If you are an owner of a 2010-present XF V8 5.0 or XF Supercharged, I'll like to hear your feedback as to whether the engine as a carbon fouling problem on the intake valve(s) and/or throttle body.

In 2010 Jaguar introduced the 3rd Gen AJ-series V8s with direct injection. Direct injection, as many of you know, allows for charge cooling, more precise fuel metering and a higher degree of atomization. This consequently permits a higher compression ratio to be adopted which in turn affords greater fuel economy and higher performance. Sounds good right? Well, there's a catch. Direct Injection also presents a few problems... Noise from the injectors for one, but more importantly carbon fouling of the intake valves, intake tracts and/or throttle assemblies.

The reason is simple. Every engine has some degree of blow by past the valves when they are closed and many deliberately circulate exhaust gases into the intake side -- via valve event overlap and/or EGR valve(s) for emissions control. These "dirty" gases carry carbon particles (soot really) which over time can stick to intake valves, runners and throttles. In port injected or, heck, carburetor equipped engines the intakes are "wet". Fuel is constantly misted over the intake tracts and valves. If the gasoline is of any decent quality, it will containt detergents which gently cleans the valves of carbon deposits. It won't be completely spotless, but in general there won't be a problem with significant build ups. Direct Injected engines have completely dry intakes, anything stuck on this side of the intake valve never gets cleaned off.

Mitigation strategies are available. They generally involve timing and angling the fuel injection event so no fuel vapor gets back up the intake. Also, close tolerances of the valve seats may be specificed ensure that blow by is minimized. The valves and intakes can be coated to reduce the amount of carbon that actually sticks. Finally, combustion chambers and mixtures may be optimized to mimizing sooting. However, completely eliminating carbon particles on the intake tracts is largely impossible. And, many respectable companies (Audi comes to mind, BMW & GM too to a lesser degree) has serious carbon fouling issues on their direct injected engines. Carbon build up can be so bad that by 40K miles you may see a loss of about 10% of "when new" output. To make matters worse, there is no easy fix. Injector cleaners and oil additives do nothing because they don't reach the trouble spots. The only cure is for a complete dis-assembly of heads and manual scrubbing or replacement of the valves and other components -- which is essentially an engine rebuild.

To be honest, every DI engine has this fundamental problem. The difference is in degrees. In an Audi RS4 for instance you'll lose 20~30 hp in 10,000 miles and for the 2.0T engines, its pretty darn ugly and somewhat performance impacting by 50~60K miles. In GM and BMW engines it's about 1~2 secs off your original 0-60 times by 50~60K miles and visible build up, yet not horrendous. Ford and Porsche on the other hand have been relatively clean -- just thin visible coating of grey but no discernible impact on dyno or real world numbers. The question is -- how's the XFs doing after 4 years on the road?

To provide readers and researchers with a useful reference, please include the year, model and mileage of your vehicle, along with any symptoms or service you have had.

 

I've used this for 40 years and never had an upper cylinder engine issue of any kind..always had peak performing injectors and clean valves..(compression testing)...I just wanted to share, not trying to sell anyone on the this product, but I swear by it..I have only added it to my gas..6oz. to every 10 gallons...Use it regularly and you will not have ANY carbon fouling..

 

Not sure if I totally believe in it or not but once a year I have used Sea Foam to clean my valves. I have not felt or seen much difference if any at all but many swear by it. It is easy and cheap to do in just a few minutes on the Jags .

 

The problem is that with direct injection, fuel is sprayed directly into the cylinders. The intake valves, intake tracts and throttle -- the "upper cylinder" if you will -- will never see this detergent if it is added to the fuel. Unless you have a leaking valve stem, they will also not see this additive if it's added to the oil.

This is how some Direct Injection engines' intake ports look like after a while...


Audi/VW TFSI 2.0T



Mini Cooper S 1.6 Direct Injected Turbo

 

Never heard of anyone having any issues with the 5 liter engines. One of the best and sophisticated engines out there.

Which survery company do you work for?

 

First of all this MMO is not a detergent..If it is introduced into the Intake port or into the cylinder it don't matter..remember fuel is not injected at the ignition point, but long before.. it will lubricate and coat the intake valves/stems and exhaust valves/stems..and cleaning and preventing post combustion deposits from forming (ANYWHERE) in the cyclinder head..

