I thought that some of you would be interested to read that I have now succeeded in remapping an XJR6 Engine ECU. I have spent the morning driving my 95MY manual XJR6 fitted with an engine ECU that has revised ignition and fuelling maps that I have created myself.

Last weekend I removed the standard ECU from my car and dismantled it. I removed the two EPROMs (Erasable Programmable Read Only Memory), otherwise known as “chips”, from the sockets that are soldered onto the printed circuit boards. I copied the hexadecimal data from these chips into a PC. I was then able to manipulate this data to advance the ignition timing and reduce the level of fuelling over-enrichment.
I then loaded the revised hexadecimal files into two new chips. These chips were then fitted to an ECU that had previously been fitted to a 3.2L X300. It is this ECU which I now have fitted to my XJR6.

Using this same process, I can, in principle, change any of the data in the ECU. There are over 600 constants and 200 maps in the ECU so the possibilities for making changes are enormous. The key is being able to find where any individual map or constant is located in amongst all the data and knowing by how much to change it. Fortunately, as I was originally responsible for creating much of this data when I worked at Jaguar, I have a big head start compared with anybody else trying to perform this process. I hesitate to refer to what I am doing as “chipping the ECU”, since the companies who “chip” cars rarely have access to the “inside information” that has allowed me to reprogramme these ECUs. Nonetheless, it is a term with which many of you are no doubt familiar.

I normally assess potential improvements in engine performance by measuring in-gear acceleration times. It is important to perform the tests on a level road, with the car at minimum kerb weight, AC off and at a typical ambient temperature in order to make comparisons. I log vehicle speed using software on a laptop PC connected to the car’s diagnostic connector.

From these measurements I have calculated that the in gear acceleration times over the full engine speed range has reduced by 7% compared with original road test of this car. I think this is quite an achievement for a car which is 17years old and has no mechanical modifications that would improve its performance.

I will be developing further changes to maps in the ECU to improve performance and fuel economy in the coming months. If anyone is interested in having their ECU reprogrammed then post your questions here or feel free to contact me directly.
I shall be concentrating my effort on reprogramming ECUs for XJR6 vehicles, as these tend to be driven by owners interested in high performance cars, but it would be possible to apply the same process to the ECUs for naturally aspirated 6 cylinder X300 cars (X304).
I will be continuing to offer my revised crank sensor bracket as an alternative method of providing increased ignition advance for all AJ6 and AJ16 engines.

 

I would be very interested if you could turn off my rear o2 sensors in addition to the remap(got rid of the cats), is this possible? Also around how much would you charge to modify an ECU? This is quite an achievement and opens up a whole new world of possibilities with these cars

 

Great to hear from somebody with inside info. Are there any "chip" improvements to the 97 XJ6?

FYI for all the X300 XJ6's out there who want superb handling. I've just finished design/prototype with 41 inch 7/8 rear sway bar for these slushy handlers. Installation includes: Sway Bar, Links, Differential Mounting Plate, and "U" clamps with bushings. Uses existing bolts.
The meek 5/8 inch XJR6 sway bar that I previously fitted on the XJ6 was little better than no sway bar. I wanted to out corner MB's and BMW's.
This 7/8 inch baby does the trick. Next is making 1 inch sway bar for the front.

This 6 banger is the best Jaguar engine ever.

 

Hi Limegreenclown,
On 6 cyl X300s the rear oxygen sensors actually provide the closed loop fuelling control. This is the opposite of what you will find on most other makes of car on the road. If you had a European spec X300 you would see that it only had downstream sensors. I would strongly recomment leaving the rear sensors fitted to provide closed loop fuelling control, even if you have removed the downpipe catalysts. The upstream sensors provide the additional signals from which the diagnostic system determines the catalysts conversion efficiency. I assume your exhaust modification has given you a check engine light. I could probably turn off all the dignostics, but I no longer have the software documentation that would allow me to just turn off the catalysts monitor diagnostics on their own. It's probably best that you contact me directly for cost info. I'm new to this site and don't know what the policy is on matters that might be regarded as advertising.

