Hi everyone, I really hope someone can give me some pointers, because I may lose my mind otherwise. I have a 2002 S-Type 3.0 which I love, but she's driving me crazy at the moment.

So back in about October 2022 it started having terrible misfire, loads of error codes, so I looked through the forum and concluded it was probably a coil pack. So I changed all the coils with new ones. That solved the misfire problem, she ran beautifully for months. Then at the end of March she started misfiring again, this time worse (flashing engine light - obviously had to stop driving to avoid cat damage). I changed all the spark plugs and the misfire went away, but it's back again now. I'm getting error codes 0305, 1316 and 1315.

I'd add that I found I was getting water into the engine bay from where I'd had to remove the cowling back in March to replace the wiper motor. I can't see any water in the engine bay or spark plug wells though at the moment.

I feel a bit like I'm chasing my shadow here! Any suggestions?

Thanks for reading!

 

Welcome to the forum.

The $64,000 Question:

What brand of coils did you install? The forum is littered with sad tales of woe caused by the failure of brand new no-name coils. The house brand from the discount chains can be just as bad.

Here's my sad experience of a new coil failing, and it was a quality brand. Not only that, I had the misfortune to install the new bad coil in the same spot as one that had previously failed:

https://www.jaguarforums.com/forum/s...attack-265787/

The moral of the story? Assume nothing. Suspect everything.

For some low-cost troubleshooting, swap a known-good coil into the suspect #5 (P0305) position. If the code follows the suspect coil to a different cylinder, then you have your culprit. While you have the coils out, be sure to inspect the spark plug wells for oil. These cars are notorious for oil leaking into the plug wells and interfering with the ignition.

While I'm on a roll, it's time for me to get up my soapbox. Forum regulars have time to step out for a smoke while I go off on my standard rant:

[Soapbox mode] 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 an 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 clogged fuel injector. And yes, it could be an ignition problem, too, but don't overlook the other possibilities, too.

[Soapbox mode off/]

 

Hi Karl,

Thanks for your reply.

I didn't buy Jaguar coils, but then again I also didn't just buy some tat off ebay (I bought coils from a local parts retailer that supplies all the garages in the area).

I'm glad to know there are others in the world who, like I do, get a touch annoyed by the term "misfire" (hence the quote marks in the thread title haha). When I say "misfire" in this instance, I mean when the engine is at idle I can literally hear the thing misfiring and running rough. If I sit in the car and hold the revs up it *seems* ok. If I try to drive anywhere it's ok most of the time, but misfires under load (for example when accelerating after a roundabout).

I'll definitely try swapping the coil over from 5 to another cylinder - I'll move it to one on the other bank that's easier to get to! I'll probably move the plug as well just in case. I'm thinking that perhaps move the plug to, say, cylider 2 and the coil to cylinder 4. That way if I get problem on just one of those, I'll know it's just either plug/coil, but if problem moves to both then I'll know it's both plug and coil.

My car is a 2002 3.0 v6 but I think it's the later 2002 one so I think I'm right in saying that the cylinder numbers are like this:Thanks again for the reply and help!

 

Cylinder numbers as above, yes - but REGARDLESS of year if using OBD II, because OBD II numbers them that way (due to following international standards & laws).

Though there is probably an OBD II tool somewhere which gets this wrong...

If you can hear or feel misfiring it's staggeringly dire, sadly.

I wonder what short term would be better than misfire? Misfire means things didn't burn as they should have, I gather. No need for it to imply ignition parts.

 

Cylinder numbering here:

http://www.jagrepair.com/images/Auto..._numbering.pdf

If you have a late 2002 or newer, the correct figure is top row at the left.

Up to mid 2002, the correct figure is the middle row at the left.


Early or late 2002? Look at the bezel at the base of the gearshift lever.

Early models have a 5 speed transmission, so D=5. The first position to the left of D is 4.

Later models have a 6 speed, so D=6. The first position to the left of D is 5.

 

Had anybody asked me when the standards were being developed, I'd have suggested "Power Imbalance" or "Low Power". I double checked my answering machine, though. Nothing.

 

I sure hope it's not that dire... I could certainly both hear and feel a bad misfire previously when I changed the coils, which then went away once the new coils were on. I'd definitely rather suffer the cost of new coils again than something more serious!

 

Check for exhaust leaks, and check fuel pressure. Both can cause misfires.

