So appears I spoke too soon....

After about 150 miles of driving, check engine light came on. The car still runs a million times better than before, but now I am perplexed. A quick scan with AutoEnginuity revealed P0171 and P0174, with freeze frame data as shown below:



So I decided to graph some live data of absolute manifold pressure vs. RPMs and that's shown below. I'm researching what's considered normal, but if someone can comment that would be great. Immediately, the car maintains about 12-13 in Hg at idle. The first big RPM hump in the graph is the gradual increase to 3500 rpm over ~10 seconds. During that time, absolute pressure drops to below 10 in Hg. I then did a few abrupt taps on the accel pedal, and the absolute pressure seems to jump to ~28 in Hg, which is pretty close to zero vacuum, and then recovers.




The same data but in relative terms (0 = atmospheric, 29.92 = absolute vacuum) is shown below. Dashed lines represent 17 and 22 in Hg of vacuum, which is what the vacuum gauge dial normally displays as "normal motor":



Given the long term fuel trim is at ~8% for both banks, I wonder if MAF sensor replacement and injector cleaning is appropriate? I remember I was running K&N filter for a while, and did try cleaning the MAF sensor, but it is all original, and the vehicle now has 97K miles.

 

 

Thanks for the PDF. It's got 31 pages more than the supposedly same one I have - date May 2004 but yours is some time in 2013.

Codes explain why your monitors won't set.

+1 that you're making progress. It's looking like a car with fairly typical problems - the kind that are usually fixed after a bit of effort.

 

typo...thanks for catching, i'll edit the comment

 

JagV8 - i also found a second version of the document that's 113 pages and covers 2006MY V6 S-Type and XJ, and newer, released in May of 2005. It is attached below. I may have made the assumption that the 144-page document was more complete, but that is not the case, as this document shows all drive cycle information data, monitoring charts, etc, which are absent in the larger document. It also contains the evaporative system drive cycle which I was seeking in another post....Sigh....

 

That's the one I meant to post a URL for.

I may have posted the wrong URL. If so, sorry

The drive cycles are not usually needed (except the EVAP details) but can speed things up or help with fault-finding.

 

Your URL is correct...links to the same 113 pager. Interesting that it covers 0.020" and 0.040" tests in detail and actually explains what they are meant to accomplish - detect leaks equivalent of 0.5mm and 1 mm pinholes. I would have never guessed that part!

 

I felt much the same. When they put "small" they maybe could have made it "extremely small".

Shows how exactly the fuel/air mixture can be adjusted. (That those little fuel injectors can be so good also amazes me.)

Some people like this URL as a visual aid to what the PCM is doing in its control loop
OnBoardDiagnostics.com - Engine Basics

Others see that "Basics" as a bit scary when they wonder what the non-basic one would be!

 

Thank you, a good one indeed!

 

Thank you for the words of encouragement - sometimes I feel it's just easier to give up but somehow I'm still at it. By any chance, were you able to locate the fuel trim document you were referring to?

In my case, when going from idle to 2500, long term fuel trim values remain unchanged ~10%, and short term trim values increase from ~5% to ~10%. Based on the info I have found so far, this rules out a vacuum leak.

 

Give up? Did we give up when the Germans bombed Pearl Harbor?:



Don't be discouraged by the new codes. Look at it this way. The previous codes were caused by some heavy duty faults. It would be like your brain reacting to losing an arm in a cribbage accident.

Luckily, this happened in the lobby of a hospital during a convention of trauma surgeons, and they were able to quickly reattach your wayward arm. The new codes you're getting? That's like getting a hang nail on your newly reattached arm. So keep plugging away at your new fault, and troubleshoot based on your present conditions, not what you previously had.

Here is the info for troubleshooting fuel trims:

JagRepair.com - Jaguar Repair Information Resource


I've barely scratched the surface with this method of troubleshooting, but have heard many good things about it.

Remember, there is no "vacuum leak sensor" to set the P0171 and P0174 codes. It's simply the computer being programmed to set these codes under certain conditions. The root cause is generally an actual vacuum leak, but it's also possible for other faults to mimic similar readings without a vacuum leak present.

 

Nice link, much appreciate it! I also found a nice article about using fuel trims for diagnostic purposes, attached for anyone interested.

 

After doing some reading on using fuel trims, it became apparent that the trims were excessively positive across the entire range of RPMs and engine loads, which was pointing the finger at fuel supply and/or MAF sensor.

Today I received the replacement MAF sensor and plugged it in. I then went on three separate 6 mile trips with engine restarts in between. No codes have been thrown yet. I've been driving around while monitoring the fuel trims, and long term trim now floats around 0% (+/-3%). I'm guessing the car is still re calibrating the maps.

The most noticeable thing I see now, is the LT fuel trim at idle is -0.78% and +0.78% on bank 1 and 2. Before, that value was 10% and another 15% on top of that from short term trim.

I will try to drive the car tomorrow as much as I can, and with God's help, P0171 and P0174 will hopefully be put to rest and and the vehicle can complete on-board readiness tests.

Will update tomorrow.

 

Sounds much better.

 

A quick update:

I drove the vehicle about 60 miles yesterday. No check engine lights, and no stored codes - so I'm assuming things are good! Vehicle runs incredibly well and I averaged 31 MPG on the freeway over 60 miles - which is a 40% improvement over what it was doing before.

With respect to on-board readiness, the vehicle completed all tests except Evaporative System check. The workshop manual states that the evaporative purge valve needs to be cycling for evap test to complete. In my case, it does not appear to cycle, and I'm speculating that because the battery was disconnected, the drive cycle for "green" ECM needs to first be completed.

I think my next steps are:

1. Complete drive cycle for "green" ECM to enable evap purge valve function
2. Complete drive cycle for 0.020" and 0.040" evaporative leak check

If someone can think of a better way - please let me know.

 

Another quick update:

I completed the the "green" ECM drive cycle and the purge valve is confirmed to work. Next steps are to wait until the vehicle is cold again, and try to re-run the evap system monitoring test.

What a pain in the rear...

 

Generally the monitors just sort themselves out OK.

But then only some parts of the world even require them to be set. Or specify which ones.

Wanting to do it and soon is confined to very few geographical areas, fortunately.

I gather one area even changed retrospectively which is allowed unset - very very unfair if so.

 

Does your local emissions test require this? I'm a bit fuzzy on the details, but I think generally this is not required in most areas to pass an emissions test. Or do you want to complete this test "just because", which is a perfectly valid reason.

 

When I attempted to do emissions testing with check engine light, the form stated that "evaporative emissions monitor" not set. They said to drive the car some more, and bring back for re-testing. Of course that was when there were all kinds of issues with it....

I'm in Virginia, DC metro.

 

One more, and hopefully final update to my DTC saga...

All tests pasts, vehicle passed the emissions and rides awesome. Lessons learned:

1. Don't mess with the ECM - it's likely something else. However, I don't regret tearing it apart, because it led me to #2 below.
2. Only replace O2 sensors with quality / name brands...yes not cheap, but such as life. My experience here showed that not all sensors are made equal, and low-side FETs in the ECM are only capable of driving loads of 1A. If you choose to go with questionable O2 sensors, check the heater coil resistance and the current they draw.

And perhaps the most important lesson learned:

3. This forum is amazing. Thanks to everyone for incredible support and words of encouragement.