I recently purchased a 2000 Jaguar S-Type V-8 4.0. The car had 88k miles on it and seemed to be well taken care of. I took the car to a shop to have it inspected before I purchased it, and there was nothing major that came up. A few days after purchasing the car, the check engine light came on (convenient, huh). The car also seemed to be sputtering as I drove. So I checked the code and it came up as P0304, cylinder 4 misfire. I bought a new coil pack and spark plug and changed them out. After changing them out the code went away, but the sputtering was still happening. It has been a few days since then, and now the code is back P0304.

I have looked around and see that the issue could be bad fuel injectors, O2 sensor, or maybe even water rolling into the spark plug of that cylinder. I was wondering if anyone has an idea, or maybe has had this issue in the past. Any help would be greatly appreciated. Thank you for your time!!

 

I hate to ask, but are you sure you changed out cylinder #4?

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

 

Yes from all the information I could find, I changed out the correct Coil Pack and Spark Plug. If you are looking at the engine, I changed out the the Coil Pack and Spark Plug that is on the left side closest to the firewall. I will try to attach an image that I used.

 

You do know about the timing chain tensioners and that they must be changed?

Do you know if you car has had them replaced?
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I did not know about the timing chain tensioners, thank you for that information tbird6. I do not think this is my issue though, as the descriptions do not fit the issues I am having, as far as I can tell. I will put this on the list of things to do.

 

Any progress? How hard is it to access #4 cylinder? You see, I'm a big proponent of cheapskate troubleshooting. I'm not familiar with the V8, but if access is easy enough, I'd suggest swapping the spark plug, coil, and injector with another cylinder. If the problem follows, then you know one of those three items is at fault. I've had enough new parts bad from stock, so don't just assume parts are good because they are new. Swapping with known good parts will rule out that scenario.

Another thing to keep in mind is how the onboard computer determines a misfire is present. When I was young and stupid (I'm older now...), I thought the computer was monitoring only the ignition output, hence the term misfire. What's really happening is each cylinder's overall power output is compared with the other cylinders. This is done via a sensor reading crankshaft RPM, and is able to determine the pulses of acceleration as each cylinder fires. If a cylinder's output drops relative to the others, that cylinder is flagged as having a misfire. (There are usually special parameters that have to be met, such as occurrences on successive drive cycles, but I'm not sure of the Jag requirements.) This monitoring watches everything (spark, fuel delivery, compression) and not just the ignition system as I once thought. In my defense, at the time I had just learned to read an automotive oscilloscope, and so figured the onboard computer was doing something similar.

If you can swap the coil, plug, and injector, you've just ruled out two of the three likely culprits causing the misfire code. Back to my learning experience, I had low compression on the one cylinder causing the code. The low compression was easy enough to confirm with a compression test, but the hardest part was to shift my thinking and actually run the test. The problem was due to a hydraulic lifter pumping up. After replacing the lifter, all was groovy.

I'm not saying low compression is your problem. I just wanted to provide some background on what triggers the code, and how you can tackle the troubleshooting.

 

I think #4 is a mite awkward but not too bad.
A new bad coil is #1 suspect, especially if non-OE coil used.
Wiring/connector would be my next bet, way behind the coil.
Injectors don't seem to be flagged as misfires, but I wouldn't say impossible.

Can't hurt to check compression but do plan to change tensioners (etc) to the metal-bodied ones.

 

Kr98664 - Thanks for your response. #4 is not too bad to get to. The idea of these new parts being bad has crossed my mind. I think switching the Coil and Spark plug, is a good idea, I will try that. As far as the fuel injector, I have not touched that yet. I did a quick search, and it seems a little more difficult to do that job. I will first try swap the coil and spark plug and see what happens. Thanks.

JagV8 - Thanks for your response. I will look at the coils and see if I can figure it out. I have read in a few places that the code P0304 could be a bad Coil, Spark plug, fuel injector, O2 sensor, or even water getting in. That, and the way the car sputters, is why I was thinking bad injectors. This car was not driven all too much, it only had 88k on it since it was purchased in 2000. I saw in the maintenance book that there was a three year period (2004 - 2007) where it was only driven about 4,000 miles.

 

All known possible causes are in codes PDF - free from stickies & in JTIS.
I'd swap just the coil to start with but plug as well is an option.
You should know if there was contamination as it'd be clear on coil / looking in plug well.

