Restricted Performance & Changing Codes

Hello all,

I will start by saying I am somewhat new to forums and also new to being a “car guy” so go easy on me! This is a pretty lengthy story of a problem because I think I might have screwed something up at some point and idk when.

I purchased a 2003 Jaguar S-Type R(v8) with 145k miles and for the most part it drove fine. When I got it, the engine light was on and it had some error codes for misfiring cylinders(6 codes in all). It still drove fine except for if I tried to push it too hard, like passing someone on the highway. Then the dash would read “restricted performance” and the power would suffer. Also, it would take a good 10-15 seconds of turning over before starting. All other driving was fine. One day I decided to swap out all the spark plugs and ignition coils. The codes said that 4 or 5 cyclinders were misfiring and I always wanted to teach myself how to do it anyway. So I replaced ALL of the plugs and coils. I wiped the codes and drove a little bit but the engine light came back on. This time with less codes. I consider that a win. There was one code for a “random misfire” and then two codes. One for cylinder 6 and cylinder 7. Unfortunately, the condition remained the same. It would still enter “restricted performance” if I pushed it too hard at higher speeds. I was getting pretty tired of the excessive ignition time though so I thought I’d try solving that next. I had heard that it could be a problem with fuel pressure and one of the cheaper fuel things to do is get a new fuel filter. That takes us to today. I was able to swap out the old fuel filter, which looked to be original to the car. When I went to drive the car it STARTED with the “restricted performance” message on the dash. Just idling. When I put it in gear it struggles to go past 30mph. I have found that if I press the gas pedal hard it will max out revs at 1500rpm. There is a sweet spot though that I can barely press the gas pedal and it will build revs normally. I was curious about any new codes so I plugged in my code reader and to my astonishment ALL of the codes about misfiring cylinders were gone. Currently there are now only 2 codes. P0191(Fuel Rail Pressure Sensor Circuit Range/Performance Bank 1) and P1338(Fuel Pump drive circuit low/high voltage).

Is this because I changed the fuel filter? Now the car is practically undriveable. Should I put the old fuel filter back on? What happened to the misfire codes? I am so bumfuzzled about what to do.

TLDR: 2003 Jag S-Type R starts with “restricted performance” on and struggles to get up to 30mph. Codes are P0191 and P1338. Occurred immediately after replacing fuel filter.

Thanks for reading.

genuine or after market fuel filter - silly question i know but is the filter facing the right way…sounds like it’s in limp mode

Yes, it is in limp mode. As for the direction of the fuel filter, I am unsure. I installed the new one in the same orientation as the old one. If looking into the wheel well at the bracket the “flow” arrow points to the left with the wider ringed side of the filter also being on the left. As for the type, I just went into autozone and told them what my car was and they gave me a filter off the shelf. It is from Microgard and says “33595 FRAM.G8018 PTC.PG8018”.

you could try reverse flush the original filter & refit to see if that makes a difference, you could also try resetting the system back to factory, try resetting the car by removing both battery leads and clamping them together for 10 mins as this will reset everything so if the light re-appears then the fault is still there. This discharges any capacitors / memory within the ECU and around the car so ensures all memory settings are wiped clear - back to the factory default…** pay to do a little research on that method, i have done it on another make of car without a problem…

An S-Type R with 145k miles on it that wasn’t meticulously maintained and in perfect condition would probably scare a professional Jaguar mechanic even if the car was almost free. Are you sure it is an R (Supercharged) and model year 2003? I think S-Type R are 2005-2008 only.

Important that you replaced the spark plugs with the exact correct plug, IFR5N10.
Also, when someone mentions replacing all the coils, it usually means they bought a set of junk from the discount providers. Jaguar packaging or Denso (OE) only! If these are some of the ones sold as a set cheap, I hope you saved the originals, although continuing to drive a car with enough errors to run restricted performance could certainly start damaging some good parts. Restricted Performance is designed to get you to a safe spot to have the car towed to a shop.