I recently took my Jaguar XJ6 Sport 4 litre (X300) for a Mot. It failed on emissions and the exhaust fumes smell strongly of petrol also when you put the air on in the car you can smell petrol also. The mot tester suggested that I put fuel cleaner in the fuel tank and also clean the throttle body. When I went to the shop I told the guy the symptoms and he said that this would not help as it must be something more involved like a leaking injector. Im not sure what to check and do not want to spend money on fixing problems that will not solve the problem. The car also seems to use quite a lot of petrol compared to before. I have also uploaded a copy of the mot emission test results. Any help would be greatly appreciated.

Many Thanks
Mat

 

No simple, sure-fire answers to be had here. Might be as simple as a dirty air filter....or might be a stack up of different faults.

Leaking injector, leaking pressure regulator, excessive fuel pressure, skewed coolant temp sensor.....

Has the check engine light been coming on? Do you have a scan tool to check for trouble codes and check the data stream from the sensors?

Cheers
DD

 

In addition to Doug's excellent suggestions, a coolant thermostat stuck in the open position can prevent the engine from reaching optimum operating temperature, which prompts the ECM to provide an over-rich air-fuel mixture, which leads to increased fuel consumption and rich exhaust (and it won't trigger a fault code as long as the ECM believes it is operating within spec).

Doug mentions a leaking fuel pressure regulator (FPR) - you can check for a failed diaphragm by pulling the vacuum hose off of the FPR (a shiny metal cylinder near the front end of the fuel rail). Crank the engine and watch for fuel emerging from the vacuum fitting. If you see any moisture or vapor at the fitting, the diaphragm has failed and raw unmetered fuel is being inhaled into the intake manifold. Since the HVAC system uses engine vacuum for some of its controls, it may be possible for fuel vapors to be transmitted into the passenger cabin via the vacuum lines.

The fuel lines in the engine bay could also be leaking, which could lead to fuel vapors being drawn into the passenger cabin fresh air intake vents below the windshield, but that wouldn't explain why your exhaust smells strongly of petrol.

I also like Doug's mention of the Coolant Temperature Sensor or Engine Coolant Temp Sensor (ECTS). The ECM uses the input from the ECTS to determine cold-engine fuel enrichment, so if the sensor signal is indicating the engine is cooler than it actually is, the fuel mixture will be too rich.

Did the mechanic you took the car to interrogate the ECM with a scanner? Did he, as Doug suggested, examine the sensor Live Data? That may be the fastest route to a solution, assuming any codes are stored or any sensor signals are suspect.

Please keep us informed!

Cheers,

Don

 

Mat,

Did you make sure the engine was up to temperature when you took it in to the Test Centre? The drop in CO reading on the second test makes me think you may not have taken this precaution. In any event, it's not just a borderline fail - the CO reading is through the roof.

Doug's advice to get a scan tool on it is the only way to determine exactly what is happening.

The concern with running rich is that it can destroy the cats which then makes the situation even worse.

Graham

 

The engine seems to take a while to warm up but it runs normally at around halfway on the temp gauge when sitting in traffic. When driving it runs around a quarter on the temp gauge. I have not put it on a scan tool as yet. Do you think cleaning the throttle housing and using fuel cleaner would help in any way ?.

 

Also its weird but when the fuel tank is not full the average mpg is really low and the car seems to drink a lot of petrol. showing it is does about 15 mpg when its completely full it says its doing nearly 20 mpg. Weird I know i cannot understand it. I think maybe the fuel guage is faulty also.

 

The thermostat definitely needs to be changed. Fuel consumption will improve and you may even pass MOT, as the engine will not be running on the rich startup cycle. Cleaning the throttle body and MAF is a good idea also.

 

I'll echo the need for a scan tool, but point out that they maybe cheaper than you expect - ~£15 on eBay when I got mine...

My entry onto the sweepstake is a lambda sensor or two, as most of the likely options have been taken!

 

The car boot smells strongly of petrol and it gets inside the car. I have looked under the car and there is no visible leaks on the fuel tank and no petrol dripping onto the floor. Not sure what else to check im trying to find out where the petrol pump is located maybe there is a leak on the hose there or something. Any help would be appreciated.

 

The petrol pump is inside the fuel tank.

 

possibly a vapor return line blown off the tank?

 

Can't a faulty Rochester valve cause this smell?

 

The vapor line has a joint which has O rings in it, when the O rings go bad the vapor smells really bad.
Here is the link where I post some pics of what it looks like. All written in Japanese but the pics will give you an enough idea.

http://jaglover.web.fc2.com/maintena...lineoring.html

 

Cracked exhaust manifold

That being said, i think o2 sensors

I'll be interested to see outcome on this as I have similar issues

cheers

chris

 

02 sensors failing can cause an increase in fuel consumption for sure, don't know about the gas smell though?

Other symptoms can include....The OP does'nt mention any of these?

1. Erratic idling
2. Poor pick up
3. High fuel consumption
4. Engine hesitation
5. Power loss
6. Poor hot starting

 

Hello Graham

quick question, I took my XK8 for the French MOT today and they failed it on emissions, I made the mistake of taking the car from home directly to the station around 7miles, do you think if I had just given it a blast before going the emissions would have been ok?

I ask this as I have just returned from a 1000 km round trip to UK and the car had a good constant 80mph drive from Somerset back to the north of France

The Jag garage in Belgium suggests I just give it a blast but the guy I use in Somerset suggests to carry out a diagnostic check for the lambda sensors

any suggestions

Cheers Richard

 

I got my car checked on a diagnostics computer. It showed 4 fault all fault codes were reset. None showed up again after checking after a hour. After this petrol consumption was really good and car boot did not smell of petrol. After about a few days the problems came back again. Im thinking of getting it checked again and see what faults have returned but this will cost me again. Im trying not to spend more than I need to rectifying the problem. It seems daunting trying to find out what the problem is. The petrol smell is not coming from the engine bay it gets into the car because the smell is really bad in the boot. I have checked for signs of leaking underneath and on top of the fuel tank where the fuel pump is. Cannot see any obvious leaks. Im stuck on what to do about the problem and help would be appreciated ?.

 

Would a cheap (like 20 quid) OBD scanner be worth getting? I bought one and while it isn't very chatty it might save extra expense.

It seems odd to me that you got rid of the smell and got better consumption just by scanning. What did the guy testing it do - anything you wouldn't normally do like blast the throttle, or let it idle for a long time. He must have done something to make the consumption better.

I'll be very interested to hear how this pans out.

 

Did you happen to put petrol into the car after the "few days"? A long shot but a leak in the tank might only be obvious if it is high up on the tank. Maybe becoming more obvious on steep inclines/declines, parking on uneven ground etc. This might explain the strong smell accompanied by "excessive consumption". Petrol leaks, especially intermittent, can be hard to find as the petrol will evaporate, leaving little evidence, except fumes.

I'd give the tank and the surrounding area a very good look see.

 

Sounds a good possibility but I had assumed the consumption was the computer measured figure - but I only think like that as I only use my Jag in a limited way so I never brim the tank and wouldn't really notice any change in consumption from one fill to the next. I just wish I could afford to use it as my daily drive