Better Beaters - Building Cars and Daily Drivers

Trouble shooting for fun and profit. No mention will be made of desperation.

Nothing to be worried about here!

Not the sight that warms the heart of the DIYers.

The Jaguar V12 is a complex assemblage of every automotive engineering feature that you could possibly imagine. Gazing into the gaping maw of the engine compartment, the uninitiated might imagine that it looks like a gigantic shark got a nuclear reactor stuck in it's mouth!

Evaluating the problem is going to require a systematic approach. I am following the list provided by Grant Francis on the Jaguar Forums. From now on I will refer to this document as "Grant's List."

I will address each section in order.

The prevailing assumption is that it ran when it was parked, but now it doesn't. This rules out a catastrophic mechanical failure of the internal spinning bits of the motor or a complete over heating and melt down episode. It just won't run "right" when it used to.

The first check is for fuel flow, this could mean the failure of the fuel pump, or a blocked filter, pressure regulator, or injectors. I have already added a couple of gallons of fresh premium fuel.

I didn't check for fuel flow by cracking open any fittings. The engine has run for several minutes at a time. On several different instances. The spark plugs look dark and sooty. I take it to mean that there is some fuel flowing into the motor. There may be some fuel flow problems, but I'm betting that they shouldn't prevent the engine from running at low speeds. Though I may have to revisit this issue in the future.

I'm going to jump ahead to the issue of "spark." I checked and rechecked that the plug caps and distributor terminals are fully seated. I checked and rechecked the firing order and the routing of the plug wires. All were okay. Then I pulled the A3 plug and held it against the intake manifold while I engaged the starter. There was a spark visible at the electrodes. I can't say that it was a super strong blue cracker. Grant advises that it MUST be a "fat blue crack" of a spark. Anything short of this will not start the engine.

This might be an issue, the motor will run, but poorly. Maybe the spark is too weak.

This is the ignition amplifier.

It could be a failing coil or ignition amplifier. I decided to check the amplifier first. I did some researching and found some great info and pictures on line. Both Grant and Kirby indicate that a common GM ignition module is housed along with some other components inside the amplifier box.

Just flip it over and undo four little screws.

That black rectangle is the GM ignition module.
It is usually housed in the HEI distributor.

It never hurts to sketch a quick diagram
to keep track where the wires go.

In the above photo you can see the condensor and ignition module. Luckily this is just a common GM V8 ignition module. On GM cars it is located inside the HEI distributor. I paid 40.00 dollars for a new AC Delco replacement. From what I've read, since the module is working some 50% harder firing 12 cylinders as opposed to 8, the increased load leads to an earlier failure of a lower quality replacement. So I went with the better quality part. Grant recommends discarding the condensor as they are not really needed. They can fail, resulting in a grounding short that will cause a malfunction. I followed his advice.

There was some corrosion  on the terminals and connectors.

I was careful to apply the heat transfer grease to the back of the module. It helps cool the module by transferring heat to the housing. I noticed that the module that I removed did not have this grease. This may have lead to the failure of the module.

This is where the grease goes.

Replacement ignition amplifiers are available from RockAuto for 130.00 SNG Barret charges four hundred dollars for a replacement. Knowledge IS power and thanks to the forums I'm saving a ton of money rebuilding my amp.

This might cure the problem, but then again, it might not.

I was concerned about the co ax wire that runs from the ignition amplifier to the ECU. This essential wire is unprotected routed along a hot water pipe that runs along the intake manifold.

You can see where the insulation flaked off.

In thts picture I have moved the wire to make the inspection easier. You can clearly see that some insulation has flaked off of the wire. I carefully wrapped electrical tape over the co ax portion and the wire itself for support and insulation.

I don't know how the wire was protected when the car was new,
but this doesn't inspire confidence.

The wire just sits here quite vulnerable. I decided that I would at least add some protective wire conduit to offer some protection.

That looks a little better.

That looks a lot more reassuring. That's the hot water pipe running directly underneath,

According to forum members the coax is either a go, or no go situation. If the wire was damaged and shorting out, the motor would not run at all. The motor has run poorly before, and after, my repairs to this wire, but it has always run. I suppose that the wire should be okay.

Grant also advised that the carbon point of the center distributor terminal can fall out. This would result in the terminal having to jump quite a distance. This would result in a very diminished spark out put. I'm going to check this, just to make sure, before I try restarting the motor. I just want to eliminate that as a possibility. I'm very tired of inhaling that stinky exhaust.

Last night I went out to the garage to check for this potential problem. I undid the three screws securing the distributor cap. It wasn't easy to move the cap enough to check underneath with a mirror. I tried using my new "Lizard Cam" cheapie bore scope, but I couldn't maneuver it into the proper position. I finally settled for reaching under the cap with my fingers until I could verify the presence of the carbon button by feel.  It was there, so I re-seated and secured the cap. Now I'm ready to fire up the motor and see what happens.