I should have mentioned that plain old water has also been used to decarbonise
engines. Same method, introduce water through the power brake booster vacuum
hose while at high idle or more, metering it so that the engine almost bogs.

One way of controlling the metering is to tape a hose extension to the
existing hose with an angle cut into the end of the hose that is inserted
into a large pop bottle of water. The hose is then held close to the surface
of the water. Adjust as necessary to get the right amount of water running
up the hose. Don't submerge the hose for fear of hydrolocking the engine
which is a "very bad thing", (tm).


The combustion chamber is effectively steam cleaned. See some of the photos
of piston tops and combustion chambers where there has been a head gasket
failure. Invariably, the problem cylinder is much cleaner than the others.

The problem with the relocated sensor approach is that the sensors have
a specified torque. The sensors are in effect, contact microphones. If
the contact is out of range, then the sensor is out of range, despite
the signal processor setting up a background noise level.

Try these two links at autospeed.com

AutoSpeed Blog » Blog Archive » Internal engine cleaning

AutoSpeed - Dodging Detonation - Part Two

 

Come to think of it ....

the chief anti-knock strategy of the JAGUAR system is to ADD FUEL to combat knock.

kind of difficult to do if the fuel pressure is not as designed, even if the ecm thinks it actually
is doing it.

It does tie in with the retard and heat, because additional fuel would have the effect of
cooling the combustion chamber.

source? Jaguar technical literature.

 

Cam,

Just a few random and possibly pointless thoughts:

I think I recall reading that the ECM responds to KS signals within the knock frequency range by both retarding ignition timing and increasing fueling to help cool the cylinders, so if you have true knocking, you should be able to observe the ECM making both of those adjustments.

If I understand the difference, carbon deposits are more likely to cause pre-ignition than detonation. I don't know if that makes any difference at all in your diagnostics, but since the causes can be different, here's a good explanation:

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


I can't remember if you've reported the spark advance when the pinging occurs, but it might be interesting to know in case it provides any clues.

I haven't thought this through, but could a problem with VVT lead to the noises you are hearing at higher revs? I haven't studied the VVT operation on these engines to know if it's even possible for the valves to become slightly out of sync, but if, say, the intake valves were slighly open during combustion, the symptoms might be similar to detonation or pre-ignition, but would actually be continuous little backfires in the intake manifolds....

Sorry if all of these are way off base, but you seem to be at a point where wacky ideas can't hurt too much.

Cheers,

Don

 

Don't know if my idea has any value, but perhaps you could use the Torque app to see if the ignition timing gets retarded or anyhow changed during the detonation? It would confirm whether your knock sensors are functional...

 

Not sure if it's applicable to the 4.2 engine, but I have attached the quote from the AJ26 4.0 engine guide, and it tells about ignition timing retard to prevent the detonation...

 

Possibly what you're hearing is not detonation.

 

That line should go to some connection on the output side of the supercharger so that it does see boost pressure. On the XK, there is a nipple on the V8 piece of the outlet elbow that it connects to.

 

Same on this one, I can't follow that hose as it disappears for a bit behind stuff, but safe to say it's the same one.

After putting in the new fuel pressure sensor and putting cable ties around the joint, I could not get the engine to stumble by spraying the MAF cleaner around that area, so i'm 99% sure that's where the leak was.

Can it be that with the bypass valve open there is actually a tiny amount of vacuum on that line? Because the fuel trims did go back to normal after making that line tight, i.e. whatever vacuum leak I had, was gone after sealing that hose...

If it's not detonation, then what else makes that noise?

I don't quite understand the difference between detonation and pre-ignition, if it were occuring that high revs / WOT.

I had an old carb-fed Ford V8 that did both; it would ping under load, and occaisionally would "diesel" after you turned it off.

The noise on this engine sounds the same to me, although it was 15 years ago. Pre-ignition / dieseling isn't going to happen with an EFI engine because unlike a carby, fuel isn't drawn in by vacuum.

The other possibility I guess, is that the sound is misfire's, not detonation. If that's the case then by putting in new coils & plugs, i've pretty much isolated the major potential causes of misfires, except for maybe the cats being blocked up and unable to flow enough >5000rpm WOT.

I get no codes for misfires, but I wonder if the system can detect misfires with all the noise/vibration at high rpm/load?

Just a theory...

 

If your ECM is not responding as it should to detonation, then perhaps the frequency band of the noises as detected by the KSes falls outside the range typically produced by detonation or pre-ignition. IIRC, knocking produces sounds within a narrow band of the audible frequency range. Filters in the system reject sounds above and below this band to avoid false triggering of the ECM's knock responses. To the human ear your noises may sound like detonation, but the knock detection system may think otherwise.

Is there no possibility that a problem with the VVT or some other issue is leading to small, recurring backfires within the intake manifolds?

 

No VVT on this engine Don, only the very last 4.2 s/c engines had VVT.

 

Loose/broken brackets, rattly engine bay stuff. Lots of people here were convinced they had detonation when catalytic converters first appeared and the heat shield came loose and rattled.

 

But in this case it's not just the noise, it's also a hesitation at the same time.

 

Detonation is not usually accompanied by a noticeable hesitation.

 

But misfires would be, right?

 

I thought I had read that more than once, so before I posited the idea here I checked the '04 X350 New Model Dealer Training Manual, and here's what it says:

"The supercharged version of the AJ-V8 4.2 liter engine shares all the advanced technical features of its normally-aspirated partner." (p. 4-2)

and

Variable valve timing (VVT)
Faster engine response at all speeds is available due to inlet camshaft timing that is continuously varied according to demands and conditions. The V8 VVT system uses principles similar to that used on the AJ-V6 3.0 liter engine. The V8 uses a three vane unit in lieu of the four vane unit on the V6 variants." (p. 4-8)

I can't find anywhere that it states that VVT was omitted on the S/C engines. So only the N/A AJ-V8s actually got VVT, or not even those? The Dealer Training Manual makes it sound like all the AJ-V8s, even the S/Cs had VVT.

Bummer!

 

The AJ26S & AJ27S did not have VVT.

The AJ33S & AJ34S did not have VVT in the beginning, but towards the end it was added, supercharged cars after these VIN's have VVT;

X350 XJ, from G49701
S-Type R, from N52048

The X150 XKR and the XF SV8/XFR had VVT from the beginning. The X103 XKR never had VVT.

 

Do all the N/A X350/X358 V8 engines have VVT?

 

All the N/A V8's have VVT

 

+1 V8 NA have VVT. Early (to when I don't know) SC don't - my UK 2004 STR doesn't, for example.

Fuel trims at idle at low & high revs, then if they're OK under load (i.e. driving) should tell a lot. Sound to be heading the right direction.

 

2006MY onwards STR and XJR / Super V8 got VVT, according to the VIN's...

I know 0% at idle is good, but what's an OK fuel trim under load or at a certain rpm?