4.0 AJ6 not starting then very rough

[tommad]

Hi all,

Some help would be much appreciated from this knowledgeable group. '93 manual coupe XJS has been used lots over last few weeks and generally good, but problem today after quickly popping into Halfords to buy it some stuff (typical). Just would not start initially; cranked fine, electrics no problem. After trying a lot it would eventually start then immediately stall. A lot more nerve-wracking cranking later it eventually started more consistently with a lot of black exhaust smoke and by keeping the revs really high it eventually settled somewhat. Then nursed it home with "Check engine" on, but did not sound great
Now it will occasionally start but similar issues and very rough sounding. Have consistent code FF44 and, unless I imagined it, also very briefly FF26. In the run up to this it has occasionally not been quite so willing to start as before (previously has been great) but only a few seconds. Also whilst driving have had occasional odd sensation of very brief power loss, when also battery power seemed to dip and steering/brakes seemed very heavy, but again only for a couple of seconds and really too quick to even process what was happening before it went normal again.

Any thoughts on where to go with this? Not really that mechanical but can do a few things and even if just to point the professional I suspect I'll have to take it to in the right direction.

Thanks, people has been very helpful on a couple of things I have posted previously and it's great to have a forum like this.

Tom

[SimonR]

Hi Tom,

That fault code reminded me of something I read on the Jaguar Forum:

https://www.jaguarforum.com/threads/cod ... -up.37037/

Specifically in your case the post by 'jonnie'

https://www.jaguarforum.com/threads/cod ... ost-671954

Might give you a starting point at least.

[almcl]

FF 44 is the lambda sensor. A new Jaguar one is £320, so you might want to get it checked first, although after market ones can be a lot cheaper.

FF 26 is an air leak but might be caused by an intermittent fault elsewhere.

[steve_m]

93 manual, good choice!
Rather than spend £320 on a sensor I would spend £120 on a good battery.
Then get your codes checked again.
If it is all the same then you have removed problem 1, power supply.
And have a spare battery for your lawn mower.

[tommad]

Hi,

Thank you for the helpful replies, had checked out those codes and saw it could be either lambda or oxygen sensors (subtle difference between those slightly lost on me).
I think a battery issues is quite unlikely as it's a new battery only been in a few months and has caused me no other concerns (normally reading just over 13V),
With the fault codes, I am supposed I am slightly unclear on whether these mean a problem with the actual sensors or a problem with what the sensors are there to detect (or if I can even know this).

Thanks again,

Tom

[almcl]

The Lambda (or Oxygen - they appear to be used interchangeably) sensor returns a small voltage, between 0.1 and 0.9v. The ECU uses this to adjust fueling. If the voltage is outside these limits (can be high or low depending on the fault condition) a fault is signaled.

Your local Indy should be able to test the sensor output.

[tommad]

Thanks, unfortunately the Jag specialist I normally take it to can't do it, so taking it to garage down the road. They are pretty good; have looked after my middle-aged Alfa well and seem to do a few older cars, so hopefully they can help.
Will let you know,
Tom

[tommad]

Well, my local garage could not find any obvious problem (but were not able to fully interrogate the fault codes). The car seems fine currently and no Check Engine light, so I will continue to use it but have booked it in to see the specialist garage next month.

Thanks again,

Tom

[ptjs1]

Tom,

Your question as to whether the fault lies with the sensor, or with the root cause of the sensors reading, is a good one.

There are some sensors that will last the life of the car and some that should be regarded as service items. In general, I would suggest that lambda sensors should be regarded as service items with a finite life. If your sensors are the originals, they are probably well due for replacement.

On the basis that your problems seem to have gone for now, I would sleep easy, but if they return I would start by monitoring the voltage output of the lambda sensors. It's somewhat more difficult as you don't have OBDII capability on your AJ6, but there are ways it can be done.

Cheers

Paul