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Fuel pressure low

446 Views 8 Replies 5 Participants Last post by  Funnyontheinside, 
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1996 Z28 LT1 T56. Thanks for reading and hopefully commenting on my problem.

Fuel pump is working, but the pressure is low. It's only about 28 with key on, engine off. It'll start, but it stays at around 28 ( but needle seems to vibrate ). It seems to run just fine even though this is about 12 psi too low. It's only an issue because sometimes it will only have about 22 psi and it won't start.

Here's the funny part. When I rev the engine, the fuel pressure drops down to about 20 psi, but the engine doesn't die. Like I said, it runs strong. From my understanding, revving the engine is supposed to raise the fuel pressure? Why does mine go down? It returns to 28 as the rpms drop back to idle.

I did the fuel pressure regulator test with a hand vac. Pumped to 21 on the gauge, it holds without dropping. I also tested the vacuum from the line that feeds the FPR, and it was 21 at idle and dropped when revving, which is normal.

Am I looking at a bad check valve or what? Are there any other options for the problem? I don't want to drop the tank and change the pump for nothing.
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F
I suspect that the lines that connect the pump to the feed and return lines inside the tank have become compromised. They allow fuel to pass, but only to a certain pressure, until lines fail completely.

My 97 had similar odd no start for a while. Priming it multiple times seemed to help, but eventually, the lines failed. This took pulling the pump to fully diagnose, because the pump would still activate, and we could hear it, even though It couldn't deliver fuel to the engine to get it to start.

It is possible to cut an access panel into the car, however, I elected to drop the tank. I had just gotten it back on the road, and this gave me a chance to look in and check out the interior of the tank.

Good luck!
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El Matador
Black Bullit said:
1996 Z28 LT1 T56. Thanks for reading and hopefully commenting on my problem. Fuel pump is working, but the pressure is low. It's only about 28 with key on, engine off. It'll start, but it stays at around 28 ( but needle seems to vibrate ). It seems to run just fine even though this is about 12 psi too low. It's only an issue because sometimes it will only have about 22 psi and it won't start. Here's the funny part. When I rev the engine, the fuel pressure drops down to about 20 psi, but the engine doesn't die. Like I said, it runs strong. From my understanding, revving the engine is supposed to raise the fuel pressure? Why does mine go down? It returns to 28 as the rpms drop back to idle. I did the fuel pressure regulator test with a hand vac. Pumped to 21 on the gauge, it holds without dropping. I also tested the vacuum from the line that feeds the FPR, and it was 21 at idle and dropped when revving, which is normal. Am I looking at a bad check valve or what? Are there any other options for the problem? I don't want to drop the tank and change the pump for nothing.
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Did you replace the fuel filter?
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Leesimmons
El Matador said:
Did you replace the fuel filter?
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It’ll be either a faulty fuel pump/or pressure regulator/ or fuel filter. I have a 97 Camaro… had the same problem until I replace the fuel pump and pressure regulator. The fuel pump sock/ or in tank filter had deteriorated. Seemed to fixed my fuel pressure issue. Hope this helps.
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I did a little more testing yesterday just to make sure. The bad fuel pressure gauge has made me second guess every diagnosis. Measure twice, cut once.

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Turns out the problem is in the pump. Low pressure using everything in the car the way it is. It was slightly higher than the other day though. I hooked up another pump in series behind the fuel filter, powered it up, and got full pressure.

Looks like I'll be dropping the tank after all.
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Black Bullit said:
Looks like I'll be dropping the tank after all.
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Have you searched on the 'TRAPDOOR' procedure, cuts a hole and accesses pump from the top...
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bobdec01 said:
Have you searched on the 'TRAPDOOR' procedure, cuts a hole and accesses pump from the top...
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Car is too nice to cut up. I'll be dropping the tank tomorrow.
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B
Tank dropped, new AC Delco Gold pump installed, got full pressure. I'm not sure what exactly was wrong with the old pump, but that fixed it.
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Glad to hear it!
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