Fuel System Check Up
Scott Simpson - Scott231@Juno.com
If you believe your vehicle has a fuel pressure system related problem, this article will diagnose the problem and provide remedies. It is designed to be all-encompassing, thus, there are several tests. Please read these tests and Notes at the end of this article before proceeding.

Step 1

    Is to attach a good quality fuel pressure (FP) gauge and take some readings. The gauge should be attached with a hose long enough to mount the gauge on the windshield (use duct tape or clip hose under windshield wiper if this is only a temporary installation.) Start the motor and remove the vacuum line from the top of the FP regulator, record the FP reading. This is known as checking the "static" fuel pressure. The exact setting you should have depends on your FP regulator, chip requirements and the HP demands of the engine. Now reattach the vacuum line and turn off car. If the FP quickly drops, skip Step 2 and go to Step 3.

Step 2

    Involves road testing the car with the FP gauge installed. The FP reading while running "X" amount of boost should be X+static pressure (i.e. if you have 45 psi static FP and are at 15 psi of boost, FP should be 60 psi.) If this is not achievable or if the reading varies at a steady throttle position, you may need to check a few items.

Potential problem Potential fix and link to procedure
Clogged Fuel filter Replace Filter
Clogged Injectors Clean Injectors
Collapsed fuel pump sock Replace sock
Weak voltage at pump(s) Run wire from Alternator or
Install Voltage Booster
Bad FP Regulator (see test below) Replace Regulator
Weak fuel pump(s)
Will usually whine loudly when bad
Replace pump(s)

    A fairly common problem TR owners find is that after they shut down the car, fuel pressure drops to almost zero very quickly. Pressure should stay in the rail for at least 20 minutes. If your system is doing this (and there are no obvious external leaks), there are three possibilities:

    1. Bad Fuel Pressure Regulator,
    2. Bad Check Valve in fuel pump, or
    3. Bad Injectors.

Step 3.

    To locate the culprit, first get the car up to operating temperature and shut it down. Next attach a pair of locking pliers (such as Vise Grips) to a rubber section of the outlet line from the FP regulator. This is the line coming out of the bottom of the regulator which goes back to the gas tank. While watching the FP gauge, turn the key to the On position (but do not start). Turn the key off as soon as pressure rises to the previously determined static fuel pressure.

    If the FP stays at the static pressure and doesn't fall, then the fuel pressure regulator was leaking fuel back into the tank after the car is shut off. Remove the pliers and watch the pressure fall to zero. Time to buy a new FP Regulator...

Step 4

    is necessary if the pressure still dropped during the test in Step 3 or if replacing the regulator did not solve the pressure drop problem. You will need a second person to help here. Redo Step 3 but this time have someone else turn the key to On and you need to attach a second pair of locking pliers to a rubber section of the fuel feed line simultaneously with the key being turned to the Off position.

    If the FP stays at the static pressure and doesn't fall, then the Check Valve in the fuel pump was leaking fuel back into the tank after the car is shut off. Remove the second pair of pliers and watch the pressure fall to zero. Time to buy a new fuel pump...

Step 5

    Is just the corollary to Step 4. With both pairs of pliers attached, if the FP still drops after shut off, then the injectors are stuck open for some reason. The first suggestion is to clean the injectors. You may also remove the injectors and send them off to a business that specializes in injector cleaning. Injectors cannot be serviced without special tools. You will probably find that the cost of disassembly and cleaning from a professional company will outweigh the cost of a new set of injectors. Thus, if the cleaning procedure on our Tech page doesn't work, Time to buy a new set of injectors...

After replacing any component found to be bad, redo the earlier steps to verify that all bad components have been found.


  1. Be careful whenever diagnosing a fuel system. Use common sense! Fuel is obviously flammable.
  2. The fuel pump relay will shut off after approx. 3 seconds if the car if the car isn't started.
  3. Keep an eye on the FP gauge whenever the pump is energized. Never let the pump run continually when the return line is clamped off or you will damage the pump or break a rubber fuel line and spray gasoline all over your work area!
  4. Rubber sections of fuel line can be found in the lower engine compartment or back by the gas tank.
  5. You need to get a good clamp on the rubber lines to ensure no fuel can flow past the pliers. But do not clamp down so tight as to ruin the rubber hose.

Last updated: