Cranks, but does nt fire and run.n

Not sure if the fault is in te original jaguar or in thr lumped part.

i’ve not been driving it for months. for a time, i started it and let it run in the garage. Teh last ime, it did not start, but did crank heartily. For a time, the gas guage shwed quite lw on each tank. We added about 5 gallons to the left tank, charged the battery. Great crank. no run. But, now the gas guage is not responsive. and, the tach needle does not repond. Igntion or fuel issue?

Fuze issue?

wire issue?

Jag harness?

lump harness.

I will study the S57 later today. and, after the storm goes by, check out what might tbe the fuse involved.

lump set or jaguar set.

5 gallons should be plenty to prime the pump. That still leaves you with fuel and spark.
Try fuel first, correct tank selected:
valve stuck? - do you have return into the tank if you look way down the filler neck?
or pump - noise at least?
or injector stuck.

The fuel sender can be checked, when you remove the rear light and short the wire to the tank, ignition on, the gauge should peg. if it doesn’t the switch is highly suspect.
if it pegs the float has sunk or the gauge is stuck from sitting. I don’t think anything in the fuel system is fused!

as to the needle… if it is different to how it used to be it’s an ignition issue but that’s so easy to check.


[quote=“Cadjag, post:1, topic:429423, full:true”]
Great crank. no run. But, now the gas guage is not responsive. and, the tach needle does not repond. Igntion or fuel issue?

I would suspect ignition, Carl - have you checked, with a spare spark plug, if you have sparking?

You can check if you have power on coil ‘+’; the ign key may fail to power the ‘original’ white circuit. It depends somewhat on how much of the original wiring was kept - no power on the white circuit will give the symptoms described. The batt warning lamp should originally come on with ign ‘on’ if the key gives power.

The involvement of the inertia switch, being tripped, may warrant investigation. A fueling issue would relate to the engine fitted and rewiring to match - not covered in my manuals of course…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Good evening Carl - and still a very happy and healthy year for you and your cars!

As you describe it I’d almost be sure it is a - simple! - ignition problem. - A petrolhead like you (no offence!) would have smelled if there had been a fuel leak drying out the car, - Does the LS engine have any ignition relays or anything of the kind that may go wrong?

Good luck


75 XJ6L 4.2 auto (UK spec)

Evening or now it is morning here! best New year wishes to you and yours.

Petrol head, gear head? No problem, guilty as charged!

Not a matter of spilled gasoline. Well, a bit. Son was over and added 5 gallons to the left tank. I had suspected that i just ran the tanks dry or too low for the pump to pick up.

Son supected ignition switch issues. I not so much. NOs sweithch installed a few years ago. How many? son and i disagree!!!

Yesterday, I had another go at it. Fuel selection switch now works. Gas guage reflects left tank about half full. Right tanmk, very low. Makes sense.

Teh wipers also work, as does the radio.

So far, i see the ignition switch aquited.

Under the bonnett.

As frank suggested, a sparlk test.

And, yes, as you suggest, ifnition and fuel pump relays.

And, the fuel pump is fused, as i recall. Many years since I wired up the under bonnett stuff.

The car is outside, and more rain expected to day. it may be a day or so before i try again.
Best Wishes


It looks complicated but there is no fuse originally, just the ignition switch and the AFM and the safety switch and and…

Thanks. Bt, i have acquited the behind te dash jagar part

now it is under the bonnet, to the Cadilac stuff. Relays and fuses abound!!!

Day off today. our version of football, the pa off games in progress.



[quote=“Cadjag, post:5, topic:429423, full:true”]
Yesterday, I had another go at it. Fuel selection switch now works. Gas guage reflects left tank about half full. Right tanmk, very low. Makes sense.

Still, Carl; do you have sparks when cranking? Also, the gauge reading is independent of the changeover valve position. You may draw petrol from an empty tank - it’s not unique for the changover valve to fail…:slight_smile:

A somewhat cumbersome way; dram each cylinder with a teaspoon of petrol - then crank. If the engine catches and runs briefly; it confirms that the ignition is working.

The ignition system is a self contained sub system - with power on coil ‘+’ (jumpwired from batt ‘+’ to bypass ign switch) a functioning ign system will work irrespective of other faults…

More intriguing; in wet weather, dampness of high tension leads and/or dist lid will disable ignition…

xj6 85 Sov Europe (UK/NZ)

Or just try starting fluid and if it fires it is a fuel issue. All the basics Carl knows very well.
In the original the ECU gets its rpm information from the distributor and fires all six injectors with every third spark. If it gets fuel (which you can tell easily from the return into the tank unless the system was changed) I‘d go to the tailpipe and see if there is a fuel smell. If not either it’s not firing the injectors or they are all stuck.

