Hello Folks,
I'm new to this site and likewise new to Jaguar. My uncle gave me a 1987 XJ-SC which I am pretty unfamiliar with...Although I have done just about everything that can be done do a Camaro, I don't know what I'm doing with this Jag. On a recent cruise in the XJS, I was experiencing misfires and rough idle. The car was certainly behaving like it needed a tune up so I proceeded to break down the engine to replace the spark plugs. I have never experience anything quite like replacing plugs on the 5.3, I nonetheless gave it a shot. Not having a factory service manual, I am essential flying blind with every job. But to save time let me get to the problem. I replaced the plugs (the were certainly in need of replacing), the wires, and the cap.

Having buttoned everything back up, I proceeded to start the car and it would not come to life. From the way the car sounds, it seems that I am not getting any spark. It spins on the starter but will not catch. I used motorcraft platinum plugs and tired my best to gap them to the .025 factory specification.

I really don't to disassemble this again so any and all suggestions would be greatly appreciated. Sorry for the length of this thread but I wanted to be thorough. Thanks in advance folks!

 

On mine (1989 w/Lucas ignition), the ignition amplifier (circled in the pic) was the problem.
http://www.flickr.com/photos/40397102@N07/6988283081/
The bad: This part is no longer available.
The good: There are people who know how to fix it.

I deferred to a Jag expert when I had the exact same problem.
Basically, it wasn't sparking AND it caused the fuel pump to not fire up.

Worth looking into.

 

Backtrack over your work carefully. You'll probaby find a broken wire or loose connection....very easy to have happen when changing plugs. Lots of brittle wires down there.

Cheers
DD

 

Haven't shopped for one in years but this is the first I've heard of the amp being NLA. Are you sure?

1986-1989 Jaguar XJS Ignition Amplifier – Lucas W0133-1599520 - Direct OE replacement


In any case, the *primary* component inside the amplifier---the ignition module---is readily available froms dozens of source, including AC Delco, part # D1906

Cheers
DD

 

When the guy who looked at it called the Jag dealer, he was told what he needed was NLA. Not sure if it was a particular part or connector or what.
He did explain, though, that the guts were the AC Delco parts.

 

Thanks for the information folks.

It's worth mentioning that in my bewilderment of the task and haste of disassembly, i failed to keep track of the connections for the ignition coil. There are three connections, one that runs along the fuel rail and two the originate from the amp. what goes where? The photograph was somewhat helpful but when i tried to mimic the order in the pic and turn the car over, i stumbled upon the same result...

 

Solid white wires go to the coil "+" post.

White/black wires go to the coil "-" post.

There might be another...memory a bit foggy

Cheers
DD

 

thanks for the help doug,

last question. positive and negative is not marked on the coil. is the negative the connection closer to the firewall?

my man.

 

i lied...one more question. on my camaro, when i want to check to see if im getting spark i simply remove the #1 spark plug and turn the motor over. is it possible to remove the wire that goes from the coil to the cap, connect a plug and check for spark that way?

 

Yes you can check for spark there. If there is no spark. Turn the ignition on and measure for voltage at coil Neg (on the primary) it should be under 2Volts if not check wiring for a break or bad earth. Edit Sorry Measure voltage to BATTERY EARTH only.

The XJS is notorious for bad earthing and broken wires especially in the engine bay where the cheapo wiring that Jaguar used breaks. Not to mention all those mechanics that have been rumbling around in there.

 

well, no spark coming from the coil...i guess it's either that of the amp. thanks for the help guys

 

warrjon, im not the most experienced mechanic. please elaborate on battery earth. no spark from the coil. will have to borrow a voltometer from someone. thank bro

 

Battery earth is Aussie-talk for the ground on the battery or the negative post.
Check your coil carefully, it should have the markings on it for +/- but it may be hard to see.
Unless someone has updated it, you actually have two coils. The primary coil which is the obvious one, and if you follow the wires coming off it that go towards the front of the car and through the radiator support you'll find the secondary coil in front of the radiator. These two coils are wired in series (+ to +, - to -). If you have the wires mixed up I believe it will cancel each other out and...no spark!

 

I have brand new ignition amplifier sitting on my bench, I believe internals for it are still available here and these.

 

Sorry sometime we make incorrect assumptions.

