A 10% bigger supercharger pulley will not improve fuel consumption since it only causes the engine to runn less rich at very high airflows, which is not a condition that happens very often; ie wide open throttle at speeds above about 4,500rpm. In fact if anything, fitting a bigger pulley will make the fuel economy slightly worse because the supercharger is being driven faster all the time. Increasing the drive ratio by 10%, increases steady state torque at all speeds, so increases performance. Power won't incresse by as much as the increase in drive ratio due to the worsening supercharger efficiency at higher speeds., but certainly won't be worse. The bigger pulley is an aftermarket part. I don't know the names of any suppliers in the US, but I know of at least one supplier in the UK called Powerhouse-UK. This is not a supplier recommendation, just information. If you are trying to source this aftermarket part, by sure to specify that you want the one for the 95-97MY XJR6 not one for the later XJR V8.

 

Eurotoys also offers an up size crank pulley for the xjr6, but is nearly double cost of Powerhouse.

 

The more of these you sell the more proven they become. To the point where every AJ16 engine will want one.

I have a question. Is this 5 degree timing advance something that could alternatively be done in the ECU without modification to the CPS position?
Also what is the status of programming access to the ECU or switching to an aftermarket ECU? I have seen threads on this but they seem to fizzle out before anyone says how they got on fitting an ECU.

 

I can reprogramme the ECU to put the extra ignition advance into the ignition maps, but it is much more time consuming and requires the ECU to be sent to me. The bracket is a much easier and more convenient solution for most people.


I don't recommend reprogramming if it is just is in order to get more ignition advance. I only recommend it to owners with more complex requirements, such as engine performance modifications that increase airflow by more than 10%, or fitting the engine into different vehicles, or converting from auto to manual transmission.

 

Andy....glad you have responded.....as you know my new ride has all the toys....Niger supercharger pulley and your bracket.....but one thing It didn't have was the ECU reprogrammed for the manual transmission conversion.....

I'm a bit concerned this may be the chase of my high idle speed in neutral when the car is in motion....as it was described before it idles at around 2000 Rpm when in between gears and even more strangely it increases from about 900 to 2000 when I simply let it coast down an incline from rest....as soon as the car moves the revs pick up.....

Is this a sign that the auto ECU is sensing speed it should be incorporating into auto gear change management

HELP

 

As I comprehend it ECU settings and mappings are altered to gain more power. Sometimes this is to get the settings inline with actual hardware changing to the engine but changing the settings on their own can bring more power or efficiency. It seems the Jaguar ECU does not lend itself to this sort of tuning. Fitting the bracket maybe easy but the actual setting which says what the advance should be is in the ECU somewhere. I would love to get in there and find out how it works. Without breaking my car.

 

Dear Scimitar,
If your car is a DIY auto to manual transmission conversion, this could explain some of the strange behaviour that you are experiencing. Depending on what was done with the park /neutral input (pin 27 on the red ECU connector). I can't remember whether it should be grounded or open circuit on a manual car. Changing the pin from its current state may help, but the best solution is to fit an ECU that has come a manual XJR. Alternatively I can reprogramme an ECU to manual specification. Email me directly andystodart@metronet.co.uk if you wan to discuss this option.


Dear Wayland,
I have reprogrammed engine ECUs for AJ16 engines to increase the ignition advance; what you describe as "changing the settings". It is a a better engineering solution, than fitting my bracket, but the work is much more complicated. It takes many hours to identify the correct data in the ECU software and then modify it. My bracket offer most of the benefit of reprogramming, for a fraction of the time.

 

I am happy to modify the signals fed to the ECU in order to get the required result. I am disappointed that the ECU is such a black box. Would fitting a Megasquirt be a real mission or is it a case of patching in some wires and start setting up with a laptop?

 

Wayland,
The engine ECU of an AJ16 engined Jaguar is no more of a "black box" than the original equipment engine ECU of any other vehicle of a similar period. Jaguars are generally not popular vehicles to modify, and so I believe that there has been little appetite in the aftermarket industry to invest time in "hacking" the software in order to modify the ignition and fuelling maps. The XJR6 is mapped quite rich as standard, so is tolerant to modifications that increase airflow by up to 10%, which is enough for most owners. It would not be possible to achieve the same level of driveability with any aftermarkets EMS as is achieved with the OE system, which has had 1000s of man hours of development using equipment that is not at the disposal of aftermarket tuners.