Frank & David:

I have satisfied myseltf tht the fault is not behind the dash. The gas guage responds to the tank selection switch correctly. it had not done so!. i attribute that to exercising a switch that has been dormant for quite some time.

My focus will be now, under the bonnet. depart from jaguar stuff to the Cadillac stuff.

Aye check for spark with a spare plug. i have one with a ground lead for that purpose. plus check the inertia switch. long shot, but easy.

I do have a relay under the bonnett for the fuel pump and I think I installed a blad fuse.

Priming the V8 is not feasible vai a spar plug hole ss it is in the OHc 6. I may have some ether to squirt in to the intake Not sure if i can do that drectly.

I can crank with a specia wire while under the bnnnett. Installed when i had starter issues.

However, it will be a few days. when our storms give us a break and when i do my med visit this thursday.

Thanks to the both of you.

Tske Care.


So if the switch that changes tanks didn’t work correctly at first it would be highly suspect as the contacts for the gauge are of course not the same contacts as those for the three solenoids.

Without power to the solenoids it should run off the left tank though. So keep going in the engine bay. And just check that there is any fuel pressure on the lines, then it should at least cough if the rest was okay.


Aye, but not for a while. It is just after 8 AM. Temp is 37F. Too cold for me! i do heat far better than cold!

Son was by yesterday. We had another bout on the jaguar. under the bonnett. all fuses that might be involved checked. Blade fuses as a part of the transplant.

could not find my 'spare" spark test plug. but, used a timng strobe to detect spark at any cylinder. NO flash. Clear, no spark! supports thery as the tach needel lies idle when cranked.

Checked connections at coil/module. tight.

Remaining theories:

  1. Bad coil module. Not hard t replace.

  2. Optiite distributor That is a PITA to swap out. Knwoning that, when I instaled the GM engone twenty years ago, i installed a genuine new Optilite, That was sans bonnett and radiator. Now that was nt easy, now, oh boy!


1 Like

I’m not familiar with the ‘Optilite’ distributor, Carl. But if it uses the same external ign amp (4-pin) module as the Jaguar HE ignition - there should be 2 wires from the dist to the external ign amp…

These modules are natural suspects - and it is generally easier to replace a module than to test for module failure. Any fault in the dist (pick-up) can be addressed with the dist in place - access depending. of course.

It may be a coil issue - have you checked coil primary resistance? Also, since external amplifiers are usually powered from coil ‘+’, as is the ignition itself, a jump wire from coil ‘+’ to battery ‘+’ is another quick test to bypass other electrical faults…

xj6 85 Sov Europe (UK/NZ)

Thanks Frank.

That is next on the agnda. The GM ccoil & module is packaged in such a way so as to make it near imssible to jump +battery to = coil!
There is a way to bench test. Complex.
i have the Gm manual iut for research. it is a big tome!

today is out. and the next. Doctor visit. and a day after to recover.



Good luck, Carl! … First, with the doctor’s visit, then with the coil!!

All the best


75 XJ6L 4.2 auto (UK spec)

Thanks, gentlemen!!

My son came over yesterday. Armed with another coil and mdule via Amazon and Ebay. Swappd mthem in. Still great crank. No fire. Went over fuses and did some contact cleaning. No fire, again.

checked inertia switch. OK.

went to relay rack. This is GM territory. One labeled ignition. swapped in another relay. No fire.

OOOPs! blackeed wire! At the Igniotion relay. Stripped moff shrink tubing. revealed a solder jint. My work! Rosin dust!!! Removed wire. Replaced. Temporary twist joint and tape. INSTANt Start on crank.


Son displeased with solder. Looked good yo me. Nope. Next vsit will use heat set +crimp connectors. I have seen others use them.

Well, that solder joint was good for about twenty years??

Son a master diagnostician.



Awesome! Solder again, good for another 20 years or more? Crimp will also do… happy you guys figured it out!

Can’t argue with success, Carl…:slight_smile:

‘Ignition relay’ is obviously an add-on, but should show some general symptoms beyond ‘no start’ when failing?

A well done solder joint would last for ever…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Great you guys made it! Now good luck with the weather to take her out for a spin to recharge the battery :slight_smile:

Good luck


75 XJ6L 4.2 auto (UK spec)