Battery earth is in the boot on the RHS of the battery there are quite a few wires that are earthed to the chassis, follow the battery earth lead and you will find where I mean.

Uuse a set of jumper leads connected to this earth up to the front of the car.

First measure between there and the Pos side of the coil you should have 12Volts.

Connect the meter leads between the jumper lead and coil Neg. If this has under 2Volts you can assume all of the ground wiring is good.

If you have 12volts (or there abouts) you have broken wire or bad earth some where. Leave one lead on coil Neg and follow that wire back and measure there, (so you should have the meter leads between coil neg and the other end of the coil Neg wire, if you have under 2volts that wire is good.

 

New amps are available. SNG Barratt stock them, for example.

I think, that if you take a really close look at the coil, and clean it up around the top, you will see a tiny + and - cast into the black casing nearby the terminals.

Greg

 

the positive side of the one in the car is the one with three male posts. the negitive has two. if you are not getting spart you could update your coil, either with the single coil that people recoment of two with a combines resistance of atleat 1.2 ohms, for example i run two coils that were for a 74 vette witha 454. fill the second coil top with silicone and then place it where the first one went. you could also check your star on the hei ignition cus that could be beat up or not working, also the grounded wires that connect to the amplifier, they could be kinked causing one to ground out (thats what happened to my engine speed sensor and left me baffeld for months)

 

The ONLY reason to run dual coils is to lower the inductance of the primary winding. Find a coil with 0.8-1Z primary and you will be ok.

A bit of coil theory for those who have insomnia.

A coil is basically the opposite of a capacitor. In series with a DC source the coil acts like a piece of wire (ie a short circuit) so if you were to measure the voltage across the coil it would be effectively Zero.

Now if we use an AC source the coil characteristics change and it becomes kind of like a constant voltage source. What happens is - as the current passes through the coil charges as it tries to keep the voltage constant. Then as the current turns off the voltage (or more precisely the magnetic field collapses) . As this happens the field is transmitted to the secondary winding, because the secondary has more turns the voltage is stepped up and the current is stepped down. So with 50volts and say 10amp on the primary of a 1:100 coil the secondary will be 5000volts and the current will be 0.10amp.

Other stuff is happening as well like the current sign wave lags the voltage by 90°. If anyone has ever opened a speaker or DIYed a speaker you will know capacitors and inductors are used as filters. An inductor in series with an AC source will try to oppose its transmission, in other words if tuned properly it will filter out the AC.

To charge/discharge a coil (to 99%) it takes 5 time constants (some math for those that are still awake) one time constant is T=L/R so for a typical ignition coil 1Z 8mH

T=0.008/1 so one time constant is 8m seconds

Also the coil will charge 63% for each time constant so if we charge the 10A primary to one time constant the current will be 6.3A, the second time constant is the difference between 10A and 6.3A, so 63% of 3.7A is 2.3A so the current flow in the second time constant is 6.3A+2.3A= 8.6A. THIS IS IMPORTANT as this is what is known as the DWEL time.

So if we increase the coil primary inductance to 10mH

T=.01//1 one time constant becomes 10ms so the charge time increases 25%

Now I have bored everyone to death I’ll go to bed

 

Two coils from a.vetted are 30$ a piece and the bigger one was quotes at like 100+$ so I picked the two

 

Warrjon, It has been quite a long while since I have wrenched on my XJS. Other projects and school have consumed my time. Needless to say I am still where this thread left off.


I tried to do as you suggested but I'm not sure If I completely follow you. Perhaps it's because like most Americans I don't speak English, I speak American.


I connected a Voltmeter to the hot wire that leads from the ignition to the coil and got 12v. However like I said I am unsure of what you are suggesting with regards to testing the coil Neg. I identified the multiple ground posts in the Boot adjacent to the battery. Are you saying to run a Jumper cable from the boot to the bonnet, connect the negative lead from my meter to the jumper cable, and then connect the positive to the Coil Neg and test? I'm a complete Noob when I comes to these cars. Subaru's and chevy's are my forte. Could I simply have the wires connected wrong, as I mentioned before? I'll add some pictures below...I should mention that a single coil conversion was performed on this car, presumably when the car was under my uncles ownership.


The first picture are the three wires that attach to the coil, the two on the right run from the Ignition amp and the single wire on the left is the hot wire. Cheers to you sir for whatever advice you offer...