Questions and Answers
Ford Backfires
Q. I have a 1989 Ford 460 cid fuel injected V-8 in my motor home. While in hilly country, and I climb hills no problems, until I took foot off accelerator at start of down hill, moving I suddenly got a loud pop at exhaust outlet if I applied gas no more. Did not happen every hill.
Went to big Ford truck dealer. He installed all new plug wires and replaced a vacuum line for $350.00. No hill when I had work done to test. On way back down 81 in high country same thing happened. Any suggestions?
Thanks,
HaroldA. The Thermactor (air injection) Exhaust Emission Control System reduces the hydrocarbon and carbon monoxide content of the gases by continuing the combustion of unburned gases after they leave the combustion chamber by injecting fresh air into the hot exhaust stream leaving the exhaust ports.
At this point, the fresh air mixes with hot exhaust gases to promote further oxidation of both the hydrocarbons and carbon monoxide, thereby reducing their concentration and converting some of them into harmless carbon dioxide and water. During different engine operations, such as cruise and WOT, the thermactor air is dumped to atmosphere to prevent overheating and backfiring in the exhaust system.
Now, what is happening is that the air from the air pump is not being diverted. This extra air in conjunction with the rich fuel mixture on decel is what causes the backfire. So the problem is in either the Air Bypass Valve, the Air Bypass Valve Solenoid or one of the check valves.
Additional Information provided courtesy of ALLDATA
