My XJR is failiong the MOT on emissions. (is always difficult to get it through).

MOT mech thinks it is overfueling anyone got any suggestions of where to look ?

no error codes, starts no problem etc. averages around 16 mpg.

 

If no codes I'd be cleaning the MAF sensor, part load breather and throttle body.

How long is it since it's last oil change? whats the condition of the plugs? It may be worth renewing both before your retest, and clean the above listed bits too.

The main culprits are the O2 sensors as they monitor the engine's output of CO/CO2/02...Does your car have 2 or 4?

 

Hi There

MAF and throttle body were cleaned along with plugs changed and oil changed <5000 miles ago (full service done).

I believe the cat has 2 o2 sensors but they were checked due to the same problem last year and found to be good.

It failed the first test on emissions (and numerous other things) but improved to within limits with a Terraclean but next test (first garage appeared to be trying to make work for themselves) failed on emissions again which makes me think something is gummed up somewhere

 

You need to look at fuel trims.
Since you're in the UK you could get one of these
Android Torque Mini V1.5 ELM 327 OBD2 OBDII Bluetooth Car Diagnostic Scanner UK | eBay
which pairs with an android phone and an app called Torque.

 

Does the engine run smoothly and does the car accelerate normally? I ask because I wonder if the Eaton compressor does its job as it should.

If emissions aren't within normal range there are mainly two reasons for it: bad combustion or failed emission control.

Bad combustion is caused by a disproportion of air and fuel. Normally the engine management system monitors the process of mixing fuel and air and corrects if necessary. This brings us to the EMS and the fuel injection as other possible causes of your problem. I don't assume that the EMS failed but maybe the injectors need to be cleaned.

Broken-down catalytic converters should throw errors. But we should keep them in mind for further troubleshooting though.

 

Has your car got an EGR valve assembly? if so where it connects to the throttle elbow could be carbon caked and blocked, also do you give the car a good run before taking it to the MOT station? Engine cooking hot on drop off? Always a good idea

How many miles? wonder if an injector service might be in order...

 

Engine was replaced by jaguar in 2002 and has done around 45k miles.

where would i find the egr and do you know how to clear it ?

Car runs beautifully. failures for mot are on co2 and lambda.

 

Do try the Torque route.

 

According to my information, the engine management system was changed for the 1999 MY cars & the emissions system now had 4 O2 sensors.

Each side of the V8 has it's own catalyst & each catalyst has 2 O2 sensors-an upstream 'linear' Air/Fuel ratio sensor & a downstream normal 'on/off' Oxygen sensor.

The upstream sensors have high-current heaters & a higher failure rate. When they fail, the ECU goes into 'basic' fuelling mode which allows the engine to start & run normally-the only symptom is higher fuel consumption & the edge disappears from the power delivery.

Usually the system stores a fault code as well...

If the system was overfuelling the engine, then the downstream oxygen sensors should show this as the catalysts would not be working properly & the expected sensor output would be incorrect.

For this system to fail the emissions check, the car itself should recognise the fault as the 4 O2 sensors monitor the exhaust gas quality before going into the catalyst & also when exiting the catalyst. Any discrepancies would show as either an O2 sensor fault or a 'catalyst efficiency' fault.

The front 'upstream' sensors are a unique type & quite expensive-the 'downstream' sensors are the more usual type & not as expensive.

It may be worth giving the car a long, hard drive to make sure the O2 sensors & catalysts are thoroughly warmed up-this can improve the efficiency of an old catalyst.

Interestingly, in the UK most modern cars fail their MOT on emissions, because the cars are not driven hard or fast enough to keep everything nicely hot & cleaned out. Take the car for a long hard drive-at least 50 miles & take the engine round to the redline-then cruise on the motorway at a steady speed for 10 or 20 miles.

Then check for any stored fault codes & then re-check the emissions before doing any further fault-finding.

The biggest killer of emissions systems is slow, plodding driving & lots of cold stop-start trips. Engines are meant to be run hot & driven hard

 

I put an obd reader on and used torqaue.
Anyone know how to interpret these results ?

Fuel trim bank 1 longterm 1.56%
" " " 1 sensor 1 0%
" " " 1 sensor 2 0%
Fuel trim bank 1 short term 0%
Fuel trim bank 2 longterm 14.84%
O2 volts bank 1 sensor 1 0.04 to 0.78 v fluctating
" " " 1 sensor 2 0.02 v
O2 volts bank 2 sensor 1 0v
" " " 1 sensor 2 0.02 v
second readings
Fuel trim bank 1 longterm 5.47%
" " " 1 sensor 1 0%-0.78%
" " " 1 sensor 2 0%
Fuel trim bank 1 short term 0%-.78%
bank 2 long term 14.84%
bank 2 sensor 1 19.53%
bank 2 sensor 2 0%
bank 2 short term 19.53%
O2 volts bank 1 sen 1 0.2 -0.67v fluctuating
O2 volts bank 1 sen 2 0.2v
O2 volts bank 2 sens 1 0v
sens 2 0.02v

 

Check the following link
https://www.jaguarforums.com/forum/g...ed-quiz-49317/


It explains the basic concepts of fuel trim (positive values mean too much O2 is measured post combustion) which basically means one of three or more things
1) you have an air leak post MAF (more air enters the cylinder than what the MAF believes it let through = leak somewhere in the inlet plastic deal)
2) you're misfiring like a bugger and the O2 sensors measure unburned O2
3) your MAF is lying and telling you it measured 3g/s when in fact 5 g/s went by

As it is is only one bank, it seems unlikely it was a MAF (mine went mad and said -15.6% all the time for both banks), also a leak in the inlet pipe deal should probably affect both banks, maybe you have a leak on one of the bank specific vacuum areas, not sure what they are, I#m sure someone will be along to advise soon enough.

