I am helping a friend with a 2000 XKR. He periodically will throw a p0171 and P0174. The last time it threw a CEL, but never put the car in restrictive performance and the freeze frame showed the st on both sides to be +25 and the long terms were in the +13-14 range. So will a ST trim lead to a code?? I have never understood it that way. Further the freeze frame showed he was just cruising at 58 at a steady speed. He has also had one P0455 at a cruising speed of about 60 and then never came back , but in over 4 years-- no matter what the drive cycle he has tried can he get the evap to complete and therefore the ccm will not complete. The idle and 2500 rpm test do not show a vacuum leak. In fact if you take the dipstick out and/or open the oil fill cap- nothing is shown as changing on the fuel trims? Is that normal for this engine?

Any thoughts will be appreciated and all the normal tests for a vacuum leak show none, but then there are areas that have not been looked at. Is there any way that a gross vacuum leak from p0455 could cause a p0171 or p0174. The purge valve by the drivers fender has been replaced.

Thanks

Tom in Plano/Dallas

 

First the STFT and LTFFT all at a + means you have a severe vacuum leak. Plus mean it is adding fuel due to the unmetered air coming in. P0171 and P0174 codes mean right and left bank vacuum leak. Removing the dipstick and fill cap won't change the fuel trims that high are already dealing with a massive leak. You need to locate and repair the vacuum leak.
Start at the air filter and just after the MAF sensor and start checking the components for cracks. Also, check the part load breather tube and make sure it isn't cracked.
After that it will most likely take a smoke test to find the culprit.

 

I appreciate all of that and the time and effort, however this is known/understood by me. I have been dealing with this for more than 2 years for a friend whose car knowledge stops at about 1990. First, we do not show any indications of a vacuum leak at the idle and 2500 tests. second according to the guides that Gus has provided before : http://www.jagrepair.com/images/Auto...el%20Trims.pdf and http://jagrepair.com/images/AutoRepa...mer%20Rev2.pdf removing the dipstick is used as an example of altering fuel trims and that is not happening and as a separate question is that normal with the 4.0 sc?.

Third all the area from the air filter to TB is new/ A smoke test will only show certain leaks and not all -per the forum. However a smoke test was run several years ago and showed nothing and spraying ether around where leaks might occur showed zip/zero.

But for the thought process, if I take the idea of a mass leak then why is not happening every time the car is run and it does not and only occasionally and only at cruising speed- be it 30-, 40, 60, or 80?

My other question was the relationship between a P0455 and the 0171 and0 174 if any. The guide of error codes does not indict either as related and it may be 2 problems with the eavp system falling in to the problem area as sighted by 3 TSB and the 171 and 174 into another. My frank opinion is that it is in the throttle body and egr area, but I fail to get cooperation from the owner who really understand ODBII systems slightly. I know it is before the split off as both sides are affected equally.

However do you know the answer to the question of would only ST fuel trims at +25 cause the error codes to appear?

If interested- here is one thread that lays out in more detail: https://www.jaguarforums.com/forum/x...6/#post1618134
and yes, we did pull a p0455 after this post as well, so changing the purge valve did not solve the problem.

I suspect the best thing for him to do is to run the car down to Houston and turn it over to Brutal and let him figure out what gives.

Tom in Plano/Dallas

 

It can also mean bad MAF sensor. Clean MAF

 

Done consistently. It may be a bad MAF, but dirty it is not. Having had that problem early on in my Jag, I learned the lesson quickly. I have always leaned to the fact that if it were a sensor- then the MAF would be the first one I would choose. The rare and intermittent problem makes you think it could be a sensor

But thanks, as always.

Tom

 

Remember, fuel trims are a function of load and rpm, it's not just a number under all conditions like water temp. In other words, the engine management maintains a matrix of fuel trims indexed by Load and rpm. Same for short term trims.

Typically, you start by checking fuel trims at idle. High long term trims mean unmetered air. EVERYTHING counts here, i.e. all leaks contribute to the code, it is not necessarily just this one leak. Replace o-rings on all connections to the head and throttle body. Check oil leaks (oil out likely mean air in). Double check the air intake tube and all resonators. As you hit those leaks, fuel trims should come down (short term trims become negative).