Fuel pressure should be around 3 bar (300 kPa).

 

Ah now that's interesting, because when I was out fidding with the car earlier today I did think that perhaps I heard the exhaust blowing a bit. I didn't realise that could cause misfires?!

 

I've just been checking fuel pressure and it's sitting at around 54 psi. I think that's about 3.6 bar. Is that too high or ok do you know?

 

you have an answering machine?

 

It’s right next to the fax and dial-up modem.

 

Was that measured with a mechanical gauge before engine start? Or on a scanner, engine still off? Before engine start, you should see around 55 PSI on either a scanner or mechanical gauge.

With the engine running, a scanner should always show around 40 PSI. At higher power settings, actual fuel pressure increases but the value reported to the computer (and your scanner) stays the same. Potentially confusing details here:

https://www.jaguarforums.com/forum/s...estion-261975/

 

Absolutely ensure your exhaust leaks are fixed! However, when you changed the plugs and coils did you notice any oil on any of them? Common cause of a misfire is oil leaking from the cam-cover gaskets into the plug wells. Solution is replace the gaskets and thoroughly remove oil from coils, plugs, and plug wells.

 

It was with a scanner but with the engine running. It was sitting around 54 to 55 psi. Engine off was about the same.

 

There was no oil in the wells that I could see when I changed the plugs etc. I'm going to hunt down any exhaust leaks and fix them.

 

Hmmm, this doesn’t sound right.

Before engine start, when the pump runs briefly to pressurize the fuel rail, you should see 55 PSI. A scanner and mechanical gauge will see the same thing.

After engine start, engine at idle (low power demand), you should see 40 PSI with either a mechanical gauge or scanner.

With the throttle wide open (high power demand), fuel pressure increases and a mechanical gauge will show 55 PSI. However, things get confusing because the scanner should still show 40 PSI. This is because the sensor does not show absolute pressure, but a differential pressure compared to manifold pressure (inverse of vacuum).

Follow the link i previously posted for a better explanation. But I’m very confused because the scanner should always show 40 PSI with the engine running, regardless of power demand. I’m not sure how you’re getting 55 displayed.

Is this the root cause? Heck if I know, but it’s perplexing. Definitely get a mechanical gauge on there. There’s a test port just forward of the oil fill cap. It looks like a valve stem on a tire.

Check the vacuum line between the intake manifold and fuel pressure sensor. Mine popped off one day and caused rough running and other issues. It would also skew the feedback for fuel pressure. Not sure it would cause your exact symptoms, but is easy to check:

https://www.jaguarforums.com/forum/s...-p1151-254009/

 

I double checked this on my ride to work this morning. Before starting, key on, my scanner showed 55 PSI. As soon as I started the engine, the scanner showed 40 PSI (+/- 1.5). I even tried a couple of full throttle accelerations and the scanner always showed around 40. I data logged the entire trip and the scanner never budged more than 1.5 up or down from 40. Only after I stopped the engine did I see 55 again.

What has me really perplexed is the computer tries to regulate fuel pressure to 40 PSI. I've no idea why it's trying to maintain 55.

The sensor can be inaccurate, and the computer will happily adjust the pump to this inaccurate input, as long as the feedback shows 40 PSI. I had this happen a few months ago, when a mechanical gauge showed 30 PSI but the scanner showed 40. The computer thought everything was good. A new sensor brought the reading on the mechanical gauge back to the normal 40. But your symptoms are different, as the computer is trying to maintain 55.

Anybody got any thoughts? Is there some weird mode when this higher value is the target? Could the computer think the engine hasn't started, and is trying to maintain the 55 PSI used to prime the lines before start? Scratching my head here...

 

Thanks Karl, that's really helpful. What's really bizarre is that the car has literally stopped misfiring. She's now running beautifully and I'm absolutely scratching my head as to why or what's changed.

 

I just thought I'd drop in and give an update on this issue. The car is now running beautifully, no misfire or anything of that nature. It seems that there were two issues:

• In heavy rain (UK so it does happen) there was still water getting down into the engine bay, but it was really hard to see it - there wasn't water getting into the plug wells, but the water was getting onto electrics on back of the engine. When I finally found that and sealed it all up to stop it happening, the issues seriously decreased.
• Vacuum leak, detected by checking fuel trims whilst spraying quick start around various joints in the engine bay. Fixing this then improved the situation further.