Fuel system problems can be among the most frustrating and time consuming issues that you will ever deal with on your car. Many of us have been there, and if you’ve ever chased a fuel system gremlin until you’re ready to pull your hair out, then you’ll sympathize. You’ll also want to punch us when we say that it in reality, the causes of many common fuel system problems are obvious, can be remedied easily.
To prove it to you, we asked the fuel system experts at Aeromotive to give us an overview of the most common fueling problems they receive calls about, the root causes, and the solutions. Aeromotive knows a thing or two about fuel. Their fuel systems have fed some of the world’s quickest race cars, and recently GM picked Aeromotive to supply the fuel systems for the new COPO Camaro.
Fuel pumps always seem to be the bad guy when it comes to fuel system troubles, but the truth is that improper plumbing is at the root of many issues like vapor lock and cavitation.
Jesse Powell with Aeromotive gave us the low down: “Hands down, the most common issues we help people deal with are vapor locking due to hot fuel, and cavitation. All of these problems are related to each other, and they are all ‘Fluid Dynamics 101’ issues. It’s easy to blame the fuel pump on your issues, however, most fuel problems have nothing to do with your pump and everything to do with your plumbing.”
Physics Behind the Problems
Let’s just take a minute to talk about a few basic fluid dynamics principles.
Cavitation: The term “cavitation” refers to a phenomenon that occurs when a fluid is under low pressure or high vacuum and is imploded as it is pulled over an impeller, like in a fuel pump, and turns into vapor or bubbles.
Vapor Lock: The term “vapor lock” refers to a condition that occurs when fuel transforms from liquid into vapor, either from being cavitated or boiling, and the engine shuts off because it can’t run on vapors, or the pump stops due to the lack of lubrication from the liquid fuel.
First, lets examine some of the common problems that an EFI engine swapper might encounter, especially in a muscle car application. “Many people are starting to make very respectable power,” said Powell, “in both EFI and carbureted engines, so they are using these huge in-line fuel pumps with stock pick-up tubes and tanks, and vapor locking becomes a huge problem. What’s happening is that the fuel is getting hot, not the pump itself like most people think. Fuel is sent to the engine bay, and gets hotter and hotter as it cycles through the system. And with the negative pressure caused by the restrictive pick-up tubes and stock lines, the fuel’s boiling point is lowered and the pump literally sucks vapor. Hence…vapor lock”
When a fluid is put in negative pressure or vacuum, its boiling point is lowered. So when you mount a pump on your frame rail, and you have 3 feet of line going to your pickup tube in the tank, you are forcing the pump to suck the fuel. In this type of set up the fuel is under negative pressure. “As the fuel gets hotter and hotter from radiant heat from the engine bay, exhuast, etc., eventually the lowered boiling point and the temperature of the fuel reach critical mass, and the fuel will begin to boil in the pickup or in the inlet of the pump.” explained Powell. “When the fuel begins to boil, the pump is just sucking vapors and both the pump and the engine shut down because neither can run on just vapor. The pump can ‘lock up’ because it depends on the fuel flowing through it to lubricate and cool it.”
Common Solutions to Common Problems
Luckily there are simple plumbing related solutions that can help you solve all of these problems. First of all, you need to get rid of all that negative pressure that is causing bad mojo in your fuel lines and get some positive pressure on your fuel pump.
Return Lines are Important:
Most fuel system problems have nothing to do with your pump, and everything to do with your plumbing.
Aeromotive recommends a return-style fuel system regardless of whether your car is EFI or carb’ed. A return-style system provides a number of performance advantages over dead-head style systems, including more consistent fuel pressure and quicker response from your system. Returning the fuel to the tank will keep it cooler, prevent many “hot fuel” issues, and just keep the whole system happier in general. Of course, the cornerstone of any good return-style fuel system is the fuel pressure regulator which maintains the necessary fuel pressure in the fuel rails, and sends the unused fuel back to the tank. Another advantage to a return-style system is keeping the fuel from being under constant pressure and boiling under the hood – even if you’re using a carb.
Fuel Pump Location and Positive Pressure: Next, you have to get rid of the pick-up tube set up that just runs through the top of the tank and sucks the fuel out to the pump. There is no scenario where that type of system won’t put negative pressure on the fuel. You have to gravity feed the fuel pump by welding in a sump to create a new low point in the tank to pull fuel from. Also, mount your pump lower than the tank so you have gravity helping to feed your pump, and a positive pressure system. With positive pressure on the system, the fuel can’t turn into vapor, regardless of how hot it gets – even if the fuel was boiling in the tank. Having an in-tank pump works pretty much the same way, because you have a column of fuel above the pump pressing down on it and creating positive pressure, and the benefits of cooling the pump by having it inside the fuel.
Powell says, “Many problems that people face could be eliminated by using and in-tank fuel pump. By putting the pump in the tank you maintain a positive pressure on the inlet at all times. And so hot fuel problems like cavitation and vapor locking go away.” It’s as simple as that. If you don’t want to deal with vapor lock, put your fuel under positive pressure by gravity feeding it, or submersing it inside your tank. See, we told you this was easy.
Are Your Lines Too Small?: Another problem that might be causing your fuel system woes is an obvious one that all too often gets over looked; your lines are just plain too small to feed your engine. “It’s not uncommon to look under the hood and see someone who is having fuel troubles trying to feed 550 Liter per hour pump with a 5/16 inch hard-line. That just can’t happen. It’s just too restrictive, and you’re going to likely kill the pump. Running too small of a filter plays right along with this, and can create a huge restriction on your system. You must have a filter that is both large enough in micron and surface area.” Powell says. Luckily the solution to this problem is rather simple – get bigger lines and a fuel filter to match.
