Hy, i recently bought a XJ 12 5.3 H.E.
It did run well, idle well and start well when hot or slightly warm. The only issue was when starting from cold you need a few tries and fiddle with the throttle to get it running. Then it starts with 300-400rpm. When you pull it up with the throttle once it setrles at 700rpm and idles perfectly fine and smooth, runs perfectly.

So, since i had no clue about the service status of the engine i did a complete service and check on the engine:
- There was a huge vacuum leak at the vacuum reservour of the brake servo
- the vacuum advance of the distributor was leaking and broken

I also did following things:
- checked the advance system in the distributor
- new plugs with checked gap
- renewed all fuel hoses in the engine bay
- checked all injectores, put in new caps, filters and seals
- cleaned throttle bodies, checked clearence
- renewed all vacuum hoses in the engine bay
- checked AAV (works fine).

Build it up again - startet it - exactly the same
Any ideas what i can look after now?

Thank you in advance!

 

Good work so far!

The "could be list" might get a little long. But you've got a good start on things

A key player in cold starting is the CTS- Coolant Temp Sensor. This is what tell the computer that the engine is cold so extra fuel can be provided. Sort of like a choke.

Only about $25 and 15 minutes to replace. Worth a try. It's on the left water rail just behind the thermostat

If you want to test rather than just replace we can give you the specs

Cheers
DD

 

Thank you for you quick reply

I forgot, i also replaced the CTS and the Thermostats since i already had the intake Manifolds removed. That reminds me that the clip of the connector to the CTS is missing. I read something about faulty connectors, so i will try to replace the connector next.

Also, since i assume this will be the next question: Yes i did retighten the nuts of the intake manifolds


What i also noticed:
There is quite a lot of white smoke after cold start. The engine did not run much and always only for short periods of time. The smoke comes symetrical from both exhausts, there is no coolant consumption, so i stress this not too much by now. I kinda suspect the main brake cylinder. slightly leaking there.

 

That "fiddle" with the pedal on cold start is familiar.

I read your list, very good, as Doug said.

The HT leads are suspect, these beasts really need a Blue Cracker of a spark to get them awake when cold.

The AAV, I know yoiu checked it, is suspect. 1000+RPM cold is normal, settling to the 700ish as the coolant heats up. I am not seeing that in your scribe.

Not sure where you call home, as some markets have all sorts of odd things we never got, helps a lot really if we know.
In the meantime, try this:

Ign ON and then OFF 3 times, NO attempt to start it. On the 3rd ON, press the accelerator to the floor and back up, GO FOR START.

The on/off really primes the fuel system, the pedal down/up actuates the Injectors and squirts some Bang Juice into the beast.

If that solves, changes things, the list is shortened somewhat.

One of my PreHE ONLY starts like that, and after 35 years, I care not, and declared it female,

Another suggestion.

Take you Digital Volt Meter, attach the Red lead to the +ve of the coil. Earth the Black lead. Crank the engine and observe the volts while that is happening. Any more than a 1 volt drop and you have spark issues. ALL mine, and most others here, have had a relay fitted in that WHITE wire, That ensures a good supply of battery volts during cranking. #1 cause is a tired Ignition Switch electrical section. Age related more than anything else. I have a PDF on refreshing that switch if you need/want it, just ask.

 

I will try this, but for now i have to wait for the temperatures to rise - not fun testing cold start at -12°C. I live in Austria

I keep you updated as soon i can test the suggested things.

Edit: The battery is not the best either - maybe the voltage drops to far for a good spark. I have a new AGM battery here that would fit in. I know that the AGM will not charge properly but to test the cold start it should work, or could it damage anything?

 

I tried to start with priming multiple times and pressing town the paddle befor starting. I can hear the injectors when doing so but it does not start better when doing so.

Soo, its still cold so i had time to have a better look in the ignition system.
The leads were a little britte and the cap was quite worn. I replaced them now. Also i put in a new battery.

My dealer recommendet to change the two coils to one high performance coil. I took out the two coils but my dealer forgot to send the high performance coil so i cant test it now.
Also i read that the high performance coils do have temerature and life time issues. What is your opinion?

Also do you know what to do with the +12V connection to the second coil in the front from the relais in the front? Just plug it off? Or leave keep the + connection to the coil in the V?

 

There are two wires, one linking the two + posts and one the two - posts. Just disconnect them from the coils and remove them from the engine bay.
The replacement coil MUST be of the correct OHM-age for the HE system or you will fry the ignition. eg
https://www.ebay.co.uk/itm/335158552...Bk9SR_6PhO-fYw

 

Im getting one with 0.62Ohm, should fit the H.E. Engine.

The Coil in the front has three connections. Two connecting the two coils. And one on the + connector to a relais on the front above the fans. And i was wondering what to do with the last one.

I would assume thats a additional +12V connector to hold up the voltage? So just blank it - or keep it connected to the main coil to give it a more stabe +12V?