 

Hello Andy,

My bracket arrived today. Nice bit of engineering, thanks.

OK you think the ECU is the best it can be. Fair enough.

I'll report back when I have fitted my bracket.

Thanks.

 

Megasquirt is about the furthest thing you can get from plug and play. You are recreating all the work the development engineers at Jaguar did to develop the code for the ECU, but without the benefit of the tools they have, like chassis dynos.

Between a friend and myself we have done MS on 3 different cars. They run ok, but it's not OEM quality the way the X300 runs. 8 years later we are still tweaking to try and bring it to that level. The first 90% isn't too bad, the next 5% is hard, and the last 5% is nearly impossible.

There are close to 200 parameters that have to be set in MS, and of course they are not all existing in isolation. A change in one will affect others. In many ways, that last 5% is like a dog chasing it's tail. You get close, but never achieve the prize.

The lack of information is a big thing too, many things have to be measured or guessed, and then refined by trial and error. One that I am working on now is the pulse width vs voltage correction table. How much does the pulsewidth of an injector change as the voltage supplied to it changes? You'll never find that data published. I was chasing a problem where the car went quite rich when my electric fan came on and went back to normal when the fan shut off. Only at idle of course! Turned out that the voltage correction graph was off by 0.0001 seconds/volt.

Of course, it depends on your tolerance of the "wrongness level" of drivability. However, don't expect it to drive like a modern car, MS isn't the holy grail that will be an easy fix.

 

Andy, I'm curious about that statement. If the airflow is increased, by whatever means, wouldn't the AFM read the increased airflow and the ECU fuel accordingly? I could see it leaning out if it was a MAP system, but it's not.

What is a target AFR for an XJR, say under motorway cruise conditions? I would have thought slightly lean for economy, or is that not the case?

 

I have never read anything like this about the MegaSquirt. Cars used to run OK with a carb and distributor but it was a no brainer to see that this could be done with a computer with it's ability to be programed how to respond to conditions. A carb can only work with in it's own physics but a computer could be programmed to do some very weird things if the theory suggested that would be good.

It ought to be much much easier to tune a car with an ECU.

It really sounds like people are saying that Jaguar did such a good job building their cars that improving them is impossible. Maybe this is true. Does this mean that people who improve other brands of cars are deluded or that those cars were so bad that any mod would have been an improvement?

After fitting 3 cars with MegaSquirt you never managed to improve on the original ECU? 90% drivable is not 120% drivable. Surely a massive failure for the whole concept of an aftermarket ECU?

One of the principles of tuning your car is that you can put in more attention to detail on your particular car than the manufacturer could. They had to come up with a way of making their cars identical so they are all equal. Not so that some of them happen to roll of the production line better than others.

Maybe you're right but it seems to go against a lot of things I think.

 

The cars I have does were originally all with carbs and distributors, so Megasquirt is a definite improvement. One is my 1966 S Type, the other was a 1970 Ford F350 with a 390 the other was a 1967 Chrysler 300 with a 440 engine.

Yes, they drive better with MS than on carbs, no question. Do they start, warm-up and drive as well as an X300? No. Yes, an ECU can be programmed, but that takes a lot of skill and knowledge to get the right program to respond to all conditions. Steady state when hot is easy, it's the transients that are difficult to manage. One that I struggled with all last year was when part warm if I had to come to a stop the car would stall. Started right up again and ran fine as long as I was moving, but put the clutch in and it stalled. In the end it was a combination of several settings that weren't quite right, but figuring out which setting to change and by how much is the difficult part.

I've said this before, but MS's biggest advantage and greatest liability at the same time is it's versatility. It can be adapted to any gasoline engine, so that means you are starting with a blank sheet of paper. Sure, for popular engines others have gone before you and you can copy their homework to a certain extent, but there are still a lot of other things that have to be set right. That takes skill and experimentation.

