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Do I need a new fuel pump?

Old 04-12-2018, 08:30 PM
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1993C4LT1
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Default Do I need a new fuel pump?

93 LT1
I know fuel pressure should be at 42psi, key on engine off.

Mine is anywhere from25-30psi, it never goes above that at key on engine off.

Weird thing is, running the fuel pressure is fine.
Idle: 36-38psi
Vacuum off FPR: 42psi
Snap throttle test is good as well.

Any input?
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Old 04-12-2018, 09:14 PM
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Originally Posted by 1993C4LT1 View Post
93 LT1
I know fuel pressure should be at 42psi, key on engine off.

Mine is anywhere from25-30psi, it never goes above that at key on engine off.

Weird thing is, running the fuel pressure is fine.
Idle: 36-38psi
Vacuum off FPR: 42psi
Snap throttle test is good as well.
Snap throttle test isn't telling me much. It tells me how it performs at 5000 rpm WITHOUT a load. I'm more interested in seeing how it performs UNDER load. Tape the gauge to the windshield and do a WOT. That tells me how the pump keeps up.

Tell me how it is after shutdown. So if you turn the key on without cranking, pressure shoots up to 42. Turn the key off. Will it hold pressure for a while? What about the hose in the FPR? Does it smell of gas?
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Old 04-14-2018, 12:45 AM
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Oh yeah, it hold pressure for a while. Injectors, fpr and fuel filter are about 3 years old. Fpr line does smell like gas, but it has been like that since new, and it's a part from the dealer. Don't know what fuel pressure is at load.

It's just odd that it doesn't make 42psi at key on anymore.
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Old 04-14-2018, 08:24 AM
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Sounds like a voltage issue to me. When you start the car the alternator is running. Maybe hook up a battery charger to check key on pressure and see what happens. In either case I wouldn't worry about replacing the pump unless the car was running funny.
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Old 04-14-2018, 09:54 AM
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Originally Posted by 1993C4LT1 View Post
Oh yeah, it hold pressure for a while. Injectors, fpr and fuel filter are about 3 years old. Fpr line does smell like gas, but it has been like that since new, and it's a part from the dealer. Don't know what fuel pressure is at load.

It's just odd that it doesn't make 42psi at key on anymore.
That really sounds weird. I don't know what to say.

Lets try this. Use proper hose crimpers and crimp the return line. Turn the key to run and see if it gets pressure?

BTW, when you did the pump, was the pulsator replaced by a fuel hose that was rated for immersion or was the pulsator kept?
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Old 04-14-2018, 10:34 AM
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Never replaced the fuel pump. Not sure if it has ever been replaced either. Car only has 84k miles. With that said, went to go start it just now, had 25psi of fuel pressure. It fired up perfectly. Have not noticed any weird drivability problems.
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Old 04-14-2018, 10:38 AM
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Originally Posted by 1993C4LT1 View Post
Never replaced the fuel pump. Not sure if it has ever been replaced either. Car only has 84k miles. With that said, went to go start it just now, had 25psi of fuel pressure. It fired up perfectly. Have not noticed any weird drivability problems.
That is probably too low so kudos to the ECM for compensating. I'd definitely check what the stock fuel pressure is before going too far. I place NEGATIVE value on most SOTP dyno feelings. ECM compensates, you feel it is running "just fine" and one day, circumcisions force the car out of the adjustability area and we have a problem then. Usually far away from home.

Do the crimp test first and see if the feed or fuel line crimp changes anything. Crimp return line and turn the key to run. See if it gets to the right pressure. If not, have your assistant turn the key and a second after, crimp the feed line to see if it holds the pressure
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Old 04-14-2018, 11:07 AM
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Stock lt1 fuel pressure at key on is 42psi. And when my car started, fuel pressure was 36-38psi, that is,with,in spec. I'll do the crimp test.
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Old 04-16-2018, 11:21 PM
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Originally Posted by bosshog8 View Post
Sounds like a voltage issue to me. When you start the car the alternator is running. Maybe hook up a battery charger to check key on pressure and see what happens. In either case I wouldn't worry about replacing the pump unless the car was running funny.
Battery is at 12.41 volts sitting over night. Doubt it's a voltage issue, but good suggestion! Yeah, car does not run weird at all.
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Old 04-16-2018, 11:23 PM
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Originally Posted by aklim View Post
That is probably too low so kudos to the ECM for compensating. I'd definitely check what the stock fuel pressure is before going too far. I place NEGATIVE value on most SOTP dyno feelings. ECM compensates, you feel it is running "just fine" and one day, circumcisions force the car out of the adjustability area and we have a problem then. Usually far away from home.

