03-10-2010, 12:22 PM
Join Date: Aug 2008
The flashing is to get your attention. Check the codes and you'll see it has a bad misfire.
A bad misfire puts unburned gas in the cat. If the cat gets too much of it it plugs the tiny holes in it, rendering it useless. It can even cause a fire if there's enough unburned gas in it. It will run hot!
If the cat's just mildly plugged from it, sometimes driving it after the misfire is cured it can clear itself out, but it will get super hot when it's clearing. Try it!
I suppose it could affect an auto trans from all the heat.
The cat is not causing the problem, the misfire is. Plug, cap, wires, vacuum leak, injector, coil rail, etc.
If you try to fix it by replacing the cat without curing the misfire, your new cat will plug and burn too. $$$$
I'm surprised he's complaining of a flashing light and NOT a misfire. It makes me wonder if it's a later model 6 cyl TJ with the coil rail. A coil that's failed in the rail can kill 2 complimentary cylinders. If both are misfiring it won't feel like a misfire - no running rough, it just has low power. Being new to him he might not realize it's low on power. Wonder if that's why the previous owner sold it?
To check to see if a coil has gone south: Use a laser thermometer, go underneath right after it's been running a few minutes. It doesn't have to still be running, just very warm.
Use the thermometer to measure the exhaust manifold as close to the exhaust ports as possible. Write them down as you go.
If a coil has failed, you'll find one cylinder is much colder than the others, and another is either cold or very hot. One will be in the front 3, the other in the rear 3 cyls. Those 2 are the compliments of each other.
Typical temps of a 6 cyl running right are about 300 degrees at each port. But they are all the same.
One with a failed coil will have one a bit lower maybe 200-250, and it's compliment around 700 degrees! That's hot!
Autozone has the coil rails - they are Chinese junk!
CarQust and NAPA carry the same rail the dealer does made by Standard Ignition. Theirs run about $150. Dealer's is close to $250.
BUT CHECK IT FIRST!
Let us know.
It's no wonder the country is falling apart - stupidity abounds!