Classic/Antique Car Repair: 87 jag xj-6, air gap, diesel battery

Question
when we drive the car it runs perfect.but sometimes when we shut it off it will not start (no fire).or it will start back and shut off when we put it in gear.it is very erractic about when it wants to start but almost always starts after we let it sit for a hour or so.

Answer
Hi Blake,
When you say "no fire", if you mean no ignition, You need to do some tests at the time of the failure. First confirm power to the coil with the key in the ignition position. Then check to see it has power with the key in the start position. Put a volt meter across the battery terminals and read battery voltage, then have someone try to start the engine and read battery voltage. If the voltage is down around 9 volts during starting, look at the battery to see if it is a "Deep charge" battery or a "diesel" battery. If not, connect a known good battery up as a jumper battery as though it needs a "Jump Start". Even though the engine sounds like it is spinning over fast the XJ-6 up to 87 required a Diesel or Deep Charge battery. A standard battery will not always start this car under certain conditions.

The XJ-6 up to 87 used a GM moduale inside the Lucas box mounted on the front of the intake manifold. A two lead plug on the head side of the box goes to a pick-up in the distributor. The pick-up can be tested with an ohm meter. with the plug disconnected from the box. The pick-up should be 2.2 to 4.8 ohms. The air gap between the pick-up and the reluctor is .008" to .014"

If you are not a mechanic and want to do some of these tests you can e-mail me at longez8@bellsouth.net and I will go into more detail so you can still do the tests.

I hope this helps,
Howard