Do i need a high volume fuel pump?
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Junior User
Joined: Sep 2002
Posts: 83
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From: Kingston Springs,TN
Do i need a high volume fuel pump?
Ok here's the deal. I have an 85 351w HO that i swapped into a 1990 Jeep Comanche. The motor is stock except for a Edelbrock 4barrel intake, Holley 670 truck avenger 4 barrel carb, Comp 274xe cam, and headers. Motor has good power until you give it more than half throttle. Then it will fall on it's face and start popping through the exhaust. Sometimes i can pump the gas when it starts it and it will clear up. So i'm wondering if i need a high volume fuel pump. What do ya'll think? Thanks
BTW- I'm running a new factory manual pump.
BTW- I'm running a new factory manual pump.
Lead Driver
Joined: Sep 2003
Posts: 7,018
Likes: 210
From: SoCal
Unless you have restrictions in your fuel line, a stock fuel pump should be good for at least 50 gallons/hour, which translates to about 700 hp. So unless you were actually putting out that much sustained power, it's unlikely that you drained the fuel in your bowl. You can check that by shutting down the engine at the moment that happens the next time. Then look down the throttle as you push the plate open, and see if the pump squirts enrichment fuel. If not, then I would look for an obstruction, or test the flow of the pump by directing it to another container as you run the engine.
Your symptoms do point to lean running problems, however. Is it possible that the secondaries are opening too fast too soon? Do you have a vacuum leak?
Your symptoms do point to lean running problems, however. Is it possible that the secondaries are opening too fast too soon? Do you have a vacuum leak?
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Junior User
Joined: Sep 2002
Posts: 83
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From: Kingston Springs,TN
From NAPA's website the stock pump that i bought is only 30 gph. There are no restrictions anywhere in the fuel system. Also there is no vacuum leaks. It could be possible that the secondaries are opening to fast. I did change out the spring that controls them with the "softer" spring it came with in the box.
Lead Driver
Joined: Sep 2003
Posts: 7,018
Likes: 210
From: SoCal
Well a softer spring will definitely open sooner, so I'm thinking that's the cause of your bogging run. Can you re-install the original spring and try the same runs?
Also, at 30 gph, that's over 400 hp. Do you think your engine is generating that much power? If so, I would start looking for a bigger fuel pump.
Also, at 30 gph, that's over 400 hp. Do you think your engine is generating that much power? If so, I would start looking for a bigger fuel pump.
Junior User
Joined: Mar 2006
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Get a fuel pressure gauge hooked up and watch it as you run the motor. I had a similar issue a couple weekends ago when I was at the track. It would run great through 1st and 2nd (with little traction at least) and when I hit 3rd and the motor actually had to pull hard it just fell on its face. I blocked off the return side of my pump so it bumped the fuel pressure up to 10psi (6 is all you need) and it ran great for one more run. Never had an issue on the street before or after the track though but I still replaced the pump on a warranty and havn't had a pressure drop since. The carb's tune could be a big part of it.
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