Hi Swaybar,
I had plans to do a rear sway bar upgrade myself. Could you post some pictures of your installation. Have you managed to move the mountings further apart so that the bar is more in torsion and less in bending. Have you also moved the mounting points of the ends of the bar further ourboard to increase the effective angle of torsion of the bar for any given lower wishbone movement? Have you used heim joints (rose joints) on the drop links? Sorry for all the questions, but I'm very interested in your design

 

I am loving this turn of events.

So Mr.Engineer, would the new ECU pair well with the crank sensor bracket, even if only giving better miles per gallon?

And also for Swaybar (Welcome to the board, friend!), how would you say your sway bar affects ride comfort? I wouldn't be asking except that I drive a Vanden Plas model.

 

When I got my XJR back in september, I found out very fast, that the X300 didn't have a "chip", and that the owners really wanted one! It's been almost ten years since I last drove a car on original chip, as I want every drop of "easy" power drawn from my engine.

If/when you do a chip for us to purchase, can you make two editions, so those of us who already have the bracket installed, can get the chip without having to reinstall the old bracket?

 

FWIW, I'd be very interested in a larger rear sway bar and ECU enhancements


Cheers
DD

 

'engineer great to have you on the 'board...

Are the ECU's 16 CU like the XJS? I only ask as Roger Bywater at AJ6 engineering has been doing tunes for these engines for years. Do you know him?

THE JAGUAR AJ6 ENGINE - 3.2, 3.6, AND 4.0 LITRE / AJ6 Engineering

 

I've just today put version 2 on the XJ6.

 

sbc,
I could produce chip that worked with the bracket, but I would still want to make some changes to the ignition map. given the work involved in reprogramming the ignition map, it's a better technical solution to make all the changes in one place, the map rahter than add some ignition in the map and some using the bracket. It takes me 15mins to fit a bracket to an AJ16 engine, so I didn't really see having to remove the bracket, as particular issue.

Sean B,
The 16CU is a completely different ECU to the GEMS 6.2 system used on AJ16 engines. 94.75MY and later 6 cylinder XJS cars also had the GEMS ECU as they were fitted with the AJ16 engine.

Roger Bywater left Jaguar before I started there so I've never met him. We have exchanged a few emails inthe past.

 

Oh, that depends... Due to a herniated back, I can't do that kind of work myself, so I had a jaguar mechanic install the bracket for me. Took him an hour equalling something like £100. Not much fun in paying that amount again to have the original refitted... :/ But of course I can see your point, that it is too much hassle having to do an extra chip.

If the bracket scores let's say 5 on a performance scale, how much would the chip score?

 

Dear SBC,
I understand your reason now for wanting a remapping option that worked with a bracket. It is something that makes sense in your particular situation, and is something that I could do.

My bracket modification is very effective at delivering much of the benefit that could be achived by remapping the ignition timing. Using your rating score of 5 for my bracket, I would give a revised ignition map 6.

The bracket offers a better value solution in hp/£ or hp/$. The option of remapping the ECU is mainly of interest to people looking to achieve something that isn't possible from simply advancing the ignition timing. Here are a few examples of reasosn why people might want a remappped ECU:-

vehicle converted from automatic to manual tranmission - because the engine ECU will go into "limp home" and apply 5degrees of retard, when it can't detect the trasnmission ECU

downpipe catalysts removed requiring disabling of catalysts monitor (MIL) on US spec vehicles

fitting the engine to a different vehicle - requiring disabling of security system that would otherwise prevent the engine from running at all

modifications to the engine that would increase the airflow by more than about 10% resulting in under-reading of the airflow by the saturated air meter and excessive enleanment of the fuelling

replacing the standard fuel injetors with parts with a different flow rate, due to lack of availablity of replacement standard parts

increasing the engine speed at which fuel cut off occurs, if engine being modifed to achieve peak power close to or above 5,950rpm

increasing the idle speed

The need for changes such as these would drive a decision to re-map the ECU.

 

The XJR is fast enough for me, but consumption is really an issue. What improvements on fuel economy do you think could be expected with your ECU modification?

 

freda155 - it use to be unusual to get requests for what we would call is an economy tune, it really depends where your consumption is now. Typically, on a well maintained XJR we would expect 8-10% reduction. Sorry I do not know anyone in Sweden to reccommend but there are plenty. If you like I could try and find some one

 

My modified bracket adds a extra 5 degrees to the ignition map across the whole speed and load range. Most peoplewho have fitted one report about a 2mpg (imperial) improvement in fuel consumption. My remapped ECU should deliver similar improvements.

