I added this to another thread, but found another leaker on my car...the exhaust gas recirculation, coming from the positive crankcase ventilation (PCV) on the right side manifold, leading to the lower throttle body elbow was leaking pretty badly. Line was plastic, and the norma fittings have o-rings that were dried out and no longer sealing. Since it was 'sucking' air, I was getting way too much unmeasured air into the engine...thus my short and long terms were always in the plus range (lean)...now they're falling even more closer to zero with all of my efforts on this emission system.

 

Sounds like there are a bunch of opportunities for slight vacuum leaks that add up to a big PIA. I've added your Suggestions to the diagnostic list.

Back in the old days a can of carb cleaner was an easy way to find a vacuum leak if you could not hear it. I doubt that trick will work with any of the leaks you are describing as they each are all really small and are likely not the single cause.

Thanks! Ken

 

BTW, I'm almost certain it's a lean stumble I'm chasing.

There's no evidence of spark leakage at the boots and I've had a chance to "Walk" a brand new coil on all 8 plugs with no change in condition.

 

OK, I'm live with "Live Data" and took it for a drive. Here's what I see:

MAF seems to be very linear in it's values both up and down. At idle it's about 4.8 g/s and at wot about 187 g/s. All transitions in between are very smooth.

TPS seems to be very linear in it's operation. At idle it's 2.4% and at WOT it's 82.4%. With a slow and steady push I can walk it all the way up and down in 0.2 to 0.5 increments without so much as a twitch in the wrong direction.

Spark advance moves normally. While driving it's in the mid 20 degree range but it does drop to 14 degrees adv. only after the engine sputters so I'm thinking the Knock Sensors heard the sputter and dropped the timing as a result.

Intake air temp sensor is also behaving in a linear fashion. At Idle it's 41 degrees C (The surface temp of the MAF was 54.8 at that time) As I get moving the temp drops. Temps are not erratic.

ECT also behaving in a linear fashion. It reads 94 degrees C and when I measure the temp on it's surface with my laser thermometer it says 88 degrees C. It behavior is not erratic.

Idle speed is 648 to 657 rpm.

LTFT's are around 5.5% at Idle and 7.0% at 1300 rpm The highest I've seen them is 9.4%.

STFT's bounce around quite a bit they are pretty hard to read since I don't know what to look for there. Mostly they are around +/- 2.0%

O2S readings are almost always 0.99 and 1.0 Lambda. Their voltages and MA are consistent with each other.

What do you guys think?

 

According to the fuel trim tutorial pdf posted somewhere in one of the stickies, your fuel trims indicate that fuel is being added to get to the desired A/F ratio. The LT is adopting what you see in the ST and the ST then tends towards zero because LT is now taking care of it.

That would imply, as you suspected, a vacuum leak.

Have you tried spraying brake cleaner in the suspect areas to see if idle speed increases at a those points?

 

Here is a link to the thread Matt [h20boy] started that has my Fuel Trim Primer referred to by plumbsauce.

https://www.jaguarforums.com/forum/g...ed-quiz-49317/

He's on the right track, but now that you have a tool to read the live data, use it. Watch the short term trims and then spray suspect areas with a brake cleaner or other petroleum product. That fuel trim will reading will jump negative if a leak sucks in the spray way before you will notice a change in the idle. If you find a spot you can repeatedly, I say repeatedly get the trim to jump negative, you have found your unmetered air leak.

The Primer will also help you understand why the short term trim bounces back and forth all the time.

Good luck!

 

Nice write up. You got a double thanks on that one. However when I look at the percentages compared to mine I'm even more frustrated. For example your 2009 XF hovers around 0 to around 3 and when you pulled the dipstick the trims shot up to 12 or 13%. Considering my car is ten years older and has 144k miles on it does it make sense that my trims are only a couple of point higher? Even during huge throttle transitions (Idle to WOT then back) the highest number I've seen yet is only in the 9 range and never a double digit. If I had a vacuum leak wouldn't my numbers be higher?

I've already sprayed enough brake cleaner to just about wash the engine to no avail.

The car runs so smoothly at idle that I can't notice a change. I might have my wife watch the rpm readings on the scanner while I spray connections one at a time. Hopefully we can see a change in rpm that way.

 

At least I can now duplicate the issue in the driveway.

FWIW, yesterday when I was doing a slow smooth press on the accelerator to check the TPS I was able to find an rpm range that had a stumble 100% of the time.

It starts right about 1340 rpm and is gone by 1500 rpm. Fuel trims are not going haywire while it's acting up but they do inch up 1.5%.

Is this rpm range (parked in the driveway) significant to the part or full load breather system? Maybe I can narrow this down....

 

That gives me an idea. Do that same thing but instead of the TPS, watch the spark timing PID. See what happens to the timing at the 1340-1500 RPM range.

Cheers,

 

Timing starts off at 5 degrees at idle then climbs smoothly to 20-21 degrees in the 1300-1500 rpm range. Timing only advances as I slowly depress the throttle. It never goes backward or jumps around.

Also, as I roll on the throttle while in the driveway the engine runs kind of rough (not bad but not smooth) from about 1200 rpm up until 1700 rpm. Once I cross the 1700 rpm threshold it runs smooth as silk. From idle to 1200 rpm it is smooth.

 

Can u monitor manifold pressure live also?

 

Unfortunately they didn't use MAP until the 4.2L on the V8. X-Type got one in 2002.

Cheers,

 

I'm chiming in only because it doesn't look like there's a clear culprit here. Have you considered a professional injector cleaning? This can sometimes make a surprising difference in an engine that isn't throwing any codes but still isn't quite right. YMMV.

 

Tim,

Actually that was my first thought before I even tried diagnosing the issue. The only reason I haven't done that already is I need the car every day. I'll be able to disable the car after the 18th and send them out then.

I'll be willing to bet it's the #7 and #8 injectors. One of the first things I did was read the sparkplugs and #7 and #8 looked lean compared to to the rest. Pics are in this post.

https://www.jaguarforums.com/forum/j...ly-same-51863/

 

Update:

I just received a text from the guy that is testing and servicing my injectors and he says there is as much as 10 ML of variation in the injectors.

Once I have the full report I'll post the results.

 

10ml is a big difference, I gave about 2 and a half sets of injectors to my diesel specialist to clean, he made up a set that were all in the same ballpark. Can you buy cheap second hand injectors easily where you are? Your guy might get them clear with a few sonic baths.
Hope this cures the stumble.

 

The injectors were definitely the problem. I reinstalled them and took it for a ride on the freeway and the stumble is gone.

It may be placebo but the car seems more responsive off idle too.

At $80.00 this is the least expensive repair I've done on the car to date.

I've got a video of the injector test. It's easy to see which one was the problem. Once I figure out how to convert it to a format supported here on the forum I'll upload it.

 

Here's the video. I know that Quicktime opens and runs it. Not sure about Windows Media Player though.

You can see the one on the left has a weak pattern compared to the others.

View My Video