#1  
Old 08-20-2012, 02:21 PM
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428PHIL 428PHIL is offline
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Unhappy Low fuel Pressure

A buddy of mine has a 67 Bird 400. Been having trouble with fuel pressure. When he starts it up pressure at 6-7 psi. After about 5 mins it drops to 3 psi and the motor starts to back fire and runs ruff. He's running a electric pump which seems to be installed correctly. HE was concerned that the pump was not getting flow from the tank so he ran a line from a gas can direct to the pump, same problem. Any ideas would be appricated.

  #2  
Old 08-20-2012, 02:46 PM
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Greg Reid Greg Reid is offline
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Vapor lock?
Faulty Fuel pump?
Where is the pump mounted?
The closer it is to the tank the better.

Maybe you could detach the line from the carb and just let the pump work for 5 minutes...That is, let it pump fuel from the tank and back into the tank....just to see if it slows down when it gets hot.

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  #3  
Old 08-20-2012, 04:35 PM
BMFH BMFH is offline
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Hello

CAUTION! DO NOT MAKE ANY SPARKS WHILE THE FUEL SYSTEM IS OPEN, GASOLINE FUMES CATCH FIRE VERY EASILY

Check and make sure the Power Wire going to the Electric pump is Heavy Gage, if it is too light in gauge it may be getting hot and not supplying adequate voltage at the pump.

You can check this by putting a Digital Volt meter probe on the power wire at the pump and turn the pump on and see how the Voltage stays, If the engine is running it should be around 14.0 volts steady and not drop as the pump runs, if not running put a battery charger on the battery and charge it at the 40 Amps rate, a trickle charger or battery tender probably will not put out enough amperage to keep up the battery fully charged under the load of the Electric Pump.

Also check that the suction screen, hoses and filters in front of the fuel pump to see that they are not collapsing out of the tank or in the tank.

Make sure all filters are clean, i.e., they should be fairly NEW.

Hope This Helps

Dusty

P.S.

If the charging system is not putting out enough amperage this too could lead to a poor running engine since the ignition system is starving for power too.


Last edited by BMFH; 08-20-2012 at 05:15 PM.
  #4  
Old 08-21-2012, 08:07 AM
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428PHIL 428PHIL is offline
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Thanks for the ideas to look at. The original pump was replaced with a new one, as he thought it was bad. Most likely not the pump. He mounted it under the trunk area below the tank which was how I mtd mine in the LeMans. Will give him the info on the wiring issue. This maybe the answer, as he had the car rewired by two different people.

  #5  
Old 08-21-2012, 11:48 AM
BMFH BMFH is offline
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Hello Again

I forgot one thing in troubleshooting the Power to the pump.

Make sure you have a ''0'' Resistance Ground for the pump ground lead.

Set your Digital Volt OHM Meter (DVOM) on the DC Volts position, you need to use a DVOM Meter, Not an Analog style Volt Meter. The reason you need a DVOM is because it is much, much more sensitive and can see and you can read a .001 volt reading easily. You can get a cheap one at Radio Shack or just about any Auto Parts store, probably less that $20.00

FYI this is also the type of meter you need to troubleshoot any modern system with computers, these will not damage the delicate computer components, where as the Analog tester can damage computers and their components if used incorrectly.

This test is actually a VOLTAGE DRAW TEST, but easier than a resistance test and test components during their actual operating conditions.

You can check this by putting the Test Leads of the DVOM OHM Meter on the ground connection, Put one Test Lead on the bare wire itself, and the other Test Lead on the metal where you are getting the ground connection for the pump. Turn on the pump and watch for ANY VOLTAGE READING AT ALL, any reading you get above "0", tells you that you have a bad connection for the ground.

You can do this same test on the POWER Wire, although it is some times harder because of the distance from one end to the other end on the power wire. On the power wire this test is called an VOLTAGE DRAW TEST TOO, any readings on this test above .500 (1/2 a volt) tells you that you are loosing voltage from one end of the power lead to the other end. If you get any reading at all, try to reduce the reading to "0" by checking all connections, even fuses and OEM connections where you tapped for power, and or increasing the size of the wire gauge, I always use a gauge of wire the next size LARGER than what is needed, to be sure that I don't have any power problems.

To test the power and ground wires before or after a connector you can use a Safety Pin, "T" Pin, or straight pin to pierce the insulation of the wire JUST ENOUGH TO GET A CONNECTION, do not push it all the way through the wire, this will damage the insulation and allows moisture, water/oil etc. to gain access to the wiring, this is NOT GOOD, especially on today's computer controlled vehicles. These systems operate on
a range of 0 to 5 volts, the Oxygen Sensors work on a range of 0 to 1 MILI-VOLT, this is why you need a DVOM so you can read these MINI Voltages and not damage the computer controlled systems.

To get very good "0" Resistance connections, include a STAR WASHER under the terminal and whatever you are trying to get at that connection, either a ground or power. Everyone has seen them at one time or another, they are special washers that have little sharp blades either at the outside edge of the washer, or the inside edge of the hole in the washer. They really dig in and give an absolutely positive connection at that connection. I prefer the ones with the external blades, I think they dig in harder and give a better connection.

You can use this same procedure on any circuit to test connections for a ground or power for any component, the hard part is getting a good connection at each end of the wire, plug or connector, at the connector you can back probe it with the Safety Pin or the "T" Pin and get at the connector terminal, just be really careful to NOT SHORT IT TO GROUND OR PUT POWER ON IT if it is not supposed to have power, this can get REALLY EXPENSIVE IF YOU DAMAGE COMPUTERS AND SENSORS.

Sorry this got soooooooo long,

I hope it helps

Take Care,

Dusty


Last edited by BMFH; 08-21-2012 at 12:03 PM.
  #6  
Old 08-21-2012, 01:26 PM
BMFH BMFH is offline
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Hello Again

One Minor correction

Oxygen Sensors work on a range of 0 to 1 MILI-VOLT, this is why you need a DVOM

This should have said

Oxygen Sensors work on a range of 0 to 1 VOLT and Displayed in MILI-VOLTS, this is why you need a DVOM

Take Care,

Dusty

  #7  
Old 08-21-2012, 03:55 PM
BMFH BMFH is offline
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Hello Again

Hate to do this again, but

When I said

This test is actually a VOLTAGE DRAW TEST

I should have said that this test is a Voltage DROP Test

Sorry about the confusion

Take Care,

Dusty

P.S.
I sure wish we could edit our post after posting, instead of having to re post the correction like this, or at least give everyone maybe a couple of days to make sure it is right before locking the posting.

  #8  
Old 08-21-2012, 04:01 PM
BMFH BMFH is offline
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Hello Again

Hate to do this again, but

When I said

This test is actually a VOLTAGE DRAW TEST

I should have said that this test is a Voltage DROP Test

When I said

On the power wire this test is called an VOLTAGE DRAW TEST TOO

This also should have said Voltage DROP Test

Sorry about the confusion

Take Care,

Dusty

P.S.
I sure wish we could edit our post after posting, instead of having to re post the correction like this.

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