I've been fighting a P0171 code on my '99 XK8 for a several months. I don't drive the car all that much...pretty regularly but no real long runs so I've only driven it between 10 & 11K in the last 3 years so it hasn't been a front burner issue. To boot it only goes into restricted mode when I'm at idle or in a very slow traffic as at a light or stop sign and then clears up within the next 1/4 to 1/2 mile and runs perfectly.

Today I decided to get semi-serious about it and decided to find that damn leak come hell or high water. I'd already checked all the hoses, vacuum connections, VVT seals, MAF and IAT sensors had been cleaned and re-cleaned, full and part load breathers had been checked and cleaned so I was pretty much left thinking intake manifold.

It had also thrown a P300 & P306 so I swapped in a new coil on #6 to no avail and the plugs had all been replaced within the last 1000 miles. The P306 code went away but not the lean condition. STFT had re-learned so it was a 0 while the LTFT had stabilized itself just shy of 20.

Here's were I need help or advice.

I hooked the OBD up through my laptop and started the car up. Since I had run it around town earlier it was still near operating temperature and since it was idling the RP was active. I took a can of spray carb cleaner and sprayed it pretty liberally at the intake manifold to engine joint at #6 and watched the STFT go about -10% for a few seconds (10-20 I wasn't counting) and quickly afterwards the P300 & P306 codes reappeared and it ran even rougher for a couple of minutes before settling back to an off key sort of loping idle.

Am I right in thinking that it might be the O-ring seal at the base of the intake manifold at #6 where the air leak is and that going rich caused the computer to go lean in the short term (-10%)...or am I coo-coo for Cockopuffs?

I got no response from any of the other intake runners on that bank, only #6.

I was not all that happy about spraying carb cleaner all over the place so I switched to a small propane torch I have and nosed it around the TB and connections as well as the various intake and breather hoses with no response but to be honest I wasn't really careful with it and didn't hold it anywhere for very long so I could have missed something.


Another question. How would I go about rigging up a home smoke tester (there are several how-to's on you tube) and where would be a reasonable entry point be?

 

Do you have the numbers (STFT and LTFT) for both banks at idle and at 2500rpm? By no means am I an expert, but I've done quite some troubleshooting with lean conditions.

 

It certainly looks like the seal at #6 is bad and that would explain the misfire.

 

Bank 2 both the STFT's and LTFT's are within about 2% in either direction so it's definitely a bank 1 problem.

I'm really not anxious to pull the intake manifold because it's a pain in aft section to do because of all the plumbing and other crap that has to be removed to do it. I'd farm it out if there was anybody reasonable and qualified but there's not a Jag dealer closer than 120 miles in any direction and the locals only speak 4x4's and mud trucks

 

If it's a bank 1 problem it can't be #6. Up to MY 2002.5 The right bank ( A or 1) was # 1 to 4.

 

Your right but up until 2002.5 they numbered the cylinders 1-4 on BOTH sides but that isn't the firing order. To make it even worse the cylinder #'s don't correspond to the P codes either.

It's hard to explain but the bottom line is that the firing order is the same for both engines but the cylinder numbering scheme is different and the P codes are different. You can't use the post 2002.5 P codes on a pre 2002.5 engine even if you renumber the cylinders to match.

To make it even worse Jag has an illustration of the different engine's and the corresponding cylinder #'s and P codes but they don't match the P code cylinder cross reference in the '99 svc. manual.

My problem is, for example, the P306 code I'm getting corresponds to which cylinder. Is it cylinder # 4 on bank 1 where the lean condition is or is it #4 on bank 2...or is it cylinder #2 on bank 2 which is cylinder #4 in the firing order AND in the post 2002.5 V8's...which, if I were to follow that numbering sequence would be P304 in the post 2002.5 V8's.

Confused? So am I

Bottom line is that the intake runner at cylinder 3 on bank 1 (pre-2002.5 sequence) was the runner that appeared to be sucking air and the confusion over P's is Jag's fault as in the '99 svc. manual P306 is cylinder #4 but they don't say which side as the manual and the illustration don't match either on P codes or cylinder #.

Somewhere that's been corrected I'm sure but I don't have a copy of it and I'm no better off now than I was an hour ago when I tried to figure it out<G>

 

That's strange. I've dealt with misfires before and found 1-4 on the right bank and 5-8 on the left.

 

OBD requires certain codes and I expect Jaguar adopted consistent numbering (the newer kind, for Jaguar - ISO/SAE). P0306 is always cyl 6, and I suggest to use the standard numbering rather than Jag's old kind.

