Hi Mac

Been out of the game on non-related Jag Stuff, came back and found my PM box overflowing and still haven't emptied it yet

Sorry to hear your having problems but Warrjons the Guy for electrical stuff although I may be able to help a little bit or maybe not, we'll have to see

Anyway on a Marelli, the Fuel Pump doesn't have a fuse but it does have a couple of Relays in the Boot Trunk (as has been mentioned) by the Gas Strut behind a Black Plastic Cover: The one in the Red Holder is the Main Relay and the one in the Black Holder is the Fuel Pump Relay and Both of these need to work for the Fuel Pump

Also they are Not interchangeable as the one with the Red Stripe has a diode

If you want to Stop the Pump you can either take out the Relay in the Black Holder or else disconnect the Positive Wire from the Pump, although either one would do

Fuel Pump Relay is in the Black Holder behind a Plastic Box in the Boot/Trunk near the Gas Strut

Could also be the Crank Position Sensor, which is often more likely to be the Front One just underneath the Belt Pulley and fairly easy to get to (don't lose the screws!) these are horrendously expensive (at least to me they are!) so I hope its not that

Where for some strange reason the Flywheel Sensor is only half the price, although visually there isn't a lot of difference and they do the same job

But I do have a 'Conspiracy Theory' on what your Slow Crank problem might be and I am thinking 'Dead Cell' in the Battery' where you need a Shop to Test it under load with a special device that Greg might know the name of

 

Thank you Orangeblossom
I turned off the fuel pump
Slow crank was earth wire, fixed with Grant, Greg and Mac Allan help. PM's
The jag being 30 years old,Im thinking of replacing all sensors.
Can you tell me the electrical road map from the battery to the spark plugs and possibly part numbers?
Would like to replace all that I can.

 

Hi Mac

You are going to need someone like Warrjon for that but the Crank Position Sensor and the Flywheel Sensor are not Service items like Spark Plugs and those Sensors really either work or they don't and your Car is probably fitted with Genuine Marelli like mine is

So I myself would not be keen to swap them out for ones that could be of inferior quality, so probably more important to change all the belts because if one of those breaks, it will almost certainly take out the Crank Sensor anyway

Glad you got your Car sorted

Alex

 

if sensors don't work, is there a fix or order new

 

Hi Mac

There are only a few things that I know of that can have the Crank Sensor Cut Out

It could come loose on its bracket (unlikely) or maybe get a knock that might alter the Gap (possible)

Or just plain wear out and loose all its magnetism, unless one of the belts breaks and it gets hit by that, in which case the engine will suddenly cut out without any warning but what I would not do is try and tighten the bracket or the Crank Sensor holder unless you can feel that its loose as you could easily strip the threads

If it ain't broke don't fix it, is the way that I would go, as it could last for a lot longer than you might think

 

Does a crank sensor go bad, how do I tell if it is bad, If so what do I do.

 

Thank you. Found it.

 

They go bad all the time, Mac. they have to be changed, the front one can be got to from above (Orangeblossom has threads on changing his). The rear on I think has to be changed from below, and it's gap to what it is measuring is crucial. There is a thread on it somewhere, not that old.
I have no personal experience of it, so cannot help further. Someone will though!

 

Hi Mac

Somewhere I have got a thread on how to Test the Crank Position Sensor which I will try and resurrect, as Crank Position Sensors can be a problem for everyone at sometime, although to be going on with the Gap on the CPS is ultra crucial

Maximum Gap of 0.042 any wider than that and the ECU won't be Triggered (That Gap applies to both the Front and Rear Sensors) although its much more likely that if there is a problem it will be with the Front one, which unlike the rear one sits in a bolted on Bracket/Holder

 

I unplugged the cps as Grant,Greg and Orangeblossom said, I plugged and unplugged several times, cranked and no spark.
I then put on some magnifying glasses and looked at the 2 prongs in the plug, looked to have build up on them, so I folded a sliver of 120 grit sandpaper and cleaned them,
plugged back together, sat in jag, turned ignition and as Scotty would say " there be spark here Captain "

I thank all members for your time and effort on this problem.

I want to give special thanks to Grant Francis, Greg in France,Orangeblossom, as they PM'd me, what to do, till it was fixed.
Now I will go back out in a little while and put distributor cap back on, reconnect fuel pump, air breathers.

 

Well done Mac

I knew you'd get there in the end

Alex

 

I went back reading all the replies and if I had check CPS plug as Greg in France suggested in reply # 33, this would have been a short thread.
Hind sight is always 20/20

 

Good work.

I've fixed a lot of problems over the years by cleaning connections. And almost certainly replaced a lot of perfectly good parts that only needed the connections cleaned. Sometimes I have to remind myself "Check the Connections. Check the connections. Check the connections" !

Cheers
DD

 

WELL DONE.

Simple cars these Jags, always remember that, and what Doug has stated.

 

Before I start the engine.
In the past several days I have cranked the engine maybe 12 to 15 times maybe more.
Im concerned fuel has built up in cylinders and in the Cats and don't want to ignite a fire when I start the engine.
Should I disconnect fuel pump and crank engine several times to let fuel escape and then let the Cats dry out for a day or so.

 

I would just let it sit, enjoy that JD for a day or 2, and then enjoy the car.

Gasoline evaporates quickly in warmer weather, and I reckon it is still warmish up there.

Once you start it, go for a loooooong drive, maybe a couple of hours without shutting it down, that will A) Do the engine a world of good, B) Dry the system out 100%.

 

A few minutes ago, first time Ive tried to start since (CPS) was cleaned. As soon as I turned ignition it fired up, has never started this easy, always a couple seconds before starting, now instant start.
Thanks again to everyone.