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Fuel problem

24K views 34 replies 11 participants last post by  vinniekq2 
#1 ·
I'm currently dealing with a vapor lock in my Chevelle, got a rebuilt BBC 427 bored .60 over with 75 miles on the engine, ever since I put the motor in I'm having a fuel issue, I'm running Edelbrock Performer RPM Mechanical 110 GPH fuel pump with a 3/8 steel fuel line from the tank wrapped with rubber hose, today was a humid day here and as the engine temperature went up I was also losing fuel pressure, when the engine reached 200*F idling in the driveway my fuel pressure went down to 0 PSI and the engine shut down.


I do have a Autometer Mechanical liquid-filled fuel pressure gague mounted on my cowl today when my pressure went down to 0psi I took a ice pack and put it over my gauge and it didn't make a difference the car still shut down so I believe the gauge was working,

when I had the car out in my may when the ambient temperature was cooler I didn't have any issues driving around the city, but I had issues on the freeway when the car was revving at 3500RPM and my engine temperature was increasing I was losing pressure and the engine shut down and I had to wait for the motor to cool off, but once I got off the freeway my pressure jumped back up to 4 psi on the streets and I was fine,

this is my 2nd mechanical fuel pump which I thought it was issue, I have my headers wrapped in header wrap, I have all my fuel lines wrapped and I'm running a carb spacer, I'm getting frustrated and losing hope,

I have a 160*F thermostat and when my temps stay around 150-160*F on cooler days the fuel pressure stays steady 4-5 PSI until at WOT when the engine temps increase I start losing pressure
 
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#3 ·
Make sure the fuel tank has a vent also, either at the top of the tank where the outlet port and sender are, or with a vented gas cap.
You could be pulling a vacuum in the line because of a restricted or missing vent (maybe gas cap has been replaced with a non-vented version, should be vented on '68 Chevelle IIRC from the one I had). Vacuum together with heat makes vapor lock occur easier
 
#7 ·
yes the tank is vented, the vent goes through my trunk but it maybe blocked???, how can I unblock it shoot compressed air in the vent tube? I have the same gas cap that was on it when I bought the car in 80's and never had an issue back then.

can I do a test to see if I can have any restrictions? I read that you can time how long it takes to fill one gallon of fuel and this will tell if u have any restrictions?
 
#4 ·
I am not saying that you have a fuel pump problem. Edelbrock usually makes quality parts. My preference would be a Holley 12-454-13 or Carter CRT-M4845 if I were to use a mechanical fuel pump. Make sure your fuel line is run along the outside frame all the way to the pump. Can you give some detail on your cooling system. You need to keep your temperature down when idling. What type radiator do you have (overall measurement) and core measurement. Type of shroud and fan? If you have a clutch fan be sure to check it.
 
#9 ·
I original had a Holley 12-454-13 and it gave me the same issues, I figured since it was made in Korea something was wrong with it so I changed to the Edelbrock USA pump and still having the same issues, I have a 4 row Aluminum I think 190-200*F is pretty good for big block Chevy,

I have 4 row aluminum radiator 22-1/4" (H) x 27-3/4" (W)
Champion Cooling Systems MC289 Champion Cooling Systems Four Row All Aluminum Radiators - Free Shipping on All Orders @ JEGS

I have a stock 1967 chevelle shroud, and running a Hayden clutch fan and blade
 
#13 ·
fuel problem

1981zapper, Here is a test to check out your fan clutch and it is fast and easy. BTW how many fan blades does your fan have? I have a 491 ci Chevy engine in my 67 Camaro and is cooled by a Be Cool Direct Fit Module. It came with relays, wiring, dual fans with shroud, and a screw-in sender that turns the fans on at 195* and turns them off at 175*. My temperature stays at 185* even sitting idling. I just thought of something as I was reading over these post again. You might want to drop your tank down to check all the rubber hoses on top of the sending unit. These dry rot and crack.
 
#14 · (Edited)
A higher flow fuel pump pulls harder on the fuel in the line from the tank lowering the pressure in the line before the pump.If the fuel in that line is hot enough from the heat off the pavement or passing near hot exhaust or machinery of the car at this lowered pressure it will flash to vapor inside the line. The pump is not designed to pump vapor so there is no further output. When that happens the pressure in the line from the pump to the carb goes to zero and the engine stops. Restoration occurs after the vapor in the fuel line condenses back to a liquid that the pump can pump. This process starts as soon as the engine quits and the pump stops as now the pressure in the feed side line from the tank recovers from the fuel depth head in the tank above the outlet of the tank brings pressure in the line back above the vapor point for the tenperature of the fuel in the line. A sensitive place is where the fuel exits above the tank. The lower the fuel level the greater the negative pressure forces on the fuel to climb up and flow over this hump become.

Thinks that help:

- Insulate the line with a material that also has a reflective coating. You rubber jacket attracks heat by its black color. Wrapping it in aluminum foil may be a big help.

- A larger line with a high capacity fuel pump this will reduce the feed side pressure drop in the line by reducing resistance to flow to the pump. If your losing pressure at WOT I say the line isn't big enough to feed the pump. This will drop pressure on the feed side big time and poof you get vapor lock.

- Backwards from insulation is a heat sink, this more helpful if the fuel in the tank is hot rather than gaining heat in the line.

- Rerouting the line to avoid hot places such as the exhaust and side of transmission and engine or providing the line with a metal heat shield in these areas.