Check obvious things like bank specific gaskets and so forth, also check the dipstick (see OBD primer)

Cheers

Lincoln

 

Hello Lincoln,

the link doesn't work for me, klicking it opens a blank page. Could you please check and change it?

Merry Christmas!

 

Give that a whirl, if not just search for OBD primer or Fuel Trim, that will find it in short order.

Happy Christmas

Lincoln

 

The link works now, thanks and thumbs up!

 

Looking at the fuel trim results, the fault seems to be restricted to Bank 2 of the engine & it seems like the ECU is overfuelling this bank to compensate for what it thinks is a lean mixture.

Bank 2 on UK vehicles is on the passenger side of the engine. Sensors (1) are the upstream sensors, before the catalyst. Sensors (2) are the downstream sensors, after the catalyst.

Interpreting your results, the fault seems to lie before the catalyst so I think the catalysts & downstream sensors are all ok.

The problem you have is the air/fuel ratio before the catalyst-the system thinks the mixture is too lean & is overfuelling on Bank 2. Also, you're getting no voltage signal at all from the upstream sensor 1 on Bank 2.

I'm thinking that you've either got a big air leak in the inlet side of Bank 2, or a misfire, or the upstream Oxygen sensor has failed on Bank 2.

Now if you had a misfire then the ECU would detect this & throw up a fault code-the engine would also not run as smooth & be down on power.

I had the upstream O2 sensor on my 2001 XJR fail & it caused the same symptoms as yours-higher fuel consumption but the engine still started ok & the car drove fine.

The upstream O2 sensors are special linear air/fuel ratio sensors & to replace the Bank 2 sensor is a pain in the *** as you have to remove the coolant reservoir to access the upstream sensor.

They're fiendishly expensive from Jag dealers at over £300, but you can get the same part from ebay Jag sellers for around £120. I also found out that the grey upstream sensors from the X-Type will also work on the V8 & they can be bought on ebay for around £30 or so.

Guess which one went in mine

 

Good analysis from Red October. The bank 2 LTFTs are hard against the stop.
I'm afraid this normally means an inlet manifold leak.
It could be the oxygen sensor though - you haven't told us mileage.
If you're able to record the trims we can get more info - when started the car is in 'open loop' and fueled by a map in the ECU, once warm it starts using the O2 sensor to adjust fuel trims. This won't help with sorting a leak from a bad O2 sensor though.
You can reset the fuel trims with a 'hard reset' https://www.jaguarforums.com/forum/x...ect-faq-74146/

Can we PLEASE have a part number for the alternative X-type O2 sensor??
The equivalent type in the UK seems to be this
http://britishparts.co.uk/products/7...nsor-C2S51801G at £78

 

Which X-Type engine? the 2.0/3.0? and where did you get it? this is something I NEED to know also

 

If you can get upstream sensors for $30 the whole Forum needs to know !!

 

I found out by examining & comparing the circuit diagrams for the engine management systems on the X-Type (2.0L, 2.5L & 3.0 V6 models from 2001 onwards) & the later X308 V8's (1999 model year onwards with 4 O2 sensors in the Upstream & Downstream positions).

The circuit diagram symbols for the sensors showed that on both the X-Type & later (1999 MY with 4 O2 sensors) X308 V8's, they both used the Upstream linear Air/fuel ratio sensors & the standard 'switching' Downstream Lambda sensors.

The Upstream air-fuel ratio sensors work in a totally different way to the normal 'switching' Lambda sensor. The upstream sensors are 'Wideband' sensors operating on the principle of a linear current analogue which is directly proportional to the air-fuel ratio. The Downstream sensors are the more common 'Narrow Band' sensors & have the standard 'switching' output voltage swing from < 0.2v to > 0.7V.

All 4 sensors have electrical heaters, but the Upstream linear sensors have to run much hotter to work properly-so they have more powerful heaters which are prone to failure at high mileage. The downstream sensors run cooler & are only used to check the catalyst efficiency-they play no part in the air-fuel ratio adjustment & don't have a high failure rate.

When my Upstream sensor failed on my 2001 XJR & threw up the EML light on the dash, the ECM went into it's 'basic' fuelling map & the car still ran alright-although the fuel consumption was higher & the 'edge' had gone off the power.

So I looked around & after having a coronary at the price of new Upstream sensors from Jaguar, I considered an alternative method. Both sensors are made by Denso, so I looked on ebay & bought a couple of cheap X-Type Upstream sensors for experimentation. They were not new & taken from a dismantled X-Type.

I put one of them on my XJR, reset the EML light with my cheapo scanner & then went for a drive. The EML light stayed off & the car drove normally again-all the power was back to normal & after several long drives of a few hundred miles everything was still fine.

Anyway, it worked fine & because there are loads of X-Types being scrapped compard to X308's, there is a plentiful market for cheap used sensors.

The part you're looking for is from the 2001 onwards X-Type V6 models, from either the 2.0L, 2.5L or 3.0L V6 models. You need the GREY plug UPSTREAM sensor-you can recognise them as they only have a couple of holes in the body every 90 degrees. The Downstream sensors have black plugs & have lots of holes in the body.

The part number on the X-Type sensors I used was a Denso number: 9F472AA.

I didn't bother buying new ones-there were so many cheap used ones for sale on ebay that I just got a pair of used ones for £60, and you can get them for a lot less than that if you're in the right place at the right time on ebay

 

Just started a new thread to advertise this subject across the forum