I subimit your pictures of the Cooper and VW are; 1. using bad gas, and/or 2. probably using Alcohol (E10) too..and ran a lot in pure city driving and not getting hot enough as with a long haul open road drives..all that combined will foul up like your pictures..I've seen it before in a half dozen cars driven under the same senarios I described...Had those engines been burning pure 100% good gas and MMO, these pictures would of been spotless and free of any deposits..

 

I had major problems with my 5.2 V10 audi. Its what prompted me to sell and get the XFR. I would lose about 10 HP / year and the build up eventually become so evasive it managed to blow the entire intake manifold off the engine. Once every 6 months i would need to pay for a manual cleaning or things like plugs, injectors, intake systems and purge valves would get so gunked up they would need to be replaced. Seem to happen to some degree on all DI cars but Audi, vw and bmw seem to be the hit the worst
Im not reading much about jag owners dealing with this and some of the RS guys on the audi forum saw it happening with as little as 7k miles driven in the car. Hopefully our cars are designed with a built in solution to this extremely annoying problem. fingers crossed

 

Yes, fuel is injected before the ignition event. But, that's not the point! The point is that in direct injection engines, fuel is injected into the cylinders directly (hence the term Direct Injection); it is not injected upstream of the intake valves and therefore does not flow past it. From the time it its injected to when it is lit, the fuel does not ever touch the backsides of the intake valves, the valve stems, the intake ports, intake tract, or any of those places. Hence, anything added to the fuel also does not intact any of those places.

The carbon gets there because of blow by past the valves after the mixture ignites and the valves leak a tiny bit of the explosion it is trying to contain past the valve seats. It also gets there due to exhaust gas recirculating -- either through intake / exhaust timing overlap, or through the EGR subsystem used for emissions control.

Unless his particular additive is functional AFTER it has been burn to crisp during combustion within the cylinders it's not going to do anything.

 

We have definitely seen carbon fouling on the Land Rover 5.0L S/C. Here is a pic of the intake valves on one I had apart today. I have yet to see a Jaguar with this problem. The early 5.0L on the rovers also have a nasty habit of timing chain tensioners letting go. This particular rover has 60,000 KM. I have seen XFRs with that kind of mileage, but no problems with 5.0L. Maybe because they used the 4.2L in 2009 all he bad 5.0L went to rover.

There is no scheduled maintenance to clean the intake, honestly I don't know if the recommended BG intake cleaner recommended by Jag to correct clogged injectors would even help. I've never performed one (don't have the equipment at Jaguar), but have used BG intake cleaners on Suzukis in the past that didn't seem to do much. With fouling like that makes you wonder what the longevity of these 5.0L will be without regular cleaning of the intake valves.

 

I suspect that most 5.0 owners wont be able to give me much an answer as I doubt many people have taken their intake manifolds off. This is a question I have been curious about, especially knowing the well documented problems among the Audi enthusiast community, particularly the RS4. I can assure that the problem for most of these owners, some of the most meticulous out there, was not bad gas or extensive city driving. Some tried running a catch can but results were mixed/inconclusive.

 

When I was over on the Audi forums the RS4 owners lost a lot more than 20-30hp. Some had dynos showing 100hp losses. It's one of the major reasons I didn't move from my B7 S4 into a RS4. I haven't seen anyone post about carbon build up in a XF yet.

 

I've had exactly the same experience as you over a slightly longer time span, except that I've never used this product or any other. The worst vehicle I ever owned for intake valve carboning was a GL1000 Honda, but that was caused by the use of leaded gas. Switched to unleaded in the early 80s and never a problem since.

It might be that the OP is barking up the wrong tree, but I've come away with the lesson to not buy an Audi or Mini. Not that I was going to anyway.

 

Gausten, thank you for posting the pic, though I was hoping never to see one for JLR. If you don’t mind I have a few questions:

- Just to confirm, is this is from a 2009 AJ133 5.0 S/C on a Range Rover?

- You mentioned not having found any carbon buildup in DI 5.0 V8 Jaguar engines to date. Can you describe your sample (i.e. how many, what model year, what mileages you have inspected)?

