I was driving my 2003 S-type R yesterday when my engine light came on and it said restricted performance on the dash. I stop at a near by garage to see what the problem was. He hooked it up to the computer and told its getting too much fuel. I never had this problem before and i dont know too much about cars. Please if anyone can tell me what you think the problem could be and how to fix it?
Thanks, Mike

 

Mine was the opposite: there is an auxiliary fuel pump on R's for high demand times. The fuse for this blew (#47 in the trunk). I wouldn't be surprised if that pump is the problem, as it may be running too much. However, there is fuel regulation so I kind of doubt the diagnosis. Check the fuse. If the car runs ok on light acceleration but bogs badly under heavy throttle, it is the same problem area I had.....

 

The same thing happened to me. Thee car also feels like it is down on performance so I strapped it to the dyno and I was right, it seems to me that the computer pulls timing and goes very rich according to the AFR's and the restricted performance light comes on and I got a couple missfire codes and a P1313 (cat damage?) This sounds like a common problem?

 

i started the car this morning & the engine light was gone....when the problem first happend i never lost no power everything felt the same unlike alot of other ppl that had this same problem. i spoke to jaguarabout this they said when its says restricted performance the car puts its self into safe mode to prevent further damage to the engine & wont let the rpms hit above 3000 but my car never lost no power at all...im confused lol maybe just a simple computer problem ...i hope

 

usually brake booster plastic hose.. leaks in air... a smoke test will find this easily..

 

also noted from the dyno run, it was making about 13psi boost.. the car is still pretty much stock with the exception of running the intake pipe and K&N filter on this dyno run. the car has been doing this "restricted performance" before the intake pipe (pic below) I was thinking the cats might be clogged because I've seen similar results on a supercharged car (loss of power due to exhaust restrictrion) but seems odd on a car with under 50k miles. It's bugging me now because the car is down on power all the time, other than that the car drives and idles fine. I'll try checking the throttle body and hoses again later today and let you guys know if i find anything!
pic of the intake:

 

take it to a dealer and get the fuel trims checked shud be between -2 to about +3 STFT.. i have never seen a newer style jag cat get clooged.they always brake apart. you experiencing air fuel ratio .. to rich or lean the ecm try's to counter it.. up to 25% which can cause loss of power due to RESTICTED PERFORMANCE. sounds like brake booster pipe leaking.. leaning out a/f ratio and ecm is enriching mixture to max .

 

Thanks for the advice jag genius. I watched STFT and looked good and I never had a chance to look at the car today because i was too busy but tomorrow I will check the brake booster line and if not I'll datalog a pull on the dyno and your right, it does not act like bad cats just more of an ECU issue that is causing it to pull timing and enrichen the fuel (sub 11:1 AFR) Hopefully I'll find the answer soon

 

it depends on temp and load for this pipe to shrink and leak.. common problem on str.it has a push in sleeve then the pipe comes out.. can be difficult..to get out.. once out you can try putting some grease on it or replace it..

 

a little update: I pulled the top intake tube off and checked the plastic line after unclipping out of the connector. no leaks from the connector to the booster. I wasn't able to follow the other line it connected to that went under the throttle body. I didn't see anything out of the ordinary and the inside of the throttle body looked good. I changed the plugs and the driver's side looked a little lean compared to the pass side...odd. The car still runs the same, down on power under WOT but I didnt get on it enough to get the light to come one. One hard pull will get that restricted performance light on.