 

What does the relay control? It might be the 12v feed for the relay trigger circuit, if that was earthed by a temperature switch for instance? In any event, rigging up an ignition switched 12v to it will do the job.

 

I just checked the plans for the lucas ignition and you are right, there should be only two connection.

It is conneted to this relay: does anyone know what this controls? i have to have a closer look to it, what pins are connected to the coil to understand this.

 

just spent some time in the engine bay and in workshop manuals. Still didnt figure out what the relais is for. According to the manuals it could be the cold start relais, but my car doesnt have cold start injectors.

But i figured out that the connector to the coil does not operate the relais since its still switching when i turn the ignition on and i have a 12V on the connector to the coil.
When i unplug the relais the fuel pump does not prime anymore when i turn the ignition on. Bjt the fuel pump relais is the one next to it.

Anyway, i will blank off the connector to the coil. And then i have to wait for my new coil to test further.

 

The essential relays are the "Main Relay" and the "Fuel Pump Relay". The third relay is probably an idle over ride relay or feedback inhibit relay. Different years/markets had some variations. The best way to ID them is to note the wire colors and go back to the schematics.

And I'll add that not all schematics show all the different build configurations

What year and original market is your car?

Cheers
DD

 

In which case there must be some sort of elecrtrical connection between the two relays. If you use a test light or meter you can identify the pole on the FPR that is live/not live when you disconnect the 12v to the unknown use relay.

 

I did some more testing and it appeaars to be the main relais for some things. there is a thick brown +12V going to the relais and several connectors from the relais.

Since i am still waiting for my coil i was not able to measure the voltage while cranking yet. BUT i did measure the voltage with ignition on and compared it to the battery voltage: Battery 12.6V, Connector to Coil 11.8V.
Well thats not too good, so i checked the + Connector at the Firewall wich was pretty corroded:


cleaned that up and also checked the ignition switch. That didnt look too bad, but i also cleaned the contacts.


Put it all together, measured again and now i have 12.6V at the Battery and 12.3V at the connector of the Coil.
Still too much Voltage drop, since there is no Load when im not cranking?

Also i cleaned the switch a bit too good and didnt put grease into it. it switches pretty rough now. do you guys have suggestions wich grease to use? pole grease since it should not be conductive?

Now im waiting for the coil to start it up and do some more testing

BTW the Car is a XJ12 Series 3 Sovereign, date of manufactor 13 Sept. 1984, original market germany. According to Jaguar Heritage Trust since there are no original documents coming with the car.

 

Grant advised me to use the coil positive from the ignition switch to activate a relay that is connected to that firewall post, this relay load side going to the coil positive. This ensures a good 12v to the coil abd also takes the load off the switch. I used a fused relay to protect the coil and all good, better starting.

 

News from my research. The second connector to the front coil + is standard and appearentlyis the only ignition + connection to the ignition system. I found this in one of the many different plans i have collected by now:


183 is the ignition amplifyer with 4 cables coming out, just like mine.
293 is the ECU, thats where i measured the "lower voltage"
95 is the tacho
38 is the mysterious connector in the front...the only ignition+

so i have to put in the + part of the connection and hook this up, it wouldnt work otherwise.

here is another plan to this system:


Now i only have to find out why there is one too much connectors ro the + side of the main coil

 

i spent two hours measuring and testing today and i can't find what the third connector to the plus pole of the main coil is. I looked up pictures on the internet, it appears to be original:


Its a thick plane white cable and goes into one bundle with the white/blue tacho cable and the green cables from the kickdown switch. The bundle goes down in the V and then to a connector on the right front, near the ballast resistors of the fuel inection. There it goes up and back at the side where i cant follow it anymore.

I measure 0.3V under Battery voltage when ignition is on. There are about 300Ohm resistor to the ignition switch. Anyone has a idea what this is since i dont know how to find out.

Since it seems to be original i will hook it up to the + from the new coil, but i am curious what it actually is for.

 

Later I'll go look at my car for a memory refresh.

In the meantime....

Maybe....

1 white wire from ignition switch to main coil
1 white wire from main coil to secondary coil
1 white wire from main coil to amplifier

Cheers
DD

 

that was my first thought too, but according to the plans the ignition feed goes to the secondary coil, just like in my car. The one on the secondary coil has 0.0 Ohm to the Ignition switch. And the one on the main coil has a 300ohm resistance to the ignition switch.

 

Schematics are sometimes correct in terms of the electrics but not the actual physical layout of the looms and wires.

On my car, which was converted to single coil, there are presently two wires at the coil "+". One to the ignition switch and one to the amp.

The secondary coil, when it was in place, had its own dedicated 2-wire sub-harness. When I removed he coil I removed the harness. The white wire from that harness was the third white wire at the main coil.

Anyhow, the 300 ohm resistance you mention suggests a poor connection or damaged wire or corroded wire.

Cheers
DD