My XJR6 fitted with one of my remapped ECUs passed its annual UK Ministry of Transport (MoT) test. This includes a check of closed loop fuelling and HC emissions at idle. I believe there is a similar "Inspection and Maintenence" test in the US.

 

Andy, great work as this was the greatest hurdle - those damn government tests.

 

Very nice Andy, i'll be emailing you in a few months.

 

XJREngineer

Last year I converted my 1997 Jaguar XJ6 to an XJR6 from a 1995 donor car, switching out the entire engine, gearbox, engine wiring harness and ECU's. I had a small problem with the after cat O2 sensors as I had crossed the plugs over (even though both plugs fit into each others receptors). Once that was sorted that car has been working great...that is until recently. When the car is cold it runs fine, all be it with a minor miss-fire on one of the cylinders. When it warms up it is constantly miss-firing/backfiring and will cut out almost immediately. The engine waring light comes on when it does this, but then goes back off again as it attempts to recover. We have plugged in a diagnostics computer and when it is cold the computer can see the various info of the ECU. When the car starts to misfire/engine light on, the diagnostics computer cannot see any of the information from the ECU. My colleague, who's diagnostics computer we are using, has suggested that the ECU is faulty and as it is getting hotter is causing the issue. Does this sound like a plausible explanation for these symptoms. If it is the ECU will have to obtain another one or at least the chips. P.S I am located in Florida, USA (although I am from Staffordshire) and the car is therefor American Spec.
If required could I use an ECU from a UK Jaguar XJR6.

 

I am very impressed that you have undertaken such a conversion. You didn't mention whether you had fitted the twin fuel pump tank from an XJR6 or V12 X300 bacause the single pump in the tank of a naturally aspirated 4L car will not supply sufficient fuel at max power. Anyway, that won't be the cause of your current problem. If you had been able to maintain communication with the ECU during the poor running, then I would have suggested you were experiencing the early signs of crank sensor failure. This first starts to occur when the sensor gets hot. However, the loss of communication with the ECU suggest something more serious. ECUs themselves are generally reliable, so the problem is more likely, though not definitely, elsewhere. You may be losnig power our grounds to the ECU. Some X300s suffered water ingress which ran down the engine harness and into the ECU connector corroding the terminals. I suggest you check out the conditions of these connectors.

It is plausible that the ECU is suffering some kind of internal failure. You could fit the ECU from a non US spec XJR6, but make sure it is an auto spec car. You may need to take it to a dealer / specialist who can reset the adaptive closed throttle voltage as this will have been learnt on the original car. If you car has ahigher closed throttle voltage, then the replacement ECUwill not recognised closed thottle and will not operate closed loop idle speed control.

You could try taking the EPROMS out of your ECU and putting them in an ECU from a naturally aspirated car. You will definitely need to reset the adaptive throttle and perform a lambda orientation test which requires quite sophisticated diagnostic equipment usually only found at dealers or Jaguar specilaist independents.

 

XJREngine

Thank you for responding to my previous post. I purchased an OEM crank case sensor and fitted it the weekend. As the car had been standing for a while the battery had gone flat. Connected a battery charger to it and started the car WITH the battery charger still connected to the battery.

Let car idle for about 40 minutes. Got the very occasional miss, but other than that the car idled fine. Yes i thought, the sensor was the problem.

Disconnected battery charger and took it for a test drive. Opened her up and for the first 2 or 3 miles everything was fine. Then the engine light started flashing again with a loss of power.

Took it back to the house. Engine would cut out at junctions when stopping. Got it back on the drive. Same symptoms - even on tick over. Engine light flashing and rev counter drops to 0 - then it recovers, all be it with my foot nursing the throttle.

There is only one fault code (secondary air flow), but I have had that for ages before this issue started occurring.

The points that are of interest is that the car was idling fine before the test drive, all be it with the battery charger connected. Secondly, when the issue occurs, the rev counter drops off to nothing. It is almost like the ignition switch is being turned off in the background, as the diagnostics computer losses connection when it does this.

I am open to any more ideas or suggestions. My friend feels pretty strongly that it is the ECU, but I think that it is something else that is controlling the electrical power to the engine/computers.