HELP ! Remote Fuel Pressure Gauge keeps dropping
09-23-2013, 05:30 PM
#1
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HELP ! Remote Fuel Pressure Gauge keeps dropping
1970 454 cid. Coupe.
Electric Fuel Pump . No Regulator. Typically delivers 7 psi .
Fuel Pump has 5-6,000 miles on it : http://www.summitracing.com/parts/hly-12-125
3/8 i.d. Fuel Injection grade hose running from the Fuel Pump to the carb.
What happens is : When first started, the inline fuel gauge registers 7 psi but within 10 minutes of driving , it starts going down slowly . After 20 minutes of driving , its only registering 3-4 psi. 10 minutes after that its close to 0 psi. ( Thats when the water temp guage starts going up due to a very lean condition ) . When the fuel pressure is nearly 0, the carb fuel bowl level shows about half way on the primary and secondary. Engine feels sluggish at this point . I quickly get it back to the garage.
Things ive done to try to correct it :
1. Measured voltage at various times during operation right at the Fuel Pump : 11.8 to 12.1 vdc. Fuel Pump doesnt sound like its surging at all. All electrical connections are tight and the negative wire is run directly to the Battery Neg. post. Supply wire from the Battery Pos. Post goes thru a kill switch then to the Pump.
2. Changed the two Summit Racing canister type replacement inlet fuel filters (one before the pump and one right after the pump) .
3. Checked inlet fuel hose (at various times) going from gas tank to Fuel Pump , and its not collapsing .
4. Tried a new Fuel Pressure Gauge. No change .
5. Shined up the Battery Posts . Shined up the Neg. Connector that goes to the Cars Frame underneath and used a star washer . Very tight.
6. Wiggled the wires going into the Fuel Pump . No change in its sound.
7. Closely examined the entire fuel line run from Pump to Carb. and its not pinched.
8. Insulated the Fuel Line before it enters the Engine Bay and all the way to the carb. including the dual fuel feed (Carb is a Double Pumper) .
9. The original Fuel Tank metal-mesh Sock Filter was replaced about 10-15,000 miles back .
10. Disconnected the Fuel Hose near the Carb and ran the Fuel Pump temporarily and it squirts fuel thru like a water hose. I tried this when the fuel gauge registered 5-7 psi.
Im leaning toward replacing the Fuel Pump even though it only has 6,000 miles on it, max.
Any thoughts ? Thanks for your help.
Electric Fuel Pump . No Regulator. Typically delivers 7 psi .
Fuel Pump has 5-6,000 miles on it : http://www.summitracing.com/parts/hly-12-125
3/8 i.d. Fuel Injection grade hose running from the Fuel Pump to the carb.
What happens is : When first started, the inline fuel gauge registers 7 psi but within 10 minutes of driving , it starts going down slowly . After 20 minutes of driving , its only registering 3-4 psi. 10 minutes after that its close to 0 psi. ( Thats when the water temp guage starts going up due to a very lean condition ) . When the fuel pressure is nearly 0, the carb fuel bowl level shows about half way on the primary and secondary. Engine feels sluggish at this point . I quickly get it back to the garage.
Things ive done to try to correct it :
1. Measured voltage at various times during operation right at the Fuel Pump : 11.8 to 12.1 vdc. Fuel Pump doesnt sound like its surging at all. All electrical connections are tight and the negative wire is run directly to the Battery Neg. post. Supply wire from the Battery Pos. Post goes thru a kill switch then to the Pump.
2. Changed the two Summit Racing canister type replacement inlet fuel filters (one before the pump and one right after the pump) .
3. Checked inlet fuel hose (at various times) going from gas tank to Fuel Pump , and its not collapsing .
4. Tried a new Fuel Pressure Gauge. No change .
5. Shined up the Battery Posts . Shined up the Neg. Connector that goes to the Cars Frame underneath and used a star washer . Very tight.
6. Wiggled the wires going into the Fuel Pump . No change in its sound.
7. Closely examined the entire fuel line run from Pump to Carb. and its not pinched.
8. Insulated the Fuel Line before it enters the Engine Bay and all the way to the carb. including the dual fuel feed (Carb is a Double Pumper) .
9. The original Fuel Tank metal-mesh Sock Filter was replaced about 10-15,000 miles back .
10. Disconnected the Fuel Hose near the Carb and ran the Fuel Pump temporarily and it squirts fuel thru like a water hose. I tried this when the fuel gauge registered 5-7 psi.
