Ok I think what Gavin is looking for is the cosy feeling that his car won't let him down with clients in the car.

Gavin or if your not confident with playing with volt meters and ohm meters a friend that is.

disconnect the battery

Then

Disconnect the TP sensor and look a the pins for any corrosion. Or water ingress
If nothing is visible reconnect and disconnect it a few times which will give you a fresh clean connection as the pins will have tarnished slightly over the years.

Do the same to the MAF sensor and MAP sensor

The same to the accelerator sender

Gain access to the ECM and do the same with the main connector.

Next step would be continuity checks between the sensors and the ECM to establish the wiring is good (resistance values bellow 1 ohm would be expected any higher then follow the harness and look for corrosion or damage)

And also insulation checks ensuring all harnesses are disconnected from sensors and ECM etc (250v from an insulation test will fry them) this will ensure you are not getting cross talk between sensors or to ground or another feed.


If that all checks it only leaves the sensors. I don't have the tech info for them but they may be already posted on the forums. Or the techs on here can tell you what to expect as things like the MAF sensor will be affected by the ambient temperature.

If everything check out you will need to reconnect the battery and if you still dont have a warm cosy feeling you can conduct live checks but looking at the components I would not expect large variations in volts drop due to impedance in the wiring.

This should take anything up to two hours if you do it methodically and take your time. And gather the reference material and a good circuit diagram before you start.

The end result will be peace of mind that you just had a glitch your connections will all be fresh and if you find any faults you can rectify them.
And don't forget you will need reset the windows and parking brake and enter your radio code after reconnecting the battery.

I have been looking at the wiring diagrams and expected values from the sensor.

The output signal drops to (Tp1 0.6v) and (TP2 1,4v) from the TP sensor at idle, if there is any corrosion/resistance in the connectors or wiring the 0.6v could be reduced to next to nothing throwing a fault. Also copper wiring increases in resistance the higher the temperature is which could also affect the signal voltage

The ECM sends a common 5v supply to the above mentioned components and they share a common ground.

Starting to waffle now lol hope this helps any mods or techs spot duff info please correct me
And help me learn a bit more about this system.

I prefer to fix things myself right down to component level before paying for someone else too replace parts until its fixed using my beer tokens

Regards

Jeff

 

Ps
I am not a mechanic or a tech. And have limited experience Jags

I am however an old school vehicle electrician and the basics apply to everything regardless of how fancy the controll software gets

Regards

Jeff

 

Sensor(s) and/or throttle plate slightly out of adjustment and/or a bad MAF or similar connector will never cause his reported faults. Failing battery can and is known to fairly often.

 

JagV8

There you have the benefit of experience

I had simular fault symptoms as Gavin and in simular driving conditions and was putting in temporary solution which appears to be working for me.

I understand jags are tempemental cars at times and batteries cause all sorts of weird faults when they start to go on all modern cars.
But please take into account a battery in rude health can hide minor electrical weak points by producing a stronger cleaner supply (a good thing ) but the downside is the £100+ to buy one ( yes i'm a cheapskate lol )

Will be checking my battery too from your advice as mine is probably the original fit to the car.

I do believe another member Leedsman has made a capacitor based smoothing circuit to stabilise his battery supply. I wouldn't mind seeing how he has implemented it. Before paying silly money for a new battery


Regards

Jeff

 

His car has a fault, never seen before or since. He also has a diesel, unlike almost everyone else (not sold in USA/Cdn etc). It has a different make of PCM, EGR, turbos, even the oil cooler is different.

 

Typical Jag. ........ they know how to pick the right moment !
Its happened to me - you have my sympathy

 

Wow there certainly are a lot of cooks on this thread Gavin. It sounds like you're going to need to professional help. As expensive as it is Jag dealers will KNOW THIS CAR and most everything we're all talking about.

I can imagine your embarrassment.

As people have already mentioned this is a very electronics oriented car. Most cars are now. So when it loses it's mind all kinds of bad stuff that seems illogical to you can begin to occur.

The reason people mention water and the battery is because these are two of the well know culprits for causing such mental breakdowns (the car's).

There are a lot of electronics and the battery in the trunk. The trunk also has a habit of allowing water in and then it settles on the electronics. It could happen in a thunderstorm, which Las Vegas gets. I've seen gully washers there. It could happen at a car wash too. it might be a while before the symptoms show up.

I just went through a long experience with a brand new Bosch battery that appears to have been sent directly from Hell. It had an internal momentary short but until it discharged quickly right in front of me I was suspisious that I had an electrical drain in the car.

I got all sorts of electrical phantoms from the lower voltage when the battery was doing it's thing.

 

It was embarrassing at the moment especially beings the client had complimented the car earlier and asked about the reliability in which I foolishly answered it had been a great car for me. (still has been just had a bad experience which is to be expected on any car.)

Thank You for the information on checking the electrical components I will do that when I find sometime tonight. I let the car basically sit this weekend and got some use out of our Lexus so there has not been very many miles to cause the faults to come back yet. Will see in the next week or two if the faults come up again. When they do I will be sure to take the car to Jaguar as much as it kills me. Just amazing how random the faults were. If it is the throttle body how much would a replacement be? Btw no not raining, throughout the day I had been showing homes meaning a lot of short trips and on and off for the car. Maybe that had something to do with it too?

I should be thankful the car started back up and was fine after a little time, last time when I was in New Mexico for christmas driving an 04' XJ8 in the snow I backed out of a tight parking lot onto a one way one lane plaza where the car decided to not go into the gear the gear shifter was in. It locked in Reverse and wouldnt start. Came out to a $600 fix and was somthing with the shifter cable. While waiting for a tow truck I was stuck out in the snow for an hour telling people they would have to hop the curb to go around me ...

 

Good thread, you talked about the battery and its age, just curious what was the brand and model number of battery? If you mentioned somewhere here sorry. Thanks.

 

It does sound like something battery-related (which would include cracked terminal, loose terminal, corrosion, etc as well as a bad cell or the like). We've had so many like this and they're nearly always battery related.

 

A lot of stop/starts with the AC etc on may have been enough to pull the battery down enough to cause a fault.

 

I am surprised the alternator is not capable of holding the voltage up on these cars.

The Foden DROPP's I used to work on would get weird transmission faults if the batteries started to fail. Even though they had heavy duty24v 90a alternators. But they had a manual override as part of the design,

Off topic Would love to be able to convert the auto box on mine to a paddle shift or simulare

 

Penny just dropped on the batteries it's not the measured voltage that's the problem it's the ability of the system to provide enough power/current. Will take myself around the corner and give myself a good talking to

 

It's been behaving ever since Jeff?

 

Ok

 

I think that's roughly back to front. It needs to provide the voltage even when providing the current. Current peak pulses (such as firing coils) must not make the voltage sag (because it upsets computers, as is hardly a surprise).

 

The sudden currents required may be the problem and beyond an alternator to also keep the voltage high enough.

You can get paddle shift but is very expensive. What's your budget?

 

I got the abs fault and then couldn't drive faster than about 3 mph one time. Shut it off and it started back up and ran fine. I haven't had it happen again since. I don't recall if that was before or after I switched my original battery out.

 

JagV8

That's what I was trying to say lol.

I dont really work to a budget, have money available to cover most whims ( cause I'm tight lol )

Really thinking about trading in for a newer XF or something with an R at the end or calming down a bit and getting a diesel, at the same time looking at gas for this one but finding a good converter with experience with the 4.2 is not going well. They generally see the 3 ltr.

 

I've seen a couple of lpg STRs and it'll be about the same to do a 4.2 NA.