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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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Discussion Starter · #1 ·
This post is partially in relation to an issue I had with my fuel pump red wire getting hot and burning. To get the whole story you may want to look at this post first. If not you will still understand my issue.


I finally got around to trying to trouble my fuel pump wiring issue and I did a number of things. First as a precaution I ordered a new fuel pump and installed that. I found that the ground wire that was connected from the fuel pump was poor and replace that with a 10 gauge ground to the frame where the battery is. I ran all new 10 gauge wire from the fuel pump up to the relay and replaced the relay connector with a painless wiring connector that is much more heavy duty and that seems to have solved the issue.
But in fixing this issue a new one has arisen. When I turn on the car, the accessories come on, fuel pump primes and it starts as it should. But it runs about 30 seconds, then the fuel pump starts making some noise, like it’s starving for fuel and the car dies. I almost think it’s like I’ve got air in the line and it’s getting some sort of vapor lock but I’m not sure what to check.
If I turn off the ignition, wait a few seconds, turn on accessories the pump primes and I’m able to start it again. The fuel pressure gauge shoots to 80lbs but when the fuel pump starts starving, I can see the fuel pressure start to jump all over and slowly drops and the car dies.

ideas?

Jim
 

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Where is the pump in the tank or out.

How much of the LT4 electrical system are you using, as in factory computer, factory wiring, factory pump, etc.?

Bogie
 

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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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67 Posts
Discussion Starter · #4 · (Edited)
I was thinking maybe with the new pump it's drawing more fuel and my gas cap is not vented. Going to try and remove it to see what happens. External pump, frame mounted.
 

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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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67 Posts
Discussion Starter · #5 ·
Where is the pump in the tank or out.

How much of the LT4 electrical system are you using, as in factory computer, factory wiring, factory pump, etc.?

Bogie
It's from GM performance with the connect and cruise package that included the 8L90E tranny. There are many systems I am sure I am not using but it's an aftermarket pump, new painless wiring harness for the entire car.
 

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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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67 Posts
Discussion Starter · #7 ·
It's below tank level just in front of the right rear well. New pickup and sock, along with new tank.
 

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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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67 Posts
Discussion Starter · #8 ·
As a test I went back out to the garage to loosen the gas cap to see if that would make a difference. When I loosened it, there was an air release as it is not a vented cap. I started the car and same issue. And, now I have the smell of another burning wire. I found the burning wire and it's a small peach colored wire that ran from a fuse block that was mounted under the dash with 4 fuses in it. No idea where this runs to as I have to now trace this wire.

Now, just thinking out loud here...could it be I have a clogged fuel filter or even the sock in the tank that is causing the pump to work too hard and draw more voltage than is required and overheating wires? I thought I would blow a fuse, but all fuses are good.

This is quite frustrating.
 

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What lt4? A second gen? Or a new one? If second gen 80 psi is wayyy high! My lt1 runs about 40.
I had some pickup issues with my setup in a jag, external pump, right tank would starve pump for fuel and it would make a screaming sound, but never shut the motor off! I unhooked the fuel line and used compressed air. To blow the sock off in the tank! And installed pre filters before the pump.
 

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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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Discussion Starter · #10 ·
What lt4? A second gen? Or a new one? If second gen 80 psi is wayyy high! My lt1 runs about 40.
I had some pickup issues with my setup in a jag, external pump, right tank would starve pump for fuel and it would make a screaming sound, but never shut the motor off! I unhooked the fuel line and used compressed air. To blow the sock off in the tank! And installed pre filters before the pump.
It's a 2nd gen LT4 and I just went and double checked the pressure. It's 60lbs and not 80, so that is my mistake. I plan to pull the fuel filter, which is an inline replaceable cartridge type filter and I am going to drop the tank and check the pickup/sock. My thinking is there may be a clog somewhere which is causing the pump to overwork, drawing too many amps.
 

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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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Discussion Starter · #13 ·
I wanted to give a status update on my progress here...I removed the fuel filter and took it apart (as it's a fitech filter that has a replaceable cartridge). This is what I found on the top of the cartridge.

