Does anyone know off hand what the OE specification for the AJ133 5.0L Supercharged spark plugs is?

I am trying to cure a persistent pinging issue with the 2010 XF Supercharged. It's a very light pinging which is persistent and ever present. it occurs only after warm up and is not there when the engine is cold or during the first 5 minutes of driving. It is most prominent between 2500 and 3500 rpm at moderate throttle although it still happens on and off at higher engine speeds.

• 100 octane gas does not completely eliminate the symptoms although it seems to be slightly less pronounced.
• Tried BG44K (6 cans in a row) -- no effect
• Redline SI-1 (4 bottles in a row) -- no effect
• Dealer -- claims that it's normal since the engine pulls strong and there is no CEL!!!

Usually, there are two reasons engines knock. Pre-ignition due to spark timing which the knock sensors can adjust for, and pre-ignition due to cylinder pressure/heat which the knock sensors cannot do anything about (because it'll happen even if you do not fire that spark plug at all). The latter is usually due to one of three reasons. A heavily carbon fouled combustion chamber leading to high enough compression ratios to cause self-ignition. A clogged injector causing a lean or uneven mixture which is locally too lean and too hot in some parts of a cylinder or two and -- most commonly -- a spark plug that is too hot, too fouled or has a badly eroded electrode.

I intend to pull the plugs and read them to see if I am running rich or lean, and look in the hole to see if I have egregious amounts of carbon. But one of the things I may try is to use plugs that a one heat range colder. Did that a lot when modifying turbocharged cars in the past -- when I up the boost beyond stock levels. Does anyone know the OE specs for the plug?

 

Usually the ECU will pull timing and display a message on the dash if there is a pinging issue. I think it has to be fairly severe before it will pop a code. Almost to the point where you can feel the car start to jerk/stutter. The car will go into "Restricted Performance" that won't clear until you restart the car. For me it's always been due to dirty injectors. Injector cleaner has been the only way to cure the problem. I do have the Supercharged 4.2L motor though. I'm not sure how common dirty injectors are on the 5.0L. I use BG44K injector cleaner about once every month or two and I don't have the issue any more.

I know the DI motors like your 5.0L are much more prone to carbon build up. If you don't mind doing a little work you might want to look into pulling the intake and inspecting the ports for carbon near the valves. Intake cleaner might help if there is carbon and isn't too bad.

 

How can you tell the engine is pinging?

Generally speaking light pinging is normal from time to time in modern detonation limited engines. Such pinging does no harm whatsoever.

If using 100 octane fuel doesn't eliminate this then it is normal, has to be as the engine is tuned to run on 91.

The plugs are spec'd for 100,000 mile change interval, ie lifetime.

If your ECU isn't throwing a CEL then you will find nothing and be able to cure nothing.

 

I have had a similar problem but with a Shelby GT500 which has a 5.4 supercharged ford engine. I know is not a jag but the spark plugs that came from factory I could buy them for very cheap so i started thinking they put some cheap crap on the car to reduce cost. Sure enough I put some ngk spark plugs which have muuuuch better temperature ratings and sure enough it went away. The way you described the problem reminds me a lot of the owner of the shelby is like you know something is wrong but the dealer just claims its normal. Of the top of my head we put some NGK Laser iridium. I think the 5.0 has NGK but they are not the top of the line. You could try and this is a total guess but if you do please let us know!

 

I know what pinging sounds like... it's not very serious and the engine still pulls smoothly but you can definitely hear it (sounds like pebbles in rattling in a tin can). By the time you have jerky drivability you will be hearing knocks (sound like someone hitting your engine block with a sledge hammer) or more likely it is not detonation at all but one or more cylinders missing (not igniting). The latter is more likely with dirty injectors.

DI engines are more prone to carbon build up on the intake valve, stems and tracts. This is because valve overlap sometimes allow dirty gases to back flow up there, while injecting fuel directly into the cylinders instead of through the intake ports do not allow fuel additives to clean the intake valves and ports. They are not really more prone to carbon inside the combustion chamber or injectors. If anything they are less prone to these because injection is at thousands of psi instead of tens of psi. It's pretty hard to plug a hole with squirting liquid at thousands of psi and that thousand psi jet (with detergents in the fuel) is like a power washer inside the cylinders.

