Mot emissions high

so mot today and the old girl only needed some adjustments to headlights and a couple flexi brake hoses but the main issue was the emissions

lambda readings up and down and running rich

I’ve replaced the following over the last year

air filter
spark plugs
cps
cts
thermostat
cleaned throttle body
cleaned idle control valve
cleaned maf sensor

as well as cleaned all electrical plugs and contacts concerned

any other ideas because other than a very occasional stalling when coming to a stop she runs spot on and gets about average 21/23mpg

help appreciated and thanks a lot

 

Have you considered a”Terraclean”? I have heard of this being done to improve emissions although I have not had direct experience.

 

My xjr6 failed on emissions last year due to a cracked manifold. Take the cover off and have a look.

 

Been having a look today ,also had a slightly rough idle and occasional stalling when coming to a stop ,

I took the injector loom cover off and the injector closest to the windscreen had a wire pinched tight between the plastic cover and the metal base plate !

as soon as the plastic cover was removed the engine stalled ...

I manipulated the wire back into place and replaced the cover ,started up instantly on key turn and idled smooth and flat ,taken for a drive and has much more power and responsiveness !

could that shorted out wire have caused the computer to over compensate for a misfire or similar and dump more fuel into the cylinders ?

it even smells better at exhaust now and no visible smoke any more

 

Was the wire shorted or only compressed? If shorted and not working I'd expect quite rough running but originally you said engine ran very well


Just thinking out loud here, so stand to be corrected. In theory yes (I think), a single faulty injector could cause over fueling. So if a single injector is not supplying the amount of fuel that is expected that would register as a lean condition (O2 sensor). As there are only two O2 sensors, each monitoring a bank of 3 cylinders, the ECU would command extra fuel for all 3 cylinders on that bank.

 

That was my thinking ,it was compressed and completely flat at that spot ,as soon as I removed the plastic cover ,engine ticking over at that time ,the engine stalled ..so it would appear that it suddenly over fuelled and flooded itself possibly ?

the engine has always run well apart from occasional stalling when coming to a stop but thinking back it has had a sort of hunting at idle at times and the exhaust always smelled rich ,also when I first bought the car it would easily achieve 27/29 mpg on a good run and even Upto 31 at times ,recently it’s been hovering around 23 on a run so obviously a lot of fuel has been being wasted somewhere

 

Pleased to hear you found the cause of the problem. Not often a Jaguar fix is "zero cost".

Good luck with the re-test.

Graham

 

Three times emissions have reared their head at Mot time over the years.
First time it was a failed O2 sensor, second and third times it was a leak at the joint between the manifolds and the downpipe (I had already replaced cracked manifolds) .
Totally counterintuitively, at least to me, is the fact that an exhaust leak can let air IN as well as exhaust out. In the lull between pulses of exhaust gas coming from the cylinders, air is sucked in which causes the O2 sensors to detect too much oxygen, signalling an apparently lean mixture, so more fuel is added, and excess emissions produced. Cracked manifolds can produce the same situation for the same reason

 

Would a cracked manifold result in this being so far out ?

I don’t have a cracked manifold to my knowledge however ,

 

Hi X300exec,

The X300 On-Board Diagnostics system is notorious for its inability to provide much in the way of helpful diagnostic information. I assume the MOT inspectors found no Diagnostic Trouble Codes (DTCs)?

Along the same lines as your fuel injector harness pinch, the coil wires are also known to develop problems such as deteriorated insulation that can lead to shorts and broken wires, especially in the bend at the rear end of the cylinder head (in the section with the over-wrap). But these problems usually trigger misfire codes, though the codes often fail to identify the actual cylinder or cylinders that are misfiring.

Low transmission fluid has been associated with stalling while slowing to stop or make a turn, so it would be worth checking that. Check it hot, after a good drive of at least 15 minutes. Park on a level surface, set the hand brake, and with the engine running, hold your foot on the brake pedal and move the gear selector through all positions (PRND32), holding each position for at least 3 seconds. Then put it in Park and check the transmission fluid level. It may take several repetitions of removing the dipstick and wiping it off before you begin to get a clear line on the dipstick. The fluid level should be right at the HOT or MAX line.

We'll all be anxious to learn the results of your next MOT!

Cheers,

Don

 

Don,

MoT Testers are not even permitted to check DTC's as part of the test procedure. The test was introduced to assess roadworthiness and, despite becoming more stringent over the years, is still not intended to troubleshoot any faults. Not a problem with a tyre, bush or bearing where the fix is obvious but with an instrument pack warning lamp, you're on your own to find the cause.

Graham

 

Just been and stuck some petrol in and thrashed her about and indeed it’s like a different car ,sounds better pulls harder and even spun the wheels in 3rd when I kicked down ...fingers crossed and thanks 👌🏻

oh and .....

after a five mile drive to the petrol station at a cruising speed of 55 this was my mileage reading ...8mpg more than the usual trio there 😳I’ve cured something for certain ......

 

Graham,

Thank you for enlightening me. That's very curious!

In our area of the U.S., in order to renew our license tags, our vehicles must pass an emissions test, during which a diagnostic system is connected to the OBDII port (data link connector) and the ECM scanned for the P1111 code, which indicates all diagnostic readiness monitors have completed. If any other Powertrain DTCs are present they are noted on the failure report. The exhaust gas content is also analyzed with a sniffer probe, and the exhaust system is checked with floor mirrors to confirm the catalytic converters are still present. As far as I know, our inspectors couldn't fail our car if the entire suspension was riddled with rust holes!

Cheers,

Don

 

With a cracked manifold the Fast Idle tests produced a fail on CO ( reading 2.81% volume) and Lamda (reading 0.925). HC was a pass although a little higher than previously.

 

Here in Canada having a "check engine" light on is an automatic fail. They won't look at the codes, but the light can't be on.

 

Don,

I recall our Californian members in particular have this challenge every time to get a P1111 to pass the emissions test. Members from other States have also made reference to the emissions test and doing endless Drive Cycles to set the completion code. I had expected our MoT would have been changed long ago to include this but we still just have a probe put in the exhaust to check gas output:




This was the report from mine at the last MoT. The tester tells me I'm the only customer who asks for a printout but I like to compare year on year.

The test is very rigorous on brakes and suspension. Powered rollers check the braking force on each wheel and the parking brake. Another device shakes the steering and suspension to find any wear. To stop the cheats who were painting over the CEL, the startup sequence is now checked for a full set of lamps and any warning lamp remaining on when the engine is running is a fail.

Graham

 

That's the same as we now have in the UK. The CEL check is only a recent introduction.

Graham

 

Basically any warnings showing are a fail now in the UK, apart from low fuel, low washer fluid and low coolant . What Graham says about scanning for codes is correct, and testers are not allowed to do it.
The looming nightmare is trying to suppress the myriad warnings which modern vehicles are capable of generating as they age and drop down the food chain. A set of problems we dont have to worry about for once!

 

Agreed.

I think failing electronics will be what eventually kills most of the recent and current Jaguars. Unless values rise sufficiently to encourage aftermarket support for rebuilding modules etc, vehicles with good body, interior and mechanicals will just be scrapped because the expertise and specialist support isn't available to repair them.

Graham

 

I had a similar situation on my 97 XJ6 and had to replace an O2 sensor down from the cat.