617119


That is metal shavings that are stuck all around the outside of the filter. After I took this off, I decided to drop the tank and when I removed the return line, there was a ton of pressure behind it, even though I had the gas cap removed. I noticed when I took the sender out of the tank that there was no hose connected to the sender, instead the sock was cutoff, and they added a fuel supply line next to the return line.

617120


Here is the sending unit, showing it was cut and capped.

617121


I ordered a new sending unit from Classic Industries and please correct me if I am wrong but can I connect my fuel supply line back to the sending unit and just cap the one that was installed to bypass the sender? I do not see any type of sock in the tank on the supply line that was added and that would explain why I have so many metal shavings on the filter (and the fact they did not clean the tank before installing it). Also, can anyone explain why I had back pressure on the return line? I was going to see if the return was plugged by blow it out with my compressor.

What is the best course of action I should take here?

Thanks
Jim
 

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First thing I would do is to drain the tank completely and flush it out. The best course of action would be to install an "IN Tank" pump. Thats a lot more work, but the pumps last longer when surrounded by fuel. A factory style fuel pump might be adaptable but it depends on how deep your tank is. You could get an old tank at a junkyard or someone parting out a car. If you get one that uses the correct pressure pump , you could cut the area out of the tank that holds the fuel pump and weld it into your existing tank. You have to be aware of gas fumes igniting when you grind or weld, so the tanks need to be almost full of water when making any kind of spark. You also may be able to find a replacement aftermarket tank that already has provision for for a factory style pump.
With your existing set-up it basically just a matter of gravity allowing the gas to flow down till it reaches the suction of the pump. The return line is to prevent your pump from constantly pushing against a "head" of fuel with no flow or little flow which causes it to get hot and eventually fail. The tank must have a vent so as fuel leaves the tank air can replace it instead of creating a vacuum.
 

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There should be no back pressure on the return line.

The system is not plumbed correctly. The first consideration is the pump cannot be allowed to suck air. For factory units that are in the tank there is always a surge box around the pump and it’s pickup that prevents fuel from migrating away so quickly such that it could expose the pickup sock to anything but liquid fuel. Along with this idea of protecting the inlet from disturbances that could introduce tank vapor and air rather than fuel the return is usually some where isolated from the pick up. This is also to eliminate the immediate reintroduction of return bypass fuel as it is quite warm and the designers are trying to eliminate fuel heating loops where return fuel just gets immediately pumped again.

For an external mounted pump on a tank with no internal baffles that hold fuel from escaping the pickup there is the use of a small tank between the main tank and the external pump. This usually is half to to a gallon in size small enough that it doesn’t have slosh issues but large enough that main tank slosh will not uncover the pickup for so long a period that the auxiliary tank would be pumped out. As with tank baffles (which can be a foam fill in the tank) this is intended to protect the pump from access to vapors and/or air during fuel slosh events.

The return line on an external pump should not be a tee with the tank inlet line as this puts the bypass fuel into a continuously heating loop.

The line pressure throughout the system is set by the regulator except as the bypass fraction approaches the tank it should indicate the same pressure everywhere between the pump outlet and return to the tank.

The pump whether in the tank or out is dependent on fuel flow through it for cooling. Dead heading the pump on the outlet side or restricting its intake will overheat the pump where one of the effects you see of burnt wires is possible as the pump gets hot and it’s internal resistance goes up. You should consider the pump is junked. An in tank pump is quieter and cooler as it can use the surrounding fuel as a heat sink and acoustic damper.

Edlebrock and other sources sell an engine compartment mounted fuel system where a normal low pressure pump in or by the tank fills a reservoir that contains the high pressure injection pump. This reduces the use of high pressure fuel lines between the tank and injector system.

Remember that some systems use a Pulse Width Modulated (PWM) pump to manage system pressure, these do not use a bypass return. This obviously starts with a specifically programmed computer, so you have to check these things out when mixing and matching parts together.

Kerp in mind that fuses are to protect you from system failures, the fact you’re frying wires and not blowing fuses says something is wrong with the electrical system. A couple YouTube videos of automotive fuel fires should be enough to get your attention to the importance of correctly sizing fuses to protect circuits before the wiring melts.

Bogie
 

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Can you just moch your system up outside the car to see if it is providing pressure AND flow thru the return?

