429 backfire
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429 backfire
I just built a drill rig on a 1995 F-700 with a 7.0 liter gas engine. The truck was originally a Oregon dept. Of Forestry truck, well maintained. It has an Allison atoumatic tranny, fuel injected with a govener. My problem is the truck has started to backfire when going down hill using gears to control speed, drives fine when accelerating but when on the compression especially in lower gears on steep grades it backfires loudly. The truck is california smog legall.
Fleet Mechanic
Joined: Nov 2011
Posts: 1,825
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From: Land of Taxes
If it has a gazillion miles on it the cam or valves may be worn. A compression and leak down test will verify this. Un-burned fuel will cause this. It could be running on the rich side. First be sure all tune-up items are in good serviceable order...plugs, wires, filters etc...Check any sensors in the closed loop system that tell the injection system to increase fuel such as a cold start temp sensor. Exhaust system leaks will induce this problem as well.
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