Hi

Don't worry, mine is running fine on one amp, but I have the job being Tech Support for Jaguar Club of Denmarks members, and one of them is now struggling with an issue, that could be overheating ignition amp, and he has now come up with the idea: Why not put 2 amps in parallel, if one amp overheats.
I suppose this idea must have popped up before and that someone can tell if it could work or not.

The issues with the car is that it starts and runs well when cold, and starts and runs badly when warm.
I think that will exclude TPS errors ?
Today he experienced bad pinking after hot start, where it was running only on some cylinders. I suppose that must be caused by ignition advance regulation failure due to vacuum unit failure or seized mechanism ?

The car is a 1984 HE. I'm not sure if the car is euro or US spec, it is probably imported used.

 

Nope, electronics do not work like mechanical switches, cannot put them in parallel. As for other issues, I suggest removing the distributor and overhauling it. As described in Kirby's book.

 

As Sega said, the amp relies on a signal from the dizzy pickup to fire the spark. You would have to fit a second dizzy, and ensure each one had only 6 teeth on the trigger star wheel, to make that idea work, with one dizzy running one bank via one amp. Funnily enough, when the V12 was first developed in the mid 1960s, it did have two dizzies, one for each bank, running conventional points.
As Sega also said, your friend should go through the system from top to bottom, (plugs, coils, leads, amp, dizzy internals, vac capsule etc etc) renewing all the bits, and it will work perfectly.

 

Thanks to both of you. Makes sense.

He has changed a lot of parts, I will try to make a list from our conversation. I agree that it must end up running properly, if all the small fixes are done

Leo

 

Easiest thing to test is the coolant temp sensor. Could be that simple?

 

Leo,

All my findings with overheating, running hot, amps is a bad coil/s, or wrong coil/s.

The original coils were approx 1.2ohms across the +Ve and -Ve posts EACH, and when joined as Jaguar did, APPROX 0.8ish ohms combined.

The module inside that amp is HAPPY at up to approx 1.0ohms, and over that it gets HOT and DIES.

Mine runs a single coil, a Fuelmiser CC215, "Universal Electronic Coil", and is happy, and the amp is cold, albeit mounted out the front of the radiator now.

 

Did he change the ignition module? I changed mine and I used a aftermarket brand module that was new. No change, car ran terribly when warm. Then I went to the junk yard and pulled a used, but genuine GM module from an 80's Chevy truck. Put that in the car and it ran perfectly.

So if the module isn't a genuine GM module, change it to one that is and see what happens.

 

The single coil that the late Series III V12 saloons used ( and they never went Marelli even until the end on 92) was a 0.5 ohm coil.

 

He has bought a new amplifier, complete AB14 as I understand it, and it does not help.
He has tried single coil, but the car runs better on the old twin coil setup. That could point towards the coils as the problem, especially when Grant tells us that it is a normal reason for this issue.
I will ask him to measure resistance !

Thanks all

 

At these very low resistances, it's important to account for the resistance in the test leads to the meter. Some meters have a zeroing function, so touch the leads together and adjust until the display shows zero. Then you'll get a true measure of the item you're measuring.

 

ALSO

How old the HT leads??, and if newish, what brand, they may have astronomical resistance, and that will "feed back" the amp.

Plug gap, MUST be 0.025", or the HE is not happy.

 

New HT leads has just been mounted, no difference. All I know is that they are red...
Plugs are new and should be gapped correctly

Thanks to Jagboi64 for the comment on measuring low resistances. I know the issue, My job is in solenoid valve development. We are using a 5.5ohm coil in my current project, and that is giving us measuring issues...

Leo

 

OK,

Red is the "Aussie go faster leads", maybe OK.

Plugs being new and ":should be gapped correctly", I could write a best seller on the number of times I have been told that one, make sure, PITA I know, but most plugs are 0.030 out of the box, UNLESS the spec is otherwise in the part number. NGK BP5EFS-13, the "13" being 1.3mm gap as packaged.

If that amp is getting hottish at idle, normal, and I have had then too hot to touch at idle, as they are dumping a shiit load of energy to Earth. Hottish running is not normal, but then the engine bay is HOT, and that Inlet manifold is HOT, maths dont add up, hence I have moved many to the front of the radiator, nice and cool out there.

One car, The Blue Goose, had all sorts of issues with that amp until I moved it, some 11 years ago, car still running just fine in Qld now.

Coffees up, I will keep thinking.

 

Leo
Just a further thought:
What is the situation concerning the injectors and fuel pressure? The hot-running pinking/misfiring symptoms may well be caused by poor injection patterns, or iffy fuel pressure.

 

Fuel pump has been changed, and it keeps pressure well. The pressure has not been measured though.

The pinging was maybe not pinging after all. It just sounded awful when it was running on a few cylinders at one occasion, where it was particularly bad. It's not easy to do a proper analysis on long distance...

No feedback on the coil resistance yet

Leo

 

I have a couple of comments, one tangenital and the other not so:

1. Heat is the mortal enemy of the amplifier aka module., As Grant states!! when mounting, a "goop" is needed. It enhances heat transfer from the heat sink that comes with the module. Big difference between no goop and the right goop properly applied. Check heat transfer, not the more common dielectric, Different goops.

2. The "dual amplifiers" concept struck a chord. MSD ignition is used widely. The NASCAR guys mount two! But, not in parallel, apart. In the heat of a race, if ignition issues arise, the driver can switch to the alternate MSD. They mount theirs in the cabin, not the engine bay!!!

3. I've thought about "heat sinks" and their function. some what related is a starter failure in my lump. No heat sink there !! As the amplifier as do most electronic devices function, so do amps. And, heat and electronics do not "get along". Heat wins that battle. So, add a chunk of alloy as a heat sink. OK, so far as it goes. But it has a capacity. Transfer from the "heat sink"? In my mind, GOTTA BE. How, as grant says, move it, Where ? to the coolest spot available.

Carl

 

Check out the heat thing...

 

Thanks Carl

I believe it’s a complete new AB14-amp, we are talking about. When I bought one, I checked if goop has been applied, and it had. I added some of my own, just because I could. I choose one with high high heat transfer, when I ordered from eBay.
The NASCAR setup would definitely work and make it very clear, if the issue is amp temperature related.

 

So, my own XJ-S was ready to go again today. Quite warm day, 28C or thereabouts

what happens after 3-4 km slow driving ? You guessed it, it started missing just like before I changed my ignition amp. We continued for a while, but did quickly realize, that we might as well turn around.
When I floored it slowly nothing much happened except from puffing, but eventually it took off. Kick down worked well, it still pulls like stink.
back home I left it idling, picked up a small bag of ice cubes, placed them on the amp and drove off again.
Guess what: It drove without a single puff. Just smooth and nice.

i will now move my amp out to the front. Will I need shielded wire, or can it be done just with ordinary wiring ?

 

Is it the standard HE amp, i.e. the GM module? I think only the signal wire to the ECU is shielded, the rest is regular wire.

That behaviour sounds like an amp on it's last legs. The GM modules were mounted inside the distributor at the back of the engine, so they operated in a hot environment. Jaguar was rather clever actually, mounting it on the intake manifold means it has a large volume of cool air coming through the manifold and that acts as a great heatsink. If you've ever taken an IR thermometer around the various parts of the engine, the intake is considerably cooler than the rest of the engine.