Losing Fuel Pressure

I had this problem once, and it ended up being a stuck open injector. Check your fuel pressure regulator first. Unplug the vacuum line that is connected to it and see if fuel comes out of there(it shouldnt). Also, have someone turn the ignition on, but dont start the car. Listen to the fuel injectors. When mine was leaking you could almost hear fuel dripping inside the intake

A word of warning: injectors are designed to work with a pulse of electricity. Applying a continuous voltage can overheat the injector and burn out the coil inside the injector.


Fuel pressure OK, the injectors are not firing, OR one or more injectors stuck
open

Do a cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a
jumper wire or paper clip to put the computer into test mode. Start
the engine and let it go through the normal diagnostic tests, then
quickly press the throttle to the floor. The engine RPM should exceed
2500 RPM's for a brief second. The engine RPM's will increase to about
1450-1600 RPM and hold steady. The engine will shut off power to each
injector, one at a time. When it has sequenced through all 8 injectors,
it will flash 9 for everything OK, or the number of the failing cylinder
such as 2 for cylinder #2. Quickly pressing the throttle again up to
2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is
weak and isn’t putting out power like it should. See the Chilton’s Shop
manual for the complete test procedure


The red wire on each injector is powered up whenever the ignition switch is
in the Run position. The computer provides a ground to complete the circuit
and fire the injector. The injector must have a ground to squirt fuel on
command. A short to ground in the injector return wiring can cause one or
more injectors to be continually open or triggered
The wiring for the injectors may have some bare spots in it causing the
injector to computer control wire to ground out. This would cause the
injector to remain on anytime the key was in the Run position. Remove the
injector wiring connectors from the injector. Note that each injector has one
red wire for power and a non red wire (wire some color other than red) for
computer controlled ground. With the key off, disconnect the computer
connector from the computer. Use an Ohmmeter between the non red wire
and ground. You should see more than 100000 (100K) ohms resistance.


See the following website for some help from Tmoss (diagram designer) &
Stang&2Birds (website host) for help wiring Mustang FAQ - Engine Information

Diagram courtesy of Tmoss & Stang&2birds



Using the above diagram, check the resistance between the injector and the
computer. Clean and check the 10 pin connectors since they are a potential
trouble source. Any resistance greater than 1.5 ohm between the injector to
computer wire and the matching pin on the computer connector is a problem.



See http://fordfuelinjection.com/?p=6 for more help
Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical





If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.



The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.

What you could do, with the car running is unplug each injector one by one and note how the engine reacts. For example: if you unplug one and the engine stumbles and wants to cut out, that injector is probably good as when you unplugged it, it stopped working, and caused the engine to stumble and starve for fuel. If you unplug one and it has no effect that probably means there is something up with that injector. This is how i found my faulty injector.

Hope that helps

Good luck

87foxstang said:

What you could do, with the car running is unplug each injector one by one and note how the engine reacts. For example: if you unplug one and the engine stumbles and wants to cut out, that injector is probably good as when you unplugged it, it stopped working, and caused the engine to stumble and starve for fuel. If you unplug one and it has no effect that probably means there is something up with that injector. This is how i found my faulty injector.

Hope that helps

Good luck

Click to expand...

It'd be easier and more precise to do a cylinder balance test. Jsut remember that one has to further investigate the cause of the issue.

Strype, have you used fuel-line pliers on the return line to see if this helps you maintain pressure?