What do these symptoms indicate?
1998 Ford Ranger 4 cylinder with a rough idle/misfire
There's no check engine light.
Its got new sparkplugs, ignition coils, new fuel filter.
When you start it up, it runs really rough like it's about to stall out but then after a few seconds it "evens out" but doesn't fully stop running rough.
I hooked up my fuel pressure tester to the Schrader valve and noticed that the fuel pressure is low. My manual says it should be at about 40 psi (35-45 is normal according to chilton manual)
However I'm only getting about 28-30 psi when it's running, and about 25 psi if you just prime it but don't start it up.
I then hooked up my fuel pressure tester directly to the fuel filter which is under the truck coming from the fuel tank, and primed it a few times to test pressure, and I only got 27 psi max,
BUT it drains out quickly, within 4 minutes it had gone down to 15 psi.
Could this be a sign of a bad fuel pump? Or something else?
Oh, lastly, with the truck running, if you disconnect the vacuum line from the fuel pressure regulator, the fuel pressure doesn't increase, it stays at 30psi.