Im leaning toward replacing the Fuel Pump even though it only has 6,000 miles on it, max.
Any thoughts ? Thanks for your help.
Last edited by YouGotDave; 09-23-2013 at 05:38 PM.
09-23-2013, 06:04 PM
#2
Race Director
I feel that the pump is the problem.
Seeing how the pump draws only 3.5-4.5 amps...that is pretty low on current draw...so I am not too concerned on the gauge of wiring used when it was installed....because it worked...BUT....there is a chance that the wiring can be bad....even though you shook it and the pump did not change operational sound. The reason is...checking voltage does not mean squat for what I am about to explain. A wire with 20 strands to make it up can have 19 of them broken...and you will still get a voltage reading that can fool you. BUT...if you apply a current load on that wire...it will fail. Checking it with an ohm meter and or continuity tester also means nothing because the few strands complete the circuit. The way to check a wire for current load (amp draw) is to use a headlight or component that is equal or greater to the amp draw that you are testing. I use headlight(s) and wire the high beam and low beam together. I connect the headlight(s) to the wire circuit in question AFTER it has been disconnected from both ends so the wire is dead. Then I apply 12 volts to the other end of the testing wire and see if it will power up the headlights. If it does ..fine...but often times it will not do anything due to it can not carry enough amps through the few strands of copper that are still attached.
The only other thing...which does not make sense but I have seen and experienced some crazy stuff in the past is that you might have a supply hose that is damaged on the inside and it is creating its own check valve...thus reducing the amount if fuel the fuel pump can draw from. take a hose and connect it to your fuel pump with a plastic filter on it and stick it in a container of fuel and run it and see if it begins to fail. that will take out any thoughts of the supply feed to the pump.
Lastly...I have had issues with external fuel pumps and where they are mounted in and or near heat sources that can effect them working efficiently. With them being external...and not in the tank like factory ones that sue the fuel to keep them cool. possibly looking into providing the fuel pump with a cool air stream via some ducting might help so you are not going through this again. Run the car again and take an infrared thermometer reading and see how hot the area around the pump gets.
DUB
Seeing how the pump draws only 3.5-4.5 amps...that is pretty low on current draw...so I am not too concerned on the gauge of wiring used when it was installed....because it worked...BUT....there is a chance that the wiring can be bad....even though you shook it and the pump did not change operational sound. The reason is...checking voltage does not mean squat for what I am about to explain. A wire with 20 strands to make it up can have 19 of them broken...and you will still get a voltage reading that can fool you. BUT...if you apply a current load on that wire...it will fail. Checking it with an ohm meter and or continuity tester also means nothing because the few strands complete the circuit. The way to check a wire for current load (amp draw) is to use a headlight or component that is equal or greater to the amp draw that you are testing. I use headlight(s) and wire the high beam and low beam together. I connect the headlight(s) to the wire circuit in question AFTER it has been disconnected from both ends so the wire is dead. Then I apply 12 volts to the other end of the testing wire and see if it will power up the headlights. If it does ..fine...but often times it will not do anything due to it can not carry enough amps through the few strands of copper that are still attached.
The only other thing...which does not make sense but I have seen and experienced some crazy stuff in the past is that you might have a supply hose that is damaged on the inside and it is creating its own check valve...thus reducing the amount if fuel the fuel pump can draw from. take a hose and connect it to your fuel pump with a plastic filter on it and stick it in a container of fuel and run it and see if it begins to fail. that will take out any thoughts of the supply feed to the pump.
Lastly...I have had issues with external fuel pumps and where they are mounted in and or near heat sources that can effect them working efficiently. With them being external...and not in the tank like factory ones that sue the fuel to keep them cool. possibly looking into providing the fuel pump with a cool air stream via some ducting might help so you are not going through this again. Run the car again and take an infrared thermometer reading and see how hot the area around the pump gets.
DUB
09-23-2013, 06:17 PM
#3
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I feel that the pump is the problem.
