Fuel Pump/ Fuel line questions

[XCELLR8]

I have switched the stock TQ and intake to a Edelbrock 383 intake and 800 CFM thunder series carb on my 77 400 Chrysler Cordoba. I am using the stock fuel line and pump with a 3/8" hose attached to the end of it to the carb. My problem is when I go WOT the new carb seems to be sucking more fuel than I can supply, as the fuel filter gets a big air bubble in it and the car stumbles and has no power on the next WOT run. When I crank the car the fuel filter will fill up with no air in it and the car seems to run well. When I go WOT the car runs great, then after, the drivability issues return. I am wanting to know what the GPH is on a stock fuel pump? Is the stock fuel line which I think is 5/16 too small? I have not taken this car out on the highway yet to see if a long WOT will make the car bog down during the run. So far all runs have been short in town runs. The carb is brand new out of the box. I feel I need a bigger fuel pump.

 

[razreddobie]

I'm runnin a fuel pump for a 440 6pk on my Dobie with the stock fuel line and an 850 Holley with no problems.

 

[Ron Ward]

Take a long look at the rubber fuel line that runs from the main steel line on the frame to the fuel pump. Over time, these things get soaked with oil or power steering fluid and the rubber starts to break down. Under WOT, the pump is sucking hard on that line and sometimes, if it is soft & squishy, it will collapse and restrict the flow to the pump, thus limiting the fuel available to the carb.

 

[XCELLR8]

I'm runnin a fuel pump for a 440 6pk on my Dobie with the stock fuel line and an 850 Holley with no problems.

Do you have a part # for the pump. I think my new pump I put on a couple years ago is failing. I noticed when idling after my drive I was getting air bubbles from the pump to the filter and the filter was staying half full of air. If I go to a performance fuel pump how much GPH should I be looking for, as they range from 85 to 170. Thanks for the info.

 

[Ron Ward]

Do you have a part # for the pump. I think my new pump I put on a couple years ago is failing. I noticed when idling after my drive I was getting air bubbles from the pump to the filter and the filter was staying half full of air. If I go to a performance fuel pump how much GPH should I be looking for, as they range from 85 to 170. Thanks for the info.

See my previous post.... If you have a supply side hose issue, the pump may be sucking air from a worn/fatigued fuel line or fitting connection.

 

[razreddobie]

I would do what Ron Ward said first but if you need a pump it is an Airtex #4845. Cost about $30 at Advavce Auto Parts.

 

[XCELLR8]

See my previous post.... If you have a supply side hose issue, the pump may be sucking air from a worn/fatigued fuel line or fitting connection.

Thank you! I'm going to check it out first.

 

[Ron Ward]

Thank you! I'm going to check it out first.

I like ruling out the cheap & easy stuff first.

 

[AMX364]

I had to install a fuel pressure gauge and then drive the car to find that on a long slope hill the pressure dropped to about 2 psi before cutting out. Switched to a Carter street-strip pump for 6 psi at all times.

 

[XCELLR8]

I went out and checked the supply line before the pump and the hose is not oil soaked or soft, it feels like a normal hose. I did take it off the pump and recut the end of the hose to give the hose clamp a fresh section of hose to clamp on. I still have the problem. On the fuel pump, I found that the Airtex #4845 for a 70 HP 440 and the Airtex #6935 for a 77 400 have the same specs of Max PSI of 7.5, Min PSI of 6.0, flows 30 GPH @ 1800rpm, and have a 1/2-20unf threads. Just a heads up and I would like to know if anybody has different info on the pumps. I hope this is my problem.

 

[Ron Ward]

One last easy thing to check before you tear the pump off....

Crawl up under the car and check to make sure the fuel tank vents are not plugged with dirt or dust. If the tank doesn't breath, the pump can't draw fuel. Also check the steel fuel line for any kinks or damage.

If all that checks out, I think you are down to replacing the pump.

 

[nm9stheham]

Has your gas tank ever been dropped and cleaned? The screen could be partly plugged and on the margin of flowing what is needed now. Probably easier to put on a new pump, but if that does not solve the problem, and the tank has not been serviced in years (or forever) then that would be my next step.

If you have not done so, you also need to check the rubber line out of the tank to the steel fuel line. These can rot/crack, and allow the pump to suck air and cause exactly the problem you are experiencing.

 

[SlinktRR]

I have switched the stock TQ and intake to a Edelbrock 383 intake and 800 CFM thunder series carb on my 77 400 Chrysler Cordoba. I am using the stock fuel line and pump with a 3/8" hose attached to the end of it to the carb. My problem is when I go WOT the new carb seems to be sucking more fuel than I can supply, as the fuel filter gets a big air bubble in it and the car stumbles and has no power on the next WOT run. When I crank the car the fuel filter will fill up with no air in it and the car seems to run well. When I go WOT the car runs great, then after, the drivability issues return. I am wanting to know what the GPH is on a stock fuel pump? Is the stock fuel line which I think is 5/16 too small? I have not taken this car out on the highway yet to see if a long WOT will make the car bog down during the run. So far all runs have been short in town runs. The carb is brand new out of the box. I feel I need a bigger fuel pump.

Which pump are you using? If you have the carter mechanical it should be plenty for a stock 383. The air bubble may be some sort of vapor lock/fuel evaporation issue. I recently plumbed in a return line to the tank hooked up to a napa fuel filter with return (p#3054), works similar to the OE vapor separator from the '70 six packs. This has helped for me, a mild 383 that had bog issues. I used to run a plastic napa fuel filter and would see the same air bubble you describe.

Ultimately you will want to plumb in a fuel pressure gauge and monitor the drop during WOT runs like AMX indicates. This will tell you how your fuel system is running.

Also may want to check your fuel pump pushrod. The spec is 3.25", no less than 3.23" or thereabouts. A ground down pushrod will certainly cause lack of fuel pressure, even if you install a brand new pump. Just drop it out of the motor and measure it, you might be surprised how much of it has been worn away!