 

Check to make sure the fuel injector electrical connector is fully locked and seated on the injector.

 

Well I swapped out the cylinder 4 coil and plug with the cylinder 3 coil and plug. The check engine light has now gone away. I will drive it around for a while and see if the light comes back on. At least I now know that the coil and plug I put in are not bad. So we will see.

 

Well the check engine light came back on today! Same code for a misfire on cylinder 4. I will look at the injectors and see if I can see anything wrong with them. Booo!! =)

 

FYI, make sure you didn't accidentally pinch one of the Plug Wires supplying the voltage to the coil. I pinched it pretty bad when installing the coil.

 

I hate to resurrect an old thread, but this is the exact same issue I am having and was wondering if you ever figured out your problem, nardito.

I have an 01 S-type, 4.0. Cylinder 4 misfire. Swapped coil and plug from #1 and still have cylinder 4 misfire. Did a compression test on the entire bank (cylinders 1-4) and all were within 5psi with the lowest being at 132. The injector seems to be working with a stethoscope (I can hear it clicking) which doesn't necessarily mean it is injecting fuel. So as of now, I have it narrowed down to a faulty injector or an intake manifold leak around cylinder 4.

Any advice/help would be appreciated.

 

Add a BG44K to a tank of fuel and see what takes place. I assume you checked the spark plug.

Gus
www.jagrepair.com

 

Yes, checked the plug and even swapped the #1 plug along with the coil to rule that out. It has a dead miss. even at idle. I can unplug the coil at idle on cylinder 4 and nothing changes. Any other coil I unplug results in a drop in RPM and even rougher idle.

I have verified the coils to be good and spark is being delivered to the plug as it should. Are intake manifold or injector leaks common?

 

If you have a dead coil receiving no electrical impulse, then you have to check the harness on that side of the engine. Your going to have to peel back the insulation carefully.

Be sure you have no electrical pulse to that coil before meddling with the harness as it's a PITA to deal with considering years of heat cycles that harness is exposed to being tucked right underneath the coil cover..

You might have a pinched or frayed wire to cyl #4, either +12V or ground wire. (If I recall, this happened to me with Cyl #3 - after trying to peel back the harness I would up re-wiring, soldering and crimping that harness) it's bullet proof now.

Please also take the time to go to the new members section and introduce yourself.

Just so we're on the same page, cyl #4 is passenger side rear plug...

Injector leaks are common... Manifold leaks are not but neither would be a contributor to your issue.

It sounds electrical to me...

 

My spark and voltage to the coil has been verified to be good. Plenty of strong spark. Got a new injector I will pop in today. Will report back with any progress made.

 

Sounds like you are on the right track. You've verified a good spark at the dead cylinder, so ignition isn't the culprit. Compression is good, so that leaves fuel.

One little gotcha to consider. From the "I don't care to discuss how I learned this" department: When you replaced the #4 coil and plug, are those new parts or did you swap from a known-good position? On rare occasions, I've had new parts bad from stock. Whenever possible, I like to swap known-good parts to the suspect location, and then install the new parts in a different spot. That way if the fault returns at the same location, you know the problem isn't the known-good part just installed there.

This creates a little bit of extra work, but the payoff is huge if a new part is bad. If you haven't done so, I'd suggest going back and trying that. It's possible for a coil or plug to test fine in ambient air pressure, but fail under the extra load of compression. Testing a coil/plug in ambient air is good troubleshooting, but isn't 100% conclusive. (This is another lesson which I don't care to discuss how I learned that )

Same principle goes for the injector. I'd swap a known-good one to #4 and install the new one at the donor location. Pick a different cylinder so if the fault follows, you'd know whether it was the injector or coil/plug at fault.

Keep us posted.

 

Thanks for the input. I actually did what you suggested. I put the new coil on #1 because it is easier to get to and the #1 coil onto #4 because it is a little more difficult (although I am pretty good at it now since I have had it off and on about a dozen times).

Installed the new injector; issue is still there. I did NOT swap a known good injector into #4 because that would have meant pulling multiple injectors out of the rail and I wanted to spill the least amount of gas as possible.

Kind of at a loss at this point. Has any one else done a compression test on a 4.0 recently or would be willing to do one to compare readings? One when engine is cold and one when warm?