I picked up a 1979 XJ12 some months ago to add to my collection. They are getting pretty rare. This one has about 83k on it and looks to have sat outside for about ten years, flooboards, interior, gone… Anyways, it supposedly ran when parked. The engine turned over so I was pretty hopeful in the beginning to at least get it running to move it around and eventually into the garage. I drained a tank, put new fuel in and hooked up a new fuel pump, so got good fuel pressure (caught it on fire initially for a few seconds when a hose blew, yes, they all need replaced). Put on a new distributor cap and plugs etc. etc. So I have spark and fuel, but it acts like it is out of time. Lots of popping and belches out the intakes. I have checked the plug wires for correct fitment like ten times, have the distributor cap off again and everything looks good. I am not as familiar with the older Lucas system so am checking here to see if I am forgetting anything to do with timing on that system. If the ignition system or timing is not the cause, then I am thinking something internal. The rotor spins on the dizzy so at least I have confirmed that is working correctly. The motor turns over nicely with no apparent obstructions, like dropped valves etc. I have the dizzy on TDC and need to crawl myself under the car to check the crankshaft marks (cold and miserable outside right now). After that I am a bit out of ideas. Any ideas you may have would be great. Thanks.
I will also add the fuel injection harness is in pretty bad shape, so it is possible I am getting some misfires on the injectors which could cause the problem. I need to get another new harness made which is a bit time consuming.
I have a '74 XJ12. One time when I had ignition failure in mine, it was a break in the circuit board inside the OPUS amplifier, caused by corrosion, water getting in. I was able to solder it and put it back in with sealer.
Check it again, Matt - it is typical of wrong ignition sequence…
On the V12 it is 1A-6B-5A-2B-3A-4B-6A-1B-2A-5B-4A-3B, the ‘B’ being the ‘left’ bank. But you must start at the correct cylinder. The normal reference cylinder is 1A (frontmost, A-bank), but either #1A or 1B can be used. (The ign sequence on the V12 is like two xk engines side by side but one revolution apart…)
With engine set to the TDC mark; the rotor in the dist must point to the plug cable for the relevant cylinder - and that piston must be at the compression(!) stroke. Which happens alternately for #1A and #1B with the engine at TDC - pure guesswork gives 50/50 chance of beginning at the wrong, or correct cylinder…
That done correctly, you then hand(!) trace the #1A (or #1B) plug lead to the dist where the rotor points and plug in that lead. Then hand(!) trace each plug wire from the cylinders to the dist lid and plug them in vacant spot counterclockwise on the dist lid from the reference cylinder used - in the ign sequence.
The crucial pointer is the rotor position; it always points to a cylinder ready to fire - at the TDC mark it is either 1A or 1B. I have managed to get the sequence wrong on all but one-cylinder engines - and it is very, very easy to get the V12 wrong. Though two crossed wires will not cause a non-run on multicylinder engines…
You may of course have done all things right, and the fault is elsewhere - but repeating the wrong thing 10 times, even with the best of intensions and highest precision, doesn’t right a wrong…
xj6 85 Sov Europe (UK/NZ)
One way to verify that one has chosen the “right” TDC cylinder is the valves. both should be closed to denote a power stroke.
45 year old vehicle. Sat for the last 10 years, to the point floorboards rusted out. Injector harness shot. At least one injector or fuel hose leaking. Popping and belching from the intakes. You need to pull the injectors and make sure they are operational and flowing to spec. If the hoses are leaking, then you can bet, the injectors have never been touched. SD Faircloth ps. the pre-HE injectors are like gold nuggets. Extremely rare, except in Europe where you could pay $300-$350/each.
Yes, I know how easy it is to screw up the sequence! I just completed a V12 rebuild and on first start it was obvious the timing was off. I inadvertently put the wires clockwise on the dizzy. Once I got them the right way, the engine started right up. I blame the absentmindedness on working on a bunch of other dist. systems prior. On this one, I checked to make sure the crank was on TDC and the rotor was pointing to 1A on the distributor and did hand check every plug wire on the dizzy. Next check will be to pull the AC pump and actually verify where the pistons are at by pulling the spark plug then go from there. What I need to do is pull the injectors, clean or replace, replace the hoses, replace the plugs and check the timing again, then go from there. Probably a good idea to complete a comression check while the plugs are out. I will probably have a lot better luck after all of that and insuring the injectors are firing properly. Thanks
But did you verify that 1A was on the compression stroke, Matt?? The rotor position does not make it so…
There are no easy way of verification; either turn the engine towards TDC and notice pressure build at the plug hole in 1A, or remove A-bank valve cover and ensuring both 1A valves are closed at TDC. Or assume you guessed wrong initially and use 1B as reference cylinder; replacing plug leads accordingly - and try starting…
You certainly should run a compression test, at least for peace of mind, before doing extensive, and possibly wasted, work.
Starting an engine cold turkey after 10 years of storage is fraught - what did you actually do before cranking up…?
xj6 85 Sov Europe (UK/NZ)
Is there no modern analog that can be used?