Tuning an OE ECU to make a few adjustments is a very different proposition. I wouldn't say that Jaguar's tune is perfect, nor is that of any other maker, just that people have different end goals for their car and wish the ECU to reflect that. Take the Mustang guys for example, if they want it as a track car they they can bias the ECU to run richer for more power. That's not the way Ford would tune them for general sale, where most drivers don't care about 1/4 mile times or having to comply with emissions and fuel economy laws. But it's much easier to tweak an existing ECU, than to build one from nothing.

My only real point was that MS takes a lot of work and understanding to get things acceptable, and it would be very difficult to get to the same point of the X300 as it came from Jaguar.

 

Jagboi64, Thanks for clarifying that. Those cars sound like old muscle cars which the Jag is sort of except the X300 comes already electronically fuel injected. By muscle car I mean one that achieves power by large engine size. It makes sense that the MegaSquirt and fuel injection improved your cars. It's interesting that even those it was a big improvement it still did not match the Jag.

MightyCarMods fit the Haltech ECU then take the car to a Haltech specialist for dyno tuning. Granted the purpose of this is usually because they fitted a bigger turbo and it's necessary to get this right. It's usually very wrong when they arrive.

 

Fitted my bracket yesterday and all I can say is over the moon what a difference power and torque smoother ride hope the economy improves well worth the money recommend and ice proffesonaly made bracket.....

 

Thanks Wayland for your very positive feedback,


Jagbio64,
You ask a very good question in your post 04-20-2016 09:18 about the effect of extra airflow on AFR. If the airflow meter was able to read the extra airflow, then the AFR would be maintained. Unfortunately, the airflow meter is working at its maximum measurement range at peak airflow. Therefore any increase in airflow, caused by any engine modifications goes unmeasured. In this instance the airflow may be increased, but the quantity of fuel injected is not. This result in a progressive reduction in the level of enrichment if the airflow is increased beyond about 1018kg/hr. Fortunately he AFR is mapped quite rich at these conditions, modest reductions in enrichment of no more than 10% can be tolerated.


The closed loop fuelling remains active at cruising speeds in excess of 130mph on an XJR6, in order for the catalyst to work effectively. During closed loop fuelling control, the AFR is continually cycled slightly rich and lean. At no conditions can the engine be allowed to run consistently lean as this would stop the catalyst reducing NOx emissions, though such a strategy would be good for fuel economy.


I hope this reply doesn't take this thread off topic again, just when Wayland had brought it back on topic. I've resurrected one of my old posts if anyone has further questions about reprogramming these ECUs.

 

Andy Bracket fitted. It took me 13 minutes from opening the bonnet to starting the engine with the new bracket. I spent 1 minute looking for my tools. I wasted 3 minutes trying to disconnect the crank sensor plug before giving up and fitting it in site. By the way the hole is quite tight but not too tight. Don't make it any smaller.

Now off for a drive to see how she goes.

Thanks.

 

Ok I've been for a 20 minute drive. Performance seems the same when driving sedately at 30 and 40mph but there is more of a burble to the exhaust note. Booting it in Normal gives the usual thrust but there is a hard edge to the exhaust note. Booting it in Sport means it revs more freely to 5500 than before and you get a snarl from the exhaust, nice.

I booted in Sport 2nd pulling out of a junction and got some tyre squeal which it's never done before.

Performance and responsiveness definitely improved.

I have also figured out why Jaguar did not set the timing in this position themselves. The engine is not as smooth. It's more aggressive. Some of the appeal of a Jaguar is that the power is so smooth. I've lost some of that smoothness in return for more responsiveness and more performance.

I would advise anyone not needing as much 'Sport' as they can get to leave their car as standard, it's nice like that. Anyone who loves to make it accelerate as fast as possible will need this bracket.

OK, what's the next performance improvement mod?

 

That makes sense. I had forgot that the O2 sensors are not wideband and wouldn't know how far lean the fuelling was. I'm used to tuning with my wideband sensors and knowing what the AFR is at all times.