Friend has 2011 XJ SC with 55k. He is getting a bit of vibration at cold start. He put in some sort of fuel cleaner and octane booster, which I would NEVER recommend in this car and he uses only top tier gas.

The scanner shows his car is almost perfect with LT fuel trims at any point within 1 point on either side of 0.0 and at idle it is 0.0 on one side and +0.2 on the other. Clearly not a problem.

I would be more inclined to spark plugs even though I am aware of 100K mile change intervals. Clean air filters and MAF. No problem with car in any other way when running. No codes, no nothing, except a very fast car- beyond minor vibration at cold start- and this is the summer in Dallas- so no cold weather clearly.

My real questions are:

1. Is this at all common with a cold start on these cars?
2. What is any potential hiccup to changing the spark plugs? I went to Alldata and they show no procedure, although they list the difficulty level at C (which means easy). (and please no brand argument on this post about make of the spark plugs and I know they are Iridium).
3. Does someone have the procedure for changing the plugs or is it straight forward, once you look at them or is one or two of them hard to get at?

Thanks

Tom in Plano/Dallas

 

Which SC engine? 5.0?

 

In this country we only had 3 engines for the 2011 XJ. All some variation of the 5.0. This is the middle one that is SC and produces 470HP.

TBB

 

Are you familiar with DI causing carbon fouling? He is at the right mileage too. So putting anything into the gas will do nothing to fix this.

Since the fuel is injected directly into the cylinder without any fuel hitting the intake valves all the crap from the PCV system gets cooked on the backside of the intake valve and intake tract. This affects performance and mileage and is quite variable. I have heard of Audi's (They appear to be the worst?) losing over 100 HP in 20K miles because of this buildup. They perform a intake cleaning on a regular basis.

Now a lot of guys especially on the American muscle car side run oil catch cans on the PCV system to stop it. It's quite amazing the amount of junk collected. BUT that still does not say it will prevent intake tract/valves from getting buildup but it has got to help!

Here the forum talks about on the 5.0L engine your friend has. This thread discuss it and we seem to be lucky that the 5.0L Jaguar V-8 does NOT appear to suffer too badly from this. Even Brutal has commented he has not seen much deposits. The Land Rover side has. On that thread is a very cruddy Land Rover 5.0L back side intake valve.

https://www.jaguarforums.com/forum/x...d-94489/page3/

This thread DOES show significant buildup on our 5.0L engine so it is possible.

https://www.jaguarforums.com/forum/x...3/#post1496747

One solution that would be great for me is to use Meth injection. It keeps the intake tract absolutely spotlessly clean even without using a PCV catch can.
My wife has 3.5L Ecoboost MKS which is a twin turbo and it's very common for the hot rodder's to run Meth on those cars. Snow even has a kit for them. Just so many more 3.5L Ecoboost motors out there compared to our 5.0L Jaguars.

Too bad I have not seen one for an XJR! Snow makes some very nice kits.

But if it was my car I would at least look into a intake cleaning by someone who understands DI carbon fouling. May not be too expensive. About all you can do beside taking it apart and manually cleaning the deposits off is suck some kind of cleaner into the intake and let it work.
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Very informative and thanks a heap!!!!!

So you think changing the plugs on the car would be of no value?

Cheers

Tom

 

Plugs do 100K I believe so changing them looks pointless. Look at them if you like.

 

Yea I have to agree.

I don't think at his mileage that would help and from a cost point of view I think it would be cheaper to get the cleaning done first and see if anything changes and then as a backup change the plugs.

If you can report back because as you can see this DI carbon fouling is kinda new and not 100% consistent across different engines and car brands.
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I will let you know. Not having experienced this DI carbon problem- is there any sense that a beginning symptom would be slight cabin vibration at a cold start? Would it make any sense at an early point in the carbon buildup that once heated up, the car would not exhibit any other signs of such and only upon getting worse would they show? I do understand there may not be a clear answer to this as it is a relatively new phenomenon.

Thanks

Tom in Plano/Dallas

 

Yes the vibration sounds like a slight misfire that the OBD electronics maybe don't pickup as the engine is cold and just started?

Since he has no codes I could see some carbon build up that when the engine warms up just isn't big enough to cause a problem or set a code or be noticeable to the driver.

Maybe like a small vacuum leak?
Just a guest here.
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Thanks for the info. I would doubt a vacuum leak. His LT fuel trims at all levels from cold idle to warm idle to 2500 rpm and all the way up the line at any speed are so close to 0 that one would hardly see any variance or chance for a leak.

TBB

 

Do you happen to know what is involved in cleaning? any potential estimate on the cost?


TBB

 

Sorry I only meant symptoms similar to a small vacuum leak. Something that is small and only noticeable at idle. Then when the engine/rpm/air flow picks up you can't see that small problem anymore because it's buried.

No experience yet (Hope to NOT get any experience too!) but I would lean towards an import repair place. Especially if you can find one that works on Audi's.

Like I said up thread it's not a high tech fix all you need to do is let engine vacuum suck some cleaner into the intake tract. If it was my car I would DIY but remember that if the solvent into the intake does not work you might has to go to the next step. Which is to take the engine apart and walnut shell blast the intake valve and any area covered with the deposits. That WILL be expensive.

There are thousands of pages of Audi's having severe carbon problems all the up to and including engine damage. Again certain engines are the worst. So it's a real problem for certain cars.

The amount of carbon deposits can be quite large. The pictures show how cruddy it can get.
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Could be timing chain. Tensioners can get clogged with dirty oil. This is why I change my oil every 7500 miles. The other thing to look at is engine mounts. Mine were completely cracked with no fluid left in them. I noticed my rear view door mirrors were shaking more than they shoul. New engine and transmission mounts fixed that problem.

 

Thanks, but this car is in excellent A-1 condition. Only happens at cold start and for only a couple of minutes, so that would rule out engine mounts. Oil is pristine and the car, before my friend bought it, was only driven 15k in the last 3 years and sat in a garage. We will be changing the oil every 7500 and bought several case of the proper spec. Amsoil oil to use.

Thanks

Tom

 

I would forget any timing stuff for now. Even on the old failure prone 4.0L V-8 it took more miles than that before they started failing. We have had very few 5.0L with timing problems and from my research it looks like Jaguar upgraded the chain and sprockets either in 2014 or for the 2014 MY engines.

I have heard good things about the MotorVac procedure?
It's maybe $125 so not too expensive.

Let us know what he does if you can?

I also have a SC 5.0L with only 20K miles on it and am trying to learn what might be in store for me in the future.
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