fuel pressure question
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Senior User
Joined: May 2015
Posts: 282
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From: Sonora,Ca
fuel pressure question
So how long should a fully primed fuel system at 35psi drain down to lets say 25psi. Im asking because ive been chasing a hard hot start issue on my 1990 f250 460 for awhile now. No codes popped up for this problem so i doubt its anything electrical. Used my fuel pressure gauge and it took 40 minutes to achieve a 35psi to 25psi reading. That seems way too quick. Im thinking maybe the injectors are leaking fuel into the cylinder(s). Sometimes it takes a couple trys to start the truck when its warm but starts instantaneously when its cold. What do you all think? It also has a new fuel pressure regulator
Cargo Master
Joined: May 2001
Posts: 3,208
Likes: 13
No that’s not bad. A quick way to trouble shoot that is to cycle the key a couple of times before trying to start. If you do this and it fires right off then yes there a fuel delivery issue. It it doesn’t change anything then start hunting something else.
Thread Starter
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Senior User
Joined: May 2015
Posts: 282
Likes: 3
From: Sonora,Ca
I dont think its the fpr since its new and theres no gas in the vacuum line on top of the regulator. Is it possible for the pressurized fuel to leak back in the tank? Kind of doubt that since it is hard to start when hot. Kind of leaning towards the injectors
Cargo Master
Joined: May 2001
Posts: 3,208
Likes: 13
It usually does lose pressure back to the tank. I have yet to find a fuel system that had any fuel pressure after it has set over night. When it starts is it flooded. Heat soaked coils and distributor pips can and do cause this problem. Usually a leaking injector effects only one cylinder causing a short term miss.
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