Spark plugs are made with different heat ranges. Usually 5 different grades. These are identical plugs except that the insulator (whit stuff around the electrode) have greater or lesser contact with the metallic plug body allowing greater or lesser conduction of heat away from the center electrode. A common modification when over boosting a turbocharged car is to use plugs one heat range colder than stock to account for hotter engine temperatures from upped boost levels. This shifts the operating temperatures about 100 deg downwards reducing the propensity to knock, but not so far downwards that carbon fouling becomes an issue.

Plugs can prematurely become problematic in two ways. If they run too cold -- below 475 deg C or so -- carbon can attach to the electrodes and they foul. If they run too hot -- over 800 deg C or so -- the metal softens, erodes greatly increasing the spark gap. Fouled plugs or eroded plugs won't fire right. This means that the ECU cannot effectively control the ignition timing. Either the mixture ignites before the spark fires because the plug itself is glowing orange hot or the mixture does not fire because the fouled plug cannot strike a spark or strikes a weak one. When either happens, it really doesn't matter what the ECU does to play with the ignition timing -- with the spark plug rendered ineffective all the programming in the world is pointless. Theoretically, the ECU can try to remedy the situation by enroching or leaning out the mixture, but most ECUs do not -- and for very good reasons. If you start screwing around with the mixture in an engine that is pinging or missing, you can quickly nudge it towards really serious carbon foulings (too rich) or physically damaging knocking (too lean).

 

As far as carbon build up in DI motors. I was referring to the intake tract before entering the combustion chamber and the tops of the valves. Fuel does not spray on these areas in a DI motor. Valve cover/PCV lines bring oil fumes/mist back into the intake and it can turn into carbon in the heads. Read up on Audi RS4 motors. They loose 100+hp from carbon build over about 10k miles.

You could try a colder plug to see if the pinging goes away. Make sure the gap is set correctly.

 

Dwight-

You're slightly confused on terminology.

Pinging due to insufficient octane is not 'pre-ignition', it's 'detonation'. The two are very different, unrelated phenomena. Detonation occurs only after the plug has fired. As others have said, the car was built run at full performance on 91AKI fuel, so using higher than that is simply a waste of money. If you're using leaded 100AKI octane, this runs the risk of fouling the c/converters. If the knock sensors or associated components that control/eliminate detonation were not operating within limits, there would be fault codes set and the CEL would be illuminated.

This is not the case.

The possibility of pre-ignition (fuel ignited prior to spark plug firing) due to plug overheating is highly unlikely on an unmodified engine using the stock heat range plug.

Here's an excellent discussion on the subject

Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

My guess is that the noise you're hearing is neither detonation nor pre-ignition.

 

There is no CEL. Nothing. But I know what pinging sounds like and it is definitely pinging. It also makes perfect sense since the sound is never there when the engine is cold. In fact you can drive for 5 minutes and it's still not there. Once the engine has warmed up, it's always there and it never goes away. Prod the throttle and you'll hear it. It's worse going up as hill than when going down a hill. It's worse at low rpm, high load than at high rpm low load. That's all classic pinging symptoms.

I tried 100 Octane race gas that is unleaded -- no risk to catalysts.

In anycase, I am not inclined to let it be because the dealer said it's OK based on the simple fact that there is no CEL! If the engine is pinging due to detonation, something is out of wack.

Regardless, I think the author of the article is missing one key point -- that it is possible for a mixture to ignite without the spark having fired, at a point close to TDC and in a manner which is not catastrophic to the engine. In fact, that is what HCCI (Homogeneous Charge Compression Ignition) is. It is like a gasoline engine acting like a diesel. The piston goes up, the mixture is compressed and the combination of heat and pressure increases to a point where it spontaneously combusted homogeneously. Alternatively, it need not be homogeneous. The charge would normally not reach the requisite temperature and pressure all around, but it reaches a temperature and pressure high enough to be ignited by an object that is hotter than the cylinder walls and piston crown. In diesel engines, during cold starts, that is what a glow plug provides. In gasoline engines, this can be a spark plug running hot -- not hot enough to melt, not hot enough to ignite the mixture at BDC, but hot enough to act as a glow plug.

 

You could absolutely have an engine ping and not throw off CEL.

What i find strange is the fact it only detonates at lower rpm range, given that the compression ratio on the car at idle is 9:5 and 13.5 (if i remember it correctly) at full throttle.

Therefore, it should be the opposite.

 

That's called pre-ignition, although the circumstances for it to occur as you've outlined do not exist in unmodified production engines.

You're right. The abilites of the knock sensor being exceeded while using low octane fuel would be an example, but the OP has tried fuel that's 9 points higher than usually required.

