Fuel pressure fluctuating
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Fuel pressure fluctuating
Hey guys was hopeing to get some input. I've been getting some real rough runs when I start the truck until it's warmed up then it runs great. And by running rough I mean like missing and revving high before shifting. I've been told it's an injector. But I'm curious about something else, I have a fuel pressure gauge in my truck that reads about 58psi at idle, and I was playing with my window switch today and noticed when I press it and hold it, it will drop my fuel pressure down about 5 psi for a few seconds then go back up. Why would my window switch cause my fuel pressure go down? The only thing I can think of is alternator not providing FICM with enough voltage? So alternator is bad or the ficm is just bad? I don't know. Any suggestion would be appreciated
Hotshot
Joined: Dec 2014
Posts: 17,825
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From: Jersey Shore
Is that fuel pressure gauge electrical?
Is the electrical power for the gauge possibly connected to the same electric circuit as the power windows?
FICM has nothing to do with the fuel pressure. Are you monitoring your alternator output during this time?
Is the electrical power for the gauge possibly connected to the same electric circuit as the power windows?
FICM has nothing to do with the fuel pressure. Are you monitoring your alternator output during this time?
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Senior User
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Fuel pressure gauge is not electric, it's plunged directly to the side of the fuel bowl. So still don't see why it would bring my fuel pressure gauge down. And I never checked my ficm voltage anyone have a how to on how to do that.
Fleet Mechanic
Joined: Nov 2008
Posts: 1,443
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From: South Alabama
Kind of sounds like a short dragging down your fuel pump. Does everything else work, cab lights, dash, anything else dim? The revving high could be over fueling dropping fuel pressure. Don't know how the switch would be tied to that thou. Just thinking out loud.
Lead Driver
Joined: Dec 2006
Posts: 6,496
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From: So. Jersey
For what you described, I can only imagine that both systems draw power within the same circuit. When you hit the switch to cause the issue it is drawing power down from the fuel pump causing the pump to lose performance resulting in a lower pressure.
This reminds me of a friend's car years ago. She had a Nissan Altima and if you held the power window switch on it would make the car sort of bog.
This reminds me of a friend's car years ago. She had a Nissan Altima and if you held the power window switch on it would make the car sort of bog.
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Lead Driver
Joined: May 2014
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From: Virginia Beach VA
My guess and without a meter to check, a guess;
Batteries and alternator are dying. You hold the switch, alternator can't keep up, batteries are drained. Pump boggs down, FICM is screaming for help, trucks missing and near defeat.
Batteries and alternator are dying. You hold the switch, alternator can't keep up, batteries are drained. Pump boggs down, FICM is screaming for help, trucks missing and near defeat.
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Hotshot
Joined: Dec 2014
Posts: 17,825
Likes: 3,109
From: Jersey Shore
I played with my trucks window today both at initial start and hot. Stalling the window I see maybe a 0.2v drop, but no change in fuel pressure.
I think your going to have to get some voltage readings from the elect rivals to make any sense of this.
I think your going to have to get some voltage readings from the elect rivals to make any sense of this.
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