Fuel pressure question


Old 04-13-14, 03:44 PM
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Fuel pressure question

So here's a question I've been wondering about... I have a 2002 F150 4.2L V6 with 261,000 miles. I recently got an OTC 5630 fuel pressure gauge and hooked it up tonight to see what's what. My Chilton F150 repair manual says the fuel pressure at idle should be:

30-45 psi. (Vacuum @ regulator attached)
40-50 psi. (Vacuum @ regulator detached)
30-40 psi. fuel system hold pressure (5 minutes after key off)

My fuel pressure at idle is a little under 32 psi.
With the vacuum detached, it's 40 psi.
Key off, and waiting 5 minutes, the fuel system pressure is 28 psi.

The only reading that is a little below spec is the fuel system hold pressure, but it seems like a 5 psi drop might be normal, if looking at the upper range of numbers. Do you think that a 3.5 psi drop in 5 minutes is anything to worry about or look into? Or maybe just keep an eye on it?

I suppose the bottom of the scale fuel pressure might be just because of the original equipment and the high miles? I put a brand new fuel filter on a few weeks ago, and recently had the injectors out to inspect, bench test, clean and replace o-rings.
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Old 04-14-14, 06:00 PM
Join Date: Jun 2013
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usually i look for 5 psi in 20 minutes.what type of problem are you having.i also do some snap throttle to see if there is a pressure drop.
Old 04-15-14, 05:38 AM
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No problem necessarily, just checking it.

I have on rare occasion, gotten a temporary P0302 and P0316 code, cylinder 2 misfire, first 1000 revolutions. It has new plugs, new wires, new coil, so I would think that could all be ruled out. I'm suspecting a possible leaking fuel injector. Once when I went to start the vehicle after I had gone into a store for about 15 minutes, it sputtered and ran rough and gave these codes, like it was flooded and smelled like raw gas. That made me really suspect a leaking fuel injector. But it doesn't do that all the time, it seems very intermittent. So it's not like I'm real worried about it at this point, just curious. Road conditions were dry, average temperature. There's no vacuum leak, fixed all that 3-4 weeks ago with new gaskets and isolator bolts.

It idles very well and its only done this once since my repair weekend about a month ago... and it has shown no permanent codes since then. But in watching the SHRTFT1 and SHRTFT2, it seems like the PCM thinks Bank 1 is running a little rich. The bank 1/2 numbers are most often the same, but every once in a while bank 1 will run a bit more rich, being further in the negative % than bank 2 is. So I suspect that either an injector isn't spraying a nice mist or maybe one is leaking a little. It wouldn't surprise me as they are OEM parts.

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