Hi all!

Sorry I'm a little tired to this post may contain typos and not be written brilliantly, but I'd like to get it out before work tomorrow and my weekend off, so I can get on with patching up my red beauty next week!

My car developed a misfire recently. It is only minor, but enough to feel the car vibrating and notice lack of power on the motorway.

Here's what I've done so far:

• Disconnecte each coil individully with engine running. All coils have noticeable effect on engine except for cylinder 3, so that must be where the misfire is.
• Checked the plug on cylinder 3. It is oily and black, while the others are dry and baked.
• Switched the coils between cylinders 2 and 3. Repeated the first test with the same result. So the coil is not at fault.
• Put new spark plug onto coil 3, checked if it sparks. It does. Ran first test again, still mis-firing. Spark plug is also not at fault.
• Drove a 1000mile round trip with the misfire becuase i really had absolutely no other option. I hated doing it, but it made the whole trip without issues or getting worse.
• Had a compression check done. Compression is good.
• Borrowed a code scanner and saw code P1621, which I have read is a code that isn't used on X300 and can therefore be ignored

So as it stands, the possible causes I can think of are:

• Fuel injector not/hardly injecting
• Crank Sensor Issue
• Something else...

Would be very grateful for any help on how to further narrow down the potential cause, as well as suggestions for other possible causes. I'm hoping to mostly DIY this and learn as I go.

Thanks in advance and let me know if you need any more information about the car or pictures of any components.

 

If I recall, the P1621 is for Immobilisation, not going to cause a misfire. Was the spark plug on cylinder 3 oily on the where the Coil goes on or on the tip? If the coil is firing when put into another cylinder, then possibility it could be a fuel injector not working. But the fuel injector would just make the plug wet if the plug wasn't firing, not oily. The valve guide seals have been a known issue on these engines, possible that could be source of oil getting into the combustion chamber on that cylinder. When you check the spark from other cylinders, are they the same? Such as same quality, not one is sparking some, and the others are more.


Crank Sensor faults usually give a no start or dies once engine gets warm, at least for the Jaguar.

 

By 'where the coil goes on' do you mean the actual electrical contact to the coil? IF so, that is clean. The oil is around the tip, in and around the spark gap.
Thanks for the tip about the valve guide seal. How hard is it to diagnose/replace this?
About the sparks, I'm not 100% sure. I only checked 2 cylinders (2 and 3) and I think they were about the same, but it was a bright day so it's not always easy to tell. I can re-do this test, what should I look out for, and will it tell me if they're not all the same?

 

Objak, your troubleshooting seems incredibly methodical and sound thus far, and would seem to point toward an injector. We've heard of the crank position sensor failing in a lot of strange and creative ways, but as JB said, they all culminate in a no-start or a stall while running. I don't recall any associated with misfires. Maybe if you had one or more teeth chipped off the crank pulley timing plate?

As noted numerous places in this forum, the X300 OBD II implementation is notoriously loathe to set a misfire code, but it seems you've isolated it to #3 already. Doug or Don posted the possible causes for a misfire from the manual in another thread recently. I'll try to find that and link it.

I guess your next step would be to swap the #3 injector with its neighbor. I've not pulled any injectors yet, looks like a bitter-ex-wife of a job....so maybe you just want to pull it, or maybe all, and have them refurbished. There are threads here listing some vendors who do that sort of thing.

Although you've already ruled out the coil, if it were me, I'd still pull the coil-cover off and fire it up in a dark garage at night and look for a light show before I got my hands dirty changing injectors.

Edit: It was Don: https://www.jaguarforums.com/forum/x...0/#post1659064

 

Sound advice as always from alholbro1.

One step I would do before pulling/swapping injectors is to check out the wiring/plug to No. 3 injector. Wiring in the loom can get brittle and crack.

Ideally use a Noid light (less than £20 for a set on Amazon) to monitor the injector firing signal, but you can at least visually check the wiring and use a multimeter to do some testing (I think the firing signal may be too quick/short for a multimeter to pick up).

 

I meant when you take the coil cover off and take the coil out, is the boot covered in oil? As far as the quality of spark could indicate a coil getting weak. The valve guide seals would be a last resort sort of thing. It would be a costly job, pulling the head off and sending it away to a head shop. There is another way to do it, but requires a special tool put in place of the spark plug and an air compressor, unless you had access to these both, you'd have to pull the head.


I've seen as these cars get older fuel injectors can fail, don't always log DTC's. As B1mcp mentioned, check the wiring as that has also been a known cause in the past. If nothing obvious is found, may have to try swapping injectors to see if the misfire moves.