Aeromotive's recommended sizing for an A1000 based EFI fuel system.
So exactly what size line do you need? That’s a tougher question to answer and depends on several factors. “How much power can you support with a certain line size is really dependent upon the length of line and the size of the fuel pump.” Powell tells us, “If you have a big pump, you’ll need a larger line to accommodate for the volume, and the longer the line the more pressure drop you see. That should always be considered.”
Aeromotive's recommended sizing for an A1000 based carburated fuel system
Get the Right Pump for the Job…
Remember, it’s important that your fuel pump be adequate for your application and even have a bit of room to grow with your power demands. But too much pump can cause you plenty of problems as well.
If you don’t need to feed quite as many ponies as the A1000 can, but you still need to feed more than what typical basic fuel system upgrades can handle, Aeromotive has an exciting option for you – their new Stealth 340 in-tank pump. The Stealth 340 is designed to fill the gap between the popular Walbro 255 pump and a monster fuel system like the A1000. Best of all, the 340 can be used in either carbureted or EFI applications with the correct fuel pressure regulator.
Another area to consider is the return line size. If your return line is too small, you’ll find that you can’t get the fuel pressure down. It will keep creeping up or won’t come down at all because there is too much volume to freely pass through the small line.
“The other important area is the feed line from the tank to the pump.” Powell says, “Bigger is always better here. In fact, a minimum of -10 is required for the majority of our pumps.”
Below you’ll find some basic guidance from Aeromotive on about what size your fuel feed and return lines should be based on how much horsepower your engine is making.
- Up to 600 Horsepower: -06 AN(3/8 inch)
- 600 to 1000 Horsepower: -08 AN (3/4 inch)
- 1000 Horsepower and Up: -10 AN (5/8 inch)
It Can Be a Baffling Problem: Another problem that many Hot-Rodders run into with their fuel system is fuel slosh. Powell offered this insight: “Old muscle cars from the 60’s and 70’s didn’t have baffling of any kind inside their fuel tanks. So when you turn hard to the left, all your fuel goes to the right side of the tank. In a carbureted car with much lower pressure in the lines, and a steady reserve of fuel in the lines, you can get away with this. But with an EFI Car with much higher operating pressures, like a muscle car with a late-model EFI swap, when you turn hard and uncover the pick-up point, the engine will gurgle, stutter and spit, and die.”
A great solution for this problem is Aeromotive’s forth-coming line of Muscle Car Gas Tanks, which will feature internal baffling, an in-tank submerged pump, and all the features of a modern gas tank. Powell tells us, “We have been working hard to develop and new line of muscle car tanks that feature and in-tank fuel pump that provides the ability to support big horsepower, EFI or Carbureted, operate with OE like durability, be quiet and out of site and all at a price that is unbeatable. We have developed a 1st gen F-body tank that is stamped and stock appearing by all means that features an internal baffle and a built in 340 Stealth Pump.”
A properly set up fuel tank with a sump and baffling around the pick-up can make all the difference in eliminating possible fuel system problems in your Hot Rod or muscle car. These are some of the first pics of Aeromotive's new Stealth baffled tanks for '67 to '69 Camaros
“These tanks are perfect for the EFI swap guy. They can support a lot of power. 700+ EFI horsepower is not a problem and it’s even more for carbureted system. The baffling eliminates fuel slosh issues. Hot fuel handling problems disappear due to the submerged pump and noise is eliminated due the size and nature of the pump. It’s like dropping a new Camaro tank into your muscle car. The 1st Gen F-body (67-69 Camaro and Firebird) is available now. Look for many popular applications in the future like the 64-72 A-Bodies, 1st Gen Mustangs, and Tri-5 Chevys.”
Late Model EFI Fuel Systems
So up until this point we’ve mostly discussed problems that hot-rodders and classic car guys face when looking to feed their high horsepower engines. For late model guys, who typically already have return lines, in-tank pumps, and baffled tanks in their cars, the real issue becomes finding the right pump for your application, and getting the whole system dialed in.
Powell had this to say about late model fuel system options: “Late model guys will typically start out with a ‘boost-a-pump’ type of system that ups the voltage to their stock pump, and that can carry them to 550 to 600 horsepower. Once you reach over 600 horsepower you’re faced with a choice: a multi-pump system, or pull your tank all together and go with a fuel cell system with a big pump. The problem with doing a multi-pump system is that if one of the pumps fails, your car will still continue to run and you won’t realize that there is a problem until you go for the redline, and your engine runs short on fuel right when it needs it most, and you blow the engine because you ran lean. Unfortunately, we hear about this type of thing happening pretty often.”
“For us, we realized that for late model EFI guys, it is too easy to make power, and we needed to develop a single pump system. So we set out to reconfigure our A1000 pump and find a way to put it inside the factory tank. We had to engineer a system that will bolt down into the factory location, use your OE fuel level sending unit, and go into the tank with the factory o-ring and lock ring. Now you can plumb in a true return-style system to support the power you wand and can make. With the new Camaro or Mustang you can even reuse the factory fuel line and just run a return line back to the tank. The A1000 will cover you up to 1,000 horsepower, supercharged EFI. The Eliminator will get you to over 1,400 horsepower – all from the factory tank.” He continues.
In the end, properly setting up a fuel system isn’t difficult to do. However, it does require you to examine every component of the entire system to make sure it’s right for the job – from the tank to the regulator and back. Make sure those ugly fuel system gremlins have no where to hide. Once you do this, you’ll almost never have to worry about your fuel system ever again.