Non-Runner, suggestions please...

[franrca]

Sorry for the long note and sticking this in 'General'...

I have had a non-running 1995 AJ16 (Celebration) car now for over 3 months and my usual garage doesn't have a clue what's wrong - on the slim information below I would be grateful for any suggestions as to what might be wrong. I suspect for the majority of the time the car is not being looked at due to their usual throughput and this not being an easy one.

Symptoms - so at the end of October 16, I am driving around my local town as per normal with no issues and nothing seems amiss. I then decided to take it onto a local A road to give it a blast - I select sport mode and put my foot down expecting the usual kickdown...but I got a slightly less than enthusiastic acceleration and revs that were 'hunting' I think the phrase is. It felt a bit like flooding the engine whilst driving, so eased up a little and the car struggled on whilst losing power bit by bit whilst still hunting until I had to stop it (the transmission failure warning came up). So, on the edge of the A road with the car shuddering due to cars flying past, I started it again and the revs would hold for a moment and then just cut out. Let it rest for periods with the same result.
The car was picked up and dropped off at my usual garage late on a Sunday night in darkness , but not before the call out guy plugged the car in, but the software didn't recognise it, so no joy there.

The garage tried it over the next few days and had one initial successful outing where apparently it ran incredibly richly before cutting out (once warm) and that's how it's stayed since.

They reckon they have tried a number of things including replacing the crankshaft position sensor and say they have tested everything going into the ECU and out the other side and it’s all fine. ECU is the next thing to be tested but quite frankly after 3 months I'm beginning to lose hope as whilst they reckon they are Jag specialists, they are clearly not XJS ones.

I'd be really grateful if a list of high level possibilities could be suggested and I can throw these at them.

Much appreciated
Richard

[DrSebWilkes]

I won't be of much help but hopefully posting here someone with more expertise might have a clue.

What concerns me is that your transmission light is / has coming on. That's a very different kettle of fish to engine issues and I wonder whether that is where your "hunting" for revs is coming from? Especially after engaging the sport mode since that alters the way the gearbox works ...

If the ECU was faulty I suspect the car wouldn't even start and if everthing going in and out is working I'd bet a lot on it not being an issue.

Perhaps the transmission ECU might be at fault if an ECU is to blame ... to be honest it's more likely something in the tranmission that is wrong rather than the ECU - ECUs don't tend to fail ...

[franrca]

Thanks Seb, but I am assured that the gearbox is fine and that this is almost certainly electrical....this is what they say anyway. I think the warning light might be a red herring...?

Here's it being offloaded...sniff - took 30 minutes to get on and then another 20 to get off due to clearance etc:

[Brakebuster]

sounds like a possible fuelling issue to me ?

blocked or restricted fuel supply , ( could be the fuel pump or even a blocked filter ? ) or even the fuel pressure regulators , none of these have ECU input , and wont throw a fault


i had a similar issue in my 89 V12 , the swirl pot would slowly block the pickup filter and starve the engine, then when off the debris dropped away and she started fine

i know you have a different setup , but the symptoms are very similar

BB

[franrca]

Thanks BB - will add to my list to share with them.

[pimgmx]

TPS...

On cars with the electronic ZF 4HP24 'boxes gearbox and engine 'talk' to eachother using various sensor inputs, to make down-/upshifts as smooth as possible.

One of the main inputs for the car's 'brains' is the TPS, or throttle position sensor in plain English.
A failed (or failing) TPS will trigger a gearbox warning light and could cause the engine to run poorly or not at all.
I've seen similar symptoms on AJ6 engines, which have a lot in common with AJ16s AND share the same gearbox. Solution there was either a thorough clean/replacement of the TPS.

My suggestions: clean the sensor's connectors and the throttle body (the latter will not hurt anyway!) and test the TPS' resistance values at its connector. With a bit of luck it only needs cleaning!
Or for a quick validation of this theory: get a known-good AJ16 TPS to replace the original item...

[franrca]

That's great - thanks...noted!

