High speed miss.
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High speed miss.
I have a 1986 F150 fuel injected 5.0 4x4. Ran great with out any problem until recently. The engine was running fine then fell dead while driving down the road. I replaced the coil due to no spark, no luck still no spark. Ordered a new distributor with new pick up coil and new electronic module already installed. While waiting on the distributor to come UPS I thought I’d check a few other things. Found fuel pressure at rail was 40 lbs but wouldn’t hold so removed tank and checked pump would run but not even 1lb pressure. Replaced tank pump and sock. Got New distributor dropped it in and engine fired right up. Idles great put occasionally will miss. Miss gets worse and more often with increased RPM. Changed plugs and wires, miss remains. At higher speed the miss is almost like the engine stumbles but will recover, very hard miss. The miss is so severe it isn’t drivable. At low speed it will miss every now and again like a plug wire arcing out. Again this truck purred like a kitten prior to it quitting, with no miss at high or low speed.I finally tried a last ditch effort and put on new throttle position sensor. No change in the miss. Have tried to find a vacuum leak and could not. Please help, this miss is driving me nuts. Thanks in advance
Last edited by JimmyBear; Aug 2, 2018 at 09:54 PM. Reason: Added info about throttle position sensor
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
I have a 1986 F150 fuel injected 5.0 4x4. Ran great with out any problem until recently. The engine was running fine then fell dead while driving down the road. I replaced the coil due to no spark, no luck still no spark. Ordered a new distributor with new pick up coil and new electronic module already installed. While waiting on the distributor to come UPS I thought I’d check a few other things. Found fuel pressure at rail was 40 lbs but wouldn’t hold so removed tank and checked pump would run but not even 1lb pressure. Replaced tank pump and sock. Got New distributor dropped it in and engine fired right up. Idles great put occasionally will miss. Miss gets worse and more often with increased RPM. Changed plugs and wires, miss remains. At higher speed the miss is almost like the engine stumbles but will recover, very hard miss. The miss is so severe it isn’t drivable. At low speed it will miss every now and again like a plug wire arcing out. Again this truck purred like a kitten prior to it quitting, with no miss at high or low speed.I finally tried a last ditch effort and put on new throttle position sensor. No change in the miss. Have tried to find a vacuum leak and could not. Please help, this miss is driving me nuts. Thanks in advance
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Changed the fuel filter when I changed the in tank pump. Brand new wires and plugs and already looked at them after dark. Runs the same as it did before changing the plugs and wires. No dice. Thanks for the advise but I already been there. Should also mention this isn't a small miss but a stumble, a bad cut out like a dead plug but after it misses, then picks up and does ok for 3-4 seconds and stumbles again. Any advise is welcome
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Changed the fuel filter when I changed the in tank pump. Brand new wires and plugs and already looked at them after dark. Runs the same as it did before changing the plugs and wires. No dice. Thanks for the advise but I already been there. Should also mention this isn't a small miss but a stumble, a bad cut out like a dead plug but after it misses, then picks up and does ok for 3-4 seconds and stumbles again. Any advise is welcome
Best to pull the codes to rule out the electronics. Codes in the mem may narrow it down if it a mech problem.
Cargo Master
Joined: Jun 2013
Posts: 3,177
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From: Somewhere n North America
I suggest you extend your Fuel Pressure gauge up to you windshield to see if you are maintaining pressure under load.....
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ncline
1987 - 1996 F150 & Larger F-Series Trucks
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Jun 12, 2008 10:43 PM
