Hi all

Every so often I'll drive my 06 XKR and it feels like there's just something not quite right. On cold start I can feel about 30 seconds of lumpy idle before it smooths out, which I understand can be a vacuum leak around the throttle body area. Once warmed up, regular driving (reasonably spirited acceleration) seems great, but heavy acceleration can sometimes show what I can only describe as light surging or even misfiring. It only seems to happen at higher speeds, so for example I'll enter a slip road / onramp to join the motorway and give it the beans. Up through first, second, possibly third, feels fine but by the end of the slip and into fourth I can feel a bit of surging or misfire. I have an Autel AP200 and it reports no misfire when this happens, but that's what it feels like. Also I would have thought misfire would be engine RPM dependent more than road speed dependent? The only other thing which springs to mind is a partially blocked cat, perhaps the exhaust flow needs to be just that little bit higher when in high gears at higher speeds and it's not flowing as well as it could?

I've been seeing LTFTs at idle of around 10% bank 1 and 8% bank 2 for a while now. Increasing the RPM seems to decrease the trims which seems to indicate a vacuum leak. Bought a smoke machine and did some testing and initially found smoke to be emanating from the EGR body around the solenoid. Having never seen anyone mention this on previous smoke tests I had to conclude this was not right and perhaps the inner seals had failed or something, so I sealed the EGR solenoid where the plastic plug sits on the body with some RTV sealant, reassembled and retested. No more smoke around the EGR valve (or anywhere else that I could see), but I also noticed no matter how long I ran the smoke machine I was not building any pressure at all. Eventually noticed the smoke was exiting via the exhaust tailpipes. This has me suspicious the EGR valve is not closing and could potentially be contributing to my high LTFTs, since I guess it would mean exhaust gas it being pulled in all the time.

I've had no codes pop up recently. I did have a P0430 some months back, however it was around this time that I did find quite a large vacuum leak from the quick release at the throttle body elbow to brake servo pipe. Replaced that and haven't had the code since, and I do believe I read on here that a particularly lean condition can flag a catalyst code. And I'd really rather try to bring those LTFTs down before I potentially replace the cats, since I don't want to run the car with incorrect fuelling and shorten their life.

I guess my questions to begin with are :

1. Does my suspicion about the EGR not fully closing sound reasonable as a possible cause for the high trims?
2. Should the EGR be closed at idle?
3. Should I be seeing smoke tester smoke exit the tailpipes with the ignition off, or should I be building pressure? (pretty sure I should be building pressure since again, never seen any mention of EGR caveats in other threads)

 

Can anyone who has done a smoke test perhaps confirm I should be building pressure and not seeing smoke out of the tailpipes at least? I'm pretty sure that's the case but I want to be 100% before I start digging into the EGR again. Hoping to find some time next weekend to carry on looking for vacuum leaks.

 

EGR could make some tailpipe smoke, but it wouldn't be much, and it wouldn't be the first you'd see in a test. That's a lot of volume to fill with smoke.

Your vacuum leak could also be on the intake side, as in before the throttle body. You can test that separately but you need a place to blow smoke, preferably close to the TB so everything fills before smoke gets out of the filter boxes.

 

Thanks, Cee Jay. It's certainly not billowing smoke from the tailpipes but the smoke tester is not building any pressure at all, and after 10 minutes or so of running the thing and wondering why not, I went to the back of the car and could just about see the whiffs.

I have tested the intake from the throttle body coupler back to the foremost rubber couplers before they plunge down towards the MAF sensors. Jacking up the car and checking the rest of the intake setup is also on the list but I had started to focus more on the possibility of an EGR, or at least the fact I was unable to build pressure because of the EGR and had read on here that some of the possible sources for vacuum leaks would only show once pressure had built.

If the EGR were more reasonably priced (and the ridiculous torx bolts were regular bolts) I'd have chucked a new EGR on there already, but at around £300 and the danger of snapping a bolt off I'd rather be absolutely sure before replacing it. Perhaps I could disconnect the pipe between EGR and exhaust and block it off there, see if pressure builds.

 

You never will 'Build Pressure' as there are inherent oozes for air to go. Up and around the entire PCV system which will also go out the exhaust, through the EGR as you state, and through the throttle body. This is why the better smoke machines put out a large volume of smoky air without a lot of pressure.

 

Great thank you, that's exactly the sort of clarification I needed. I will turn my attention to the intake pipes yet to be tested rather than mess about with an egr which could actually be fine.

 

Went for a long drive at the weekend and added a can of BG44K to the tank. I noticed on the way home the high speed, high gear surging was much more pronounced particularly uphill. I was able to produce it easily by switching to 6th gear manual mode and applying a decent amount of throttle pedal. Unfortunately I didn't have my OBD2 dongle with me so I went out again yesterday with the OBD2 and Torque ready to go. This time however, the symptom was not there as before but in trying to get it to happen I did manage to trip a P0430 code again. I took some readings after trawling the forums looking for exactly what information would be pertinent and I captured the following :

Fuel trims at idle and 2,500 RPM :


Some more detailed trims on a graph at idle and 2,500 RPM :




I don't know if any of the above indicates something obvious and please, anyone feel free to throw ideas around. I am planning on the following this weekend :

1. Checking for vacuum leaks again, as well as intake leaks down to the MAF sensor couplers.
2. Cleaning the MAF sensors while I'm in there; since I want to confirm the intake as a whole I'll be pushing smoke through the MAFs so they'll need cleaning afterwards.
3. Attempting to remove the O2 sensors and check the cats with a borescope
4. Cleaning the O2 sensors, and swapping them left to right to see if the issue moves

Anything else I've not thought of? Having previously found and fixed the vacuum leak I had, I am really not expecting to find any. And I had seen posts from V8Jag in my searches which seem to suggest if the LTFTs drop to near zero when revving to 2,500 RPM then it's almost certainly a vacuum leak. Mine are dropping but not near zero... is it possible a blocked / broken catalytic converter or dirty / faulty O2 sensor could give such readings on the fuel trims?

 

Borrowed a borescope and poked it into the upstream o2 sensor holes today, and it was quite telling :


bank 1

bank 2

Certainly a problem with the bank 2 catalytic converter, looks like the substrate is breaking away at the edge (is the same on the opposite edge), and I can't tell if the black parts around the rest of it are holes or blockages but it needs replacing regardless. I doubt this will be the cause of the high trims, certainly not on bank 1 anyway, but I'm not getting anywhere on my own so I'll get the cats replaced and go from there.

 

Yeah, that one is toast, all right.

 

I had some aftermarket cats installed this week, along with a new centre section - well, new front and new back so I couldn't very well have a tarnished bit in the middle. Did away with the resonators and added an x-pipe. Sounds spectacular now. And (tightly grasping wood) car runs a lot better now.

Inspecting the suspect cat once it was off the car, and looking into the downstream o2 hole (couldn't remove the sensor with it on the car) revealed this. One of the bricks has detached and slid into the sensor - you can see the groove cut out in the brick :



Deeper in, and it looks as though the bricks are not lined up any more. I guess this, combined with what looked like blockage in the previous photos, was enough to restrict flow and cause the poor running / surging / hesitating :

 

Have you thoroughly examined the plastic duct between the air cleaners/sensor locations and the throttle body?

 

Hi Bill, yes I recently removed the wheel arch liners and checked / cleaned all the duct fittings, cleaned the MAF sensors with some proper MAF cleaner, and am confident there are no air leaks in any of the ducting.

The cat replacement seems to have cured the hesitation / surging so it's just a mildly rough idle for the first few seconds and the high trims now, no other symptom that I can see.