Or a lean condition will cause a backfire......

You could try and read the O2 sensor with a volt meter under cruise. And yes check the ignition too. Make sure the mechanical advance s not sticking while you are at it.

Kevin


87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...