Fuel injected 4.9 miss
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Fuel injected 4.9 miss
I have a 1990 f150 4.9 5 speed. I acquired this truck about 10 years ago and It got parked about six years ago. Recently I pulled it out of the weeds and I've been working on getting it running. So far I had to replace the computer due to bad capacitors The O2 sensor because it was never hooked up since I had the truck. And the front fuel tank sending unit and pump. I've driven the truck about 300 miles now and I've started to develop a miss in the 6th cylinder along with terrible fuel economy. At first it was under heavy acceleration and now it's all the time. Emmisons equipment has been off the truck since I've had it. I also know I have vacuum leaks but nothing that has effected the way the truck runs ( at least not to the point of missing). I've swapped spark plugs and plug wires but can't get the Miss to move and I know I'm getting good spark. I'm going to compression test tonight but I'm not sure where else to look? Has anyone else had this problem?
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OK I did some checking today. Cap and rotor are good, compression is 120psi. Didn't check the other cylinders because I ran out of time. Wiring is all good. And the two lines that are broken have been broken since I've gotten the truck. One is a green line on the top of the motor and the other one runs above the number 6 spark plug. I will replace these when I get time but I don't think they caused this issue. Fuel pressure is unknown. It ran good when i pulled it out of Its parking spot and the last 250 miles I drove it where flawless. It was only the last 50 miles that this Miss came about. It runs the same it did as I parked it. Except for I was getting around 14mpg when I parked it and now I'm getting around 6 mpg. The only other difference I notice is that after I changed the computer it doesn't want to idle down below 1200rpm. It will after a while but it seems to fight it. If I have time tonight I'll pull codes and see what it says.
Last edited by MJohnston2448; Jul 9, 2018 at 05:52 PM. Reason: Double typed a sentence
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Also I was wondering if a possible bad injector. Is it possible to clean them or just better to replace them?
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I know it’s long over due. I’ve had the truck parked for months without much time to look at it. I did find the problem and wanted to post it to wrap up this thread. The number 6 injector was completely clogged and the others where not far behind. I replaced all of them as they where in pretty rough shape as well. The truck is now running perfect with a bit better fuel economy.