www.jec.org.uk

Well it -had- to happen to me, the next day after I was singing praises of how reliable my xj-s is, it decides to let me down and refuses to start, forcing me to use my alternative 2-wheeled motor transport to get to work !

Strange thing is over the last few days that I've tried starting it and running the battery flat after trying a few things here and there, on one occaision after recharging the battery it started up completely normally so I thought nothing of it and looked forward to not having to use the bike in the rain- ...and then it let me down again next morning!

So, maybe we should run a sweepstake, whoever guess closest the problem gets this nice yellow lightbulb >> ?

I've checked sparks - can make huge long jump over half an inch, and all the plugs spark, though when first remove them they are slightly wet with fuel but not flooded. There's smell of fuel from exhaust OK. I don't think it can be carnkshaft sensor- because there's sparks appearing in turn from the removed plugs laying on the head.

The compression in each cylinder reads about the same, some are a little bit low but I'd expect that it's a very high mileage engine. All at least 100psi.

There's fuel smell from the exhaust, and from the plug holes after plugs removed, I'd say that's about the right amount, if there was no sparks.

Latest thing I've noticed is 'Fuel Fail' and 'FF3' (coolant temp sensor out of range) but I don't think that would prevent starting, unless anyone knows different? Maybe the mixture is too lean?

I've been careful during investigation not to add any more faults or destroy the 'trail', I've not replaced any parts or worked on anything apart from cleaning the coil ht terminal and cleaned and gapped the plugs, neither was really neccesary proven as 4 of the plugs worked fine in another car.

I normally say if there's fuel, air, some compression and a spark an engine's got to run because petrol is so easy to ignite, but I think here is something else going on, like valve timing slipped camshaft jumped a tooth? or crankshaft timing rotor slipped off it's key (which is difficult to beleive since it started and ran normally for a breif period).

Does any one want to have a go suggest what it could be and I'll report back when I find out

Mark – For what it is worth. In the good old days you would no doubt be right, fuel, spark, compression etc. but what you have here is a fairly complicated but straight forward enough semi modern setup. From the symptoms you have described I would look in addition to the work you have already carried out to the crankshaft sensor and the ignition amplifier. Worth a look and hope you get your car back on the road very soon.

Nick

Ps. I think if this were a valve timming issue that you would expect to have been hearing some fairly wild noises comming from a slack timing chain for quite some time. Lets us know how you get on.

Mark, my money is on the CPS, when they fail its typical of an intermitent (sp) fault, usually, but not always heat related. Sometimes magnetic dirt can build up on the sensor head reducing the sensitivity of the pick-up signal but IMO there is no reliable way of checking them except by replacement.
Pop

I doubt the CPS is at fault, as this (should ) bring up code FF1 on the trip computer. I have encountered code FF3, although this wasn't a problem with the coolant sensor, it was either to do with a dodgy ECU or the idle speed stepper motor. (I had bother with both)

A couple of things to try? (in no particular order)

Remove coolant sensor, see if it starts
Remove airflow meter plug, see if it starts
Take out stepper motor and check it moves when you turn ignition on / try to start (dont let it wind itself off the spindle though)

Failing that I might have a good spare ECU you can try, think I've got a DBC 2910 and a 4910 in stock.

Mark
A couple of years ago my 89 3.6 after previously faultless performance had EXACTLY the same symptoms, one morning out of the blue, turned over.....nothing. Called out "homestart", spark ok, fuel ok, compression ok I thought exactly the same as you ie IT MUST START. But it didn't
I suspected crankshaft sensor U/S which I believe is a fairly common fault (and not too expensive to fix) the man from the breakdown truck who had some knowledge of Jags agreed.
I had the car taken to Swallows who after some diagnosis found "Brain" U/S.
The Ignition/Fuel Injection Control Module (ECU?) had failed. (Under your feet in the passenger footwell). Possibly due to the ingress of water running down the cables into the module. (It's another great Jaguar design, any water ingress into the passenger side of the cabin is funneled straight down into it.....
Fitted a secondhand brain and away she went good as gold
Module failed after three months but was replaced under warranty
These modules are expensive new - @ £300 I think so if you can confirm that is the fault I would go secondhand with Warranty if you can.
(Jon. Our posts crossed I'm sure your ECU's Are lovely!)
You may want to inspect your module to check if there is any evidence of water ingress, if there is I would say that is your problem.

Good Luck
DH Dove

Hi Mark,

My suggestion is simply that the engine is flooded. If you have a good spark but wet plugs and a fuel smell in the exhuast, it suggests too much fuel.
If your coolant sensor is indicating low, the ECU will richen the mixture. I have also read of problems occuring where a car with no fault is started and shut off immediately again, the excess fuel supplied during this time is enough to flood the engine and prevent restarting.
You could try disconnecting the injector leads and cranking to dry it all out.

You might try spraying some of that cold start spray into the intake, this might be light enough to get the engine to run and clear the fuel.

Regards,
Glenn.

I think Nick and I are in line for the shiny new lightbulb.........
There has been a lot of rain recently.........
DHDove

Just an addition to Glenn's suggestion, it would be easier to knock off the inertia switch near the driver's door on the 3.6 rather than disconnect the injectors.

Had another brief look at it (car sat out there in the street, it's there feeling like it has clipped wings, I feel sorry for it!). But only tried short burst with the key couple times, still the same.

