I can't imagine what else it could be that would be temperature dependent like this.
Not likely low pressure from the fuel pump because why would it fail only when the engine warms up? And its mounted where its own temp would be stable.

Since the code is rock solid P0300 random misfire that leaves out any single cylinder problem causing it. So that leaves out plugs, coils and injectors.

Not likely tensioners as it would be more of a solid symptom I imagine and would likely throw codes pertaining to one bank. With my luck it will be the tensioners but at least I already have all the parts ready as they needed to be done anyways.

And the way the problem fades in after a bit seems to point to electronics failure.

If I am missing something here please chime in.


Dave

 

Could be timing, blocked cat(s), bad wiring, you name it - even a failing battery (or other poor power/ground). I've never seen P0300 without another P030x code so I'd want a 3rd OBD tool read-out.

 

Battery is fine. The problem started on the tail end of a 300 mile round trip. The weird thing is that it runs normal for a couple of miles until the engine warms and then it slowly fades in and doesn't come on all at once. The longer you drive it the worse it gets and then it eventually trips the CEL.
I did search this this forum and others and found several examples of people getting just P0300/P1316 and in most every case it turned out to be a tensioner causing the problem. But in those cases there was no mention of the problem being temperature dependent. I guess if one was cracked the right way it might not leak until the oil warmed up and thinned out some and that might explain the delay in the misfires.


Dave

 

A cracked tensioner shouldn't cause a misfire unless the chain skipped a tooth, and the you would have a rough idle.

How long have the plugs been in the engine? They most certainly can cause a temperature related misfire, although it's not as common as it was 50 years ago.

 

When you first start the car the idle is smooth and it runs good so it shouldn't be likely the chain jumped. Then after a bit of warm up it starts to skip and buck and it gets worse the longer it runs. At that point the idle is rough. The CEL doesn't come on until after the problem fully sets in. But the same codes will be there either way.
Its strange that the 1.5 version flakey reader showed P0308 every time but the new 2.1 version reader always shows P0300. Used the same Android phone and same version of Torque Pro in both cases. Of course its always possible they are both wrong but I'd need to find another reader. And if it reads a different code yet then which (if any) are correct? The codes may be weird if the ECU is at fault again. It threw fairly useless codes when it went bad before and the symptoms then were just like a chain jumping a tooth with rough idle.
I don't know how old the plugs are but someone did change the air filter recently as it look as new as the one I just replaced it with. But the plugs are an unknown as yet.
I do have the new plugs but I don't have the right combination of extensions and joints to get them all out and I have to car to go buy some. I'll have to order what I need online I guess then change the plugs and see what happens. If no change I will send the ECU to ASI and have them check it out. If they say its fine then I will start on replacing the tensioners. But first I have to use my $2k emergency fund to buy a beater car so I have something reliable to drive in the meantime.


Dave

 

I am not totally convinced that your pro problem is related to the ECM. I see that your car is a 1997 and it is Nikasil AJ26 and looking up the causes for the P0300 / P1316 (as stated in your post #23) it directs you to P1313 and in the list of causes low compression is listed along with several other causes.

Link http://jagrepair.com/images/AutoRepa...%201997-99.pdf

Check your fuel pressure
Check your compression
Replace the plugs you say you have

Now for your coil packs I had replaced all of my coil packs on my 99 (no codes) and it made a big improvement. I thinking that you may consider replacing your coil packs if all else checks good.

You must remember that your P codes are a tool that does not always tell you exactly what is going on. You could have a few coil packs that are on the edge and not setting a hard code for a specific cylinder, I know because I dealt with bad coils and no code.

 

Many are leery of changing the tensioners, it's not truly that difficult so I'd say go all in, as Gus mentions you should change the plugs (and you will then see if you have oil seeping into the plug wells, the new seal kit will solve this). I say this because once you get to pulling plugs it's just a few more bolts to get the valve covers off, why go back in twice. I know you've done work on the car and are capable, even taking your time it should be a max of 6 hrs, I also know from other posts you need to work outdoors (I think).
I'd get the tools required, the only thing you might need it a 1/4" universal swivel to get the back valve cover bolt out, otherwise there are just a few metric sockets. Seems this is the most cost effective route for you.

IF all goes well with this you've done some 'good' maintenance, if the problem persists you can then pursue some other items (smoke test / coils) Good Luck

ps, have you checked your fuel trims with torque ? See if they jump when the symptom kicks in?

