Afternoon all

I've been chasing a vacuum leak for a while now on my 4.2 XKR, symptoms are LTFT running at 7% / 5% on banks 1 / 2 respectively, coupled with a bit of a lumpy idle on cold start. Car runs well for the most part but feels a bit restricted, almost surging, when getting into the high gears under heavy throttle. Once I've brought the LTFTs down I'll be getting the catalytic converters checked because I've had code P0430 pop up 3 times in the last year... but I digress.

Using a smoke machine from Amazon I managed to find a leak on the brake booster quick release from the throttle body, which I have now rectified. Now I am running the smoke test and seeing wisps of smoke from under the throttle body. It's very restrictive to get a good view down there but I believe it's coming from the thing circled in the below image, where it bolts to the throttle body elbow :



My questions are :

1. What is it?
2. Is it possible for vacuum to be leaking from it?
3. Is it possible to remove, clean the surfaces and replace with the throttle body in-situ or would it be all together easier to remove the throttle body first? Clearly it would be easier with the TB out of the way, but is the TB removal easier than struggling to get to this other thing?

I'm about 95% sure the smoke was coming from the gasket between this and the throttle body elbow but of course, smoke has a habit of moving around.

Oh and please forgive the boob thing on top of the intake, it's a plastic tub from one of the wife's multitude of beauty products coupled to a silicone tube to get the smoke into the intake for the testing. Seems to work well...

Thank you,
Simon

 

That's the egr valve. No vacuum connections there. It seals against the rear of the plenum, but I'd consider that an unlikely leak location.

Besides the vacuum hose you already corrected, there is a small rigid vacuum pipe that snaps in to the right side of the plenum under the throttle body. It seals with an o-ring. That was a leak source for me previously.

 

Thank you. Looking at some guides on removing the throttle body and it doesn't seem to be beyond my scope so I will do that when it gets light, at least that will give me some more access and hopefully make it easier to figure out where the smoke comes from.

Again it's only what I thought I saw with mirrors and torches, but the smoke appeared to be coming from this part of the EGR valve; I don't see any gaskets available apart from the metal crush ones for the exhaust tube, but it definitely looks like rubber around mine :



Could vacuum be drawn in there?

I'll have a look for that pipe you mentioned when the TB is off; just to clarify, is it on the same side as the EGR/photo in the opening post or the same side as the brake booster line?

 

At the upper left of the image you can see the flange where the throttle body has been removed.
just beneath the flame edge you can see the plastic vacuum line where it is plugged into the plenum.

 

Thank you. That looks like the quick release from the brake booster which I already replaced, but I'll get a better look once the TB is removed.

 

After a bit more clicking around I noticed some talk of EGR solenoids on the XJ8 4.2 which do vent some smoke during a smoke test and it's quite normal. Can anyone confirm if it's the same on the XKR X150?

 

Well I bit the bullet and removed the throttle body. Wasn't difficult at all. With it out of the way I was able to see much more clearly and it certainly looks like the smoke is coming from the EGR, I took a video while I was in there :


Before spending the asking price for a new EGR when mine is still operating, I undid the two bolts holding the solenoid and removed the top half of the unit, cleaned the surfaces and sealed it back up with RTV sealant. Nothing lost apart from some time if it doesn't work, but hopefully a better running car to gain. I've left the RTV to properly cure and I'll do another smoke test in the coming days while I wait for my new TB gasket to arrive.

 

Did a quick smoke test today during my lunch break (working from home is just the best), but to my dismay there is still smoke coming from the EGR solenoid. This time not from where the solenoid bolts on to the water cooler, but instead it seemed to come from the plastic plug/socket where it is attached to the side of the solenoid wall. I am assuming that level of disassembly is ill-advised or perhaps impossible, however I again disassembled the EGR and this time ran a bead of superglue all around the plastic plug and the plastic "gasket" which sits between the solenoid and the water cooler in the hope of plugging whatever leak there may be. Truth be told, I also saw smoke coming from the pins within the EGR connector before I noticed the silicone seal inside the loom-side plug and connected it up.

If the next smoke test still shows smoke exiting from the EGR then I may be facing buying a new one. But before I do, would someone who has done smoke tests on these cars please just put my mind at rest and confirm whether or not smoke should be vented from the EGR? I've never seen this mentioned on any previous XKR vacuum leak threads before, but the mention of EGR vents on other forums has made me want to seek some peace of mind from someone on here who has looked for vacuum leaks : has your EGR vented smoke during the smoke test?

 

Hello. I know this is an older thread, but I was curious if you ever got the answers you were seeking? I'm having a similar issue where it appears my EGR valve may be leaking when smoke tested. What did you do to correct your situation? Was the EGR repaired, or replaced? Any insight you could provide would be appreciated. Thank you.

