Jaguar XJ 4.2 1976

When Hot,ignition will occasionally not even click when trying to start,leave for a couple of hours and it starts normally , auto electrician has tried every thing he can think of. currently bypassing the micro switch at bottom of gear lever/ this fault is not consistant and doesn't happen at any set time can happen three times in day or not for a couple of weeks, help please, mr lucas at his best>

 

Firstly what beast we dealing with here?????.

This might help, depends on your sense of humour.

The rest will follow when the car is known.

Eletrical theory as per Joseph Lucas.doc

 

Darrell,

I've moved your question from General Tech Help to XJ6 & XJ12 Series I, II & III 1968-1992 forum. Members here with the same model will be able to help.

Graham

 

Yowee, I am there at present.


But, it seems in my car at the point where Lucas joins GM as my car is a "lump".


I'm to the point of changing the starter and solenoid. Wires and realy have been changed. it worked for a bit.


True, the micro switch circuit on the shift tower was suspect. Still not eliminated as a cause.


When the weather improves, I'll get after it some more.


Carl

 

Darrell,

Thanks for the car info.

That "neutral start" switch may be the issue. Only time will tell with these intermitant things.

The starter relay is now quite old, and it is a Lucas relay. It is a robust thing in the big scheme of things, but my S2 cars had issues with that relay. I opened it up and carefully cleaned the contacts inside, then washed the internals with p/pack contact cleaner, and had no further issues with that relay.

Others have replaced them with a generic starter relay, and being in Australia, I would seek out an Ingrams Universal Starter Relay, H Duty.

Before removig the starter relay, carefully label the wires in relation to where thay go, none of our memories is that good any more.

The other issue that is common on these cars is the electrical section of the ignition switch. It is kind of easy ( more fiddly than hard) to remove from the barrel section, and can be opened up CAREFULLY, and cleaned internally and relubed. I have had 100% success with that switch rework over the years.

 

What else has your auto electrician tried so far? If we know what has been done already, it will help us figure out where your bug may be hiding.


Intermittent, only when hot problems that disable the vehicle are a real bitch because by the time you get it to the shop or your garage for testing, things have cooled and the problem is gone.


I was haunted by a similar problem for years. The way to deal with it is so simple I can't believe it took me so long to see it. I guess answers are only obvious once you know what they are. The solution is to travel with your test equipment, tools, manuals, notes, hard copies of internet info and any other documents in the car at all times. The minute the bug shows up, start testing.


When the problem shows up again, if the start relay isn't clicking the first thing I would test would be the wire that goes to it from the ignition switch for +12V (when the key is turned to start), and then the wire from the start relay to the neutral safety switch for ground (when trans is in park). -Paul

 

DarrellE. sorry everyone, still trying to find my way around. car is 1976 xj6, mileage, anybodys guess, have replaced ignition switch, it collapsed, currently bypassing micro switch on gear lever bottom, iso0lated electronic ignition away from block, as someone suggested heat buildup after decent trip, thank you every one for your input, I will keep you informed, it has also had new starter, not mechanically minded so probably shouldn't own a jag, Had a 1978 xj6 as family car in early 80s and it never missed a beat. thanks again. Darrell

 

Thanks Darrell,

The Opus on a S2 can be fickle, but would not be causing what you describe.

I am still thinking the starter relay may be having a moment, as we "older" ones do at times. It is mounted on the bulkhead panel, just right of the bolt that secures the guard strut bars, so it gets very hot in that location.

Time will tell, and that by-pass may well be the culprit.

We will wait for your response when it happens again.

 

Another way:


Add a jumper from the starter solenoid. Secure it safely under the bonnet. the next time, the engine will not crank, turn the key to run and connect that jumper to battery+. if it cranks and the engine fires, the issue is in the relay, ignition switch or the connecting wires. and, possibly the neutral start micro on the switch tower.


This jump can exonerate the starter and solenoid. Sorta. As there is still the battery + cable to the post on the firewall and the cable from that post to the starter solenoid. The connections, and the cables themselves may be flakey.


Cables may look good, but be bad under the insulation.


Carl

 

I've been meaning to do a write up on the Jag starter relay for a while now, this thread has convinced me to get the whole thing done rather than just post bits of it here. Perhaps this will be of some help:
https://www.jaguarforums.com/forum/x...st-fix-132768/

-Paul