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post #1 of 5 (permalink) Old 10-14-2019, 08:58 PM Thread Starter
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No fuel pressure

1997 Z28. Freshly rebuilt engine ( stock ) just put back in. Hooked everything up but the cooling system ( wanted to hear it run first in case the opti is bad ) since it would be easier to replace a bad opti with all the extra room up front. It cranks, and hit with some starting fluid. No fuel pressure at the rails.

Before I drop the tank and replace the pump, I'd like to troubleshoot to make sure that's the problem. Tomorrow after work, I'm going to get under the car and test for voltage. Obviously if it's getting it, the problem is going to be the pump ( or the wiring in the tank ).

But let's assume I get no voltage back there. What are the other possible causes of a pump not being engaged? I looked for a fuse or relay, but couldn't find one. Is there one? If so, where?

Is there any other systems that shut off fuel? I don't think it's VATS because the security light goes off after a few seconds.

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post #2 of 5 (permalink) Old 10-15-2019, 08:19 AM
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Don't forget the relay for the fuel pump. It could have a problem. I had to use a 94 wiring diagram but, Relay should get power to it's points by IP fuse # 3 which is pcm/batt fuse. So make sure there is power at terminal # 87 of fp relay. It's an orange wire. Also make sure terminal 86 of fp relay has a good ground. Black/white wire.

Also on passenger side inner wheel well, you'll find the fuel pump prime wire. It should be a red wire just hanging out. Connect wire to it and run to battery positive post. Have relay in place. Fuel pump should run. If it does your problem could be relay itself. fuse, if there is no power on orange wire to relay. Also Pcm must supply power to relay coil at terminal 85. Dark green/white wire.

If all the above are good, then problem would be after relay. If fuel pump didn't run when you powered the red prime connector, because prime connector is a direct path to fp, check fp ground which is the black wire. If ground is good, then fp is bad or it's wire has become disconnected at rear of vehicle or in tank connector.
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post #3 of 5 (permalink) Old 10-19-2019, 01:52 PM Thread Starter
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Still nothing after jumpering. I even got under the car and checked it at the connection right before the tank. Some interesting results.

With the jumper connected on the passenger shock tower, I had 12 volts at the leads going to the tank. So this confirms my pump is probably bad.

I unhooked the jumper and tested voltage with just the key on. It only gave me about 4.5 volts, but then dropped to zero. I would've thought it would give me the full 12 volts. What problem could be causing this strange anomaly? Or is that normal on the priming cycle until the engine starts?

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post #4 of 5 (permalink) Old 10-19-2019, 04:57 PM Thread Starter
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Okay, found a pic online of the plug with the leads marked. I had hooked to the left and middle. The middle isn't ground, that's the one on the right. I connected to the two outside leads, hit the key, and had 12 volts for a second or two. Enough to have primed the pump, if it were working.

I put a gallon of gas in the tank. Could it just be that it's too low? The one time the gauge worked, it showed just under 1/4 after I put that gallon in. I'd hate to think I'm doing all this work for nothing. Would I hear the pump try to prime even if the tank is empty? Because it's completely quiet.

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post #5 of 5 (permalink) Old 10-19-2019, 08:56 PM
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If you hooked 12 volts to prime connector and you can't hear pump run, then either pump is toast, or wire in gas tank has become damaged or disconnected.
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