Other option is that the air going in is measured wrong to begin with. As the air temp is on the same sensor, check the air temp over OBDII. If off, it is a clue the sensor is bad. I have cleaned sensors before (dedicated spray), and have not seem miracle cures. Check the specifics (by DENSO part#), but for the later XK8, these sensors are pretty cheap and totally worth changing just to eliminate the problem. Key is to order the right one because they all seem to fit the same connector, but are seemingly not equivalent.

Best of luck, keep us posted.

PS: Also check the EGR pipe. It brings exhaust gas to the EGR valve from the left manifold. The accordion part can crack and let air in.

PPS: Also check the area behind the driver side front wheel liner. The purge valve is there with a bunch of plumbing.

 

Thanks, the area by the fender has been replaced and checked. Also FYI the MAF for the xkr is not the same one for the xk8 and the price is more than double- triple. I understand completely the fuel trim behavior and probably again suspect exactly what you mention the accordion pipe below the egr. The temps from the MAF appear to be correct according to the scanner. but that does not mean the MAF is good.

Let me go back to the first question in this post. Would ST fuel trims that go to +25 cause a CEL and a P0171-0174? If not that proably tells me the MAF or the ECU may have a malfunction.

Thanks

Tom in Plano

 

 

Interesting and useful information.

Thanks

Tom

 

STFT jumps around too much, use LTFT. If it's high at idle suspect leaks, including SC seals. High at elevated revs suspect MAFS or temp sensor.

 

Thanks. Again and not to sound rude or anything- all of that I know and have specific data if you would like to see anything am missing. Again Ihave one simple question. The last 5 times the car has experienced a P0171 and P0174- the freeze frame showed the ST at +25 and LT at around +14 (not enough on their own to set a code. Would a short term of +25 throw the codes? I understand how the ST jump around- but the code is set at cruising and the LT are not enough to set, only the ST.

Tom in Plano

 

I would have suggested you test whether high ST values trigger the error code by deliberately introducing an air leak and see what happens, but you said:-

"In fact if you take the dipstick out and/or open the oil fill cap- nothing is shown as changing on the fuel trims? Is that normal for this engine?"

How is that possible? Surely if you introduce un-metered air into the engine, the trims should go up to compensate. This suggests to me at least that perhaps you should be looking at the O2 sensors rather than focusing on the MAF, or find out why adding unmetered air does nothing to the trims.

 

Thanks
-That is one of the things I have not been able to figure out. I was always under the impression and on my Jag it certainly works that way- that introducing un-metered air in to the car by pulling out the dipstick or taking off or loosening the oil cap would cause the ST to move upwards and fairly quickly. Ont his car is does nothing. Yet if you monitor data when driving the 02 sensors seem to have normal graphing and fit in their voltage ranges. We have never had any codes that related to the 02 sensors at any point.

Tom in Plano

 

 

Very familiar with the 1646 and 1647. The only codes thrown have been a 0171, 0174 and 0455. Is there any way that anyone knows of 0455 (gross leak) being involved with 0171-74, but according to the diagnostic codes these two do not lead to each other and suggest a separate problem. All of these codes have been thrown when cruising at a steady speed. Once again, when monitoring the drive cycle- if the car is running at 5, 10 , 15, 20, 40, 55, 60, 80 and so forth mph the ST pop up to +18 or so on both sides and the LT are below that. When the 0171 and 0174 codes have been set- the car was just cruising on the highway at 58 or 60 mph and the ST went to +25 and LT were around +14. I still thought that the LT would have to get to +25 for the code to set.

TBB

 

I am going to once again try and introduce unmetered air via the dipstick. Perhaps I am not being patient enough and that might indeed indicate a slow responding 02 sensor, but that becomes a touch of a guess as well.

TBB

 

If it doesn't react to the dipstick I would take that as an indication the the air leak is so large that the additional opening has no influence.

 

Thanks:

That makes sense, but an air leak that large should cause a 0171 and 0174 every time he drove the car- would it not? The only issue is that at idle and 2500 rpm- he now shows no signs of a leak. The LT and ST at idle bounce around-3 to +4. So removing the dipstick should , as it does on my Jag (different engine), the ST to move upward on a pretty quick level. You can see the paradox this creates, but I will try this later and see if I wait it out what happens about the dipstick.

Thanks

Tom

 

 

It may- but he uses top of the line oil and is changed every 9 months. That has not been a cause listed by the diagnostic codes, so someone else might answer that question.

T