 

Sorry can't help but it's nice to see another jag owner in this neck of the woods!
Hello from Magnolia.
Note it's always a good idea to put your car details in your posts.
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Hi, sorry but nobody seemed able to tell me if the EGR should emit smoke during a smoke test. I ended up smearing superglue and RTV sealant around the solenoid body to electrical connector joint and the smoke stopped, but it didn't reduce my LTFT so i just gave up. On an unrelated note, the original reason for smoke testing was partly for LTFT and partly for a surging issue I had, the surging turned out to be a collapsed catalytic converter.

 

EGR valves are quite inexpensive, you should just replace it. As far as LTFTs, those take quite awhile to change, hence Long Term. To start all that over, a Hard Reset would be a thing to do. Disconnect BOTH battery cables from the battery and touch those cables together for several seconds totally avoiding the battery. That action dumps all the volatile memory from the modules and such. You will have to reset the windows after that, but every convenience thing such as vehicle settings should be unaffected. The fuel trims and adaptive driving characteristics will be reset, along with trip odometers, driving data and nitnoid stuff.

 

I agree with Cee Jay. Replace it and report back. It might be just that simple.
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Thanks Cee Jay, I did do a hard reset back then after I had sealed up the EGR valve and it made no difference, LTFT still made its way back up to the same readings. I also tried swapping the O2 sensors from left to right to see if the imbalance swapped banks but it all came back the same again. The fact I no longer have smoke coming from the EGR body and I have no EGR fault codes means I've moved on from EGR being the issue, especially as they are £350 - £400 new and I didn't want to throw that money away on a whim until I had proved it one way or the other. I don't see any smoke coming from anywhere now, and yet the trims persist.

 

(2008 XK 4.2 NA) I am facing the identical issue with the EGR valve. I slathered some RTV on mine and it stopped smoking during a smoke test, but I still have lean codes on both banks and a p0411 (secondary air injection). Now when I smoke test, I don't see any smoke from anywhere, but there is flow on the flow meter of my smoke machine.

 

Old thread I know but there's probably quite a few of us chasing lean codes on our cars, so I thought I'd check in even if just for solidarity. So far on my 2003 4.2 XKR I've found leaks through smoke tests, and ones the smoke test didn't reveal by spraying brake cleaner, and by using a hand vacuum pump to check some of those awful plastic breathers that seem to be made out of cable conduit rather than proper hose (ok fair enough it was one of the first car designs to experiment with use of plastics to save weight). I've cleaned unions, replaced o-rings, and RTV'd until the joint or pipe in question can pass a smoke or vacuum test. But somewhere early on in the diagnostic journey, originally chasing down a P0171 Bank 1 Lean, I've caused something to admit more air because now both banks are consistently trimming too much fuel for things to be healthy... like +14 LTFT and +6 to +8 on short. Always with throttle closed - engine runs beautifully on any other throttle setting, and indeed idles fine too but the computer is having to squirt too much fuel at idle. I cannot figure out anything else I've disturbed during dismantling that could be the cause of this new and unwelcome state of affairs. I'd found a definite heat damage induced leak in the part load breather and had repaired that, plus I made a proper metal heat shield for the exhaust return to the EGR to replace the crumbling original which had damaged the plastic breather as it failed. This morning I remembered that in all the focus on that definite leak on the part load breather, I hadn't ever focused hard on the full load breather which I'd had to disconnect every time I need access to the throttle body so that might be the thing I disturbed early on. Unfortunately it passed several vac tests and the o-rings looked in good shape. The last hose/pipe I'm currently investigating is the brake boost which runs from (as seen from driving position) the left of the carb elbow to the left wing via another cable conduit style plastic pipe 4/5ths of the way and then a speed connector onto a vertical metal pipe coming out of the wing. I am suspecting that union a bit but not sure whether grease or PTFE or something else is the right way to go there. The other end of this narrow bore pipe at the throttle elbow is pretty manky inside.. at first I thought 'aha! its been sucking in crud that's why it looks so dirty' but then again that union is quite low on the elbow which with the EGR is a pretty filthy environment. I'll clean it and get the best union I can but must manage my expectations on that one, especially since it is not one I actively disturbed early on in this many many day saga. I can currently drive without codes but I think it is very close to generating them and having come so far I want to find the bloody cause once and for all. All ideas welcome and happy to provide photos etc if wanted.

 

Can you put some spaces in? Hard to read a wall of text!

On any 4.2L SC engine the brake booster vacuum line on the SC elbow is a well known fail point.




The symptoms are as you state. The air leak is big at idle but next to nothing when the car is off idle. This indicates a vacuum leak that is constant. So as a percentage of air flow idle is the worst time. As the engine speeds up the vacuum leak becomes a smaller and smaller part of the air flow so it has less effect. This vacuum leak will effect both banks of the engine as well.

This may not be your problem but that port has an odd plastic O-ring fitting and by now that O-ring is hard and brittle. I replaced mine with a brass threaded fitting to completely remove that silly rotating vacuum fitting.

So something to check.
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