Seeing how the pump draws only 3.5-4.5 amps...that is pretty low on current draw...so I am not too concerned on the gauge of wiring used when it was installed....because it worked...BUT....there is a chance that the wiring can be bad....even though you shook it and the pump did not change operational sound. The reason is...checking voltage does not mean squat for what I am about to explain. A wire with 20 strands to make it up can have 19 of them broken...and you will still get a voltage reading that can fool you. BUT...if you apply a current load on that wire...it will fail. Checking it with an ohm meter and or continuity tester also means nothing because the few strands complete the circuit. The way to check a wire for current load (amp draw) is to use a headlight or component that is equal or greater to the amp draw that you are testing. I use headlight(s) and wire the high beam and low beam together. I connect the headlight(s) to the wire circuit in question AFTER it has been disconnected from both ends so the wire is dead. Then I apply 12 volts to the other end of the testing wire and see if it will power up the headlights. If it does ..fine...but often times it will not do anything due to it can not carry enough amps through the few strands of copper that are still attached.
The only other thing...which does not make sense but I have seen and experienced some crazy stuff in the past is that you might have a supply hose that is damaged on the inside and it is creating its own check valve...thus reducing the amount if fuel the fuel pump can draw from. take a hose and connect it to your fuel pump with a plastic filter on it and stick it in a container of fuel and run it and see if it begins to fail. that will take out any thoughts of the supply feed to the pump.
Lastly...I have had issues with external fuel pumps and where they are mounted in and or near heat sources that can effect them working efficiently. With them being external...and not in the tank like factory ones that sue the fuel to keep them cool. possibly looking into providing the fuel pump with a cool air stream via some ducting might help so you are not going through this again. Run the car again and take an infrared thermometer reading and see how hot the area around the pump gets.
DUB
Seeing how the pump draws only 3.5-4.5 amps...that is pretty low on current draw...so I am not too concerned on the gauge of wiring used when it was installed....because it worked...BUT....there is a chance that the wiring can be bad....even though you shook it and the pump did not change operational sound. The reason is...checking voltage does not mean squat for what I am about to explain. A wire with 20 strands to make it up can have 19 of them broken...and you will still get a voltage reading that can fool you. BUT...if you apply a current load on that wire...it will fail. Checking it with an ohm meter and or continuity tester also means nothing because the few strands complete the circuit. The way to check a wire for current load (amp draw) is to use a headlight or component that is equal or greater to the amp draw that you are testing. I use headlight(s) and wire the high beam and low beam together. I connect the headlight(s) to the wire circuit in question AFTER it has been disconnected from both ends so the wire is dead. Then I apply 12 volts to the other end of the testing wire and see if it will power up the headlights. If it does ..fine...but often times it will not do anything due to it can not carry enough amps through the few strands of copper that are still attached.
The only other thing...which does not make sense but I have seen and experienced some crazy stuff in the past is that you might have a supply hose that is damaged on the inside and it is creating its own check valve...thus reducing the amount if fuel the fuel pump can draw from. take a hose and connect it to your fuel pump with a plastic filter on it and stick it in a container of fuel and run it and see if it begins to fail. that will take out any thoughts of the supply feed to the pump.
Lastly...I have had issues with external fuel pumps and where they are mounted in and or near heat sources that can effect them working efficiently. With them being external...and not in the tank like factory ones that sue the fuel to keep them cool. possibly looking into providing the fuel pump with a cool air stream via some ducting might help so you are not going through this again. Run the car again and take an infrared thermometer reading and see how hot the area around the pump gets.
DUB
I have an IFR Thermometer so ill take some temp. measurements . If need be, i can install a sheetmetal shield around the pump. It is mounted about 10" from the exhaust pipe currently .
Im wondering if the check valve thats in the Holley Pump is defective (?)
Anyway, ill report back soon. Thanks.
09-23-2013, 07:03 PM
#4
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Have an Edlebrock pump with about the same pressure and GPH rating mounted over my RH exhaust and have no problems with temperature as far as I can tell. It is bolted to the rear frame rail and sits just under the fuel outlet. But I had very similar behavior to what you describe (started out at 6 and gradually got to 0). Ran many of the diagnostics you describe. It turned out to be a bad pressure sensor that eventually failed completely. AEM tested and replaced mine under warranty. You mention replacing the gauge??? What brand and did you replace both sensor and gauge?
I have 12 GA wire running back there and I am grounded to the frame. Voltage sounds a little low. I have about 14 volts across the pump when the motor is running. Why run a ground to the battery? There's a lot of metal in the frame to supply a return.
DUB's point is correct that it is the current that matters. Can't think of a simple reason why the current to the pump would change over time except maybe the connections are faulty. At $200 a crack you really don't want to be swapping pumps to see what happens. You could put an ammeter inline I suppose.
What do you mean by "3/8 i.d. Fuel Injection grade hose running from the Fuel Pump to the carb"? Is the metal line gone? That's a lot of hose.
