I’ve had an ongoing problem with the ignition for a while … sometimes after the engines been warm it won’t start the next day, then when it’s been left for a while it will suddenly fire up …
… I had the engine rebuilt about 15 K miles ago and a brand new plug harness installed so it’s not that … all new ignition wires dizzy cap and a new amplifier … injector caps are in excellent condition. It usually starts and runs fine, but this problem has been ongoing since car was overhauled … it doesn’t happen all the time but seems to have a mind of its own with no predictable one thing
I think the problem lies in a standard fitted OEM coaxial wire that runs under the bulkhead to the amplifier … its unmistakably different and thicker than the other wires. This wire on my car is original and may either be cracked and shorting, or no longer a good conductor due to brittleness and a lifetime of heat ( car had been boiled dry when I bought it some 15 yrs ago )
QUESTION … WHERE CAN I BUY SOME OF THIS SAME TYPE OF COAXIAL WIRE THAT RUNS UNDER THE BULKHEAD TO THE AMPLIFIER? … (((( mechanics won’t touch it because every time I take it in to the shop it starts and won’t reproduce the problem, leaving me in utter frustration ))))
It seems like il need to do the job myself but I don’t want to screw up … I know it’s a coaxial wire but Is this a SPECIFIC type of wire ie., thickness, ohms, silver coated copper strand etc???
I was under assumption this had to be a “special” wire … I read if you don’t get correct replacement you could fry everything back to computer brain in trunk
Mind you though … that particular wire transmits high amp and generates a lot of heat … regular wire might act a bit unstable, which is maybe why jag used coax …
The coax wire simply sends a signal to your ECU from the ignition, “telling” the fuel injection to operate. Not high amps, and no heat. It suffers from heat in the engine compartment , gets brittle and can fail. The reason for the “Coax” is to shield the signal back to the ECU from electrical interference coming from spark plug wires and such. Nothing more.
OK fair enough … but if this (coax ) wire transmits a signal TO the ECU from the ignition wouldn’t it need to be a specific ( at least very similar ) type of wire to ensure correct rate of current flow and ohms … ??? Anything else might damage ECU or other electrical parts …
I peeled open (a bad part of ) this multi-layer coaxial wire to see what to replace it with … it has an insulated inner core of silver coated fine copper strand with a second outer layer of fine metallic mesh which was also covered in insulation, making the wire a lot thicker than normal … about 5/32"
Maybe silver coated is no big deal but jag used it for a reason???
Go to your garage and see if you can find the old C.B. antenna you hung on the wall way back when. Cut a piece of coax and use it. Or, take a walk to the house next door, the one with the old TV antenna on the roof, and ask if you can cut a piece of coax from it. Use it on your car. There is absolutely nothing “special” about the Jag. coax. You could even use plain ole wire if you routed it carefully enough.
Well this "non-start " issue is really getting up my nose … it’s the kind of thing I can almost predict according to type of day (ie cool warm blistering hot or humid etc ) length of drive, whether needle is on N, how long it’s been on N, if it’s summer or fall, etc .
IT JUST HAS TO BE THIS WIRE … IT CANT Be ANYTHING ELSE … its either shorting out or failing to transmit the right signal … whatever the case, HEAT is the key factor …
… I noticed if car cools down SLOWLY it’s almost a guarantee the injectors won’t fire at all … the engine freely wheels over and over but it just won’t fire … it’s like … nada.
Sometimes it will stay like this a few days, then after the wire has cooled ( slowly retracting in its old brittle case like some kind of life transforming chrysalis, ) it seems to regain normality and will fire up like nothing ever happened …
I’ve noticed this cycle seems to repeat itself … When it starts after a long down spell the car really seems to ACT … it will really be on form, firing perfectly like it’s just been tuned up … that will mark (the beginning point of ) a gradual lessening of performance until the next refusal to start comes round again. At that point it’s just GGGGrrrrr.