- Any thoughts on why the results would be any different, if the JLR engines are identical? You mentioned an early 5.0 problem (timing chain tensioners) that sounds like it was resolved, but how could the DI carbon buildup issue be addressed without some kind of fundamental redesign?

Info is hard to come by on DI, so any data you can offer would definitely be appreciated. Thanks!

 

Toyota's latest DI fuel injection also uses one intake tract injector similar to the K-Jetronic cold start injector, feeding all intake branches some fuel all the time. Could this be the answer to carbon fouling of the intake valves?

Valves don't suffer any blowby as the seats and valve rims would erode rapidly if they did. All reverse flow back up the intake tract is due to valve timing, overlap and resonance effects. This is why exhaust valves never get any carbon, they are continually blasted clean by combustion gas on the exhaust stroke. Intake valves run cool as they are fully seated before combustion occurs. Ignition advance does not result in combustion gas reversing into the intake tract. Fuel injection timing is also not relevant. All the fuel has to be burned or the catalytic converter will overheat. It isn't feasible for the fuel to be the source of carbon fouling or the engine would be impossible to certify. Valve overlap exploits ram resonance effects. Fuel mixture may momentarily reverse but would then get drawn back into the combustion chamber and be burned. How "carbon" would flow backwards is a mystery.

I think the source of these "carbon" deposits is much more likely to be crankcase venting fumes which will be heavily contaminated with combustion gas blowby from the rings, oil vapour and water vapour from the crankcase. Different engines will handle PCV in different ways resulting in different carbon contamination effects. How you drive would also affect PCV based effects. Heavy throttle and high rpm would exacerbate the problem. With port injection driving hard would have cleaned the valves.

 

Hey newXF, this pic was taken off a 2010 AJ133 5.0 S/C Range Rover with 60,000 KM. I have not found build ups on any Jags, but I have to admit that I have never had to look for any. We have a fairly small Jag market here and many are only driven during the summer months due to the harsh winter/RWD combination (the AWD is awesome in the snow, fyi). We do get a lot of rovers with buildup on the injectors which causes misfires, this does not seem to be the case with the jaguars. I do have some training later this month and will definitely ask some of the techs at the bigger shops if they see these problems on the jaguar side.

As for your last question about thoughts on preventing buildup, I don't really have an answer. I think all the manufacturers are having issues with direct injection and keeping the valves and injectors clean. A friend of mine is a Porsche/audi mechanic and I recall him mentioning walnut blasting to remove carbon buildup, but this would require the removal of the cylinder head at the very least (not a simple take on the 5.0L). JLR has released a tsb regarding misfires and is specific about using BG injector cleaners, but as I mentioned we do not currently have the equipment and other techs from further south have indicated the these vehicles come back and end up getting injectors replaced.

I can't say that I have really looked into the problems associated with DI and dry manifolds combined with valve overlap and exhaust scavenging from the cylinder which I personally believe is the cause of the buildup. I would be interested to see what effect the addition of a detergent aspirated into the manifold would have on the back sides of the intake valves. As this is not currently recommended at regular service intervals, I can only imagine that it would not have much effect.

 

Generally speaking carbon particulates get into the intake sides predominantly in three ways.

• Through gasoline deposits in carbureted and port injected engines
• Through the EGR (Exhaust Gas Recirculation) system; which basically have a valve and hose that feeds exhaust gases into the intake side.
• Through exhaust/intake valve duration overlaps. At low rpms, the intake flow is not energetic enough to overcome residual exhaust gas pressure and some degree of regurgitation into the intake tract occurs.
• Through blow by through the valve seats if they don't seal perfectly.

Since DI engines have "dry" intake tracts and ports, the first is not a source of carbon fouling. This however is also the main reason for the presence of carbon fouling since there is no "detergent laden" fuel to wash off any that occurs, and makes traditionally methods of valve cleaning -- such as using fuel additives or detergents fed through the fuel injection system completely useless.



Traditionally, overlap induced back flow on exhaust products occur on engines using cam grinds optimized for high rpm operation -- the reason I suspect the 8000+ rpm capable 420hp 4.2 liter RS4 engine is more seriously afflicted than other Audi power plants which are already rather shoddy in this regard.