Last thing I can think of is that the tank is not vented and you are pulling a vacuum. You haven't mentioned the return/vent line. Is it blocked, is the cap vented?
Quite some time ago I had an inadvertant check valve that came and went. It was some debris in the supply line that would block flow to the fuel filter depending on the phase of the moon and who knows what else. But sounds like you've effectively flushed the line.
Why did you go to an electric pump anyway?
I have 12 GA wire running back there and I am grounded to the frame. Voltage sounds a little low. I have about 14 volts across the pump when the motor is running. Why run a ground to the battery? There's a lot of metal in the frame to supply a return.
DUB's point is correct that it is the current that matters. Can't think of a simple reason why the current to the pump would change over time except maybe the connections are faulty. At $200 a crack you really don't want to be swapping pumps to see what happens. You could put an ammeter inline I suppose.
What do you mean by "3/8 i.d. Fuel Injection grade hose running from the Fuel Pump to the carb"? Is the metal line gone? That's a lot of hose.
Last thing I can think of is that the tank is not vented and you are pulling a vacuum. You haven't mentioned the return/vent line. Is it blocked, is the cap vented?
Quite some time ago I had an inadvertant check valve that came and went. It was some debris in the supply line that would block flow to the fuel filter depending on the phase of the moon and who knows what else. But sounds like you've effectively flushed the line.
Why did you go to an electric pump anyway?
09-23-2013, 07:07 PM
#5
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OK, one more thing, you really want a relay tied to the ignition to supply power to the pump and a safety switch like oil pressure so if you get in an accident and get hurt the pump doesn't keep running, possibly spewing fuel or worse.
09-24-2013, 11:33 AM
#6
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Good idea...even though i installed an inertia switch for a rear end collision.
09-24-2013, 11:40 AM
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Have an Edlebrock pump with about the same pressure and GPH rating mounted over my RH exhaust and have no problems with temperature as far as I can tell. It is bolted to the rear frame rail and sits just under the fuel outlet. But I had very similar behavior to what you describe (started out at 6 and gradually got to 0). Ran many of the diagnostics you describe. It turned out to be a bad pressure sensor that eventually failed completely. AEM tested and replaced mine under warranty. You mention replacing the gauge??? What brand and did you replace both sensor and gauge?
I have 12 GA wire running back there and I am grounded to the frame. Voltage sounds a little low. I have about 14 volts across the pump when the motor is running. Why run a ground to the battery? There's a lot of metal in the frame to supply a return.
DUB's point is correct that it is the current that matters. Can't think of a simple reason why the current to the pump would change over time except maybe the connections are faulty. At $200 a crack you really don't want to be swapping pumps to see what happens. You could put an ammeter inline I suppose.
What do you mean by "3/8 i.d. Fuel Injection grade hose running from the Fuel Pump to the carb"? Is the metal line gone? That's a lot of hose.
Last thing I can think of is that the tank is not vented and you are pulling a vacuum. You haven't mentioned the return/vent line. Is it blocked, is the cap vented?
Quite some time ago I had an inadvertant check valve that came and went. It was some debris in the supply line that would block flow to the fuel filter depending on the phase of the moon and who knows what else. But sounds like you've effectively flushed the line.
Why did you go to an electric pump anyway?
I have 12 GA wire running back there and I am grounded to the frame. Voltage sounds a little low. I have about 14 volts across the pump when the motor is running. Why run a ground to the battery? There's a lot of metal in the frame to supply a return.
DUB's point is correct that it is the current that matters. Can't think of a simple reason why the current to the pump would change over time except maybe the connections are faulty. At $200 a crack you really don't want to be swapping pumps to see what happens. You could put an ammeter inline I suppose.
What do you mean by "3/8 i.d. Fuel Injection grade hose running from the Fuel Pump to the carb"? Is the metal line gone? That's a lot of hose.
Last thing I can think of is that the tank is not vented and you are pulling a vacuum. You haven't mentioned the return/vent line. Is it blocked, is the cap vented?
Quite some time ago I had an inadvertant check valve that came and went. It was some debris in the supply line that would block flow to the fuel filter depending on the phase of the moon and who knows what else. But sounds like you've effectively flushed the line.
Why did you go to an electric pump anyway?
1. I dont have an external pressure sensor ; id imagine theres one in the Electric Pump which allows its own check valve to bypass or not.
