Questions and Answers

Ford Mustang Is Having Surges Q. 1986 Ford Mustang 5.0 liter V-8 HO with automatic transmission. When holding steady speed anywhere between 60 mph to about 0 the engine stalls and surges but goes away when accelerating or coasting. It is a lot worse uphill and near 45 mph. The plugs replaced with platinum 2 about 6 to 8 months ago. The stall/surging was almost unnoticeable before the FlowMaster exhaust with straight pipe all the way up to the O2 sensor.

The plug wires, distributor cap, rotor button, throttle position sensor, and tires have been replaced within two weeks. Any advice is much appreciated.

Ian

A. A lot depends on which fuel system the engine is equipped with, a Carburetor Feedback System or Electronic Fuel Injection (EFI). Ford used both. I guess they used whatever they had a lot of on a particular day.

So, the best I can do is offer this chart from the Ford manual that will give you some idea of what to check. It seems to me that it is running lean, but you would need to have the emissions analyzed to confirm it.