Nice idea about flooding Glenn, yes that would explain a lot if it was, I'm reasonably sure it's not flooding though, my experience with flooded is removed plugs are found dripping wet and there's petrol mist flies out the plugholes when cranking, and when left half hour the fuel evaporates anyway on its own accord. The smell of fuel from exhaust is about what I consider normal if the sparks were missing, or plug leads firing order wrong.

I plugged an LED into one of the injector connectors and it blinked 3 times per revolution, which is correct for enrichment during cranking.

Yesterday I tried seeing if the mixture was not rich enough by adding some neat butane down the air intake (always worked a treat - weak mix engine will pickup and run smooth) and also today I sprayed a good glug of easy-start into the air intake just to make sure (doing that'll make the mixture strength sweep from over rich to over weak (without flooding), but no firing at all during that test. Maybe my 'fuel' is in fact water? Someone put water in my tank? Unless it is that, I think the fuel part of the ecu is working.

Interesting DHDove symptoms being the same. I did look at the ECU under the passenger feet to look for any sign of water but the area is bonedry, I previously had a piece of card under it as a tell-tale and that hadn't picked up any history. The ECU is looking like a probable until I can rule more of it out.

Crankshaft Sensor (PopRivet) would normally be high up on list because of the reputation they have, somehow I don't think it is, as I'm seeing regular timed sparks on the plugs laying on the head. As Jon says that should make a FF1 whcih I've never seen. Though I guess it could be outputting erratic pulses, but the sparks from the coil centre terminal seemed too regular to be that. If it is that after all Pop wins the light bulb!

Coolant sensor if open would be reporting to ECU 'very cold' and the engine I would thought start OK and limp, but always run rich (no cat on this car). If shorted I guess that would cause slightly weaker and may had needed butane or easy-start supplement to fire. Removing the connecter is a good one to try Jon, I give that a go and the air flow (temperature?) sensor though I would of thought these would only start to affect mixture after the cranking enrichment had ended when the engine fires and above 500rpm.

The idle speed motor (Jon) is another good one, if that was jammed closed the engine would fire a bit while cranking but will not start unless a little throttle pedal was added, I had this fault some years ago, it's not that.

The ignition amp (Nick) I think I've ruled out by the loud crack of a spark I've seen and I agree if the valve timing had slipped or something I would have had some dramatic sounds from that part of fthe engine when it started and ran normally 2 days ago.

So Guys I think it -might- be ECU, in particular the spark timing has slipped, or maybe the crankshaft tooth wheel slipped, it reminds me of when getting a distributor 180 deg out of position, no matter how much you check the timing it's always perfect until you realise it's on the wrong stroke! Test I'm going to do is get a strobe timing lamp and see if the spark is in the right place in relation to true TDC, with one plug in the engine so there's no mistaking the firing stroke. Then if wrong it'll be test-by-substitution ECU time, and DHDove might be winner.

Oh and inertia switch, that's a good one, you can tell if it's OK when you turn key to ignition, you should hear a 0.5 second timed fuel pump run from the boot area, that's OK.

Enough of this looong post it's time for a pint ...

I'm not sure if a Crankshaft Sensor failure does produce a fault code. I thought this was one of the few sensors that didn't. Might be worng!

Nick

CPS Sensor on the blink I'm pretty sure will show up in the strobe timing test as a spread ignition timing error. My gut feeling is I think it's working OK because of the regular sparks and injector pulses I saw. If it is that after all I think Nick and PopR may be joint winners of the light bulb!

I'm not sure if a Crankshaft Sensor failure does produce a fault code. I thought this was one of the few sensors that didn't. Might be worng!

Nick

Definitely brings up 'FF1' on the 9CU cars. Try disconnecting the plug

Well I tried ignition timing check with strobe light while cranking and the sparks appear in the right places on the crankshaft- so that's the CPS completely exonerated... Ignition part of the ECU seems fine too.

So.. sparks at the right time, compression, and fuel (flammable- I tried it!) and air of course. Someone suggested I look for air temp sensor, I looked all over for another but only found one, the water temp sensor, and a blank space where I think an air sensor goes.

Going back to the FF3 code, I figured I'll at least fix that then, so I removed the connector (which is rather brittle and cracked now) and measured the water sensor, measures 3K Ohm, not perfect , but about right anyway. Then measured between ground and one of the harness connector pins one at a time, one of them measures short circuit, the other an open circuit, I was expecting to see a resistance on it from the ECU. Anyway the harness connector socket I've found the latter pin crimp to have come loose and corroded, hence the FF3 code. The only thing I could do with the connector is cut it off and strip the ends of the wires and splice on a spare fuel injector connector (fits perfectly) and plugged it on the water sensor, no FF3 code any more when I turn on ignition.

Then I thought ... I wonder..... I engaged starter and the engine started without a fuss! This all occurred yesterday, and today with the cold engine it started first go, then I stopped engine, removed water sensor connector- it wouldn't start. I wouldn't had thought the water sensor had of caused this, but there it is. When the connector replaced and engine restarted the engine at first seemed to behave like being over-fueled.

The conclusion then: if I'm not mistaken the water sensor being disconnected will cause the ECU to believe the temperature is very cold indeed and it stands to reason more fuel will be delivered. This would explain why me richening the mix failed, though I'm still puzzled why the plugs didn't seem that flooded...

So anyway.. without further ado... I award to our winner (who's guess was closest as could proabably get ) ....... Glenn...... winner of the shiny light bulb>>

Well done Glenn! and thanks of course to everyone else for having a go

I shall wear it with pride......

I'm glad she's running sweetly again.