2. The external inline fuel gauge i had was from Summit Racing 0-15 psi . ANd i replaced it with a Holley 0-15 psi.
3. I ran the Fuel Pump Ground wire back to the Battery to make sure i got the best ground.
4. The original metal fuel lines are gone. The engine has been built up to another 150 h.p. over the stock 390 h.p. so i needed something larger than the original 5/16" o.d. fuel line . Like i said, i disconnected the fuel hose at the engine and the electric fuel pump pushed a tremendous volume of fuel thru ... much like a water hose under pressure.
5. The original fuel return line is plugged near the Gas tank and is not used anymore. I already had a vented gas cap and even drilled the vent hole in it a bit bigger .
6. I went with an electric fuel pump for 3 reasons : a. To get sufficient fuel volume to accomodate the engine buildup b. So i could install a hidden toggle switch as an anti-theft device. c. Ive had bad luck with mechanical fuel pumps in the past.
The thought has crossed my mind that maybe when i sit in the drivers seat being 275 lbs, the fuel hose is getting pinched by the suspension . I ran the 3/8" i.d. fuel hose from the Fuel Pump over the passenger rear wheel-well (fastened to the side frame rail) then alongside the passenger side frame rail into the engine bay . I insulated the fuel hose about 4' before it enters the engine bay and all the way to the carb inlets .
Im going to have a REAL close look at the supply/ground wires for the Fuel Pump as well as the possible pinching of the fuel line . Ill also recheck the voltage at the Battery versus the voltage at the Fuel Pump and see how much drop im getting.
Last edited by YouGotDave; 09-24-2013 at 11:51 AM.
09-24-2013, 12:47 PM
#8
Sure. This comes up all the time. The little gauges are useless as they're not temperature compensated. As they heat up, the internal pressure increases causing the pressure on the outside of the gauge diaphragm to increase. This causes the indication to slowly decrease till it indicates zero.
09-24-2013, 12:48 PM
#9
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I had assumed you had a remote sensor as I don't see how you can monitor the pressure as you are driving. But apparently that's not the case. Anyway I have an AEM sensor with a gauge mounted on my cluster. As a check I put the el-cheapo Summit liquid-filled gauge (sounds like the same one) on my fuel log. After a bit of driving and popping the hood it registers ... nothing, while the AEM gauge registers a pretty steady 6 and the car is running just fine. So I wouldn't trust that gauge. Don't know about the Holley.
09-24-2013, 12:50 PM
#10
Burning Brakes
Is this gauge fluid filled?
If so this is normal. Call jegs or summit. Their tech guys told me to dump the fluid to get it to read normal.
I don't get it and would not want a gauge that goes to zero seems usless to me.
If so this is normal. Call jegs or summit. Their tech guys told me to dump the fluid to get it to read normal.
I don't get it and would not want a gauge that goes to zero seems usless to me.
09-24-2013, 01:37 PM
#11
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Sure. This comes up all the time. The little gauges are useless as they're not temperature compensated. As they heat up, the internal pressure increases causing the pressure on the outside of the gauge diaphragm to increase. This causes the indication to slowly decrease till it indicates zero.
09-24-2013, 01:39 PM
#12
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I had assumed you had a remote sensor as I don't see how you can monitor the pressure as you are driving. But apparently that's not the case. Anyway I have an AEM sensor with a gauge mounted on my cluster. As a check I put the el-cheapo Summit liquid-filled gauge (sounds like the same one) on my fuel log. After a bit of driving and popping the hood it registers ... nothing, while the AEM gauge registers a pretty steady 6 and the car is running just fine. So I wouldn't trust that gauge. Don't know about the Holley.
09-24-2013, 01:42 PM
#13
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Again, the engine eventually runs lean as evidenced by a drastic increase in water temperature on the instrument panel Water Guage ..and a noticable roughness in the engine .
09-25-2013, 10:19 AM
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The only thing ive done since, is, I poured a bit of Seafoam down the carb bowl vents with the engine running ,for maintenance.
09-25-2013, 10:35 AM
#16
09-25-2013, 01:12 PM
#19
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Did you read my original post ?
How does an engine overheating issue make the fuel pressure decrease from 7 psi when first started, to 0-2 psi after 30 min. of driving ?
Is it possible for you to elaborate instead of making very short one sentence replies with no support ? Thanks.
How does an engine overheating issue make the fuel pressure decrease from 7 psi when first started, to 0-2 psi after 30 min. of driving ?
Is it possible for you to elaborate instead of making very short one sentence replies with no support ? Thanks.
