Dear All, My '95 XJR has just failed the MOT on emissions due to high CO and Lambda, the HC was low and easily within the limit. It normally scrapes through once the cats are warm. I have had a look with my OBDII software and the O2 sensors seem to be switching, coolant temp fine (~92 C) airflow and temp normal and all sensors respond to throttle / revs as expected.
I am now thinking something mechanical. I know that the cam timing is a bit out and have been planning to sort that for years, my first job tomorrow. I also intend to check thoroughly for air leaks. One thing I should mention is that my car has been laid up most of the year for a home paint job which really dragged on, so only done about 500 miles since the last MOT. I have an exposed cone air filter which may have been partly clogged by dust / paint mist so will try cleaning that or replacing before a retest.
Another idea would be to try cleaning the injectors, do you know if I can do this myself without messing up the spray pattern?
Any suggestions welcome!
John

 

Couldn't hurt to try a dose of BG 44K
I ran a dose through an 05 S-type that was getting fiddly with some sort of exhaust-related code which i now don't remember before taking it across state lines to swap out for my daughter's 03 so she'd have a bit more reliability. So happy with the result I bought a four-pack and treated the rest of the fleet!

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

 

If they are original, I would replace the O2 sensors. They do get lazy over time and it sounds like you are running rich. Have you measured the coolant temperature sensor to make sure it is giving the proper resistance readings for the temperature?

 

Thanks for the response Gents,
The oxygen sensors are only about five or six years old an seem to be switching properly according to my scan tool, so think they are ok - leading me to suspect something else. All the sensors seemed to be behaving as expected hence my thinking about the fuel. Interesting comment and reviews on the BG 44K, I had always assumed that such products were unlikely to do much when so diluted. I have used Redex in the past on a much older car, but a small amount down the plug holes and left overnight to free off the rings. I will see if I can find some in the UK.
I did check the cam timing over the weekend and whilst the spark plugs looked clean, the tops of the pistons had a lot of carbon on them. I plan to refit the original air filter tomorrow morning ( as aftermarket one dirty).

 

Do you have a K&N filter? Those are known for killing air flow meters, so it's possible you need a new MMAF

 

The aftermarket filter is not a K&N, it is a dry cloth/mesh cone style unit and (clutching at straws) think it could have been clogged during the paint job, as only done about 500 miles since the last MOT.
My diagnostic software shows the sensor outputs, coolant temp read around 92 degrees C, airflow (think in grams / hour) changes as you would expect with revs / throttle, but of course could still be wrong. Oxygen sensors switch about every second or so.
I did replace the MAF a few years ago so would be disappointed if it has failed already. I bought some BG 44K, should have arrived today so will tip that in and hope.

 

I have 1995 XJR and having trouble passing Emission test in Ontario Canada. Have replaced an injector, O2 sensor, Ecm and now figured the only thing left are that the cats are fouled and will replace them this winter. What scanner are you using, I have an Autel Maxidiag Elite MD802 and am having trouble getting complete readouts? Last option is to buy a lot 80 miles north of here ( no E test and my car won't pollute there) and change my address.

 

My scanner is an Elmscan 5, one thing I noticed is that the long term fuel trims used to be -77 or something like that, but had changed to -20-odd for some reason. I was thinking that perhaps they reset after having the battery disconnected for a few months whilst we did the bodywork and would readjust after some mileage / running time but the exhaust still smells of petrol! I will put the scanner on over the weekend and see if it has changed.

 

Clean maf and bg44k

 

Hi John,

LTFTs that high negative indicate very rich running. I'm surprised you don't have any rich-related DTCs like P0172 or P0175. Clogged fuel injectors are a possibility, or an exhaust leak before the O2 sensors.

Another possibility is that the diaphragm in the fuel pressure sensor has failed and raw unmetered fuel is being inhaled into the intake manifold. To check for this, pull the vacuum hose off of the FPR, crank the engine, then turn off the key. Signs of wet fuel at the FPR vacuum hose fitting indicate diaphragm failure.

Yes, you can do a proper job of cleaning your injectors at home if you have a source of compressed air and are willing make a small investment and devise a cleaning apparatus. The photos at the links below show how I did it, but there are no doubt less involved and even less expensive methods:

Fuel Injectors: Cleaning, O-rings & Filters: Part 1 of 2
Fuel Injectors: Cleaning, O-rings & Filters: Part 2 of 2

Cheers,

Don

 

Thanks Gents, I did run a can of BG44k through it, and some Redex injector cleaner afterwards, but don't think it has solved it.
Good idea about the Fuel pressure regulator Don, I will have a look at that, but if it was throwing in extra fuel would the o2 sensors not be stuck at rich voltage?
Fuel trims are something I get confused about. As I understand it, the closed loop fueling has a map as a starting point and the oxygen sensors switch rich or lean ether side of stoichiometric to constantly correct and overshoot the fuel addition. If on average more fuel is added than taken away or vice versa, or beyond the limits / timescale of the switching, then an adjustment to the long term fuel trim is made to put the starting point back in the middle. Is this correct or have I got it wrong?

 

I had a 1995 XJR for years but, lucky me, I live in an area without emissions testing.....although I did have a variety of running problems over the years which naturally brought fuel trims into consideration.

The fuel trim thing was a constant itch that quite a few of us were scratching.... on this and other forums years ago. For some, the scratching was more like clawing at an aggravating sore until there was blood under our fingernails . The eventual, but fairly well accepted, conclusion was that the early OBDII on these Jags wasn't fully sorted and a suspicion that not all scan tools communicated properly with the system.

Typically, OBDII fuel trims are intended have a max range from -25 to +25....with hovering within -5 to +5 being ideal. I could never definitively determine of Jaguar's system was intended to work within that range. If it is, then the readings I used to get (often +50, 75, even 100) and your readings of '77' suggest some sort of anomaly in the read-outs.

It's a bit like a patient having his temperature taken at the doctor's office. Normal body temp is about 98ºF. A very high fever might be 105ºF . At 110ºF your dead. If the doctor looks at the thermometer and it reads 150ºF, he'll be wondering if his patient is some sort of alien creature or if his thermometer is on the blink.

I'm not asserting that your fuel trim readings be outright ignored but, personally, I wouldn't get bogged down on the matter, either. It might be a red herring.

Cheers
DD

 

To update, I found a crack at the bottom of the downpipe between the two pipes entering the 'y' joint. Filling this with exhaust paste seems to have improved my highway average from 16 to 20 mpg (UK gallons) average so think that is the cause of the poor emissions / economy. I used to be able to average around 24 mpg if I didn't go too quickly on a long motorway journey but I have since also fitted a 4.01 rear end from a 3.2 which probably has a significant effect, so 20 mpg might be 'correct' for the engine. It ups the revs by about 800 compared with the original 3.27.

 

Oh yes, that will make a big difference!

 

The rear end swap was a temporary solution to the original having failed inner bushes and play in an output bearing. I was also keen to see the effect on acceleration, which is good off the line and will spin the tyres as it shifts into second. I plan to take it to a drag strip and time it properly once a few things sorted. After that I will probably rebuild the original rear end and swap it back as in most ways the original gearing is better, giving relaxed performance and relative economy.