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Car Forum / Ford / Ford Mustang / October 2004hold fuel pressure
How long should the fuel system hold pressure? When I park the car, it's got 39psi. After about 10mins it's down to 20psi. I don't know how long till 0psi. Is this normal or am I to suspect a leaking injector? 93 5.0 liter. Jim S. '82 Mutant That sounds about normal. It slowly goes down.. at least mine did too. -Franklin '96 Cobra It's normal, the system is not designed to hold pressure when the engine is not operating. Your fuel system is a "return" style system. When the engine's running the fuel pump operates at a fixed volume and pressure. The fuel is pumped from the tank to a fuel pressure regulator, then to the injector rail. At the regulator there is a return line back to the tank. The regulator maintains rail pressure by restricting the flow back to the tank. When the engines not running the pressure in the line from the tank and rail leaks back through the regulator and fuel pump. If you had a leaking injector you'd run rich and throw a code.  SignatureMike Silver 10th Anniversary Cobra Coupe --- > How long should the fuel system hold pressure? > When I park the car, it's got 39psi. After about 10mins it's down to [quoted text clipped - 6 lines] > Jim S. > '82 Mutant sounds good to me. >How long should the fuel system hold pressure? >When I park the car, it's got 39psi. After about 10mins it's down to 20psi. [quoted text clipped - 6 lines] >Jim S. >'82 Mutant Remove NO-SPAM from email address when replying I can't remember the spec off-hand....... sounds like you're in the ball park. Do you have a specific problem or are you hunting unicorns???? > How long should the fuel system hold pressure? > When I park the car, it's got 39psi. After about 10mins it's down to 20psi. [quoted text clipped - 6 lines] > Jim S. > '82 Mutant Well, the engine back fired a couple times today and it hesitated rather severely going from a 35 mph no throttle roll to WOT. The engine was cold. Aside from this one incident I've had no other issues, idle or otherwise. I pulled a couple of the plugs and they looked rather fouled in a running rich sort of way. While pulling the plugs I noticed the fuel pressure drop off in what seemed to be a fairly short period of time. That, coupled with the richness and back firing put my concern in the direction of the injectors. Lately, I've been making a lot of short trips 'round town without getting it heated up, so maybe that's the problem. I have an electric fan wired so it'll stay on with the ignition switch off (225 degree thermostat) and it has yet to come on in the past week or so. I looked at the HEGOS a little while ago, they were on the dirty side, but since I didn't have any cleaner on hand I didn't do anything about it. In any event, I'll put some new plugs in and clean the HEGOS. Anything else I should look at? Jim S. '82 Mutant > I can't remember the spec off-hand....... sounds like you're in the ball > park. Do you have a specific problem or are you hunting unicorns???? [quoted text clipped - 10 lines] > > Jim S. > > '82 Mutant Back when a new fuel pump and injectors were installed in my '89 they'd hold pressure for perhaps 12 hours. Now, with about 7-8K miles pressure holds for about 4 hours. After some S/C tuning the 30s weren't delivering enough fuel at WOT above ~5500 RPM. A set of used 36s were installed, cured the lean condition, but was rich at idle and didn't hold fuel pressure more than 5 minutes after shut off. After the 353 w/o S/C was installed with the 30s I had the 36s tested and flowed for sale. One injector not closing compleatly and another peeing a stream...after that expense, I kept the set. So observing how quickly the system bleeds down is a good way to determine the injector's condition IMHO. bradtx |
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