I have a 1999 Chevy 2500 crew cab with a 454 vortec. I recently installed full duals and shortly afterwards noticed a drop in MPG as well as a noticable miss during acceleration. It stops at idle. I replaced the plugs and checked the wires. What's next?
by 
Buck Hunter
ANSWERS: 1
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If you have a check engine light on and you know or can find out the code I could probably pin point it. Here are some suggestions. Start the engine at night or in the dark with the hood up, look for any sparks arching off the wire boots near the exhaust manifold. Rev it up several times and check as well. If you do not see or hear an abnormal spark anywhere thats not it. Next I would put a timing light on one of the wires and watch the flashes as the engine runs. If the light is not steady and cuts out a lot, I would remove the ignition module (next to the coil) and have it tested at any auto parts store. By the way, I have seen many issues with the cheap plastic distributor that Chevy uses in that engine. I would replace distributor cap and rotor just as routine maintenance if it hasn't been done in awhile. I don't see any way the dual exhaust could be related to a miss on acceleration. If the ignition checks out I would clean out the mass air flow sensor with brake cleaner and try and get a scan tool reading of that sensor. The mass air flow controls 75% of the fuel/air ratio.
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