Still loosing prime!
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Elder User
Joined: Dec 2011
Posts: 751
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From: Kodiak, Alaska
Still loosing prime!
Ok I am at my wits end! My 88 7.3 N/A was having cold start issues so I changed (sence I drove it last): 2new batterys, new passenger side ground cable 00 custom(nice), lift pump, return lines viton o rings, all olives, cleaned all terminals and treated with dielectric grease, new one piece fuel filter/water seperator, new starter. Ok it still will lose prime after only sitting for 10 min I have no fuel leaks. After cranking on it to start it makes a huge puff of white smoke and runs ruff for a few seconds then smothes out and stops smoking. My thinking is the fuel heater o rings in the filter head, or the soft return line in the rear of the engine other than that I don't know 
. Any ideas guys?
. Any ideas guys?
Thread Starter
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Elder User
Joined: Dec 2011
Posts: 751
Likes: 0
From: Kodiak, Alaska
Also I think it is worth mentioning I took off the electric lift pump and replaced the old lift pump with a new one. I don't think it is the tank because it happens with eithr tank, maybe the tank 1selector unit I haven't checked there yet. There isn't any steel line it has this hard plastic fuel hose that runs back to the selector unit I think I will replace that with soft fuel hose next. Then maybe a sending unit off my 92 that only has one tank and see if that helps.
Posting Guru
Joined: Sep 2008
Posts: 1,840
Likes: 1
From: On the prairie
Double check the lines going from the drivers side frame rail to the lift pump. It should be a steel line that runs under the front crossmember. It shouldnt be rubber or plastic the whole way, at least not unless someone changed it already.
Fleet Owner
Joined: Jul 2006
Posts: 20,362
Likes: 824
From: Mi'kma'ki
grab yourself some fuel hose and hook your lift pump up to a jug of diesel.start the truck,and let it suck up some fresh fuel.now shut her down and see if she looses prime or holds.if she holds,then your air leak is before the lift pump(rusted fuel lines,mainly around the holding clips,fuel selector valve,tank pickups,etc.) if she still looses prime,then your air leak is after the lift pump (engine side/fuel filter,o-rings,heater,American valve,return lines etc.)
Thread Starter
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Elder User
Joined: Dec 2011
Posts: 751
Likes: 0
From: Kodiak, Alaska
grab yourself some fuel hose and hook your lift pump up to a jug of diesel.start the truck,and let it suck up some fresh fuel.now shut her down and see if she looses prime or holds.if she holds,then your air leak is before the lift pump(rusted fuel lines,mainly around the holding clips,fuel selector valve,tank pickups,etc.) if she still looses prime,then your air leak is after the lift pump (engine side/fuel filter,o-rings,heater,American valve,return lines etc.)
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