 

Should be simple right? Well the 1999 XK8 svc. manual says, for example, that a P0306 is a misfire on cyl. 4. No matter which cyl.# system I use a P0306 code only works if I superimpose the left side red numbers of the right side cylinder numbers.

Since the lean condition in the manual is P0171 and says that it's in the right hand bank (bank 1 right?) then it's the right bank where the misfire and/or the leak is........or to really confuse the issue could I have a misfire on bank 2 and a separate lean condition on bank 1.

Remember, this only occurs art idle or very low speeds <10mph and clears up with 1/2 to 1/2 mile of normal driving.

 

I agree that this should be simple to figure out and it might be if the Jag svc. manual and also JTIS didn't muck the works up by adding yet another twist to the equation.

Here's a screen shot taken directly out of the appropriate section of the JITS on the 1999 XK8 and as you'll see it doesn't match with either the pre- or post 2002.5 cylinder numbering systems and corresponding P codes.

If I use the post 2002.5 cylinder numbering which, is also the firing order, then P0306 should be cylinder #6 and would be the 3rd one back on bank 2.

If I use the pre-2002.5 set-up P0306 would be cylinder #2 which would be the 2nd one back on bank 2.

As you can see both the hard copy svc. manual and the JTIS say that in 1999 P0306 is supposed to be cyl. #4. The question then is ..which cyl.#4? All the way back on either bank 1, or do they mean the #4 on bank 2...both of which according to the picture DO NOT use 6 as the last digit in the DTC.

It's clearly an error in editing brought about by the switch in numbering systems that has been continued down the line.

For someone starting from scratch and depending upon the factory manual, or more likely JTIS, it would lead to a string of errors and miss-diagnoses.




The only way to sort of make some sense out of it is to use the last digit of the code that is assigned in the illustration to the pre-2002.5 V8's above and cross it over to the post-2002.5 V8's and use the cyl. # in that same position (bank1 #4 = bank1 #7) so that P0304 points to cyl #7 as the JTIS says and cyl. #4 on bank1 now becomes cyl. #7 on bank 1.


In any case on the pre-2002.5 V8's the P codes last digit DO NOT follow the cyl. numbers as they can't have it both ways if we're to believe both the JTIS and the svc. manual.

How many coils. plugs, and misfires have been wrongly swapped or diagnosed incorrectly because of that bit of confusion?

 

I'm not following you. To me P0306 indicates cylinder #6 in the early model. Second cyl Bank 2. Why is that confusing?

 

Even assuming #6 is not where some think there are only a few places it can be so swap coils for each, one by one, and see when the code moves. Allow 2 warm ups after each swap, so the code can reflag.

 

Firing order from svc. manual on pre-2002.5 engines


RJ , forget what you now know or have learned and start from the same place a person new to Jags would be. They buy a pre-2002.5 Jag with a 4.0 V8. They download a 1999 svc. manual, install JTIS on their laptop, and maybe even buy a workable version of SDD. They figure they're all set to do some DIYing. They run a basic OBD II scan and up pops 2 P codes,. A P0300 and a P0306. They look in the svc. manual and read on page 803 of section 3 (Powertrain) that the firing order is as above in the screen shot. No problem they say I'll just look further and see what those P codes mean. They run a search of the svc. manual and find that P0306 is a misfire on cylinder 4...ah ha they say "I've nailed it."

Except when they look back at the firing order there are two cylinder 4's! Now what do they do? They don't know that the post 2002.5 engines have a different cylinder numbering system or that their engine and the later version have the same firing order but use a radically different numbering system. They also don't know that the svc. manual, the JTIS, and the SDD use a P Code system based on the post 2002.5 engines and not their pre-2002.5 engines.

The only reason I "stumbled" on to this is that I have both an early 1999 XK8 with the 4.0 V8 and a later 2004 XJ8 with the 4.2 V8. Even my Jaguar published 2009 vehicle specifications covering both engines shows a side by side of the two engines which shows the different cylinder # schemes but DOES NOT show the appropriate P codes next to the individual cylinders so it was no help.

I know what I know NOW but not because of the tons of stuff I've downloaded but because I also stumbled across that single Jaguar illustration that showed the 2 engines with their cylinder numbers AND the corresponding P codes and began to understand where and what they had screwed up in their manuals, etc.

How many new owners and new techs at dealers and independents know that on day one?