Community Forums

subford · 04-23-2014, 08:25 AM

The fuel pump should be able to pump near 95psi into a blocked head. The Fuel pressure regulator opens the head to maintain 39-40psi with no vacuum on its nipple. With max vacuum pulling with the spring the pressure will drop to about 29-33psi at idle depending on the engine vacuum. This is to maintain the 39psi fuel pressure across the injector under all driving conditions and throttle settings. Then the PCM Computer changes the time duration the injector is open to adjust the fuel mix.

Any air pressure put on the nipple of the fuel pressure regulator from a hand pump will make the fuel pressure go higher than the 39psi.

If the fuel pump can not maintain about 39psi pressure under full load going up a hill at WOT then I would say you have a bad fuel pump.

Elexwiz · 04-23-2014, 08:40 AM

Subford, I just found another piece of info that said your pre-start fuel pressure, after the pump primed the rail, should be up around 40 psi. If, after a few "key-on, key-off" movements, you do not have 40 psi then it's a bad/weak pump. Would you agree with that?

subford · 04-23-2014, 01:03 PM

Sometime but I have never liked that way of turning the key on and off as you have no way of telling how long the fuel lines are and how long the key was in the on position. Also if on a single tank as yours even if the check valve in the tank pump is bad it would make no difference in the running of the engine but mite make it a little harder to start.

I like the pin #6 being shorted to pin #2 or grounded of the self-test plug with the key on. Then you know what you got. Then you need the road test to make sure it is running right.

After it sets for a while I always turn the key on and off about three times to make sure I have fuel at the engine before cranking it.

Elexwiz · 04-23-2014, 01:35 PM

Pin #6 shorted to pin #2 on which connector?

subford · 04-23-2014, 02:11 PM

Opps my bo-bo. You have OBD-II so they took your connector away.
Sorry.

You have to use a scanner with the option to leave the fuel pumps on with OBD-II.

Elexwiz · 04-23-2014, 02:29 PM

Ok. My scanner doesn't have that capability. I'll do a test drive tonight. Thank you!

Elexwiz · 04-23-2014, 04:46 PM

I hooked up my gauges and went for a nice test drive. The intake manifold vacuum performed exactly as it should. The fuel pressure is another story.

- At idle the fuel pressure is a constant 28 psi and the intake vacuum is a constant 20 inHG.

- When driving around residential areas (slow acceleration and speed) the fuel pressure drops to about 22 psi. Even as I slowly gain speed the fuel stays at 22 psi. The intake vacuum is around 15 inHG.

- During more aggressive acceleration from a stop light the intake drops to 10 inHG. The fuel pressure drops to about 20 psi! It will stay there until I reach my speed and back off the throttle. The intake vacuum will rise a bit and the fuel pressure will come back up to approx 25-27 psi. This same scenario played out each time I tested it.

- During WOT (or close to WOT) tests, whether from a dead stop or jamming the throttle while cruising, the intake vacuum dropped to 0 but the fuel pressure was less predictable. Sometimes it shot up to 40 psi before quickly dropping back to 30 and stayed there. When launching off the starting line sometimes the fuel pressure dropped initially but came back up to 30; sometimes it dropped to the low 20's and stayed there.

What do you guys think?

subford · 04-23-2014, 05:31 PM

Bad fuel pump or low voltage to fuel pump or a stopped up filter.

Elexwiz · 04-23-2014, 06:03 PM

Filter is brand new. I'll check the voltage when I get to the pump. Thank you for all your help!!!

TeJay · 04-24-2014, 08:32 AM

subford, Elewiz,
Great troubleshooting. I think you'll have it figured out soon.

Enjoyed,
TeJay

Elexwiz · 04-25-2014, 07:00 AM

Planning on dropping the tank on Saturday. I think I've found a way to move the rear jacks out of the way without disconnecting them from the leveling system. I'll let you guys know what I find. Thanks again.