For those who respond, thanks for your help in advance. I'm somewhat beaten down from paying out thousands of dollars to mechanics and getting nowhere.

Auto: 1996 Jag XJS 2+2 4.0 six with 110,000 mile

Originally, the car was hesitating at after a full stop and lacking some power. I took it to jaguar specialist and they began to trouble shoot. After three years, two dealerships, and one specialist, the car still ran the same. So, I took it to a foreign auto mechanic who owns a XJS V-12 and he began to trouble shoot. He changed the following: air cleaner, spark plugs, idle throttle. Checked it again and told me it needed five ignition coils. I purchased and had him change all six. He came back and said it was the ECU (main computer). He found one at the wreaking yard and replaced it. The problem continued. He said that the car now had three codes. It needed both O2 sensors, gas sending unit, and fuel pump. He wanted $2K to repair so I told him I couldn't afford that after paying out $3K for his former repairs (included transmission oil change with synthetic, new power steering power hose, and fuel pump relay). After checking his work, I found he forgot to re-connect the hose from the air cleaner housing to the air pump. After that, I still got the sending unit issue Code 1199, and the multiple cylinder misfire code P0300. I did my research and found that he had replaced the champion spark plugs with NGK's for a V-12. I replaced them and the car ran somewhat better. I replaced the fuel pump, replaced an obstructed fuel check valve, and a very dirty fuel filter. The car runs better but still has the multiple misfire issue. It hesitates for approximately 5-10 seconds when running at the same speed. I noticed that it will continue hesitating for the duration unless I release and re-depress the fuel peddle. It responds right away.

So, that is the story. Any suggestions? I have had all of the pressure checks, compression checks, etc. and they all have come back within specs. I feel like taking it back to the specialist shop but fear that I will get the same run around.

 

I think it's time to sit back, take a breather and assess the situation. After all that you describe, especially the ECM and Oxygen Sensor replacement/substitutions, there are two things I think have to be done. One is reset the fuelling adaptions, called “RESET ADAPTIVE TERMS” in the Jaguar Diagnostic tool. The other is to run the OXYGEN SENSOR ORIENTATION.

A little background: the AJ16 engine management system is an adaptive fuelling system. It was Jaguar’s first foray into fuelling adaptions and a few things have to be taken into account. Today, most all adaptive systems have limits, [usually 20-25% plus or minus], that stops the adaptions from straying too far off program. The AJ16 unfortunately, doesn’t seem to have those limits. That means that when there is a problem, say a vacuum leak, the system tries to compensate for that extra air by ADDING fuel, or a positive fuel trim. After a while the system makes that correction basically permanent. Now, say you FIX that vacuum leak. The system is still going to run that positive trim until it is RESET, or is run long enough to work its way back to normal. Obviously that takes a good while.

The point is, if the adaptions are not reset, you really don’t know where you stand. In fact, there have been many cars brought to me over the years that have been through what your car has, and I have done nothing more than reset those adaptions to make it run right. Today with this better understood, the adaptions, or fuel trims, are limited so they can’t stray so far and complicate matters.

Now to the O2 Sensors. All 4 sensors and their connectors are identical. [Well actually three are identical and one has a shorter lead by about 2-3 inches, but they are functionally identical] Any sensor can be plugged in to any harness connector it can reach. Obviously it is then possible to connect a sensor to the “wrong” connector, say reversing an upstream and a downstream sensor on one bank. That can lead to terrible running problems, no rocket science there.
On the AJ16, that’s OK though. We use the Oxygen Sensor Orientation to let the ECU test all four sensors and let it figure out which one is which all by itself. That way we know they are straight and can be used for closed loop fuelling, and are not the real cause of a poorly running engine.
Try reversing a couple of sensors and see how ****ty the car runs to see what I mean. The orientation will fix it, or they can be reversed again.

Today we call it plus and minus fuel trims; back then the PIDs to monitor were called AMFR and FMFR. [Air Mass Flow Rate and Fuel Mass Flow Rate] Consequently it is hard to find someone that knows about these two things, or has access to tools that can monitor and reset these parameters. It requires either a Jaguar PDU or a WDS, and the WDS wasn’t always perfect at completing the tasks on an X300.

Long winded, I know.... I just don't know a better way to cover the points.

I’ve attached a bulletin that is a little off topic, but it describes the AMFR, FMFR and resetting them pretty well.

Good luck!

 

xjrguy, thanks a bundle. You've give me a lot to digest! I've read it through a couple of times and will share with another who is helping me out. I'll keep looking for solutions because I believe this car can run well without the misfires if fixed correctly.

