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1991 Ford F150 4.9 running rough


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I have a 1991 Ford F150 4.9 300 I6. It idles fine but when I try to accelerate it has serious hesitation. It also bucks and surges. It seems worse after I have driven it awhile. I have replaced MAP sensor, TPS, air filter. It has newer (2017) plugs, wires and EGR (2018) and has had less than 20k since these parts replaced. I can't decide if its a fuel filter, issue or maybe catalytic convertor. Do you have any suggestions?


2 Answers

I had a 90 f150 that had the same problems but for me it was needing the fuel filter replaced then the injectors to be cleaned and a new fuel pump. I recommend starting with a fuel filter change and see if that might help. Its good to start cheap and work your way up.


Well find a mechanic like myself to test rather than gas. A catalytic converter can be pressure tested to see if it's bad. The fuel injection system can be pressure tested to see if that's bad start there