Modern emission control schemes tend to sometimes make the overlap carbon issues worse. Instead of an EGR system, many modern DOHC engines with continuous VVT intentionally use the VVT system to dial in a significant amount of overlap at low load, low rpm operations. This is done to achieve a "virtual" EGR effect by causing some exhaust gases to feed back into the intake tract. With the same amount of fuel injected, the exhaust gases mixing with the intake air reduces the oxygen content of the intake charge. This pseudo enrichment reduces oxides of nitrogen formation and helps meet emission standards.


Traditional Port Injected engines have a lot of lee way with regards to intake carbon fouling -- not because they are clean, but because the constant wetting of the intake ports, tracts and valves allow detergent additives in gasoline to go to work washing the carbon off. Usually nothing more a very slightly glazing remains. DI engines have no such inherent cleaning mechanism and anything that gets up there and sticks, stays and clogs! It is a fundamental problem of DI engines.


As said before, being judicious with EGR and/or overlap induced feedback, ensuring the the DI spray is angled to never mist up the intake tract, and coating the intake valves and/or tracts with non-stick coatings, all help with the problem. Toyota goes one step further and use port & direct injection together. They do this in part to clean the intake of carbon, but also in part to be able to turn off DI at idle and low engine power demand states for quieter NVH (because DI is considerably louder than port injection).


Anyway, to answer a previous question... typical owners do not take apart their engines and peer into the intake ports. However, if the problem is pervasive they will generally notice a power drop as mileage accumulates. The reason I took an interest in this subject with regards to the 2010+ XF 5.0s is that a car magazine long term review vehicle showed a 0.1 sec slower performance at 40K miles vs new. This is opposite of what normally happen with cars -- they tend to be very slightly faster at 40K miles due to wear induced frictional reduction within the powertrain. This may or may not indicate a DI related carbon fouling problem, hence the tread.

 

Gausten, thank you for the additional details. A few more questions (I hope you don’t mind):

- Have you noticed any difference in carbon buildup incidence between the AJ133 NA vs. the AJ133 S/C?

- Do you know if your friend who works on Porsche/Audi has seen Porsche DI engines that require walnut blasting? Audi is the poster-child for carbon buildup, but to date I hadn’t read anything about Porsche motors having this issue.

- Do you think just a detergent could be strong enough to break down the carbon buildup after the fact? If it, or a gasoline with detergent could wash off the back of the valves ongoing, this would be preventative (ala Toyota/Lexus), but once baked in place, the only solutions I’ve turned up are walnut blasting or actual disassembly and cleaning. It sounds like the former is not a viable (or straightforward) option for the AJ133?

There was another brief discussion that cropped up here (page 3, #55 onwards):

https://www.jaguarforums.com/forum/x...n-43008/page3/

misdeismo referenced some optimizations to the PCV to minimize the amount of junk being pulled in that ends up carbonized, but presumably this is the same design across Jaguar and the Land Rover V8s where you’ve been seeing the buildup.

Please do post any news you hear from your fellow techs on the Jaguar side, good or bad. Again, thank you for sharing- information specific to JLR DI has been hard to come by.

 

I have actually seen the ports of a Porsche DI flat six at ~60K miles. There are some carbon, but it is more of a greyish dusting than any thick or lumpy build up. I doubt it'll have any effect on performance since it is unlikely to be tangible enough to affect the airflow.

Porsche engines have perhaps an architectural advantage. All the recent ones feature what's marketed as "Variocam Plus". This is a 2-stage cam switching system with concentric lifters. Each valve is operated on two cam lobe profiles -- an inner cam for low RPM operation and an outer pair for high rpm. At lower engine speeds the outer sleeve simply goes up and down against a spring and does nothing to operate the valve. At a certain switch over point, a steel roller locks the lifter and its sleeve together forcing the valve to track off the high lift cam. This may be why -- despite their high revving, high specific, output nature -- Porsche engines do not have much of a overlap induced carbon fouling issue. They simply may not need to operate off a high duration, high lift, high overlap, cam profile at lower speeds.

 

Ive opened more than a few 5 litres to replace the outlet pipe under the intake manifold that obviously requires lifting the intake up for access. Ive not see any apprieciable deposits on the intake valve or ports. And surprisingly theyre fairly clean. I did 2 this week and both over 40k miles.

 

I am still waiting for an answer for this pointless thread.