Not sure if it’s posted in the thread somewhere but I would throw a new crank position sensor at it if the 3.2 has one.
Ah I forgot, I have changed the coolant sensor already.
3.2 does have a crank position sensor and this has crossed my mind, but my conclusion was an issue with this is a catastrophic no start type situation? Perhaps I need to revisit though.
Not to offend, but you did change the coolant temp sensor (two wire connector, provides data to ECU) and not the coolant temp sender (one wire, provides data to the temp gauge), right?
As for the CPS, I have had them cause an occasional ‘hiccup’ (split second interruption in ignition whilst driving) prior to full-on failure (no start). Never had one cause spluttering.
Mike
are those the two things?
David Manners - COOLANT SENSOR XJ12/XJS/XJ40,COOLANT SENSOR XJ12/XJS/XJ40 (jagspares.co.uk)
Coolant Temperature Sensor Jaguar XJ40 XJ6 XJ12 (1987-94) INTERMOTOR - DAC2583 | Ashwood Jag Parts
if yes i will buy those for my 1990 xj40 (which has some running problems)
No offence caused Mike, I changed the one with the black plastic plug (two pin), so assumption is that this was the correct one?
I think the ignition coil is a worthy part to change next, but at the same time, running improves slightly with the MAF unplugged (i.e, enriched mixture), though replacing the MAF didn’t help. This is what’s taking me down the Lambda sensor path as I’ve changed all other fuel related sensors!
Yes. The two wire sensor (from David Manners) is the one that provides data to the ECU (engine control unit a/k/a the ‘computer’ or ‘black box’) and affects engine performance. The one wire sender (from Ashwood) only affects the temperature gauge and will not affect the performance of the engine.
Just a random thought here - could this be EGR related? If needed there is troubleshooting info in the Haynes manual, section 6.6.
That was my initial thought when the problem surfaced, but alas, UK cars weren’t fitted with EGR. I note that I didn’t mention it was a UK car though, so that one is on me.
Hmm, no EGR…you mentioned checking the coil (done that yet? Nice blue, not yellow, spark). Might also check out the ignition amplifier. From the J-l archive:
[xj40] 92 Ignition Amplifier - #4 by GBalthropXJS?
The online ebook mentioned is on the old jag-lovers.org Web site - here’s a link to that:
https://www.jag-lovers.org/ebooks/view.php?Vbook=xj40&Vsection=10.14
After re-reading this thread - is it possible you have a sizeable vacuum leak? Intake bellows holed or fitted incorrectly?
Mike - I had not considered the ignition amplifier and also haven’t checked the colour of the spark. I reckon that will of course be easy to do on my own (our bonnets open the correct way 
), will check at the weekend.
Larry - I had considered this too, I sprayed some easy start around the intake area with the engine running and didn’t note that the idle changed at all. Though, at idle, the rev counter bounces around a little which is a little suspect. Another good point that I’ll revisit at the weekend!
Check fuel line pressure at the engine. I removed the fuel line to install a schrader valve on the rail When I measured the fuel pressure the reading was 80psi and should have been around 30 -40psi. This resulted in constant over fuelling to engine as injectors opened (Flooded engine) Totally misbehaved new fuel pressure regulator made it like a new car
Thanks Gerry, the fuel pressure regulator had crossed my mind previously, so I’ve just ordered another to try.
I had thought the issue didn’t present itself when idling on the driveway, but it turns out it does. See my video below, at the end is where I find the (not so) sweet spot.
I just connected a timing light, found the sweet spot and observed what the strobe did.
At idle, i.e running fine - strobe is consistent as expected.
In the “sweet spot”, the strobe is all over the place, going dark etc.
Have I had a breakthrough? This would lead me to suspect it is indeed ignition related?
It does this on all cylinders, perhaps it is afterall CPS related? Might also explain the 3000rpm “rev limiter” that I noticed too.
Daniel, this makes me think your ignition coil is breaking down. I don’t read anywhere in this thread that you replaced the coil. New aren’t all that expensive. Or, do you have a source (friendly fellow XJ40 owner?) from which you could borrow a known good, working coil for test purposes?
The coil and the CPS are the only ignition related things I haven’t yet changed, though have at points considered both. I’ve never experienced a defective ignition coil before, does it sound more likely to you than the CPS?
Unfortunately I don’t know of another XJ40, but as you say they are not expensive.
Given the symptoms yes, I would suspect the coil rather than the CPS. How many miles on your car?
I’ve just ordered an ignition coil, so fingers crossed this is finally the end of this saga.
The car has 98000 miles, looks like the original coil too?
I read on one Web site a coil should last 80 - 100k miles. My car has 198k miles, the last 123k of which have been under my ownership. I don’t know whether my coil is the original but I have not replaced the coil in the time I have owned the car.
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I don’t think mileage can be used with confidence for assessing the lifespan of something with non moving parts, with items like coils it’s more down to the circumstances they’ve been operating under and the quality of the original manufacturing.
The coil on my my car is the original and it’s covered 147,000 mile, the one on my last car was working fine after 180,000 miles, but I’ve owned cars in the past where the coil has broken down after 33,000. Given the fault you are experiencing changing the coil is a wise move, they’re relatively inexpensive and at least you can rule it out if the fault persists after changing it.
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