This is why I feel I need to find the right wire … one that can combat heat … heat is the real culprit.
It seems like your next step is to replace a section of coax, if you are sure that is the problem. You can use RG 59U, or RG 6U, it doesn’t make any difference to the car. It’s not as though you are installing a HDTV. Another suggestion for you is this- I found, on “the other” Forum, a troubleshooting write-up that covers just about any “no start” condition. You can look for it yourself, I think it is right at the beginning of the XJS section, a PDF file, or I can send it to you if I have your e-mail address, OFF LINE. It is a step by step , well written account. I assume you have already read Kirby Palm’s “Book”. When the car refuses to start, you have done continuity tests on the coax, and checked for a short to ground, right? That’s the best I can do.
I read Sections of Kirby Palms book so many times I have nightmares … there’s so much to chew on … I have various pages stapled to the garage wall for quick reference
Sometimes it can be a challenge extrapolating the message from the words but that’s another point
But to your other point … I’ll insert a new section of coax to replace the old original … ( it’s bizarre really … entire engine and gearbox was R&R’d a few yrs back but most of the original wiring in engine bay re-used!! )
by coincidence I bought a 10 foot length of PTFE coated 24 ga silver plated copper strand coax wire this morning on eBay for $7.00 bucks … I think that should work
I still feel a bit iffy remembering the things everyone has said though … ie … oooooohh be careful what kind of wire you use … I’d watch it if I was you etc
Maybe this will help. There is no shortage of “Jag-Lovers” with more knowledge than I possess, who are not shy about jumping in if they think bad information is being handed out! So far that hasn’t happened, so I think you’re pretty safe!
Removed old coax and fit new piece today … car started and ran perfectly but I won’t really know if it worked until its been subject to same conditions that caused non-start.
those conditions were definitely not today … it was dry breezy and warm a light sunshine, a perfect California day … not cold at all but around 70 degrees Fahrenheit, absolutely perfect conditions for taking the cat out for a nice spin … my initial impressions were that it performed WELL … it was responsive and smooth like a jag should be … I found a good stretch to put my foot down and it sailed forwards … nicccce
but well wait and see what happens for those "certain conditions " when it gets warm
All good things have their own drawbacks… nice weather attracts lots of people, lots of people need roads to drive on … 1-2 -3 cars per person means crowded roads, pot holes, the occasional unwanted middle finger (and high speed car chase ) …but the sunshine definitely makes it worthwhile if you can put up with these things.
I am new to the Jag Lovers your assistance has been most helpful . My series 3 has a 6 litre HE engine . Touring very recently through Spain and France on very hot days it would quit spluttering first always outside a trendy bar where I would get ice lay it on a black box and coil that sits in the V valley .Before trouble came you could sense it missing a beat .
After 1600 glorious miles and mountain passes 30 miles from the ferry back to UK ,smoke poured out from under the steering column . Switched off no flames . The live wire had melted with the heat ,separated the wires and taped up and got back . I fear the wiring is standard BL stuff ,all new harness ,but am I right after your articles that heavier coaxial should be used . What is the black 4x4 inch box in the V engine valley for .
I have the same problem with my 1984 XJS … and did the ground continuity test back at Pin #18 at the ECU / EFI connector in the trunk. I had ground continuity which means that the wire has shorted out somewhere between the Amplifier (under the hood) and the rear of the car. I found this wire which is far superior to the original factory shielded wire and is also a very manageable size (.13" outside diameter) when compared to standard over-the-counter coax. 50 feet was app. $22. Emteq TFLX130-100 High Temperature 50 ohm Coax Cable .13 Inch O.D. 50 feet I wanted to attach a picture of the wire as part of my response but can’t get it to load.
Emteq high temperature (-55C to +150C) 50 ohm coax
Silver plated 7 strand center conductor
Tinned braid shield & bonded aluminum foil
priced per 50 feet, any continuous length _