Problems With 4.9L Ignition or ECM??
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Joined: May 2009
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Problems With 4.9L Ignition or ECM??
I Just Got a 1990 f150 and it runs when it wants to. first you have to jump the 2 red wires on the relay under the hood. (the one with 2 yellows , 2 reds and a small black) then it will crank (sometimes). when it does actually fire up it runs excellent. someone said replace the wiring harness , another said replace the ECM. I'm not sure what the problem is but i do know that the original owner ran constant power to the fuel pump which tells me that the ecm or relays werent doing thier job. but the fuel pump is running and the coil has power but sometimes it just wont fire up. Any help would be great.
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Joined: Nov 2006
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A very common problem on these trucks is the fuel relay will go back, which is probably why the previous owner ran continuous power to it. I would get a shop manual to help you diagnose problems and trace down the issue, instead of throwing money at it. I have rarely seen an ecu go bad. best of luck... let us know what you find out
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