1989 XJ40 unusual start

While driving around a few days ago I was thinking to myself, “for the first time in a long time there is absolutely nothing wrong with my car. Running perfectly, no leaks, air conditioner freezing me out etc. etc”.

Little did I know that the Jaguar Gods can actually hear you thinking and that you don’t have to say it out loud for them to jinx you … LESSON LEARNED.

Both yesterday and this morning when I started my car It fired up and then immediately died. I tried giving it several shot of gas by cycling the ignition on and off with no help. I could only get it going by feathering the throttle and then after a short drive all seemed to be well.

My first thought was fuel starvation (pump or filter) but it ran completely normal off idle. I’ve replaced the pump, filter, and regulator within the past 3 or 4 years but of course that’s no guarantee one of them couldn’t still be the culprit.

Any thoughts ?

I could really kick myself because I didn’t drill and tap and put a Schrader valve on the fuel rail when I rebuilt my head a few years ago. I actually had the valve in my hand and for some reason didn’t do it. That would have made checking the fuel pressure SO much easier.

Did you check that you have rpm showing in the tacho? CPS and connections is the first guess.

Yes the tachometer was definitely working.

The engine normally starts immediately on the first crank, absolutely no hesitation.

Now the RPM’s initially go to around 7 or 800 and just slowly die off. Nothing sudden like an electrical problem, more like fuel starvation. Strange though because if I hold the throttle open it runs normally but at idle it just dies.

Sorry: point missed from my side. I do not remember exactly but i think you have a pulse controlled Idle Speed Control valve. Have you checked its connections and that it is not gunked?

Should have touched wood when you said “absolutely nothing wrong with my car” so it’s your own fault.

Seriously though check MAF connector and coolant temp sensor.

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100% spot on, usual suspects for this behaviour as Larry (and the me) say:

  • Coolant Temperature sensor (though usually this would only result in inefficient fuelling)
  • Air-Flow sensor (start with the connection, the sensor itself can be CAREFULLY sprayed with contact cleaner
  • Throttle Position sensor (PS: these go bad due to oil seeping down the butterfly body, can be cleaned)

HEY: and then do not forget that in this EMS you also have a coil, a distributor and an ignition amplifier (though I would suspect these to be OK, as the car starts, idles and gives RPM signal) but check, the connection of the ignition amplifier get dirty due to blow-by of dust from the fan.

I’ve had them completely mess up running, causing stalling, hard starts, missing - all sorts of problems.

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Gents …

Thanks for all the great input !

Larry … Oh no no, I never SAID “absolutely nothing wrong with my car”, I merely THOUGHT it. But still the Jaguar Gods smote me !

Just went out to start my car so I could very clearly determine what the symptoms of my start problem are. I think I stumbled on to the cause …

As I tried to started the car this afternoon I had left the door open which turned on the overhead console lights. As I was cranking the engine I noticed the console lights were dimming. Wait this can’t be right. Continued cranking and saw that my ammeter on the dash was dipping well below 12 volts.
And then when the engine warmed up everything returned to normal.

So when everything cools down I’ll throw my voltmeter on the battery and see what happens when I crank it over.

Swapping out the alternator is not that big a job and if it eliminates days of troubleshooting I’ll be all smiles. Fingers crossed.

I might be wrong Groove, but I don’t think the interior lights dimming when cranking an engine is anything unusual. The starter motor puts a real heavy load on the battery and most of the current is drawn to it, and until the engine actually fires and begins to spin up the alternator its also not unusual for the ammeter to swing below 12 V during continuous cranking. I think the same would also apply if you were cranking the engine with the headlights or sidelights on, that is, you would see them dim a little during the cranking period.
As long as the ammeter swings back up to around 13V - 14V a few seconds after the engine starts I think the alternator is ok.

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Well what can I say …

For the last few days my car has started and idled perfectly, even first start of the morning. Maybe it just passed a kidney stone :neutral_face:

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Either that or it was as you first said and the Jaguar gods somehow read your mind and thought they’d keep you on your toes :grinning:
That’s good news it’s now behaving properly, I’m reluctant to say anything else just in case those same gods can hear me too, but fingers crossed that’s the end of the issue and you have a well deserved long trouble free Summer of pleasurable driving ahead. :grinning: :grinning:

Casso …

It used to be, watch what you say. Now it’s be careful what you think!

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