Hi, everyone, hope someone can advise... My 2002 XKR starts every time, runs for a few seconds then dies, (both fuel pumps were replaced only a few years ago! ) a few weeks ago, out of the blue I got a restricted performance message and codes P0172 and P0175, (fuel imbalance/rich mixture) - my car runs on LPG so I wasn't alarmed as LPG systems commonly throw up these kind of messages, although not previously on this car! - I cancelled the codes and it was fine for a couple of weeks, then the codes came back more frequently, I repaired a broken end on the breather pipe and sprayed specialist MAF cleaner on the sensor and the car ran fine... until it didn't!
It then started it's party trick of starting for a few seconds then cutting out, but once it got going it was fine, until earlier this week when I was half way across a busy dual carriageway and it died! Again, after several attempts it started and got me home again, but now it just keeps starting then stopping, I must have tried it 50 times today! Anyway, I have changed the fuel pump relays and checked all relevant fuses, to no avail, but it seems to do this on LPG and petrol, so I'm thinking could the MAF sensor have failed? I took it off to properly clean it and it didn't help but if I disconnect the MAF multiplug it makes no difference , it still starts for those few seconds then cuts out, so could it be that? I have checked the fuse to the MAF sensor and it's OK,

 

It sounds like either a large vacuum leak or a bad MAF. Are you still getting mixture-related error codes?

 

Thanks for replying, the car was running perfectly normally last time I actually got it to start! I don't know how a failing MAF sensor usually shows itself but the fact it doesn't seem to make any difference whether I connect it or not seems to indicate something? Problem is of course, I can buy one for £16 for an XK8 but for an XKR it is around £240 - a lot of money to experiment with! Second hand ones aren't easy to find and likely to have that Jaguar greed factor, where people seem to think they can charge almost as much as new for a part the same age as mine with the same amount of use!
I presume the XK8 one would run but send the wrong values to the ECU?

 

Under normal circumstances, disconnecting the MAF will cause the computer to use a "default" fuel map. So the car runs, but maybe not well. I've had a bad MAF cause the car not to start, but when disconnecting it the car did start. As yours does the same thing, either way, I think I'd look more towards a large vacuum leak. I know nothing of the XKR. I know the XK8's develop cracks in the intake boot, and in the various hoses that connect to the throttle body. Somebody more knowledgeable about the supercharger will, hopefully, chime in here.

My XK8 did something similar, but not exactly the same, once when I was doing work on it. I forgot to reinstall the intake boot (I was just testing something) and it would start and then die. My friend comes by and says hey, it's not a carburetor, dude!

 

Using the CRC MAF cleaner it often takes 3 sessions with a lot of spraying / cleaning it before it acts right.

Note: if you are thinking of replacing the XKR 4.0 liter MAF it’s not the same one as called for on the XK8. And not any commonality with other cars like the XK8 unit. Not that I’ve found anyway.
(Excepting the 4.0 L XJR

so it’s not a cheap part from Jaguar. I’ve tried some of the aftermarket MAF units for the 4.0 XKR and none of them were worth a damn. After some searching I found one from a dealer at a modest discount.

Z

 

When cleaning the MAFS please note that the sensor is located in the tube. The external one is the temperature sensor.

 

^^^^ this ^^^

specifically, the external one is the ambient air temperature sensor

​​​​​​….and don’t touch either one of the sensors with anything other than the spray that comes out of the MAF cleaner. Why not you may ask ? I don’t know, except to theorize that the wires are delicate and that they don’t really need your bear paws on them.

Z

 

As already pointed out, the car should run with the MAF connected or disconnected (you get a restricted performance warning with it unplugged, but it runs just fine).

Have you looked at the live data? If you are getting sensible values from the MAF that would surely rule it out. You can also check your trim levels and your lambda readings - all things to do before spending money on random parts.

 

Well, Ive just changed the fuel filter, (filthy job) in a vain hope it could be the culprit, and the car started after a few attempts, and ran until it switched to LPG, so I thought for a minute I'd sorted it, but half an hour later I went back and tried to start it and we're back to square one! This is what happened when my fuel pumps failed a few years ago, every now and then it would just kick in, but I think I'm in for 2 new fuel pumps after all that, unless anyone has any other ideas for me to explore?

 

Does the XKR of this year have a Schrader valve on the fuel rail? If so, you can buy/rent an inexpensive fuel pressure tester and rule in/out the fuel pump.

 

I think I should read my own posts! I just found the thread from 2019 when my fuel pumps failed, there was a helpful post telling me how to activate the pumps individually- I’ve checked and pump one is dead, pump two is working (for now) so I’ve removed the relay from pump one and the car is starting up and running ok at the moment, so pumps it is!

 

On the 4.0 XKR the car should start
and run fine off of the #2 pump without disconnecting any relay or anything else.

on other words it should automatically switch over to the #2 pump when the #1 pump is dead.


thats why many are surprised to find out they have been running off of the #2 pump for a long time. Only finding that out when the #2 croaks and the car mysteriously won’t start

Z

 

Thanks everyone for your input, We live and learn all the time don't we? fact is, my car wouldn't start for love nor money yesterday until I shorted the relay to activate pump 2, then, once it had started and run for a while, I put the relay back on (pump 2 only) and it has run perfectly every time I've started it since! I don't care if it's illogical!

2 days ago, I changed the fuel filter. Watching a couple of YouTube videos I was assured that the fuel would stop coming once the filter was uncoupled, so I put a gallon receptacle under it and waited for the flow to stop... and waited... and came back to it almost full and still coming out at the same rate, until I ended up having to shove a taper into it to hold it back until I put it back together! One soaked sleeve and one permanently marked driveway - the joys of classic car ownership!