Jorge from San Diego

 

*
Thanks XJRguy, very helpful your explanation
*
I am having a problem with the LTFT. I got one ELM 327 Bluetooth and a Scan master software that is given all the parameters , LTFT is in -94.5 % and I am not having any trouble codes* the car is very heavy on petrol. It is doing 14-15 mpg mostly city driving . I was cleaning the MAF last week but still not lowering the long term fuel trim , the short term fuel trim is in positive values 2- 3 % .* Two years ago we change the O2 sensors* and looking at then they seem to work properly plus the fuel *consumption *when up to 18 -19 mpg ( fault codes where erase . The engine is one of the first AJ16 with no EGR and just 2 O2 sensors instead of the four, it got 160000 miles on the clock so I am not expecting any miracles .
*
Firstly I would like to know if resetting the long term fuel trim will sort the problem ( high *fuel consumption) and how to carry on this operation. Scanmaster software does not allow me to do it. At least with the LTFT reset to original values and monitoring the changes *I would have a good starting point to check if it is a fuel pressure regulator, *leaky *Injector or any* vacuum leak ,fuel filter , right now I have many ideas but I do not want to start trial and error .
*
What kind of software do I need to reset all this values to the original setting . I was reading the bulletin but because the result are presented on a different format and *I a bit lost. If I reset all this values I would have any problem with alarm , radio or something else.
*
Thanks in advance any guidance is more than welcome.

 

I once had a similar problem when I was cleaning out the connection to the computer (by the front passenger's right foot).

The connection was coming loose after I filled it with some grease to keep water out. After wiping down some grease and squeezing the connection back together, I got the click I didn't hear before and it's been running fine since then.

I would at least check that connection one more time.

I would also start looking for a Jag specialist that has the old Jaguar PDU Tool. That's what you're going to need to reset your parameters.

 

Hello, another XJS AJ16 owner here.

First I would say never ever go back to that mechanic. There are something's that can be challenging on a AJ16 engine, but it's really not that complicated. For what you have paid your car should be running fine.

I would also want to know what kind of coils and o2 sensors they put on that car. Aftermarket coils are known to fail. They must have a "Made in Japan" sticker on them ......I have also known of more than one person who has installed AJ6 Oxygen by mistake because they where given the incorrect ones make sure they are the ones for AJ16 cars.

Also check that your coil connectors are connected to the right coils. Sometimes people mix them up.

Totally agree on checking the ECU. MANY Aj16 cars suffer from water ingress. The replacement ECU could have weak pins. Make sure to check the pins very carefully and also that they are on tight and that the ECU is grounded.

Check your grounds in the trunk and the engine bay. Bad grounds can cause havoc.

 

Thanks
*
I am a bit confused about what is the main different in between* PDU , WDS and IDS (hardware and software) . Can IDS read/reset LTFT in an XJS with and ODB2 port?. I have seen some of the parameters on the display of a PDU and look a bit different from nowadays . They show AIR MASS FLOW RATE AND FUEL MASS FLOW RATE. But nothing to do with LTFT plus the way of resetting and calibrating them look a bit complicated . I have attached some of the documents that I got *for the resetting a bit complicated
*
Could be a bit naïve but there is something in there that can work on a PC with one of this ELM 327 device.
*
Anyone is working with any of this autologic devices…
*
*

*
*
*
*
*
*

*
*
*
Thanks
*
I am a bit confused about what is the main different in between* PDU , WDS and IDS (hardware and software) . Can IDS read/reset LTFT in an XJS with and ODB2 port?. I have seen some of the parameters on the display of a PDU and look a bit different from nowadays . They show AIR MASS FLOW RATE AND FUEL MASS FLOW RATE. But nothing to do with LTFT plus the way of resetting and calibrating them look a bit complicated . I have attached some of the documents that I got *for the resetting a bit complicated
*
Could be a bit naïve but there is something in there that can work on a PC with one of this ELM 327 device.
*
Anyone is working with any of this autologic devices…
*
*

*
*
*
*
*Thanks
*
I am a bit confused about what is the main different in between* PDU , WDS and IDS (hardware and software) . Can IDS read/reset LTFT in an XJS with and ODB2 port?. I have seen some of the parameters on the display of a PDU and look a bit different from nowadays . They show AIR MASS FLOW RATE AND FUEL MASS FLOW RATE. But nothing to do with LTFT plus the way of resetting and calibrating them look a bit complicated . I have attached some of the documents that I got *for the resetting a bit complicated
*
Could be a bit naïve but there is something in there that can work on a PC with one of this ELM 327 device.
*
Anyone is working with any of this autologic devices…
*
*

*
*
*
*
*
*

*
*
*

*
*
*

*
*
*

*
*
*
*

 

I had multiple misfires and replaced the plugs with the ones listed in the owners manuals, have not had a problem since. The PO thought he was doing an upgrade with 12 dollar plugs which caused all my misfire problems. Again back to my Jag service rep and he told me to use the Champion plugs listed in my owners manual. $1.80 each on sale. Love the AJ16...