Cranking w/ no spark

Was working on vacuum pump, re assembled it, then car wouldn’t start. Went back over everything, was OK Not getting any spark. Both + & - on coil have 12V. + & - measure bout 15 ohms to ground each. Is this just a simple matter of it’s gotta be rotor, cap, or plugs/ Dweyr seems to think so. Be nice if it was.

Robert,

Have you checked if you are getting a spark when cranking the dead engine from the Coil HT lead to ground before it gets to the distributor? If not, the usual culprit on these engines is the crankshaft position sensor (CPS). When cranking, do you see 200/300 RPM on the tachometer? If not, the CPS or its connector is almost certainly the problem.

Hi Bryan;
I cranked it & watched tach, no movement, prob is I don’t remember if the tack worked before, so that test didn’t do me any good. I looked around for the CPS, but couldn’t find it, lots of stuff in the way .Is there another simple way to check the CPS? Would it be accessable from underneath? Is there a way to check the tach? Does the CPS have to be timed?
Frustrrated
Joebob

Robert,

Take a look on the timing cover on the front of the engine above the crankshaft pulley and you should see something like items 11 and 16 in this picture :
https://www.jaguarclassicparts.com/uk/jaguar-xj6-parts/engine/timing-chains-and-adjusters/timing-cover-3-6-litre
That is the CPS. If you don’t have one, no wonder the engine will not start.
It is easily accessible from above.
If you do have one, about the only thing you can check is the continuity from its connector and the resistance should be around 1300 to 1500 Ohms. However even one which checks out that way may still be defective and if you get no tachometer readings whilst cranking and no spark (and no fuel injector pulses either BTW) the chances are that you need a new CPS.
Outside of a laboratory test rig I know of no way to test the tachometer.
The CPS does not require timing - it is a Hall effect magnetic sensor and it is pulsed by the gaps in the castellated wheel behind the crankshaft pulley - item 8 in this picture:
https://www.jaguarclassicparts.com/uk/jaguar-xj6-parts/engine/crankshaft-and-pulley/crankshaft-and-main-bearings-3-2-4-0-litre

I knew it was down there, but there’s not much open space around it. There are 2 large rubber cooling pipes that cover it up very well, may have to remove them. I just bought a rotor, cap, & coil. Looks like this is gonna be a beautiful car w/ many new spares, but it don’t run.Only has 46k miles on it, beautiful body, inside & out.
Joebob

Robert,

As with most work on the XJ40, a little dexterity is required. IIRC you may find it easier to remove the bracket holding the CPS on to the timing cover with the two hex-head bolts and then detaching the CPS from the bracket with an Allen wrench.

If my memory serves me correctly, if the CPS is dead, there is no spark to the plugs, AND the injectors will not operate…ie no click open/closed… Have a helper crank over the engine and use a mechanic stethascope held to one or two injectors and listen to hear if they click. If the injectors click, it is NOT the CPS. Hopefully someone else can confirm.

SD Faircloth

Correct, as I mentioned in an earlier post -

“and if you get no tachometer readings whilst cranking and no spark (and no fuel injector pulses either BTW) the chances are that you need a new CPS.”

Bryan, Oops, guess I overlooked your post. Asked and answered. SD

Many thanks guys for your valuable info. I just ordered a rotor, cap,coil,
& a CPS. I’ll get it on in a fw days.
Hope it all works, but
I’m looking forward to whats next w/ the no start.

 Robert

It’s probably easiest to purchase a 5mm Allen wrench with a 3/8 or 1/2" drive then with a long extension you can remove the CPS retaining screw, these can be very tight, the connector lies across the front of the timing chain cover, this ‘can’ become dislodged if the retaining tang has been destroyed.

Thanks, Robin;
Just what I wanted to know. Still waiting on
parts. I will try to find a 5mm ball allen 3/8" drive, (the kind that will
work at an angle like a u joint). It’s a tight place to get to. It was also
suggested to remove the bracket w/ it, don’t know whats easier.
Cheers

Joebob

I always remove the bracket with the CPS, 1 bolt and another securing the harness clip, never seemed too difficult on my car?

Finally got the prob solved. I waited 4 weeks for that CPS from that bloody Amazon,shoulda watched the delivery time more closely. I got one for bout $168,some were up to $.350, 5mm ballhead allen. shop arround. I found the perfect wrench for the allen mach. screw. Allen is a ball end, bout 4" long, w/ a 3/8" socket drive Just the perfect tool. for the job You can get it at Lowes Now its on to the AC & speed control,Many thanks for the info. ,m

Hi guys
Got the car running. I didn’t tell you before that I was on hospace. I had a very bad near death experiancc & now they tell me no more working on Jag. At least I got it running. I will have to sell it now.It’s an 1988 XJ40 w/ what appears to be a totaly rust free body. & a beautiful interior. Someone will get a beautiful car. Details.
Thanks again for all your wonderfull help.

Hello Rob, My lady partner of 15 year has been an LPN for 40+ years and a Hospice patient care nurse for 7-8 years. She takes immaculate care of every vehicle she has owned. She now has a 2008 Saturn Sky roadster convertible. She is out and about as I post this, but she might say…“they said you can’t work on the Jag, but they didn’t say you can’t drive it !!” Take a Sunday afternoon ride and post us a pic. Best wishes, SD Faircloth

Hi S D
Many thanks for the nice reply. Actually my nurse suggested that I shouldn’t be driving some time ago, although I still can. There are some minor bits that need to be put back on,( interior panels) , hence the work required
Cheers
Joebob