P0305 code - misfire on cylinder 5. Started after a coolant leak, changed the coil pack and spark plug for that cylinder.

When code is cleared it’s fine but when the speed is increased it goes back to restricted performance.

A mechanic should it could be the fuel injector but for s types they are glued in and really difficult to remove.

Anyone any ideas or had similar problems ? The mechanics I’ve called don’t seem to want to even look into it and just said go to Jaguar.

 

Okay, gotta ask: Why did a coolant leak lead you to replace a coil and spark plug?

And to make sure I understand correctly, this is a brand new problem that started immediately after changing some parts? If so, that would point to defective parts or something that was disturbed in the process.

What brand coil did you install? Was it a no-name eBay special or the house brand from a discount chain? Some cheap coils are garbage right out of the box. Don't fall into the trap that a part must be good because it is new.

For troubleshooting, swap this suspect coil with a known-good coil from another position. If the fault follows the suspect coil, then you know it is bad.

 

I was advised by the Aa that the coolant had likely caused the misfire as it sprayed everywhere and had probably gone on the spark plugs.

I have a thing with the Aa where they paid for £500 of the repair if they don’t fix it by the road so the garage replaced the coil pack and spark plug but then said it still misfires, they don’t know what’s wrong and to take it to Jaguar.

 

Please be patient while I pick your brain for more details. Trying to help, but have been needing to read between the lines to figure out exactly what happened and when.

First thing, telling us the model year and engine will really help. V6? V8? V8 supercharged?

Back to reading between the lines, I take it you're having all work done by a shop, as opposed to doing it yourself? I think your shop is out in left field if they say you must take the car to a Jaguar dealership. These cars are not some rare exotic models. Any competent mechanic can handle nearly any problem you might encounter. If not doing the work yourself, I'd suggest trying another shop.

Time for me to get up on my Misfire Soapbox™. If the computer has set a misfire code, please be aware "misfire" wasn't the best terminology that could have been used. Misfire sounds like an ignition problem, at least to me, meaning the fuel and compression were there, but for whatever reason, the required spark was missing or weak. This might lead a good-looking aspiring mechanic to troubleshoot the daylights out of a perfectly good ignition system. I do not care to discuss how I know this.

In OBD-speak, misfire simply means one or more cylinders is putting out low power compared to the others. Pretty much anything affecting the output of a cylinder can set a misfire code. It can be low compression. It can be a valve not opening fully. It could be a bad fuel injector. And yes, it could be an ignition problem, too, but don't overlook the other possibilities, too. [/soapbox mode off]

Can you please provide a timeline of exactly what happened? I'm back to reading between the lines, but it sounds like you had a major coolant leak that left you stranded and required a tow. Did you shut the engine down right away? Had the car been driven for some time with no coolant?

When exactly did the misfire code show up? Immediately after coolant sprayed everywhere? Or was it a day or two after the leak was repaired? You mentioned coolant getting on the spark plugs. This could cause a misfire if still wet, but once dried off, the spark plug shouldn't be affected. Even the coil should have been okay once dried off. And if they changed it as a precaution versus confirming it had failed, it seems like the new one is bad from stock. This is VERY easy to rule out, by swapping coils with another cylinder.

Back to what the shop found, any competent shop should be able to test for a spark from the suspect coil. If the problem was elsewhere, such as an injector, they should be able to listen to it with a stethoscope to make sure it is operating.

 

I can advise you that I am having the exact same problem after my recently purchased 2002 Vanden Plas 4.0 overheated spraying coolant on the record hot day in July. The car was showing misfire on 3 cylinders and the owner who was a retired school teacher was charged $2,500 for new coils and plugs on 3 cylinders for misfires which solved nothing. They then said she needed a new head gasket for $2,500 at which time she had enough and sold the car to me. I completed a compression test after finding no hydrocarbons in the water to support a head gasket leak. The result of my compression test was 200 on every cylinder except #8 which was ZERO. This was putting the car into low performance mode. I shot air into # 8 cylinder with an adapter to screw my air hose into the spark plug hole. With the engine turned to TDC on #8 it blew are out the throttle body revealing that one of the intake valves was not closing. After some research I discovered that after overheating valve guides can drop in some Jaguar engines. I am currently waiting delivery of a bore-scope camera to look into the cylinder to identify that or a piece of carbon lodged in the seat. Perhaps a broken valve spring. The most important lesson is to not chase misfire codes. They only cost money and do not properly identify the problem. The old fashion compression test never fails to reveal.

 

Excellent point, well taken. I often suggest swapping coils for initial troubleshooting, as they are a common failure point and it's easy to rule them out before digging deeper elsewhere.

Sadly, in this case, we still don't know most details of the coolant leak and subsequent misfire problem. Was the leak something simple caught in time, with no actual overheating? Or was it a full-blown overheat, followed by a self-destruction of the cooling system? We still don't know the engine and year. The OP has never posted back after several days, so this may likely become another unresolved ghost thread.