of the cylinders that are affected.
If no spark then you would have to suspect that you may have a dizzy cap issue as I would doubt that two spark plugs and leads would fail together unless you are getting arcing between the two leads that are maybe a bit past there best.

I doubt it would be the rotor arm as I would think that you would have a no start problem but don't rule it out and ckeck its condition.

If you are getting a spark at the plugs, are they wet with fuel :?:
If they are then it may point to the injectors being stuck or the ECU not sending a signal to these two injectors, if you don't have the nessecary test bulb ( Noid light) Then a test bulb will suffice, unplug each affected injector one at a time and connect your test bulb and check to see it the bulb lights up on cranking, if it does then you are getting a signal, if not then you need to suspect either the wiring or ECU.

If your getting a signal to the injectors, good :)
then with the engine running and being carefull you can check with a long screwdriver to your ear and the other end directly at the end of the injector where it enters the inlet manifold to check if it's firing. You should detect a distinctive clicking, if not then it may be stuck, a gentle tap with a small hammer will free it up.

If this all proves ok, then do a compression test.

Either way, please let us know how you get on :D

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Re: Not firing on two Cylinders

Postby leo_denmark » Fri May 18, 2018 9:34 am

I would take the less optimistic approach and do the compression test first. It's easy to do, and 2 neighbour cylinders failing does unfortunately point towards blown head gasket

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Re: Not firing on two Cylinders

Postby Steve_D » Fri May 18, 2018 4:34 pm

When I got mine it had a complete misfire on cyl 5 and the cause - after much investigation - was a failed inlet gasket between the manifold and the head at that cylinder - the thin lower edge of the gasket had worked its way out and the resulting rush of unmetered air caused a failure to fire at all. Also, it couldn't be seen from the top of the engine at all but was very evident when I took the manifold off. Yes - unlikely to have happened to two cylinders at the same time suddenly, but stranger things have happened. Good luck.

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