1986 Jaguar XJS Ignition Quandary
#21
12-07-2023, 06:16 PM
FYI, all of the spark plug wires that I’ve been using our carbon core and actually did not even consider a dirty distributor with rogue carbon trails. Interesting phenomenon with the Packard. For what it’s worth, I too used a vacuum guage and I teed into the back of the passenger side manifold. Oddly enough, the 18° BDTC without vacuum advance would need to be increased to 19° in order to achieve the highest vacuum of 17 inches.
#22
12-07-2023, 06:19 PM
A comment on plug wires,
Depending on the type of plug wire, if you have fiberglass/carbon cored wires, as used for radio static suppression, you can break the inner core with sharp bends, or sometimes the metal ends get separated from the core. metal core wires of course, have much lower resistance.
IIRC, graphite core wires should have something like 600-800 ohms/inch resistance, if you get one a lot higher, something is wrong.
My theory, on induction induced bad timing readings may also include dirty distributor caps such that some amount of voltage crosses over to other plug wires even if all plug wires are good, giving an improperly timed flash on the light.
Just about a year ago, I had bad timing readings on a V8 motor, the light said the timing was 20* retarded, attempts to rotate the dizzy to make the reading right, resulted in an engine that didn't want to run as it was way too advanced, so i reset it using a vacuum gauge (vac advance connected and operational, tee to vac gauge in the vac line to dizzy, adj dizzy to highest vac reading at idle and back off 2" of vacuum.)
The wires were new looking Packard wires, and I didn't want to remove or damage those, so i replaced the plugs and the dizzy cap. Timing reading went back to normal, the vac gauge timing method had me with in 2* of the 10* static advance (vac adv disconnected) I was seeking. It was either the plugs, which were very dirty, or the cap causing the problem. The problem back in 1975 was bad plug wires.
Doug
Depending on the type of plug wire, if you have fiberglass/carbon cored wires, as used for radio static suppression, you can break the inner core with sharp bends, or sometimes the metal ends get separated from the core. metal core wires of course, have much lower resistance.
IIRC, graphite core wires should have something like 600-800 ohms/inch resistance, if you get one a lot higher, something is wrong.
My theory, on induction induced bad timing readings may also include dirty distributor caps such that some amount of voltage crosses over to other plug wires even if all plug wires are good, giving an improperly timed flash on the light.
Just about a year ago, I had bad timing readings on a V8 motor, the light said the timing was 20* retarded, attempts to rotate the dizzy to make the reading right, resulted in an engine that didn't want to run as it was way too advanced, so i reset it using a vacuum gauge (vac advance connected and operational, tee to vac gauge in the vac line to dizzy, adj dizzy to highest vac reading at idle and back off 2" of vacuum.)
The wires were new looking Packard wires, and I didn't want to remove or damage those, so i replaced the plugs and the dizzy cap. Timing reading went back to normal, the vac gauge timing method had me with in 2* of the 10* static advance (vac adv disconnected) I was seeking. It was either the plugs, which were very dirty, or the cap causing the problem. The problem back in 1975 was bad plug wires.
Doug
UPDATE
Doug – Thanks so much for suggesting a “dirty“ or carbon tracked distributor. Using an ignition test penlight that voltage was tracking all over the distributor. In fact, one of the strongest instances of ignition spark was traveling through the top of the distributor following the now vulcanized rubber vent hose. Even the timing light would register when it was connected around that hose.
#24
12-07-2023, 07:48 PM
When you say ignition test pen light, do you mean something like this?
http://Akozon Ignition Test Pen Prof...a.co/d/d2NsGGU
http://Akozon Ignition Test Pen Prof...a.co/d/d2NsGGU
#25
12-07-2023, 08:19 PM
#26
12-08-2023, 12:18 PM
I have owned my 1986 Jaguar XJS for about 15 years. Incidentally, I recently restored my Rolls Royce Silver Shadow and I’m also an owner of a 1966 MGB. So needless to say I am a glutton for punishment and personally restored each one.
I recently rodded out the radiator and installed dual electric fans from a 2001 Nissan Maxima. The car currently runs at 82°C (82° thermostat installed). The car runs beautifully. However, I am concerned because after checking the timing at 800 RPMs it is 18° BTDC with the vacuum removed and plugged. It is 30° BTDC with the vacuum connected. Interestingly enough, I get an additional 18° advance when I reach 3000 RPM. I have driven the car vigorously, trained very steep hills with no preponderance of pinging or pre-detonation. How is this possible?
I was concerned that the harmonic balancer had slipped, so the timing marks on the balancer would no longer be relevant. However, I have chaulked the pulleys and there is absolutely no movement. I simply cannot imagine that the Woodruff key could’ve given way. Keep in mind, the timing has remained constant as reported above.
I should also mention that the current distributor adjustment screw is totally retarded. Also, the engine will accept more advancement and actually responds with increased vacuum to 18 inches.
I recently rodded out the radiator and installed dual electric fans from a 2001 Nissan Maxima. The car currently runs at 82°C (82° thermostat installed). The car runs beautifully. However, I am concerned because after checking the timing at 800 RPMs it is 18° BTDC with the vacuum removed and plugged. It is 30° BTDC with the vacuum connected. Interestingly enough, I get an additional 18° advance when I reach 3000 RPM. I have driven the car vigorously, trained very steep hills with no preponderance of pinging or pre-detonation. How is this possible?
