Intermittent restricted performance light

[xj40s]

On my 2004 4.2 X350 I occasionally get a restricted performance warning light. However performance seems to be as normal a no fault codes are stored

Any thoughts?

[J44EAG]

Two thoughts. Both conditions have affected my R version over the passed four years.

Have a look at any small 1/8"/3mm rubber vac pipes atop the engine. With age, these can split, rot or even part company from metal stub pipes. That will inevitable cause small or even large air leaks which affect engine management. A length of OE spec pipe can be sourced from your local Jaguar dealership but I`ve found a better spec pipe on the ready rack at Halfords. Its also cheaper than the thinner walled Jaguar part.

The second issue I had concerns the cleanliness of the Lambda 02 sensors. There are two above the catalytic converters and two below. They can get in a dreadful state over the years and can often respond to a good degunking. Cats also block up over time. Many of us have found that Cataclean (again on the shelf at Halfords) or Oxycat from a supplier in Romsey via eBay. often does great things to clear cats of accumulated crud. Put one whole can of Cataclean in a quarter of a tank of fuel and drive carefully until that fuel is consumed. Almost certainly you will note a difference in the way the car delivers its torque. My old V8 S-type changed character after about a half hour of driving. Users have reported that the product can help extinguish the restricted performance occurrences. Realistically, I found dumping a couple of cans of Cataclean into half a tank of fuel helped restore further performance and also the issues of reduced performance. Oxycat is used reguarly in my modified XJR 4.2 which has very touchy sports cats fitted. These need to be kept sqeeky clean or I can find myself reguarly extinguishing the dash MIL lamp and clearing restricted performance error.

PTJS 1 advised me that if the engine management system sees three occurrences of a particular fault, it pings the restricted message into play. The faulting may only be for micro seconds but it is enough to send the management system into panic. This in turn leads the driver to start panicking as well....Often just a tiny problem such as a rotted two bob vac pipe can lead to mayhem. I recall my "Nineteen day glitch" article which described my hunt to find a restricted performance issue. Eventually I found a rotten pressure pipe (same type of rubber pipe as described above) from the supercharger to the by-pass actuator. Ripping that severely rotten pipe out of the car and replacing with a better quality Halfords pipe solved the mystery in two minutes. No more restricted performance messages.

For every fault there is a reason. The challenge is to find the defective part. Often, the cause is quick and cheap to fix. I`d recommend changing all small bore rubber pipes as soon as possible. Old age takes its toll.

Have a look at these ideas and see what you might be able to find.

Mike

[xj40s]

Thanks for quick response, I will look at the things you suggest and let you know the outcome but it will probably take me a few weeks to get round to them all. The car has done just over 160,000 miles but I think the engine is in good condition. Virtually no oil consumption and near zero emissions on MOT tests.

Cheers
Tony

[ptjs1]

Tony,

I'm surprised you're not seeing a fault code generated following the system generating a Restricted Performance Light. As Mike says, it only takes a minor vacuum or wiring connection fault to throw the message. However, the system is designed that the message is thrown on generation of certain codes, often when certain sensors, such as MAF, go temporarily out of range.

Which code reader are you using to view fault codes?

Paul

[xj40s]

A couple of days ago I had a look at the tubes on top of the engine and all looked to be in good order,no sign of cracking, leaks or looseness at all. This morning i drove the car over 90 miles, no warnings. This afternoon my wife drove about 50 miles and the restricted performance light came on followed by the engine warning symbol which is still on. Put the code reader on it (Foxwell, NT510 I think) and it came up with P0333 knock sensor 2 circuit high voltage. Also Instrument pack B2139 data mismatch. Car still runs fine.

Am I right in thinking KS 2 is passenger side bank and located under inlet manifold? I have the OTP manual but can't find KS sensor location. What such a job is removing the inlet manifold and should I also replace serpentine belt at same time?

Will it do the car any harm to drive it at up to say 70mph / 2500 RPM with the faulty sensor. I assume it will have a pretty good default ignition timing map even with inoperative sensor? I don't really have time to fix it until late October.

Cheers
Tony

[ptjs1]

Tony,

Before you pull the sensor check all the wiring going to it. I reckon there's as much chance of faulty or corroded wiring connectors as much as the sensor itself.

Good luck

Paul

[xj40s]

The problem is identifying the wiring that leads to the sensor, anyone know where the sensors connector plug is located?

I know it could just be dirty contacts - I fixed my X400s ABS fault just by unplugging and re plugging the connector at the ABS unit, also on my X350 DTC MAF fault no longer present after disconnect / reconnect.

[J44EAG]

Anti-knock sensors are located on top of the cylinder heads. They are well buried and will probably require the removal of the inlet manifold. To gain access, there will be quite a lot of dismantling involved.

Check plugs, sockets and as Paul suggests, wiring. Knock sensor contact to the heads has been known to be caused by the sensors themselves, corrosion or just loose bolts.

Mike