89 4.9L bucking
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New User
Joined: Apr 2009
Posts: 14
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From: Amherst, MA
89 4.9L bucking
I have an 89 f150 4.9L w/5spd. 92,000. The engine is bucking/missing intermittently when under very light load/only maintaining constant speed, doesent do it on decell or under loaded throttle. I have litteraly replaced every ignition componant on the truck short of the ecu. I have also replaced the majority of the fuel system parts. injectors, filter, high pressure pump, I use lucas fuel treatment religiously. any new ideas would really help, im fresh out!
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Joined: Dec 2009
Posts: 374
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From: Portsmouth, Va
Fuel pressure regulator possibly? If I understand you correctly the engine won't buck if you open the throttle with the truck parked?
You can still hook a fuel pressure gauge up to your truck and while it's parked open the throttle and watch the fuel pressure. If it drops in a way that's abnormal it'll cause bucking when you've actually got a load on the engine besides itself.
Does the truck do anything else besides this? Any codes?
You can still hook a fuel pressure gauge up to your truck and while it's parked open the throttle and watch the fuel pressure. If it drops in a way that's abnormal it'll cause bucking when you've actually got a load on the engine besides itself.
Does the truck do anything else besides this? Any codes?
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New User
Joined: Apr 2009
Posts: 14
Likes: 0
From: Amherst, MA
Figured it out!! Too much egr.
Follow this link to learn more
https://www.ford-trucks.com/forums/9...-throttle.html
Follow this link to learn more
https://www.ford-trucks.com/forums/9...-throttle.html
