Fuel pressure drops after pump primes lines
02-23-2010, 11:17 AM
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Fuel pressure drops after pump primes lines Hey guys, ive got a hard starting issue. The previous owner said he replaced the fuel pump right before i took ownership of the car. He said it was a 255lph pump(no idea what brand). Anyways, ive put a pressure gauge on it and when you turn the key to start the car, the pump runs for 2 or 3 seconds and the pressure comes up to about 55 psi but then once the pump stops, all the pressure is relieved. So if the car isnt started within that small window while it has pressure then it cranks and cranks before itll start. Any ideas??
02-23-2010, 06:41 PM
#4
Could be alot of other things, test it to find what is leaking down before you replace anything. The fuel pump assembly includes the fuel regulator, so its probably safe bet its not that if it was just replaced unless they bought a chepo ebay or autozone pump assembly. Why did the prior owner replace the pump assembly and was it a gm replacement?
02-24-2010, 08:38 AM
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He didnt say exactly why he replaced it or with what brand, but he acted like it was a good one that would keep up with the 150hp wet kit he had on there. I have removed the nitrous kit now.
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02-25-2010, 04:56 PM
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Remove the pump from the sender and look at it. It may say what brand it is...or it may not. Typically a fast bleed down like you are describing is the pump, the regulator, or the fuel line from the pump to the bottom of the sender.
02-26-2010, 09:40 PM
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An injector that causes an immediate bleed down in pressure would have to be stuck in the wide open position. Typically the injectors I have seen leak will just drip and slowly bleed down over the course of a few hours. If its an immediate bleed down like he is describing, that would point more towards fuel flowing back into the tank back thru the feed line. Not saying it cant happen, just rare.
02-27-2010, 04:15 AM
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02-28-2010, 10:05 AM
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Is the tre340 a decent pump? My fuel pressure is always solid except for when the pump stops running before the car is started. Is there a pressure regulator in between the fuel rails also? I located the one with the fuel pump but i dont know of any way to see if its bad.
02-28-2010, 11:02 AM
#18
Ok i'mma try to help you through this problem logicly. Your car has a returnless type fuel system with the pressure regulator in the fuel tank with the pump. There is no return or regulator up at the fuel rail, the round object you see mounted on the fuel rail is "pulsator" or accumulator. Its job is to smooth the pulses in the fuel rail, everytime a injector opens and closes the fuel rail gets hammered with a pulse, that round object absorbs the energy.
Ok on to testing to find your leak, I'm almost 100% sure you have a leaking check valve in the fuel pump. easy way to test that would be to replace it of course. The other way is to CAREFULLY do this.......
Under the car at the fuel filter attach a fuel pressure gauge. This will eliminate EVERYTHING but the pump for testing. You are going to use a piece of high pressure fuel injection hose OR other safe way to connect to the line going to the fuel filter Or if its easier connect to the outlet of the fuel filter. SAFELY attach your fuel pressure tester so that ends the fuel system. The rest will be disconnected. Turn the key on and watch the pressure gauge, it will go up to about 75-80 psi and should STAY there until you release the pressure. If it doesn't the pump check valve is bad and the pump needs replacing.
My honest opinion without even looking at this is the pump is leaking back. Its very common. Good Luck.
Ok on to testing to find your leak, I'm almost 100% sure you have a leaking check valve in the fuel pump. easy way to test that would be to replace it of course. The other way is to CAREFULLY do this.......
Under the car at the fuel filter attach a fuel pressure gauge. This will eliminate EVERYTHING but the pump for testing. You are going to use a piece of high pressure fuel injection hose OR other safe way to connect to the line going to the fuel filter Or if its easier connect to the outlet of the fuel filter. SAFELY attach your fuel pressure tester so that ends the fuel system. The rest will be disconnected. Turn the key on and watch the pressure gauge, it will go up to about 75-80 psi and should STAY there until you release the pressure. If it doesn't the pump check valve is bad and the pump needs replacing.
My honest opinion without even looking at this is the pump is leaking back. Its very common. Good Luck.
02-28-2010, 06:51 PM
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okay im having the same problem but the tre pump the guy posted is a 235 lph, isnt the stock pump at 255, and i hear that ebay isnt the place to buy fuel pumps! ive seen this exact one on ebay, any opinions..