95 GTS - Fuel Pressure bleed down / How quick?

doctorj357

Member
Aug 7, 2018
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Have a few questions about fuel pressure bleed down.

  • Engine non running, fuel at 20psi, turn the key on & pump run few secs, pressure climbs about 5psi during the prime, but then falls back down. If I turn it off/on multiple times I can prime it up to about 35-40psi, but when key is off, it drops like stone. Here's a video: https://www.youtube.com/watch?v=C-J2QgXbgNs&feature=youtu.be
  • Engine running, fuel steady 35-37psi. Turn key off the pressure instantly drops back to 20psi. Is that right?
I'm still periodically suffering a stall at idel or stops. I'e replaced the fuel filter, FPR. Injectors are original as well as pump. Car only has 57k miles on it, but age is catching up on stuff. Just wondering if I have a week pump. But guess at same time I'm curious about the bleed down, what is normal behavior?
 
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doctorj357

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Aug 7, 2018
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Michigan
No codes. Might be worth pulling the pump. But I've also wondered about a stuck open injector. Cause when driving, there always seems to be the faintest bit of missing. The dizzy was replaced, timing set 12deg TDC, ignition control module replaced, coil, wires, plugs, same behavior.

I did read somewhere else a simple test to try:

Unplug all the injectors and turn key on to prime system
If the pressure stays it's not a bad fuel pump.
With pressure steady, plug in one injector at a time.
If pressure drops as you plug one in......ding ding ding ding
 
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Mustang5L5

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Feb 18, 2001
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Bad check valve in the pump most likely. However it shouldn't affect how the car runs. I drove many years with a failed check valve that the FP would instantly drop to 0 once the engine was off. Engine ran strong

If you are maintaining 39psi at WOT, then the pump is moving enough fuel to keep the engine running.
 

jozsefsz

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Aug 11, 2013
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I wouldn't sweat it, same experience as @Mustang5L5. Only thing the fast depressurization can cause is making you have to crank a bit more before the car starts. It does not cause stalling, especially if your fuel pressure is good at idle.

More likely you need to adjust your throttle plate and idle air bleed according to the famous surging idle checklist, and do an ordinary check for vacuum leaks. A hint of missing at idle is normal if your timing is more advanced than your engine likes. Try backing off a degree or two and you'll see it smooth out. A vacuum leak could cause that too.

A stuck-open injector will announce itself with the huge cloud of smoke (white raw fuel vapor) coming out of the tailpipe and horrible driveability. A cylinder balance test can help you eliminate that more easily than unplugging injectors (not so easy when you have to take the upper intake off 8 times).
 

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