judwall

I have an 89 that I purchased not running. Engine cranks, but won't run. It will run if I pour a little gas in the Plenum until that runs out. Injectors blink with a test light. I bought a pressure gauge but it is reading nothing. I can hear the fuel pump turn on for a couple seconds when I turn they key on. Replace fuel filter to no avail.

pcolt94

You can depress the Schrader valve and see what's there. There should be about 40 lbs and it will squirt a long way. If it just drips out, there is not much there.

So either the pump is no good or there is a restriction to flow. In the tank at the end of the pump there is an item called a pulser. If it fails or breaks, it will kill the pressure and flow. Never the less I would look at the items in the tank at this time. The unit comes out pretty easy from the rear.

leesvet

Then the pump sock is totally plugged, OR the inline filter under the passenger seat area is plugged.

If there is some fuel in the rails, enough to have a little spray out of the schrader valve...thats deceptive. It takes at least 30 psi to spray thru the injectors. Normal is 40. IF you charge the system, press the valve with a pick or nail, it should spray enough to soak everything within 3 ft. If its just a 6" spray...thats nothing.

Pull the pump, may as well have a new one bought and ready with NEW tank gasket and new strainer and go thru the pump/sender assy.
The ONLY other thing that could cause zero or no pressure is a defective pressure regulator and that is usually diagnosed by fuel getting into the vac line to the regulator.
A FSM will describe how to pinch off return lines to test the regulator and pump check valve.

BTW..

once you DO get pressure, it should be 40 psi key ON, and hold pressure for several hours...slowly dropping after the first 30 minutes of holding the full pressure. Should be 20 psi in the system tomorrow morning.....

judwall

Thanks for the help, I have replaced the fuel pump and the inline filter. Maybe it is something in the fuel line itself. I think I will disconnect the inline filter and see if I get anything out. I suspect I will get a little like when I replaced it. I have pressed in the schrader valve and most times just got a dribble. One time it shot up 2 or 3 feet. Thanks for the input.

Cliff Harris

The ECM turns on the fuel pump for 2 seconds when you turn on the key. It does this to pressurize the fuel rails to prepare for engine start. It shuts off after 2 seconds so the fuel pump won't be running constantly while the ignition is on, engine not running.

After the initial 2 seconds, the ECM will not turn on the fuel pump again until it sees DRPs (Distributor Reference Pulses), meaning that the engine is cranking/running. A bad ignition module in the distributor or wiring problem might cause this.

There is a backup system: an oil pressure switch on the back of the engine will turn on the fuel pump when the oil pressure reaches some value I don't remember (4 or 6 PSI).

You can force the fuel pump to come on by applying 12 volts to terminal G of the ALDL connector. The ECM bypasses this connection when the engine is running, so do this test with the engine off. There is fused 12 volts on the cigarette lighter at all times, so that is a convenient place to get it. I have always thought it would be nice to wire 12 volts into the ALDL connector pin H just for this test...

Monitor your fuel pressure while cranking to see what's happening.

illenema

It might be the oil pressure sensor switch, it thinks there is no oil pressure so its wont let the car start

94z07fx3

Tape the jaws of a pair of visegrips. Clamp off the return line to the gas tank. If you remove the fuel door you will see two rubber lines that are easy to pinch off. I forget which one is the return but you can figure that out by either tracing it to the front where the supply will have the filter on it or by pulling the fuel pump and seeing which one comes out of the pump. Test for fuel pressure as you have before. If you have fuel pressure now then the fuel pressure regulator is failed. If you still do not have pressure then you have a failed check valve inside the fuel pump.

Clogged fuel filters and socks will normally present as a car that idles ok but dies or sputters on throttle opening.

The oil pressure sending switch supplies power to the fuel pump in parallel with the fuel pump relay actuated by the ecm. The oil pressure sending switch will never keep the car from running whether you have oil pressure or not.

Muffin

Not true. I believed this for years until someone here proved me wrong. I am with Cliff here, force power to the pump.

leesvet

all ya gotta do is install the GM paper clip in the ALCL

pcolt94

From what I have read so far and the facts, these are my current thoughts.

Fuel pump replaced, so I can't believe the sock is clogged, that would have been visible.

Even if the ECM did not keep the pump running from the pulses the fuel rail should still pressurize from the 2 second run when the key is turned to ON. The oil pressure switch which closes to put 12 volts to the pump only requires 3-4 psi of oil pressure to close. They don’t fail much and between the switch and the ECM closing the fuel pump relay, I don’t see both being bad at same time and don’t think there is a power to the pump problem.

The fuel filter has been replaced.

I would still like to have the pulser checked out thoroughly. If it clogs, it will kill fuel flow. Aside from some strange event happening, I can't think or anything else to look at other than the FPR and it would be real strange for it to close down.

Another troubleshooting method is to pull the rubber output fuel line off the tank and connect another hose to the pipe. Then run the pump and see what comes out. Then you might have a better idea if it is tank or car (other) related.

judwall

Turned out to be the fuse panel. There was some corrosion so I replaced all fuses and cleaned the contacts. I noticed the fuel pump fuse contacts were broken. I lightly bent the contact up and put the fuse back in and noticed the fuel pressure gauge building pressure. Turned the key and it fired right up. Thanks for all the help. I have learned a ton from this forum!

pcolt94

Glad you got it going. Don't quite understand, you did get the pump to run when you turned to key to ON. Maybe it did not run long enough due to the poor power connection. Never the less, seems like you got it.

Steve Goetsch

Might seem overly simple but my 96 as of today has 42k on it. Last year I replaced the fuel pump, but if I don't drive it for awhile I sometimes have to tap the gas filler if it don't start to "wake up"the fuel pump.