Actually, quick Q - excuse my ignorance, but is the TPS different from the Crankshaft Position Sensor...? Sorry if that's the height of stupidity

[pimgmx]

Common mix-up: crank position sensor is abbreviated CPS, only one letter difference!

Two different parts indeed: the cps is located at the front of the engine block on most inline sixes, next to the crankshaft pulley; the tps is located on the throttle body, LH side of the engine block, last part before the intake manifold.

And sensor is a bit of a big word for the cps, it's nothing more than a variable resistor, like the volume dial on a radio.

[franrca]

Thanks for clarifying for the intellectually challenged i.e. me

[pimgmx]

My pleasure!

And since a picture tells more than 1000 words:

The lumpy thing marked 1 is the actual throttle body, the part marked 2 is the AJ16's TPS...

It could be something else completely, but the combination rough running/gearbox warning light makes this one of the more plausible causes...

Hope your XJS is back on the road soon!

[BigCatXJS]

Thats bad luck Rich having your pride and joy break-down like that. Reminds me of the time my ECU failed and flooded the right bank with fuel, at 70 mph - picture fuel vapour pouring out of the right-side exhaust, being stranded in the outside lane of busy dual carriage way, starter motor burnt out (never a good idea to actuate the motor when the engine has suffered hydraulic lock) and a 45 minute wait for the RAC. On the up side, although a new starter motor was required and the ECU needed repair, simply removing the spark plugs cured the fuel lock! Compression was fine - no engine damage and my exhuast did not catch fire at the time of the incident! Sometimes it pays to have somthing thats a bit agricultural compared to the high-reving 700bhp+ Italian V12s of today. That said - i might consider a swap for an Aventador S

Hope you get it sorted soon. Otherwise I might think that you are looking to avoid the London to Brighton ermm Eastbourne...again...

[franrca]

Thanks.

Not on for London to..er..the coast this year Rich (Brighton is so 2015), but am doing the Donington thing yet again...we've just bought an XF Sportbrake, so will take that if the XJS is still crocked...the weeks are flying by after all and I'm getting more fed up by the week by my garage...no comms, no idea and I suspect it's just gathering dust. I even went in before Xmas to ask them realistically if they could fix it- otherwise I'd get it flat-bedded out....sigh...

[franrca]

Ok so update is - phoned for a progress report on Monday - was advised that they were at lunch and would call me back...no return call.

Chased today and advised it's now running and the issue was the airflow sensor...but there was some caution here as there are apparently issues with the wiring and the compression, so should it get through a successful test drive today I need to drive it a bit over the next week to see how it goes...apparently some expenditure is going to be required soon...will report back on how it gets on.

Thanks to all for your suggestions - I was pretty depressed after speaking to Chris Knowles and Graham Hallett and the possible outcome should the ECU have died...doesn't bear thinking about.

[BigCatXJS]

Before you part with more hard-earned, have you thought about changing your garage for one with stronger XJS knowledge?

Faulty MAF sensor should not have taken that long to diagnose. Wiring issues - well, that certainly can happen with brittle wiring, corrosion, dampness ingress, faulty connectors etc . Compression issues with an AJ16 ? Thats unusual - they are pretty robust and can take a fair amount of punishment before anything major like that happens.

[franrca]

Yes Rich, I was already planning that - I've had a few niggles with this place before, so this has been the last straw.

So got the car back - cream leather typically filthy and a hefty bill of around £1500. The advised 41 hours of labour over the period and only charged me 50% of the rate considering I had had the confidence to leave it there (!). They also advised they'd saved me over £300 by trying parts and sending them back that I hadn't needed...i.e. their trial and error.

So basically they saved me some money by not paying as much for them to p!ss around in the dark and also not paying for parts I didn't need - that's propaganda even Goebbels would have struggled with.

So car feels ok for the moment, but if it fails now I won't be darkening their door any longer..am looking out for somewhere else, but shame is that clearly I can't trust a place that's a Jag specialist any more - they need to have XJS experience as you say...and that's more difficult for such a niche car with very limited parts availability. My garage is a large concern with lots of decent classic jags being maintained andthe owner races them, so I despair! Will contact the local regions I think.