Low fuel pressure

Good morning,


Did you flush the tank of all the old fuel? Sitting that long, the fuel is no good and must be changed.

If the pressure is that low, the pump is the issue. The new pump may be loaded with dirt and debris from the old fuel in the system.

As far as the injectors, good chance they are the issue as well because all the dirt and debris could be up there as well.

https://www.2carpros.com/articles/how-fuel-injection-systems-work

Roy

We did clean out the tank when we replaced the pump/sending unit (since we had to drop the tank anyways). And I ran some fuel injector cleaner as a precaution knowing how long it had been sitting.

Injector cleaner, the additive, has no effect at all on the injector.

I would remove the injectors and have them cleaned or replaced.

Roy


REMOVE
Disconnect negative battery terminal.
Relieve fuel system pressure. (Refer to Fuel Delivery / Service and Repair.
See: Fuel Delivery and Air Induction > Procedures
Intake manifold plenum.

NOTICE: Use care in removing injectors to prevent damage to the electrical connector pins on the injector, and the nozzle. The fuel injector is serviced as a complete assembly only. Since it is an electrical component, do not be immerse it in cleaner.

Fuel rail assembly.

DISASSEMBLE
Injector retainer clip.
Discard retainer clip.
MPFI injector assembly.
Injector O-Ring seals from both ends of injector and discard.

CAUTION: Each injector is calibrated for a specific flow rate. When replacing fuel injectors, order replacements with the identical part number as the old injectors.

ASSEMBLE
Lubricate new injector O-Ring seals with engine oil, and install on injector assembly.
New injector retainer clips on injector assembly.
Position open end of clip facing injector electrical connector.
MPFI injector assembly into fuel rail injector socket with electrical connectors facing outward.
Push in far enough to engage retainer clip with machined slots on rail socket.


INSTALL
Fuel rail assembly. Refer to Fuel Rail.

Inspect
Temporarily connect negative battery terminal.
Turn ignition switch to the "ON" position for two seconds, then turn to the "OFF" position for ten seconds. Again turn to the "ON" position and check for fuel leaks.
Disconnect negative battery terminal.

Intake manifold plenum.

Tighten fuel filler cap.

Negative battery terminal.

IDLE LEARN PROCEDURE
Any time the battery is disconnected, the programmed position of the Idle Air Control (IAC) valve pintle is lost, and replaced with a "default" value. To return the IAC valve pintle to the correct position, perform the following procedure:

Restore battery power.
Connect Tech I "Scan" tool.
Select "IAC SYSTEM," then select "IDLE LEARN" in the "MISC TEST" mode.
Proceed with idle learn as directed.

This procedure allows the Electronic Control Module (ECM) memory to be updated with the correct IAC valve pintle position, for the vehicle, and provide a stable idle speed.

Try this:
* Connect your fuel pressure gage to the fuel rail.

* Unplug the vacuum hose that goes to the Fuel Pressure Regulator. (the fuel pressure regulator is located under the intake plenum - it should be possible to locate the vacuum line that runs to it. Since you can't get to the fuel pressure regulator with the intake in place, follow the vacuum line to its source and unplug it there.)

* Start the engine to see if the fuel pressure goes higher than the 10 psi you reported (it should).

* If it goes to normal or near normal, then the Fuel Pressure Regulator is faulty and needs to be replaced.


*****
If you need to replace the Fuel Pressure Regulator, this is the procedure.

To replace the fuel pressure regulator on a 1987 to 1990 Chevy Celebrity with 2.8L/3.1L engine:

1. Remove the air duct from the throttle body.

2. Remove the two bolts that hold the throttle body to the plenum and move it slightly aside. You do not need to remove the throttle body from the engine.

3.Remove the nuts that hold the EGR valve to the plenum along with the vacuum line. Move the EGR valve aside, it does not need to be removed from the engine.

4. Remove the seven bolts that hold the plenum to the intake manifold.

5. Lift the plenum off of the intake manifold. Be careful to move the plastic vacuum lines out of the way without breaking them.

6. Unplug the vacuum line from the pressure regulator.

7. Remove the two fuel lines from the pressure regulator and move them aside.

8. Remove the two screws that hold the pressure regulator bracket from each fuel rail. Remove the two screws that hold the rails in place from each side..

9. The fuel rails can now be moved away from the regulator . The "O" rings may be stuck and require some force to pull them out of the fuel rails.

10. Remove the two screws that hold the bracket to the fuel pressure regulator.

11. The fuel pressure regulator should now be loose. There are four fuel connections, two on each side. One on each side is larger, the "O" rings often stick in their bores in the fuel rail, remove them from the fuel rail if they are stuck there. The other two connecting fittings have two "O" rings each. Sometimes they stick in the fuel rail, sometimes in the regulator. If they stick in the regulator remove them for use with the new regulator.