 

Spark plugs will have no effect on detonation. Using hotter or colder plugs cannot influence detonation of end gas. That answers your first post. Whatever you have different plugs won't cure it.

 

The theory at least goes like this…

(1) At some temperature and some pressure, the fuel-air mixture starts to combust without the spark having fired its electric arc but simply from contact with hot surfaces within the combustion chamber.
(2) The spark plug is one possible source of such a “hot” surface.
(3) Spark plugs are intentionally insulated to get them to self-cleaning temperatures and tends to be the hottest object in the combustion chamber.
(4) When the engine is first started, the plugs are cold. Heat build up over time until they stabilize at a saturation temperature.
(5) Hence, while increase in pressure during the compression stroke is not enough to cause pre-ignition when the engine is cold, it may be enough with the plugs heated up.
(6) In either case, the mixture is never hot enough or pressurized enough to be lit by the hot plug at BDC and only cross that threshold after being squished close to 9.5 parts to 1. Hence the pre-ignition event occurs at near TDC and is not particularly damaging or power robbing to the engine.
(7) Using colder plugs reduces the operating temperature of the spark plugs and – if they are the source of pre-ignition – denies the fuel air mixture contact with a surface just hot enough to set it off.

 

dwight-

This is not theory, it's fact. I've experienced it myself back in the bad old days with leaded gas and my misguided attempts to better the OEM's idea of engine design.

It's unlikely to happen on a modern engine in OEM config though.

 

Well, it is happening on mine. If it's not the spark plugs it's something else. And, there aren't that many something else. If it's clogged injectors I tried cleaning them as much as I can with in the tank stuff to no avail. I can try removing all the injectors and having them flow tested and cleaned. But that is expensive. If its massive carbon build up in the cylinders there is not much I can do without a complete tear down and rebuild of the engine. That'll cost more than it'll cost to replace the car! The dealer isn't helping, so spark plugs become the cheapest thing to look at and change.

If it is some degree of carbon build up which causes enough rise in compression to barely cross the threshold of compression ignition with spark plugs of the stock heat range, dropping one heat range may at least cure the symptoms if not the underlying problem.

 

dwight:
I see no disconnect in your logic, except; "Why is your engine experiencing this malady with the stock plugs and others do not?" One answer is you might just have a bad run of plugs, or it could even be you hear what others do not.

I sure hope you keep us posted as you figure it out!

 

dwight- I understand you've convinced yourself that it's either pre-ignition or detonation. Your dealer and people here are pointing out that there's no other data such as engine codes or a known history with this car or engine to support this.

It could very well be some completely unrelated issue- a rattling metal bracket for instance. I'm very surprised you can hear any engine noise at all inside the cabin.

 

Rattling bracket or lose heat shield that makes noise when you open the throttle but doesn't when you drive with small throttle openings. One that makes noise only after warm up not when cold or during warm up. One that makes noise very similar to light pinging I heard on a Celica All-trac Turbo, an Eclipse GSX, an Audi S4 when running higher than stock boost. One that makes LESS NOISE and in a smaller range of RPMs when 100 octane gas is used? Doesn't compute does it?

If you CANNOT hear engine noise in the cabin there must be something serious wrong with your hearing! It's not loud or crude by any means, but yes, you can hear it quite prominently.

The Dealer did check all the heat shields, tensioners, belts and brackets. If you believe them they found nothing lose or in contact. The car is completely stock -- it is, afterall, still under it's new vehcile warranty and has Jaguar Select CPO warranty until July 26th 2016.

 

Take a rubber mallet and smack on your Cats..they will rattle sometimes after getting hot...and that sounds like pinging

 

Maybe you are more sensitive to the engine than most owners? Remember this is a Jaguar and for the most part the drivers are not enthusiasts like us!! They are just not that aware. I constantly ride in other peoples cars and ask about a noise or rattle. Most of the time I get a blank look and they say what noise?

Modern electronic controlled engines are always run right on the edge. The computer is constantly pulling back timing as it gets feedback from the knock sensors. It like a fine ballet between too much timing when you get knocking and too little timing which means the engine is not running at its maximum power/economy and minimum emissions.

I only have the 4.2 supercharged engine but have always had a bit of what you describe. Bugs me but after 93K miles I think it's just part of the engine management system.
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All very true, but the knock sensors are umpteen times more sensitive than the human ear and will pull timing long before a person would hear it. The OP has also tried very high octane fuel which would stop detonation even if the knock sensor was not operative.

It's something else.