It could very well be a bad upper O2 sensor... (The easiest one)
Using a scan tool, monitor the signal voltage of the O2 sensors and/or A/F sensors and
make sure they are operating correctly. If a scan tool is not available a multimeter can be
used to read signal voltage.

Another possible cause for those codes is the MAF sensor, Remove the MAF sensor and
look for signs of contamination. Debris that makes it past the air filter or oil from an
aftermarket air filter can stick on MAF sensor and cause inaccurate signals. If dirty,
clean the sensor using a quality MAF cleaner. Using a scan tool or multimeter check
the MAF sensor signal reading..

 

Maybe my page isn't loading properly or something, but is there a photo of the codes or something? What are the codes you're seeing?

 

The codes are listed right underneath the picture of his red Jaguars.

 

Aha!

 

They are the P0175 & P0172 Codes. Banks 1 & 2 Rich. I wonder if the fuel pressure regulator is faulty?

 

I'll put the scan tool on there and check the O2 sensors but I did swap the MAP sensor which did not resolve the problem. Thanks guys!

 

I have found that P0172 and 175 are often dirty injectors: on my SC RRS, years ago, a can of a good fuel injector cleaner (then, Lucas; I now use SeaFoam or Gamout's Seafoam look-alike) cleared the codes . . . Your injectors are spitting instead of spraying.

But all along the air intake -- clean aircleaner, clean air tube, clean MAF, clean throttle bore and plate, and tight vacuum hoses . . . were checked. Finally, it's getting colder: a stuck temperature sensor could be an issue (tells the ECU to enrich like an old choke).

 

I changed the thermostat in my XJR today, hopefully that'll cure the fans running on as I'd proved it was running to hot with live OBDII data.

What a surprisingly easy job, I'd squirted the back of the bolts with WD40 a few days ago but growing up with BL products I was expecting them to be rotted or seized etc but no they just came out completely without fuss. The old stat looks ok but is so stiff I couldn't move it with my fingers at all & I normally can. I ran it up to temp after topping the coolant up & everything seems happy & leak free. I'll recheck the coolant tomorrow & then call that fixed.

 

I drove mine to work today, with the live data off my dongle displayed just to prove to myself the new 'stat fixed it. Temps are sitting between 87-91c now so it's more stable than it was months ago so the old stat must have been slowly dying.

 

Nice. It's strange they chose a design that's capable of failing closed. Glad that fixed it.

You're also lucky, mine decided it wanted to leave half a bolt in the block.

Phil

 

I've been putting off changing the diff oil in my 106,000 mile Super V8 after going through the pain of doing the job on my XK8 convertible. This week I decided to bite the bullet and bought a couple of litres of 85W-90. Today was the chosen day.

So much easier than the XK8! A 2.5 inch wobble extension got the plug out and a hand pump extracted about 1.5 litres of foul-smelling, horribly dirty fluid. I feel confident that this was the first change in the car's life.

I didn't measure exactly how much fresh fluid went in but it was between 1.5 litres and 2 litres. The hardest job was getting the plug back in but a good pair of gloves with good finger grip did the job.

Here's a photo of samples of the old and new. Guess which is which....

 

I was just reflecting - It might be dirty, black, burned and incredibly smelly but isn't this gear oil amazing? It's been in the diff for 24 years through huge temperature changes, and kept the gear lubed for 106,000 miles - so over 70,000,000 revolutions.

Makes you realise what a nonsense "sealed for life" is....

 

You've made me make note that I probably need to change mine.

 

Not anything I've done to the car, but for the car. My uprated intercooler pump arrived today, so now I've got a nice little pile of bits to make it even more fun once fitted.

 

Mine has probably only been in there 23 years , but my car has covered 172,000 miles so it’s done a lot more revolutions than yours! However as part of my renovation work I was going to give the diff a fluid change whilst I had the rear subframe off the car.

 

That will make things a whole lot easier (and less mess)...

 

After several months of getting the P1647 code every time I start the car and driving with my OBD reader plugged in all the time, I finally decided to do something about it. As has been documented in many other posts, the sensor that throws that code is the one that is the biggest PITA to get to.
I wanted to avoid the headache of going in from the top and pulling everything out of the way, so I thought I'd try from below, even though many folks have said it isn't the best way. Fortunately I have the luxury of a vehicle lift.
I dropped the exhaust after the cats on both banks to give myself some wiggle room. The sensor removal tool I have wasn't fitting on very securely, so I went ahead and cut the wires off in order to get a 7/8" deep socket onto the sensor. With a couple of universal joints and a collection of extensions reaching to above and behind the transmission, aided by some less-than-politically-correct observations about engineering design, I actually managed to break the sensor free (with a rather large "mechanical advantage" added to the ratchet).
Now it's just a matter of waiting for the replacements to arrive. I decided that if I was pulling everything out of the way anyway, might as well do them all.
So, it is possible to get the sensor from below. Now whether it makes sense to do it that way...

 

Car threw a code for a coil failure of cylinder four. When it was replaced the car idled smoothly for a few minutes and then started shuddering a bit and stalling. After gunning it a bit it started working fine again. I'm starting to think the fuel pump is failing. I replaced it probably ten years ago so am familiar with the process. TBD

 

No, Fuel punp does not affect only one cylinder. You have the same issue what I was having thru out the whole last driving season. Randomly sttarted to miss only one and same cylinder that usually did fixe by accelerating fast.I measured a lot of things but eventually replaced ecu.

 

It seems rather odd that an ECU would cause only one cylinder to fail.