The new fuel pressure regulator should come with replacement "O" rings. A dab of oil on each will make re-assembly easier.

Re-assembly:

Reattach the bracket to the fuel pressure regulator. With the new "O" rings in place on the regulator slide the fittings into the fuel rails bringing them back in place. Put the screws that hold the bracket back in place and put the four screws that hold the fuel rails back in place.

Re-attach the fuel lines and the vacuum line to the fuel pressure regulator.

Using fresh gaskets put the plenum back in place, route the vacuum lines back in place. Re-attach the EGR valve and the throttle body along with the air duct from the air filter to the throttle body.

Thanks to everyone for the responses. I will try these things and update if still having issues.!

You are welcome.

We are always glad to help.

Roy

Sorry for the late response, its been raining all week and I haven't gotten to work on the car until now. I tried what FREEMBA suggested and the fuel pressure did not change. Do you think the new pump may have gone bad?

Yes, I do. As I stated in my first response, dirt or debris could have got in the new pump and is causing the low-pressure issue.

The simple answer is yes, you need a new pump. Look in the tank for any debris or dirt at the bottom.

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

Roy

We did clean out the tank when we replaced the pump/sending unit, but I agree all the problems point to a bad pump. Luckily that part is pretty cheap, it’s just having to drop that gas tank again to replace it. Thanks for all the help, I’ll let you know if that doesn’t fix it!

You are welcome.

Always glad to help.

Roy

Sorry for the late response, it has been raining a lot here lately and haven't had the chance to get out to work on it until today. Replacing the fuel pump did restore the proper fuel pressure, but the idle is still a bit rough and it sputters out when you press the accelerator (taking your foot off the pedal restores it back to rough idle). On a hunch, I unplugged the Mass Airflow Sensor and now it doesn't sputter out anymore, but still idles rough (I assume because the sensor is unplugged). Should I replace the MAS?

Was there a code for the sensor?

You could try that as it was a very common failure for that year.

Roy

The check engine light is only on when the sensor is unplugged (probably due to it being unplugged). I do not have a diagnostic tool to check the code though.

Okay, try the sensor. If you get one, get a AC/Delco from your supplier.

Roy

Okay. I was thinking of also replacing the O2 sensor as well, so all the intermix stuff will be new.

You could but I doubt it has anything to do with your issue.

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

Roy

Just to test I unplugged the O2 sensor and it will crank then sputter out immediately. So I guess it’s working?

With everything plugged in, it will idle rough and shut off when you put it in gear. If I unplug the MAF sensor, it will still idle rough but will not shut off when put in gear. It will also move Forward/backward but has no power even with the pedal to the floor. What do you think it could be other than the MAF sensor?

Okay, let us start with the fuel pressure. Can you tell me the fuel pressure?

No to the mass air flow and the O2 sensor. They will not cause this issue. If they did, they would code.

Roy

Today I plugged the MAF sensor back in and now it won’t even stay running at all, it sputters out immediately. But if I unplug it again it will run. I’ll get those fuel pressure readings later when my neighbor brings the gauge over...

Sounds good. Let us eliminate a fuel pressure issue before we move on to the next step.

Roy

Okay, we hooked up the gauge and with it idling it’s getting 35-40 PSI, but it doesn’t go up when we rev the engine. We are going to try replacing the fuel filter (again) since it’s cheap and check it again. hopefully it’s not the pressure regulator....

Revisit the post I sent you on July 6, 2020, it may help you diagnose the fuel pressure regulator (and may explain why the fuel pressure doesn't increase with engine speed).

Hello, we are still getting the same pressure with the vacuum hose disconnected. It’s possible the fuel filter is partially clogged? We cleaned the tank out but who knows what leftover gunk might have gotten in there, considering the new fuel pump we put in originally also burned up.

The pressure should rise when you disconnect the regulator hose.

It may only go up 5 pounds or so but it should rise.

What brand pump did you use?

Roy

The original pump we installed was a generic one and it burned out. I replaced it with an AC Delco one and it will crank and idle but has no power when you rev it and shuts off after a few revs. It will crank right back up though. Fuel pressure doesn’t go higher than 35-40 PSI, even with the regulator vacuum hose disconnected.

I attached the chart for you for the pressure.

With the key on, engine off, what is the pressure?

Roy

Key on, engine off, the pressure goes up to 35-40 then drops to 0 until I try to crank it then it goes back up to 35-40.

Looks like your pump has a bad check valve.

Roy

Here are flow charts to use in order to diagnose a fuel pressure problem for your car. Just remember that the problem of the vehicle stalling can be caused by many different things, so let's use these charts in order to either cure the problem or at least eliminate the fuel system as a possible suspect.

Thanks for all the help. I ended up selling the car as-is due to becoming unemployed from COVID-19. Hopefully the new owner will have better luck with it...