no fuel pressure
Thread Starter
5th Gear
Joined: Apr 2012
Posts: 5
Likes: 0
no fuel pressure
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.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
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.
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.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
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.
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.....
Thread Starter
5th Gear
Joined: Apr 2012
Posts: 5
Likes: 0
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.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
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.
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.
Race Director
Joined: Dec 2006
Posts: 10,383
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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.
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.
Last edited by 94z07fx3; Apr 19, 2012 at 01:53 AM.
Race Director
Joined: Jun 1999
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From: Merritt Ils Fl
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Le Mans Master
Joined: Jan 2006
Posts: 5,621
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From: Orlando FL
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.
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.
Thread Starter
5th Gear
Joined: Apr 2012
Posts: 5
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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!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
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From: Orlando FL
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.
Intermediate
Joined: Jun 2012
Posts: 49
Likes: 2
No fuel pressure
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.
6th Gear
Joined: Jun 2024
Posts: 6
Likes: 0
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.
Moderator
Joined: Jul 2005
Posts: 28,808
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From: Parrish FL
St. Jude Donor '06 thru '26
ive got an 84 same issue crank no start rats did a number on the wiring harness in the dash but i replaced fuel hanger assembly the filter and rewired the fuel pump relay connector and put a new relay on it. I cant find the theft relay but I think the rats ate it as it sits behind the radio where the most harness was destroyed. Any ideas? Ive checked voltage to fuel pump and the connector to it was good last I checked.
