I changed my spark plugs, belts, fuel filter, oil/filter, transmission/filter, changed out the differential fluid, all the coils seem to be firing ok, but I'm still getting unusually poor gas mileage and doesn't really feel like she has full power.

So this afternoon I stopped by the local foreign car shop and was promptly told that maybe my catalytic converters was stopped up and their suggestion (since we live in a state that does not inspect) was simply go up to the muffler shop and pay them $40 to remove the cats totally and have a section of pipe welded in their place with a threaded bung hole for the feedback line if there was one. I was honestly kinda surprised a shop would suggest that (as opposed to trying to sell me an over-priced replacement). Part of the guys philosophy was that the cats was only added to make them importable to America anyway and the cars was originally never meant to have such restrictive exhaust in the first place. He said he's done it to other XJS including the later computerized models like this '96 facelift model and they all ran better and sounded better and more like a Jaguar should.


Umm, ok... Anyone have experience with this? this guy is well respected around here, but is he talking big and/or lumping all XJS (I'm sure what he said was true of earlier models) together or what? Anyone actually removed their cats from a later model? Did it run better, get better or worse MPG? Even if it frees up some power I'd be afraid of it hurting the MPG's, the very thing I'm trying to improve.

 

Speaking as the Owner of a 1990 XJS V12 Convertible and a 1995 XJS 4.0L Celebration Convertible with an AJ16 engine.

All I can say is that after you have been driving an XJS V12 The XJS 6 cyl 4.0L is not my favorite Car.

As the V12 tends to spoil you for anything else.

While the Celebration Convertible is beautifully appointed and swathes you in all of that luxury wood and leather.

It feels as if you are driving a totally different Car.

And doesn't have that 'Lightening Bolt' Insane Acceleration of the V12 and as a result when you drive the 4.0L it 'feels very slow' in comparison, although it is probably not.

Although the 4.0L may give you a bit more MPG it isn't worth the Sacrifice of the pleasure I get from driving the V12 even though it costs me a fortune in Petrol to run.

Better buy one or the other, or you may for ever be spoiled for Choice as to which one you love best.

 

Thanks Orangeblossom and we are keeping our '95 V12 also but the thing is we've had a 4.0L before, a 1994 model. The 1996 should have even more power, the thing is right now we are not getting the full power nor the gas mileage we should be out of a very low mileage car that's been meticulously well cared for all it's life and we're trying to figure out why.

 

'Maybe' stopped up?

It's easy enough to verify.....which I'd want to do before removing them.







It's still against federal law, FWIW....but that's a different topic. I don't think the FBI will be hunting you down





Your OBDII system will surely throw cat convertor efficiency codes, though, and you'll be staring at a check engine light all the time.





By the 90s many (most?) cars had cat converters regardless of market/country and, besides, the USA has always been Jaguar's biggest market. So I'm fairly certain the Jaguar anticipated this and engineered the things fairly well.....with full knowledge that cat converters would be needed. So, it's not as though the cat converters were a hastily installed afterthought. And, modern properly functioning cat converters are not particularly restrictive




IF the converters ARE indeed clogged then, yes, removing them would make a car run better....any car

If they are not clogged then removing them won't solve anything and you'll very little, if any, power improvement.






I wouldn't do it until/unless I knew exactly how the OBDII would react. You have pre-and-post converter oxygen sensors. Seems to me that the monitoring system, not seeing the effect of a converter, wouldn't be happy.

Cheers
DD

 

Those was some of my concerns Doug. Now I know on V12 cars it's fairly common to remove the rear cats on each side (since they had 4 total/2 per side) as a performance improvement, some people remove the rear cats and put a freer flowing performance cat in front. I don't actually even know if the I6 has 1 or 2 cats, I haven't had this one up high enough yet to see under it that far. That's part of why I was asking if anyone else had actually done it. I could see maybe doing what people do with the V12 and removing the rear cat and replacing the front cat with a performance model might be an improvement IF the I6 also has 2 cats. Heck, maybe it even has 4 like the V12, I'm not sure how far back the pipes split or if it's using a dual header design (3+3) so has dual pipes all the way back... I'm still learning on the 4.0L

 

SouthernGypsy,

I know you've changed a number of items but have you monitored your lambda sensor voltages for correct operation. These sensors really need to be treated as consumables. even in our less-restricted cars over here with just 2 sensors, correc operation makes a big difference to both emission and consumption.

Even a simple check to see correctly fluctuating voltage in the right range might give you some insight as to whether they are working ok.

Or perhaps this gently-used car needs an "italian tune-up" to burn off the combustion deposits in the cats and run better?!

Good luck

Paul

 

I really can't comment about the 6, but opening up the exhaust on a V-12 is the way to go! I wanted POWER!, so I removed the entire exhaust from the front cats back. Then 3" exhaust began where the front cat was. It goes through very small "mufflers" then exits in front of the rear wheels. Had it this way for 4 years now with NO problems. Talk about a Power Increase! When this Jag hits second gear, it's sideways! Oh and yes it's a bit LOUD!

 

I've have never done anything to a lambda sensor on any of our cars, in fact I'm not even sure what that is and certainly not how to test it though I'm sure I can do a search and find some info... Bing Search - one of an XJS owners best friends! ~ ROFL!


She got an Italian tune-up the 2nd day we had her on the trip home. 2+ hours at over 90mph with a few times getting up to 117, which oddly felt like she was reaching her power limit, I know our last 4.0L went much faster top speed and didn't feel it was at it's limit.

 

SouthernGypsy,

That run home should have warmed up the cats just fine!

I use a cheap £10 bluetooth OBDII plug-in module and a £2 app on my android smartphone called "Torque Pro" to monitor some engine diagnostics. Works really very well. The lambda sensor voltage readings are one of the things it can read.

Your car, I think, has 4 sensors in the exhaust system. 2 before the cats and 2 after the cats. They read the. O2 levels and send signals to the ecu to then enrichen or lean off the fuelling. It's a simple check to see if the voltage is fluctuating. If one or more of them sit at a constant voltage, that's usually a sign that they are shot.

Paul

 

Oh, that's what your calling the O2 sensor, actually those are new. That's one of the things the original owner had receipts for that he's changed in just the past 2 years. Can still check them, could have gotten a bad one.

 

Oh yea, it was a 1200 mile 2 day trip, 17+ hour driving time. I know the two upstream ones (in America we call the ones before the cat upstream and the ones after the cat downstream) was replaced, actually don't know about the downstream ones. We have three different OBDII readers, two basic ones and one professional model that none of us can hardly decypher the manual for. No codes came up with the basic ones. I don't know if either of them will let me directly monitor the O2 sensors or not but will check.

 

Oh, and forgot to mention but since the trip home I have been using it to run errands including several trips to other towns and into the city several times. I use a great iPhone app called "Road Trip" (actually not a very accurate name for the app for what all it does) to track my tank-to-tank and running average MPG and also keeps track of maintenance and other records if you want. I just looked and from our first fill-up just 1.5 miles from where we picked up the car, to my fill up 40 miles from here on the way home this afternoon, we have put 1,991 miles on the car, so add that 40 miles from that station to home and we have put over 2k miles on it in the week we have had it. Of course 1200-1300 miles of that was just the initial trip home.

Our running average out of 8 tanks so far our best was 19.39 MPG and our worst was 17.53 MPG and our running average is 18.41 MPG, all way less than a 4.0L XJS should be getting. In fact my V12 gets those kinda numbers and better. The three best have all been since changing the plugs and air filter, so they made an improvement, but not by much.