Back Fire / 10sec after turning off

Friend has a 95 wrangler, 2.8 4cyl. It usually backfires about 10 sec after turning ignition off. What can be done to stop it from backfiring?

I think a tune up would help...how many miles has it been since they've put in a new set of plugs, and a new cap and rotor? Also, is it the 2.5 liter?

ya 2.5L He's put plugs, wires, rotor, all that. I'm now thinking maybe the time chain & sprockets are worn. Has messed up exhaust manifold or exhaust as its loud. Runs smooth, but lacks power.

Correction to the facts... its a 89 , 2.5 . Yesterday, it went through a tank of gas at a rate of about 10 mpg. Its a throttle body injector system, ya? I figure a sensor is causing an immense rich mixture. After shutting down, the residue and excess is coming to temp in the exhaust manifold and igniting some time after the ignition key is turned off. Maybe why the exhaust manifold gasket is shot and needs replacing. Thats my guess now.

Have others run into this??? j

sounds like timing problem, to much in advanced

At 10mpg, it is extremely rich. Have the O2 sensors checked or replaced. Insure it's tuned up recently. Replace the air filter and check the vacuum hoses. Exhaust manifold gasket won't hurt, but the backfire may have (in part) caused it.

How many miles?