I've had a 1991 jaguar xj6 sovereign for a few months now and i have some questions.

so first and foremost, we (stupidly) cut off all four cat converters. the exhaust still isnt quite sealed yet due to money issues with getting the clamps we need, but we're going to run the pipes out both sides rather than all the way to the back. soon after we removed the cats though, the car got very angry and started running horribly. (misfiring, dying while driving but starting right back up, all 6 spark plugs covered in soot, just running really rough) and throwing code 12 for the mass airflow sensor. we replaced the spark plugs along with the air filter, which made it a little better temporarily until it started throwing code 44 for the o2 sensor. i figured out that this was because of the o2 sensor downstream from the first set of cats off the manifold was now telling the vcm that there was an issue with the cats and throwing off the air/fuel ratio. so we tried the spark plug non fouler trick to make the o2 sensor think the cats were still there and functioning properly. we drilled out one non-fouler and attached the o2 sensor to it and screwed that into another non-fouler and screwed that one into the exhaust. it totally fixed our issues, we even drove the car about 45 miles to the next town and back with no problems at all. the code was cleared and everything. after a few days though, it started doing the same thing again, this time throwing code 12 once again. so we took off one of the non-foulers to see if this would help and just kept the one we drilled out in the pipe. no change. it seems to be gradually getting worse. its running so rich now that you can smell it from the exhaust every once in a while and the car dies damn near at every stop light. she always starts right back up though and it idles just fine. i just dont understand why the non-fouler trick worked for a few days and then suddenly didnt anymore. could it be partially because of the exhaust pipes not being sealed or is it something else?

another annoying issue we've been having is with the abs accumulator or the pump motor directly below that sphere, not sure exactly which one is the culprit here. we noticed that after we would drive somewhere, after we shut the car off, either the abs accumulator or the pump motor thing keeps running. it makes a buzzing noise and only stops if we disconnect the battery. it used to only run for a few minutes after shutting off the car and then stops but here lately, if wants to continuously run until it drains the car battery. and if it does run continuously after we shut off the car, it gets stupid hot which is why i dont know for sure which part is making the groaning noise. i do know pumping the brakes inturrupts the buzzing sound bu doesnt make it stop. i also know that we have no issues with our brakes at all really. the anti lock light on the instrument panel is lit and has been ever since we got the car but we have never had any issues with the brakes. i remember reading somewhere that this system can be taken apart and cleaned to see if it helps before we start replacing components but i cant find wherever it was that i saw that again, but is that a thing i can really do?

 

Hi Shaina666,

Welcome to the Jaguar Forums! It's great to have you with us.

I don't know if it will be possible to get the engine running properly without the oxygen sensor (O2S) being mounted in the exhaust stream. The O2S provides a primary feedback signal to the Engine Control Module (ECM) for closed-loop fueling management. Without real-time feedback from the O2S, the ECM cannot maintain stoichiometry. You can learn a lot by studying some of the excellent Engine Management System manuals from Jaguar. Here's a link to one of them:

Jaguar Engine Management Systems Training Course 801S

Regarding the brakes, my first guesses would be that the combined pressure and warning switch has failed and is not shutting off the pump electric motor when proper system pressure is achieved, or the accumulator diaphragm has failed and it can no longer store sufficient pressure. You can test the switch by shorting the wires that cause the pump motor to run when the system fluid pressure is low. In the diagram below, the accumulator is part #5, the pump/valve body assembly is part #1, and the pressure switch is part #2:





You can download the wiring schematics at this link:

Jaguar XJ40 Electrical Guide 1991

Please visit the New Member Area - Intro a MUST and post a required introduction so we can learn something about you and your Jaguar and give you a proper welcome.

Cheers,

Don

 

Yes, as Don wrote above: Oxygen Sensor.

I edited the following - thinking this is more to the point:
Seriously, you removed the catalytic converters? And now you are wondering, why you Jag is playing up?
What about removing one of the four wheels?

While you should throw out all cats and dogs of all Jaguars (there is no place for them in Jags! , the catalytic converters are keepers!

They are there for more than one reason for catalytic converters - No. 1 reason is the environment. While there does not seem to be an official rego check in Australia regarding emissions, having no catalytic converter is still extremely bad for the environment. The automotive industry, which saves every penny, would not spend a fortune on platinum and palladium for catalytic converters, if it would not have a very good reason - platinum is half the price of gold, palladium is currently 27% more expensive than gold. Thus understand, that catalytic converters in cars are not just a gimmick, which ca be removed.

And note that e.g. in Germany your car could be technically OK in very aspect, but rego would still be a fail, if the emissions test (not done in Australia) would be off in the slightest (that test is called ASU (Abgas-Sonderuntersuchung).

And No. 2 reason: Your Jag is controlled by more than one computer, and that computer-module, which controls the engine does so on the basis of input parameters - these input parameters are coming e.g. from sensors - and the oxygens sensor is a very important one, as I just had to learn on my Ford Fairlane: I fixed everything in that car, and still: stalls, misfire (mainly on LPG) and ridiculous high fuel consumption. Now I swapped the oxygen sensor, which seems to have solved the issue.

Cheers, Peter

 

Without the oxygen sensor the car will run over rich and will stall easily every time you pull up. Been there and done that!

 

@ Bill Mac: Exactly. As mentioned above my Fairlane just had that issue (oxygen sensor apparently defect, even though it looked OK and the resistance measured just like in the new sensor). The Fairlane's favorite spot to stall was bang right in the middle of a roundabout... Not the best spot... But I wonder, if someone can explain, why I had this issue while on LPG and not while on petrol... Now with the new oxygen sensor, things seem to be fine so far.
Cheers, Peter