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July 29, 2021 8 min read

10 reasons your fuel system sucks… or is leaving you stranded!

 

We all have made mistakes when putting systems together as we often times do it in stages and progression takes place over time, its easy to overlook. Don’t feel like this is a slight on you or your project. I have learned all of these lessons from our partners in the industry or from our own past mistakes. Our goal here is to share the things we have learned to improve your current or next project, or simply to keep you from breaking down! I really hate to see friends and colleagues on Rocky Mountain Raceweek broken down or dropping out due to fuel component failures, but it absolutely happens and often.

 

So here goes… Often times a lot of these items won’t be exposed at the track, but rather on a long drive when more fuel is being returned to the tank than used and for excess time periods is when you will find the weak point in a fuel system.  This is why we made this list, most folks will call us saying “it has always been fine but then I went on a cruise, or I went on Raceweek and its been acting up the whole time”.

 

  1. Your Pump Feed Line or Filter is too small (and can’t suck): if your fuel pump is limited on the amount of fuel it can intake (or siphon/suck) compared to its capability and what the engine is demanding its going to begin to starve and heat up, you will run it dry and also have performance issues from this. Within reason, it is always best to OVER size a fuel pump inlet. For a quick example even a Magnafuel 4303 pump needs to have a 12AN inlet to maximize performance. We OFTEN times see these issues when folks have a stack up of multiple pumps externally, they keep adding pumps but don’t add inlet capacity.    

 

  1. Your Fuel Filters suck: Not all fuel filters are created equal. We often hear “But I have a 12AN filter). That is kind of like comparing one 350 cubic inch engine to another and saying they’re the same because the bore size is equal, it is what’s inside that counts. A fuel filter is made up of several components that matter, I will list them below.
    1. Micron Count: Pumps need a certain micron as a pre filter, if you make it too small (too small being 10 micron versus 100 micron which flows better as example) you can reduce flow as its harder to pull fuel than it is to push.
    2. Orifice size: This does matter and can be a limiting factor, for instance a 5GPM Aeromotive pump needs to have the CORRECT big 12orb orifice size filters pre and post.
    3. Filter Style: Especially this day in age you will see a cheap Chinese piece of crap made to imitate a good filter. They may look the same externally, but inside the filter is different. The way the pleat of the filter is designed can greatly effect the square inches of overall usable filter.  For further explanation when you cut that filter and spread it out one can be drastically different in size than another.
    4. Length of Filter: Going back to the previous point, the length of that filter adds square inches to the pleat/filter, of course the longer it is the more it can flow all other things equal.
  2. Fuel Vent Size is too small and sucks: Just like crank case pressure, with big fuel pumps pumping massive amounts of fuel into a container like a fuel tank, that movement creates pressure, when the pressure builds up it pushes back on the return side of the fuel system thereby laboring everything in front of it including the pump itself and can damage the motor internally. Additionally, with higher pressure comes higher temperature.  This will fail a fuel pump and cause massive amounts of issues on any long trip including boiling fuel. Keep in mind a lot of these EFI converted fuel tanks were made originally for a non return style fuel system where the mechanical pump on the block was pulling the fuel it needed, completely different. When you put one or more high flow electric pumps and leave the small factory vent you are asking for trouble. Even two 340 pumps in tandem can potentially cause issues as you have a pump that is flowing likely 3-4 times what the original vent was intended for. You literally cannot have too large of a fuel vent, just keep in mind debris getting back into the tank and fuel exposure to air in terms of smell, safety, and taking on moisture if the vehicle is sitting!

 

  1. Wiring/Amperage to the pump is not enough: Electric fuel pumps have electric motors. When an electric motor isn’t supplied enough voltage or amperage it works WAY too hard and that will cause premature motor failure every time.  Every fuel pump has a different amperage demand, read that again.  Just because its good for one pump doesn’t mean its good for the next.  Follow each brand and pump’s suggested instructions and don’t forget wire size into the pump, into the relay, and the ground, they all matter. Having an 80 amp relay and 22 gauge wire is not going to cut it…. Again follow instructions, doing this incorrectly makes more fuel pumps unhappy more often than any of the other items on this list.

 

 

  1. Routing Fuel Lines:This seems simple but sometimes when we build cars it is easy to get complacent as the build progresses. When routing fuel lines remember how hot a transmission or exhaust of any kind can get. Additionally, if you are driving in one of the hotter climates, ambient temperature from the ground up on black top or concrete can emit soooo much heat.  It might be overkill but in any of these exposed areas you can consider doing heat wrap of some sort, there are a lot of good products out there. 