 

I agree with those who say that you cannot rule out your coils at this point. Keep in mind that Jaguar really struggled with poor quality from the various coil suppliers in the late 1990s and early 2000s. By the mid-2000s near the end of the XK8's run, coil quality was much better and those of us who own the later models do not experience coil issues. This is true for my S-Type as well as my wife's XK8, and I would not be surprised if it applies to the XJ model line as well....

 

I gave this thing a rest for a few days. I took it for a short drive and it did the same thing. Ran fine for a couple miles and then started with the bucking and got worse the longer it ran.
This time however when I checked the OBDII codes its now back to the original fault codes I was getting with my old OBDII reader. So now its back to P0308 and P1316. So I have already swapped the coil for cyl 8 and the problem stayed with cyl 8. So hopefully its just the plug.
But here is my problem:
I finally got an extension and joint that allows me to access that plug as its the hardest to get to. The problem is the damn plug is in so tight I'm afraid I am going tp snap it off trying to get it out. That would really suck. I'd part out the damn car if that happens. I've never seen a plug in this tight. I guess whoever put it in didn't use anti-seize compound.
Any Ideas?


Dave

 

Some plugs are spec'd NOT to have anti-seize (due to their construction).

I found it much easier getting plugs out with the engine still pretty hot.

 

Changed all 8 plugs and guess what? Same damn problem. P0308/P1316. I swapped the number 8 coil yet again and still same. So it looks like its the ECU that was just fixed a few months ago. So next step is sending it back to ASI. The plugs that came out had no obvious problems. No fouling, oil, gaps still good etc.



Dave

 

I just called ASI and the tech said it could very well be the ECU as the problems fades in after a warm up. So tomorrow off it comes and hopefully they can find the problem and fix it.


Dave

 

At least he agrees it may be the ECU. Mine is still good, but it's been less than two years since they rebuilt it.

 

Mine was done in Feb. The ASI tech said it did sound like a electronics problem.
If the ECU turns out not to be the problem not sure what to look at next. Plugs new, swapped coil twice, swapped ignition modules. I Sea Foamed it, added new gas and Octane Booster and water remover.
Only thing left would be the tensioners. But why does it fail only when warmed up and only cyl 8 throws a code? This car is starting to **** me off. 3 weeks with no car now. Will likely be another 2 or more before I get the ECU back. Its my only vehicle and no money to get something else.


Dave

 

Wiring/connector.

 

I already cleaned and reseated all the connectors from the ECU, Ignition Amps and coils. At this point it pretty much has to be the ECU again. At least I hope so.

Dave

 

A chafed wiring issue would not be resolved by cleaning and reseating the connectors....

 

Yes I understand that but it wouldn't explain why the problem is 100% repeatable where it works fine cold and slowly starts to fail after a few minutes of warmup and gets worse as the engine heats up. Its acting MUCH more like a electronic component that fails above a certain temp. A chafed wire generally would be more intermittent depending more on vibration etc to act up. Also I have tried moving, wiggling and flexing the harness while its doing it and no reaction at all. I've worked on dozens if not 100's of other types of electronic gear with similar failures with the problem fading in with heat. Usually you can trouble shoot them with freeze spray and a heat gun to find the offending part. I thought about checking the ECU that way just to verify its the problem (and yes its fan is working) but ASI has warranty stickers on it so I can't open it to spray the PC board components with freeze spray.
A coil could act this way but I've swapped 2 different coils into the cyl 8 position and the code is always P0308/P1316. And when I changed the plugs I cleaned all the boots though most were very clean. I also put the coils back into different places than they came from to see if the code would change and it didn't. And hard reset the ECU which made the engine run crappy as its relearning all the trims etc. But still the same code.


Dave

 

It actually runs a whole lot worse with the new plugs but I can't drive it enough for the ECU to adjust to them but still only gets the same codes.



Dave

 

Did a bunch of slow speed driving and found that if you keep the speed under about 30mph and don't climb any hills it will run find for up to 20 mins. Any kind of load makes it fail sooner. BUT even keeping it loafing along it still fails, just takes a little longer. Still same codes. At least now the ECU has learned the new plugs so its back to running smooth and normal before the misfire starts in.
Also tried a pro code reader at the Exxon and it also gives P0308 as the culprit.


Dave