I was concerned that the harmonic balancer had slipped, so the timing marks on the balancer would no longer be relevant. However, I have chaulked the pulleys and there is absolutely no movement. I simply cannot imagine that the Woodruff key could’ve given way. Keep in mind, the timing has remained constant as reported above.
I should also mention that the current distributor adjustment screw is totally retarded. Also, the engine will accept more advancement and actually responds with increased vacuum to 18 inches.
You can if you want eliminate the distributor. I did on one of my cars to take full advantage of the extra horsepower Alcohol offers.
( Ethanol alcohol not that cursed Methanol alcohol)
The one I did it on was a race car where the rules required carbonation and didn’t allow EFI.
HERE’s the deal. The cost of repairing a distributor is higher than buying a basic Megasquirt.. Whrn you add the difficulty of using a timing light on the bottom of the car and how little adjustment is available. To the fact that I haven’t found a way to adjust the distributor while the engine is running. You can understand why I eliminated the Distributor, like the factory did on the 6.0 liter engines. I didn’t use the slick factory valley cover I just yanked the distributor like a bad tooth and made a little plate to cover the hole.
The V12 6.0 liter is dry fired on the waste stroke so you only need 6 coils. Ford used those on their V6 So they are readily available, you don’t have to use the Jaguar coils.
However next time I’m going to use coil on plug. Probably from a LS Chevy. Those are nice and compact and really put out a massive spark.
Here the advantage. Stock you can check and adjust your timing with a laptop.while someone else is driving ( please)
If you want you can also adjust the timing on each injector instead of batch firing them the way the factory does. What that will do is get you slightly better fuel mileage and you won’t get the deposits on the back side of the intake valves the way you do now( which costs you fuel mileage and horsepower)
For that though you have to spend about twice as much and get a Megasquirt pro.
Us Racers love aftermarket ECU’s
It opens up a whole new world of power. Alcohol. Turbo, or supercharging. Better reliability. ( yep, even with turbo charging).
( don’t try this without access to a chassis Dyno). And if you can’t figure out which wires go to which sensors etc the help of someone who can. Realize these guys tend to be very smart but will need to learn the V12.
#27
12-08-2023, 12:51 PM
Kevin,
Thank you.
The wire is from the old days, and my learning curve without many tools, manuals or money.
Lots of discussion on my method, as used by many my age/era.
I, and you, know there is a variable to the wire method as the piston "rocks over" TDC, which equates to degrees of crank rotation.
Since I only use it to set the base timing for the distributor, then "drive time" after that, the few degrees that will be passed on to the jackshaft are negligible at best, and then the wear factor of the drive and driven gears at the distributor, make it zero to me.
That Boomerang is fine, except for the backward nonsense. My PreHE is just about to nudge 800K kms, and the base engine is untouched since Coventry in 1976.
The biggest killer, apart from the above, of that Boomerang, is OVER HEATING that engine, and sadly that is getting more common than I like.
Thank you.
The wire is from the old days, and my learning curve without many tools, manuals or money.
Lots of discussion on my method, as used by many my age/era.
I, and you, know there is a variable to the wire method as the piston "rocks over" TDC, which equates to degrees of crank rotation.
Since I only use it to set the base timing for the distributor, then "drive time" after that, the few degrees that will be passed on to the jackshaft are negligible at best, and then the wear factor of the drive and driven gears at the distributor, make it zero to me.
That Boomerang is fine, except for the backward nonsense. My PreHE is just about to nudge 800K kms, and the base engine is untouched since Coventry in 1976.
The biggest killer, apart from the above, of that Boomerang, is OVER HEATING that engine, and sadly that is getting more common than I like.
I also keep meaning to modify a Banjo bolt to take oil and prelube the engine after rebuilding or if it’s been laid up for a long period. ( most of the “junk” engine s I get or buy)
one final thing. A lot of overheating ( once normal things check out OK) is the distributor is supposed to get oiled ( page 65 of owners manual). I will say very few distributors I’ve worked with have free weights. Indicating a lack of oil. While the factory says 65,000 miles, it should be time not miles. Personally every year. But every 3-4 years once the weight are unstuck.
Last edited by Mguar; 12-08-2023 at 01:04 PM.
#28
12-08-2023, 08:47 PM
I don’t use the starter for that, socket and rachet. The thing I like about that method is I can feel what the crank is feeling. A little scrape or drag? I stop until I figure it out. Very rare anything is wrong. But I sure feel confident in the engine that way.
I also keep meaning to modify a Banjo bolt to take oil and prelube the engine after rebuilding or if it’s been laid up for a long period. ( most of the “junk” engine s I get or buy)
one final thing. A lot of overheating ( once normal things check out OK) is the distributor is supposed to get oiled ( page 65 of owners manual). I will say very few distributors I’ve worked with have free weights. Indicating a lack of oil. While the factory says 65,000 miles, it should be time not miles. Personally every year. But every 3-4 years once the weight are unstuck.
I also keep meaning to modify a Banjo bolt to take oil and prelube the engine after rebuilding or if it’s been laid up for a long period. ( most of the “junk” engine s I get or buy)
one final thing. A lot of overheating ( once normal things check out OK) is the distributor is supposed to get oiled ( page 65 of owners manual). I will say very few distributors I’ve worked with have free weights. Indicating a lack of oil. While the factory says 65,000 miles, it should be time not miles. Personally every year. But every 3-4 years once the weight are unstuck.
HAND rotation is the only way.
I am quite clear when I advise, bearing in mind many members are doing something alien to them, and for the 1st time, but having a go, which is brilliant.
Last edited by Grant Francis; 12-09-2023 at 03:55 AM.
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