 

  1. Feed or Return Line is too Small: there is no advantage to undersizing or sizing your return line small in any way. In fact, after the fuel exits the fuel pressure regulator it literally just needs to get back to the tank. That is all you need to know… The return line doesn’t need to have fuel back pressure or anything weird like that.  In fact, when pressure builds up after the regulator (i.e. in the return line), the fuel pressure regulator will have a difficult time controlling pressure, often times if you see uncontrollable fuel pressure it is an under sized return line and a huge pump feeding it. In regards to feed line, it too needs to be properly sized.  If you have a huge pump or pumps trying to shove massive amounts of fuel through too small of a line, it is going to put a strain on the pump which will cause premature pump failure and also pump heating. 
  2. Regulator is too small: This goes along with the previous talk of fuel return line. If you have a fuel pressure regulator that has small orifices inlet or outlet it is going to cause a back up and restriction on the system.  This often time won’t matter when racing because all of the fuel is being used up by the engine and you are returning very little.  When you are driving for extended periods, however, the fuel pump is basically running full tilt against a brick wall and eventually will spit its guts out from over laboring itself for long periods of time. 

 

  1. Turn it DOWN when driving!: There are multiple ways to do this. As mentioned before, when you are cruising or driving often times you are only using a small fraction of the fuel that your fuel pump is flowing because you likely built and designed a fuel system to support 500, 600, 1000, 2000 horsepower (but when crusing the demand is substantially lower). There are several ways to turn a fuel pump down safely.  The Aeromotive Brushless line of pumps has a variable speed pump option, which I highly recommend. This has a trigger wire that will take the pump from 100% flow to 30% flow when deactivated, simple. Brushless pumps have a logic controller internally by design of the motor.  For a brushed pump such as a 340, 450, Magnafuel 4303 or one of the many other pumps on the market you can PWM (pulse width modulate) the pump, this basically modulates the voltage going to it which reduces flow safely.  Again this can only be done on pumps that have a brushed style motor internally.  Some aftermarket ECUs are capable of doing this, there are some external controller boxes that do this, just make sure you wire correctly and still pay attention to wire size when adding this in the loop.

 

  1. Fuel Pump Location is too hot: This seems simple but sometimes we put things where they fit and sometimes there are not a whole lot of options. If you put a fuel pump in a sealed box somewhere where it can get hot and has no venting it may build up tremendous heat and cause motor failure.  If you can get air passing by the pump to cool it off it is not only better for the motor itself, but a cool pump is less apt to heat up fuel passing through it as well.

 

  1. Filters are clogged: Never underestimate how fast a fuel filter can get clogged. Especially on a new fuel system or car build. The dirtiest a fuel system will ever be is when you first assemble it, period.  There is dirt and residue from storage transport and assembly in the new lines, in the new fuel tanks, assembly dirt in fuel pumps filters and regulators and the list goes on.  A partially or fully clogged fuel filter will cause a pump to overheat and subsequently fail very quickly.  Of course there is always the opportunity for that bad tank of gas you can get that can pop up anytime.  For stainless mesh filters you can use brake clean to cleant the filters and move on.  If you are using paper or microglass post filters, I highly recommend keeping a spare in your track bag or trailer for easy replacement. 

 

A fuel system needs to be designed so that the components and their subsequent sizing and selection work together, much like everything inside of your engine. With the advancement of technology that can be confusing and difficult to keep up on if this is your first build or you don’t build cars every day. That is why we are here to help. Fuel systems are our forte and we take pride in doing things right! We offer a service called our Fuel System Builder Form.  This form allows us to have us spec as much or little of your fuel system as you want (i.e. just fittings and line, complete system, just pumps and filters).  You pay a simple $25 deposit that can be applied to your purchase, we upcharge this service in no way. You submit your goals, and some information about your ride and we do the rest. Often times customers opt to have us spec and sell them a complete fuel system including every last fitting and line they need. When that is done and they pay, the fuel system arrives at their house and you are able to assemble and build a complete fuel system in a matter of hours without ordering and reordering fittings, guessing what is compatible, and trying to learn capabilities of components. Its so simple. Link below.

https://www.motionraceworks.com/pages/custom-fuel-systems


I hope these help… Please remember these tips all came from my own mistakes and learning from other friends and colleagues. Some of these you may have already known, but if you are having fuel system troubles I am confident you will find a solution within this article. 

To shop Motion Raceworks Fuel System Components

https://www.motionraceworks.com/collections/fuel-system-components

To shop Made in the USA Fragola Fuel Line and Fittings like we use on all of our builds 

https://www.motionraceworks.com/collections/fittings-hoses

 


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