Hello All,
New owner here loving my new (to me) XK8 with 64,000 miles. Just a fantastic road car!

Absolutely no problems on the maiden 400-mile drive until getting close to home and started getting an erratic Restricted Performace message - although no noticeable performance change. Then an amber check engine light appeared, then disappeared only to erratically appear over the next few days -- usually after filling up the gas tank. Yep, check the gas cap, it is tightly closed.

Checked codes on my also newly purchased iCarsoft i930 scanner and found P0191, P0328, and P1111 codes. Cleared codes and had no problem on the second 300-mile trip until topping off the fuel tank on the return trip. The amber check engine light came on immediately after leaving the gas station and remained on until I finished the trip. There does seem to be a tie to filling the tank, but then again, the check engine light will come and go in between fillups. On the last scanner check, I did find P1000 and P0328 codes! Cleared the codes and drove 40 miles today - no check engine light, but did eventually get the Restricted Performace several times towards the end of the trip. Ended the trip with no warning lights or RP messages.

Any thoughts on what might be causing all of this?

In advance, thanks

Bill

 

DTC P0191 is the fuel pressure sensor at the fuel rail.

DTC P0328 is the knock sensor A bank.

These are what is causing the Restricted performance.

As with all things start with the cheaper fixes as it seems related to when you fill her up.

My first thought is the fuel filter, FWIW I think these are service items which commonly are not R&R by most previous owners. Lots of info here on this home DIY job if you use the search function on this Forum.

 

I would be looking at the EVAP system, particularly the vent line tank to canister and possibly the vent valve. If the tank is not venting and you are getting negative pressure - which would be much more likely on a full tank as there is no vapour pocket, then the pump may not be delivering the fuel pressure required. This may also occur with a hot to cold temperature change, the lean condition resulting could set off the knock sensor.

Look at the live data for fuel tank pressure if you can and try to re-create the condition by filling up.

 

Thanks, will check EVAP System. It appears the previous owner had a problem in the past. I found a 2016 invoice where the EVAP line was repaired and new gas cap installed.

 

Thanks, I had wondered about the fuel filter. Will check!

 

Jaguar did have an issue with XK8 gas tank caps at one time although it was probably thought to be resolved by the 2004 model. I have a '98 since new and a year or two down the road I got a surprise package from Jaguar with a new gas cap and a note telling me that the original cap had been recalled and that I should replace it with the new one immediately. I have no idea if this has anything to do with your issue but since it only seems to happen after a fill up it might simply be that the cap isn't venting properly.

 

Interesting! From records I see the previous owner installed a new gas cap in 2016. So current one is four years old. do they go bad? Or possibly he got a cheap aftermarket one. I think ordering a new one is on tap as a first step.

 

I just replaced the knock sensor on the left bank which got rid of the Restricted Performance. I did it without removing the intake manifold along with the throttle body, Sured saved a lot of time and work.

 

Bill,

Buy another Gas Cap....those are cheap.....If that doesn't do it then you can really spend MONEY! Could be Carbon Canister....or even the Fuel Pressure Senor...
I hope it's the Gas Cap!

Billy Clyde

 

Look at the gas cap closely and see if its damaged or an aftermarket cap. Who did the work? Jag or an independent? If jag they most likely used an OEM cap but an indy.... who knows. Does it give a jag part number for the cap?

Might get a new OEM cap from a legit source and try that too. I was initially thinking fuel pump since you got low pressure and misfires (from a lean condition no doubt). can you read the fuel pressure and the STFTs? maybe do that after filing up and see if the fuel pump cuts out....

 

at 1500 rpm fuel pressure is 650 kpa
stft bank 1 10.2%
stft bank 2 about same

at idle
fuel pressure 456 kpa
stft bank 1 - -2.3%
stft bank 2 - -1.6%

 

freeze frame - P0328 caused by
fuel system 1 status CL
fuel system 2 status CL
calculated LOAD Value 19.2%

 

would probably be intermittent whatever is happening

 

Here are some pix of the original & updated cap. Again, this is for a '98 so YMMV.
The old cap is on the left and has a smaller top. The old number seems to be 300697Z.
The 'new' 20 year old cap is on the right and has a larger top. The new number is 100504B.
The side view shows larger vent openings on the new one.

 

Prior owner work was done by Indy. The current gas cap is a OEM Jaguar cap but it looks old. Paperwork from 2016 Indy work show that a new gas cap was back ordered. So maybe jsut maybe this is the original gas cap! I shall hope! Pickup up a replacement cap from AutoZone earlier today. It was not the correct gas cap, So I have ordered an OEM Jaguar cap! I will let ya'll know the result. See above comments in thread for STFT numbers and fuel pressure.

Thanks,
Bill

 

My current cap is the one of the right, the newer cap. However the number on my cap is 100603F

 

I figured your '04 would have the newer cap but hopefully yours has just gone bad. I'm no mechanic but I can't think of any other reason there'd be a downstream problem just because the tank is full. have you tried filling the tank to half or 3/4 full to see if that makes a difference? BTW, when I removed the cap to take the photo there was a whoosh sound which I think is normal.

 

hmmm. No whoosh sound on mine! Here is hoping!

 

Those & many other codes only flag after 2 warm ups (not 2 engine starts), as required by law.

 

On an '04, fuel pressure is available over OBDII. It should read 55 psi pretty much under all circumstances. This pressure is relative to manifold pressure, as it should be. Absolute pressure is harder to make sense of as it changes with throttle position.

A P0191 is the sensor reading too low. You might have to do the basic fuel system homework. First, change the filter (driver side rear wheel well, 30 min job). Next, do a fuel system cleanup with a known-good cleaner (Techron has good feedback by forum members) and follow directions (don't put more than prescribed). The context is that you want to do whatever you can to make life easy for that fuel pump because a replacement (an assembly, really) is well over $500, hard to reach, with no immediate known/available after-market unit. Next, focus on the sensor (passenger side, front of the fuel rail). Check the vacuum line. Check for leaks. Replace if necessary ($60?, 10 min job). This is a return-less system, this sensor is the critical input into the fuel pump driver that controls fuel pressure.

For the knock sensor error, they are usually a sign that they are/were soaked and corrosion developed. The standard cause is a failed heater hose or two. These cheap hoses are hard to reach (under the manifold) and bring/return hot water from the thermostat to the heater pump/valve/core. They are generally neglected, eventually fail, leak, and soak that valley area where the knock sensors are. Check them (soft = bad). It is also apparently possible to replace the sensors directly with creative use of tools and some patience, i.e. without dealing with the manifold, fuel fail, throttle body, etc. but you might miss the root cause.

I'd say deal with these issues sooner rather than later because either one (failed pump or failed heater hoses) will leave you stranded of course.

Best of luck, keep us posted.