In the eighties and early ninties, the fuelpressure regulators were mounted AFTER the fuel rails and then the bypass was a separate line from the regulator to the tank.

Later companies found they could mount the regulator slightly ahead of the fuel tank and let the pressure "dead head" to the fuel rails. Then they had the return line come off the regulator and return to the tank. Much shorter return line.

Still later they designed pumps that would just dead head and had no return line at all.

Myself, I like the continual flow of fuel because it cools the pump and helps keep fuel to the engine cool.

I would disconnect the return line and put it in a container so you can see if fuel is returning when the pump is running. Be very careful............
 

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Yeah, it really doesn’t matter where the bypass regulator is mounted after the pump‘s pressure side as it will within the limits of its capabilities maintain a constant pressure throughout the system regardless of the fuel consumption by the end component be that an injection system or carburetor.

The important design things really are to keep fuel always moving through the pump for cooling it, do not tee the return directly to the inlet side to prevent continuously looping the pumped fuel without giving it a chance to cool, to that end it is returned to the tank away from the pump intake as much as possible. If you use multiple filters placing them in parallel is more effective than in series as while pressure is the same the flow amount is halved in each of the filters assuming they each are of the same restriction to flow, The regulator in the engine bay is a convince for setting pressure adjustment but does add line length by demanding the return line equal the feed line length.

Bogie
 

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Do the LT motors not have a safety feature that shuts down the fuel pump in case of accident. I believe it is triggered by the oil pressure sender. Car wrecks, engine dies, oil pressure drops to zero and ecm shuts down fuel pump……Just a thought.

Let us know when you find what the problem is.

John
 

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1972 Chevy Nova, 650hp LT4, Heidts full frame with IFS and IRS.
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Discussion Starter · #19 ·
Yeah, it really doesn’t matter where the bypass regulator is mounted after the pump‘s pressure side as it will within the limits of its capabilities maintain a constant pressure throughout the system regardless of the fuel consumption by the end component be that an injection system or carburetor.

The important design things really are to keep fuel always moving through the pump for cooling it, do not tee the return directly to the inlet side to prevent continuously looping the pumped fuel without giving it a chance to cool, to that end it is returned to the tank away from the pump intake as much as possible. If you use multiple filters placing them in parallel is more effective than in series as while pressure is the same the flow amount is halved in each of the filters assuming they each are of the same restriction to flow, The regulator in the engine bay is a convince for setting pressure adjustment but does add line length by demanding the return line equal the feed line length.

Bogie
@BogiesAnnex1 I want to thank you for your detailed reply as what you stated about overheating wires is exactly what I am experiencing. I'm trying not to overcomplicate this at all and have made several changes to the fuel system to hopefully fix my issue. First, the fuel outlet line from the tank that was installed was just connected to a rubber piece of 1/2 hose that sat flat against the inside bottom of the tank and I believe this also restricted fuel flow. I removed that, installed an aftermarket fuel sending unit with sock. On the return line, I found the exact same thing, a piece of hose that was laying flat against the bottom of the tank and this line was only 3/8", so I purchased new 1/2" id hose and will run this as the new return. I also removed the rubber line that was flat on the bottom of the tank and replaced that with one that leaves more room between it and the bottom.

Because there was no vent on this tank at all, I purchased from summit racing a rollover vent valve and plan to connect this to one of the capped emission lines, (if you look above in the image I supplied of the tank showing the return and fuel inlet lines, I plan to use the capped emission line on the far right) hopefully this will suffice.

The $100,000 question is why did I not blow any fuses? The car was rewired with a painless wiring kit for the LT4. I also found a GM manual that shows what rating the fuses should be and they match what is installed in my car.

You mentioned a reservoir that will help with starvation and I found this one on summit:


Is this what your referring to?

@johnlong, I really don't have an answer to your question as I am unsure but someone here may know.

I again want to thank everyone for their input on my issues. I am hopeful I can get this all back together soon and I will give you a status update.

Jim
 

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My bad. I was guilty of not closely reading your entire description. Forgive me for muddying up the waters.
I hate it when people answer a question without really reading and understanding the problem and just did it myself.

John
 
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