Do the crimp test first and see if the feed or fuel line crimp changes anything. Crimp return line and turn the key to run. See if it gets to the right pressure. If not, have your assistant turn the key and a second after, crimp the feed line to see if it holds the pressure
Ok, dumb question. Where is the return line? And do I just put a towel over the return line to not hurt it while crimping?
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Old 04-16-2018, 11:43 PM
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Originally Posted by 1993C4LT1 View Post
Ok, dumb question. Where is the return line? And do I just put a towel over the return line to not hurt it while crimping?
http://www.corvettemagazine.com/tech-articles/1984-1996-c4-corvette-fuel-sending-unit-installation/

I believe the lower 2 are the vent and return line and the top which is bigger is the feed. I'd use hose crimper pliers
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Old 04-17-2018, 01:58 AM
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Originally Posted by 1993C4LT1 View Post
93 LT1
I know fuel pressure should be at 42psi, key on engine off.

Mine is anywhere from25-30psi, it never goes above that at key on engine off.

Weird thing is, running the fuel pressure is fine.
Idle: 36-38psi
Vacuum off FPR: 42psi
Snap throttle test is good as well.

Any input?
A Fuel pump is cheap compared to a tow truck, I have had my c4 over 20 years 170,000 miles and two fuel pumps.
Of course it failed after 10 years on a 107F day, the little woman was not happy. So I average 10 years till the fuel pump stops working...
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Old 04-17-2018, 12:31 PM
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Originally Posted by gerardvg View Post
A Fuel pump is cheap compared to a tow truck, I have had my c4 over 20 years 170,000 miles and two fuel pumps.
Of course it failed after 10 years on a 107F day, the little woman was not happy. So I average 10 years till the fuel pump stops working...
Nothing to do with 10 years or 107 degree weather. It was the wife. If you had been driving solo for 20 years it would have been fine. The Automotive Gods were trying to screw with you since you missed the ritual carburetor sacrifice.and that was the best way
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Old 04-17-2018, 08:56 PM
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Originally Posted by gerardvg View Post
A Fuel pump is cheap compared to a tow truck, I have had my c4 over 20 years 170,000 miles and two fuel pumps.
Of course it failed after 10 years on a 107F day, the little woman was not happy. So I average 10 years till the fuel pump stops working...
Very true. If it doesn't pass the return line crimp test, what fuel pump would you guys recommend? Car is stock.
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Old 04-17-2018, 10:15 PM
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Originally Posted by 1993C4LT1 View Post
Very true. If it doesn't pass the return line crimp test, what fuel pump would you guys recommend? Car is stock.
Assuming that the FPR is not leaking and the injectors are good and the pulsator is not leaking get the appropriate one from racetronix
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Old 04-17-2018, 11:04 PM
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How do I know if the FPR is not leaking? There is never raw gas in the fpr vacuum line. Always a gas smell, even with the new fpr. Injectors are 2.5 year old Bosch 3. Leakdown on fuel pressure is slow. I'll have to run another test to give an approximation.
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Old 04-18-2018, 01:04 AM
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Originally Posted by 1993C4LT1 View Post
How do I know if the FPR is not leaking? There is never raw gas in the fpr vacuum line. Always a gas smell, even with the new fpr. Injectors are 2.5 year old Bosch 3. Leakdown on fuel pressure is slow. I'll have to run another test to give an approximation.
Lets try this. You have an idea how fast you leak down. Crimp the return line, prime the feed and crimp the feed also. See if the leakdown is slower. It should be.

IDK if the pulsator is leaking since it is slipped on and old. Old stuff won't perform as new usually will. I guess if you want to buy the kit that will remove the problem, THIS is it. No running to the parts store for anything and it will come with the bolts to replace the screws you take out when removing the pump assembly. Assuming you don't strip any of them. It makes another R&R less of a scary thing.
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Old 04-18-2018, 08:39 PM
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I've been doing the research on the racetronix 255 kit. How does all that extra wiring run through the car? I don't understand the wiring kit at all, to be honest. I know it's an option, but I don't want to risk it on factory wiring.
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Old 04-18-2018, 09:11 PM
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Originally Posted by 1993C4LT1 View Post
I've been doing the research on the racetronix 255 kit. How does all that extra wiring run through the car? I don't understand the wiring kit at all, to be honest. I know it's an option, but I don't want to risk it on factory wiring.
First off, if you are stock, either kit is fine. The 255 kit gives you the extra room to move if you should need the fuel for whatever reason. Blower, bigger motor, nitrous, etc. It is $10 more so why not? The wiring probably runs under the car but I have the 255 but didn't get the wiring. I doubt there is a risk of it blowing up. Besides, you have the problem right now. Add more parts, introduce more variables. KISS
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