- Use of an electric pump at the tank so the entire line is pressurized which will keep it well above the vapor point of the fuel.

- A bypassing regulator, this allows a high capacity pump to vent unused fuel back to the tank so fuel in the lines and pump is always circulating, except for a small length of line to the carb, which keeps these lines and the pump cooler and away from the critical vapor pressure and temperature combination that flashes the fuel to a vapor.

Bogie
 
#15 ·
I have the steel line coming out of the frame to fuel pump wrapped in DEI Heat Sheaths ( a few inches) and my line off the fuel pump to the carb is wrapped in the same DEI Heat Sheaths

I have a Brand New Carter Universal Rotary Vane Electric Fuel Pump #P4600HP 100GPH max 8 PSI, I was told I can run the Electric pump and Mechanical pump together and it will help with my issues what do you guy's think? I have also bought a Relay for it
 
#17 ·
Common problem on alot of vehicles is vapor lock usually caused by a faulty vented gas cap or blocked and/or poor functioning e-vap system. The vented gas cap is designed to vent small amounts of air into the car gas tank line. The vented gas cap has a one-way release valve that is pressure-activated. When the pressure reaches a certain point (defined by so many pounds per square inch) the valve opens by a very small amount, relieving some of the pressure. In this case, the pressure is formed on the outside of the tank, due to the vacuum formed from the displacement of fuel on the inside. After the pressure inside the line equalizes, the pressure valve closes. The valve is set to balance the pressure with the surrounding atmosphere. Air is allowed in, but no fumes are allowed out of the gas cap, because of environmental concerns.
 
#20 ·
pumps..

Why hope for that and put all the load of an electric pump on the mechanical, what if it starts to leak thru one of the 2 diaphrams, one leaks out and one leaks into the engine into the oil, not worth trusting the secondary pump, run a pr reg, then forget about it.
 
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#21 ·
I made sure that the rubber hose has no sharp bends and is wrapped in DEI Heat Sheaths, you think this Carter P4600HP electric fuel pump will feed my BBC 439, its only a street car Carter P4600HP and redline set at 6000 RPM

the pump came with some rubber bushings and installation kit to install, I had to buy separately was a Summit Racing Fuel Pump Relays #SUM-890023
I have read some stories lately of guy's forgetting to shut there electric pumps off once the car is shut down and destroying the engine from hydro lock, will Wiring the Relay to an ignition source prevent from forgetting that the pump is left on?
 
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#25 ·
The edelbrock carb is fine. But needs a regulator when using a pump with 8psi. P4600HP.
Cut the pressure to 5.5psi. The Carter P4070 does not need a regulator atr all.
The text book eddy float height setting is a good start. You can +/- it a bit to find the best.
8psi is too much pressure 5.5psi is just right.

Eddy carbs like a wood carb heat spacer under the carb. Split divided if dual plane manifold.
since I have already have the carter P4600HP, I will use it, I do have a holley regulator


Is it possible that since I'm going to run the electric pump close to the tank and get rid of the Mechanical pump that the pressure will drop once the fuel gets to the carb and I will not need a regulator?
 
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#27 ·
Make sure you are not boiling fuel in the carb. I don't think anyone else has mentioned it but those liquid filled gauges are not dependable at all and tent to fail in a hot environment. I would first check at the carb inlet when you think you have no fuel pressure to see if there is fuel there. Edlebrocks are more temp sensitive to engine temperature and it is not unusual for them to boil fuel in the bowl.
before you go tearing everything apart, check the fuel pressure at the inlet when you gauge reads zero, I would be willing to bet there is pressure there. If so get or make a carb spacer/insulator and see if the issue goes away.

As a side note, if you are using the electric pump there is no reason to also push the fuel through a mechanical pump, eliminate it.
 
#30 ·
I never run mechanical and electric pumps together. My buddy had his mechanical fail on his truck in a similar situation back in the late 70's, and it did fill his engine with gasoline! When he started having problems losing power, he pulled the dipstick and found it was a couple quarts high from the excess fuel mixed in!
Your Summit/Holley regulator will work great. I use them all the time. Just be sure to initially set it with the engine at idle, and then don't forget it and expect it to stay exactly where it initially was set. They seem to beak in or change a little from new, and I've always had to raise or lower the pressure setting after a little driving. Once they're in use for awhile they wont need anymore adjustments. But mount it away from any high heat source, or it will cook the regulator.
 
#31 · (Edited)
I haven’t had a chance yet to install the electric fuel pump, but I’m thinking of installing it just above my fuel tank pick-up, my only concern is in the instructions it says to mount the fuel pump to the frame, do you see a problem mounting it to the trunk floor?

I had a look at the relay wiring and I have a few questions;

- where does the yellow go to ? I have my distributor taking up a spot on the ignition spot on my fuse block where else can I get power when the ignition switch is on?

- the grey wire coming off the relay does that go to the Negative terminal on the battery along with the fuel pump ground??

- where is the best place to mount the 30 Amp circuit breaker and relay?

- since the relay wires won’t be long enough I will need to add more wire what’s the best to join them with bullet connectors or female and male blades? And what gauge of wire will I need to extend the wire to fuel pump?



 
#35 ·
put a guard around the pump to protect from debris. Make sure the pump does not hang below wheel lip and double make sure you wont hang up going over a rail crossing.
Test the car,if the pump helps then mount it as high as possible and protected or get an intank pump or a road race mechanical pump
 
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