When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
You might find this interesting.
Posting from Facebook, normally full of BS, but this one is from Count Iblis, I guess he does not mind sharing.
As it is a closed group, I copied and past it.
This is what happens to an AJ27 4 litre XJR piston when you change the pulley size and don't remap and then drive hard for sustained periods. The standard map at WOT at higher rpm runs about 11:1 AFR. This engine had the supercharger wound up and apparently ended up running 13:1 with mods in open loop. That's 20% leaner than stock. This indicates the engine had 20% more airflow. Stock engine peak Volumetric efficiency is 145% - this means the modified engine was boosted to run at 170%!! As the maps were kept stock the ign values were stock. The knock sensors only retard up to a point. The pics look like there was knock and perhaps excessive piston temps. Having too much advance can lead to both. The AJ27 SC has cast pistons, not forged like the AJ33 SC and I don't think it has piston cooling jets. Food for thought for those who want to modify.
Interesting, indeed. But many people have done the mod and haven't had issues. Except for the few rare cases. Wouldn't there be a lean code if it kept running lean? Mine went away. Did he allow for the ecu to adjust?
Also, I don't think anyone tunes these jags anymore.
Just read up on closed/open loop and read that on WOT, it runs on open loop. The ecu wouldn't know if it is running lean or not, so it won't throw codes at WOT; thus, hole in piston, and no codes. I'm sure the knock sensors would trigger though? Wouldn't you also feel or hear the knock/pre-ignition occurring?
I believe an octane booster would help reduce the risk of ping/knock/pre-ignition, and maybe a water/methanol injection would help reduce the engine running lean?
As for timing, I generally see a positive timing advance in my OBD 2 scanner using the Torque (Lite) app, so I don't think I have a retarding issue, unless the app is incorrect in data retrieval. But in the case of Rupak Paul, wouldn't a low (negative) timing advance be indicative of running too much boost, causing ping/knock/pre-ignition?
Last edited by AZjag1999; May 23, 2018 at 07:19 PM.
JagV8,
If that's the case, then I may be a special case where he was running more lean than usual. I'm skeptical that Count Iblis didn't allow for the ECU to adjust properly or had a bad fuel delivery component. Also, it depends on what pulley he went with. 20% increase of airflow seems like a lot.
jackra_1,
I might look into a water-meth injection soon as well.
JagV8,
If that's the case, then I may be a special case where he was running more lean than usual. I'm skeptical that Count Iblis didn't allow for the ECU to adjust properly or had a bad fuel delivery component. Also, it depends on what pulley he went with. 20% increase of airflow seems like a lot.
jackra_1,
I might look into a water-meth injection soon as well.
I do not think I had a problem at all before I installed the Snow water/meth system other than the fact that my throttle body thru and including my charge coolers were pretty badly carboned up with"soft" carbon.
So one reason I added the w/m system was to try and keep all of that clean after cleaning everything up.
Also added an oil catch can which does catch a fair amount of oil.
Also it helps cool the SC system when at high boost and I would hope it would prevent knock.
I added an extra in-line SC radiator with fans to help as well.
I am currently experimenting with having the SC bypass valve actuator disabled so that it is closed all the time.
Not 100% sure but isn't Count Iblis on this forum? ex Jaguar development engineer.
Would remap in this case be a simple hard reset, let it idle for 10 and see what occurs. Possible unmetered air leak with the added boost, i.e. marginal seal/gasket.
Not 100% sure but isn't Count Iblis on this forum? ex Jaguar development engineer.
Would remap in this case be a simple hard reset, let it idle for 10 and see what occurs. Possible unmetered air leak with the added boost, i.e. marginal seal/gasket.
It could have possibly been a vacuum leak somewhere, since there is a lot that has to be disassembled in the process of changing the pulley (If he went that route). There's still a lot missing from Paul's story. It is hard to tell if it was directly related to the pulley swap, intake leak, or just not allowing the ECU to adjust.
One thing is certain: there ARE risks to modifying, especially when doing a pulley upgrade.
The piston shown was for a 4.2 engine, so the story doesn't look complete indeed.
Just a pulley change doesn't limit the fueling, the margin for more air/fuel flow is much higher.
Of course the risks for errors increases, not just on how you use the extra power, but remember as well that over time injectors/maf/o2 sensors/pumps etc will degrade, so best to ensure all is up to spec when adding more power...
The piston shown was for a 4.2 engine, so the story doesn't look complete indeed.
Just a pulley change doesn't limit the fueling, the margin for more air/fuel flow is much higher.
Of course the risks for errors increases, not just on how you use the extra power, but remember as well that over time injectors/maf/o2 sensors/pumps etc will degrade, so best to ensure all is up to spec when adding more power...
If that's the true, something seriously was wrong, since they are "forged.... and [with] piston cooling jets." But I think it would be difficult to misjudge what engine you have, since the 4.2's only came in the x350 and x358 (in the XJ series).
I ran a few fuel system cleaners, and had recently changed both fuel pumps before the upgrade. It may be worthwhile ensuring to do a "tune-up" before a mod like this, especially if it's already down on power.
But I think it would be difficult to misjudge what engine you have, since the 4.2's only came in the x350 and x358 (in the XJ series).
Indeed, and if the supercharger in the 2nd picture was from the same engine, you can see from the gasket it was from a 4.2 engine as well.
Good that you changed the fuel pumps, after more the 18 years chances are they are not up to spec anymore...
I have no experience with fuel cleaners, for me best would be to have the injectors professionally cleaned as you then also get to know the flow per injector.
Indeed, and if the supercharger in the 2nd picture was from the same engine, you can see from the gasket it was from a 4.2 engine as well.
Good that you changed the fuel pumps, after more the 18 years chances are they are not up to spec anymore...
I have no experience with fuel cleaners, for me best would be to have the injectors professionally cleaned as you then also get to know the flow per injector.
Ahh, good catch, It is definitely not the gasket from the 4.0 Eaton.
My XJR is my daily, so having down days is not really possible. But, yeah, professional cleaning is the way to go with time/money.
And interestingly, when I bought the car, I was told the fuel pumps were recently replaced, and several months later, the primary pump went out (which had a URO Parts printed on it).
One more thing, the AJ26 ECU Knock control doesn't go higher then 3000 rpm, so these engines have a higher risk.
Interesting. How does it then advance/retard the timing without knock control after 3000 rpm then? I'm guessing the effects of a water/meth injection system would not be fully exploited, if it there is no timing control after 3000 rpm.
Only timing retard I know of for the AJ26 is via the IAT#2, but its a slow sensor. At least there the W/M will be helpful in retaining power and adds some security.
Only timing retard I know of for the AJ26 is via the IAT#2, but its a slow sensor. At least there the W/M will be helpful in retaining power and adds some security.
Oh, I see. Once I get back to Phoenix, where temperatures are +110 F, and with only 91 octane, I'm sure it'll be a healthy mod. I'll add it to the to-do list.
Some have place the injection nozzle before the supercharger, and some after. Some have use the windshield washer fluid reservoir as a means to sore the mixture, some have used another external container. It would be easier to place the injection nozzle on the intake tube/duct since it's easy to drill a hole, but some believe that the mixture can damage the coating on the supercharger. I don't know which set-up is best, but it is a DIY kind of thing since there's no specific W/M kit for these jaguars.
