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Fuel pump prime does not prime

 
Old 02-06-2019, 11:25 PM
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Default Fuel pump prime does not prime

I have a 1987 F150 with 302 and AOD. I've been having a recurring problem with the fuel pump not priming. It does not happen all the time - and only when it is cold. And even when cold it is hit or miss. When I turn over the ignition I don't hear the prime but do hear the relay click. If i continue to retry, it will eventually prime and I am able to start the engine - after starting the first time it will run the rest of the day with no issues. I had to replace the battery recently and noticed that the positive cable was a mess so replaced that as well. Afterwards, it seemed that the issue was fixed! But alas, it was not... So, basically, I don't want to start replacing things without a better idea of what might be the issue. The fuel pump itself seems to be OK.

What controls the priming of the pump? Is it the eec? The relay works so the eec is doing that job. Could it be some wiring that expands when cold and is not making a good connection? I wish it is something I can re-create and test but it is random and when it happens it could be for just a couple of turns.

Any ideas/thoughts would be much appreciated. Please let me know if you need additional information.

Thanks!
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Old 02-07-2019, 10:20 AM
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On my 94 there are a couple of ground straps in the engine bay that can play havoc with the fuel pump priming if they are not functioning properly. One of them is by the driver headlight on the core support, the other is on the bottom of the core support by the radiator saddle. Most of the times I have heard of a bad EEC causing fuel pump problems, its because it would not stop priming the pump. What you describe is slightly different, but again, my knowledge is more geared towards the 92-96 trucks.
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Old 02-07-2019, 08:13 PM
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Thanks - I will take a look at that this weekend. Your thought about the eec and the prime running on did happen but only once and has never happened again - so basically i've had both issues - though mostly the not priming. I wondering if I should replace the eec and see what happens. I hate to replace a good fuel pump and then that not be the problem. It sounds like the eec does control pump priming.

Thanks for the response!
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