Tech Tips

Electric Fuel Pumps &
Vapor Lock

Curing Vapor Lock

Some totally stock FSJs seem to be mercilessly plagued by vapor lock while others seem to experience the problem rarely, if ever.  Here's a quick checklist of things to consider.

  • Ensure your fuel filter has the vapor line oriented at the top
  • Be sure there is a phenolic spacer under your carburetor
  • Make sure your cooling system is in top shape
  • Tune for proper AF mixture and timing
  • Check your tank vent lines to make sure they work
  • Check your heat riser valve on the exhaust to make sure it's not stuck closed

One of the best cures we know of for vapor lock, common in FSJs, is to install an electric pump. Vapor lock occurs when fuel that is supposed to be in liquid form instead turns to vapor. This can happen as a result of heat soak: when heat builds up in the engine compartment with the vehicle off.

Electric Fuel Pump Install

But the vapor lock to which we're referring here happens when the vehicle is starved for fuel because of vapor in the fuel lines or carburetor bowl while it is driving down the road.

Science tell us fuel (or anything) can be induced into a vapor state if pressure is low enough and if temperature is high enough. Mechanical pumps suck fuel from the fuel tank whereas an electric placed near the tank pickup creates pressure in the line.

There are two methods for mounting. The farther back by the fuel tank is better, but there are other locations for mounting that will save you time. It is up to you to determine which is better for you.

Replace your mechanical fuel pump with an electric. (External Link, with pics)


Auxiliary Electric Pump Installation (longer, better method)

  • Loosen but do drop your fuel tank
  • Remove the fuel line hold downs along the inside of your frame rails.
  • These first two moves allow you to install an electric fuel pump just behind the boxed section of the frame, inside the channel part of the frame. This place is ideal as it is protected, cool, and easy to plumb and wire...if your metal lines are free of the confines of step two... impossible otherwise. Do not cut any lines yet.
  • Replace your in tank sock (dealer part). Get the part, new hose clamps, and 6+ feet of hose before you start all this .
  • Depending on year you may have to completely remove your tank (78 earlier) or remove all your carpet, rear seat etc. and remove the access panel over the pickup assembly for tank (wagons w/plastic tanks).
  • Wash off top of tank with high pressure water there will be dirt surrounding the top of pickup.
  • Cut hose clamps to remove them.
  • The pickup on plastic tanks is removed by first loosening a large plastic nut. This nut can be removed by using a large screw driver against one face of the plastic nut and "gently" tapping to loosen. 
  • Metal tanks require a BRASS punch to avoid sparks, to loosen them. Remove pick-up assembly make a mental note which way you ease it out.
  • Cut clamp for old sock, remove old sock and using compressed air blow out line. Slip on new sock on. Socks do not need a clamp unless they come with one. Carefully reinstall Pickup into tank. 
  • The new sock will probably press against The bottom, and offer some resistance as you try to push it down. This is okay push far enough to get The nut started then re-tighten as you loosened it. Do not skip next steps.
  • Remove intake line (tank side) from all fuel pumps and blow all lines out with compressed air.
  • Install new rubber lines from tank pick-up to frame line. I install an in line filter at This time in This location in order to save The electric pump just down stream.
  • Now you are ready to install the electric pump without getting covered by gas when you cut the line.
  • Prefit the fuel pump. You will need longer lines than come with it. The fuel line is the largest line. 
  • Cut The line using a "low clearance" tubing cutter. Drill holes for fuel pump and proceed with the install of the pump to the frame.
  • Fuel line from the tank may be bent slightly.
  • Install Wiring. Pre-solder and heat shrink enough wire for the job prior to climbing under The truck. (Throw The crimp piece away along with The wire clamps that came with The pump).
  • Wire pump through an ignition switched source, then through a lighted panel switch. (An oil pressure switch in line is a very good idea as this will kill the pump in the event of a roll over or serious accident)
  • Finish install of pump lines with screw type hose clamps.
  • Install a new mechanical pump along with all new lines and filter at engine end.
  • Final steps. Reinstall all line clamps along frame. Reinstall gas tank, check for binding of Fuel lines.
  • Turn ignition switch to on but do not start. Turn fuel pump on, you should hear the distinct sound of the fuel pump working. Get out and check for leaks.
  • Start your vehicle and enjoy thousands of miles of care free driving. Your fuel delivery system has just been overhauled front to back and upgraded with dual filters and dual pumps.
  • A few other points to cover: replace your gas cap at this time, and make sure your tank vent is clear. I run a fuel filter without a return line, but have not had problems with one as long the rest of these items have been done. 
  • Others have had to retain the return line to prevent overpressure or flooding.
  • The electric I use is the "solid state " stocked by NAPA. Fuel filters save your pumps as much as your carbs, get one upstream of everything.
  • I have run dual pumps for years without problems, by switching off your electric from time to time you make sure your mechanical is working, and you can always listen for your electric to make sure it is working.
  • Electric pumps generally help greatly with "slow starting vehicles".

(Quick method location)

Auxiliary Electric Pump Installation (quick method)

  • Mount fuel pump in desired location. The instructions for mine required a 45 degree angle so I mounted mine on The frame right below the gas pedal.
  • Cut fuel lines with a pipe cutter. Be sure to take it slow and you will not create a spark. Be sure to leave enough room to accommodate spacing for looped rubber lines.
  • Install rubber hoses from the fuel line to the pump. Use hose clamps to attach the rubber hoses to the fuel lines. Loop the hoses to avoid kinks.
  • Install an electric switch. I mounted mine just to the left of the steering column. Run wires up through the firewall and into a "hot" source.

That's it. I Do not Turn on my Electric, but use it as back-up. If The manual pump goes out, or I vapor lock, flip The switch, and off and running again.