No Start Guide

Originally by hobie237 in 2008

As a starting point, I assume that the individual has checked the engine bay for anything glaringly out of place, or any major issues. This includes checking the air intake system for blockages or large vacuum leaks- check couplers in aftermarket intake systems, see if the brake booster fell off the manifold, check the various connections and see if anything is obviously unplugged, failed, broken, clogged, jammed or otherwise inoperable. I'm also assuming for this article that the motor just stopped. More likely, it was shut down and then refused to re-start. If your motor was smoking, banging, clanging, belching, flaming, popping, sputtering, knocking, or making any other abnormal noise, smell or sight, I doubt this article will help much. This is for when a Miata just decides to roll over and play dead, not when you send the car to the firing squad.
  • When you turn the key to “START,” what happens? If it cranks, don’t bother reading this, just go to Step 2. If you’re not getting any cranking, keep reading. The solution is most likely very simple.
    • Battery- especially if the car has been sitting lately, of if it is very cold, the battery may be dead. Have it load-tested at an auto parts store- it may be showing 12V but not have much current in it.
    • Ignition switch- try cleaning the ignition switch. Several issues have been traced to the connections becoming dirty over the years.
    • Solenoid and starter- If battery checks out, it’s time to check the solenoid and starter.
      • Check for power reaching starter, listen for solenoid clicking.

Step 2: Cranks but will not fire

  • When the key is turned to “RUN,” does the Check Engine light come on?
    • If YES: Pull stored fault codes from ECU and refer to the article to decipher them. I would recommend doing this twice- pull the codes, clear the codes by temporarily disconnecting the battery, try to start it, and then pull the codes again. This will be particularly useful if there are a lot of old codes sitting in the computer’s memory.
      • Is the timing belt broken? Remove the oil cap and look at the cam while a helper cranks the motor. If the cam is turning, your timing belt is not broken. It would be highly unlikely for the belt to slip enough to cause the car not to run and still turn the cams. Make sure, though, that the cam is turning and not simply flopping around.
    • If NO: The ECU is not firing the Check Engine Light. This means that power is not reaching the ECU, power is not reaching the Check Engine Light or the computer is bad.
      • Remove the access panel under the driver’s dash and locate the fuse box. Check the 10A “ROOM” fuse in the bottom left of the box. This supplies a constant 12V to terminal 1A of the ECU. If the fuse is good, check for bad wiring by checking for power at ECU 1A.
      • Check the Main EFI 30A fuse in the underhood fuse/relay box.
      • Check the Main EFI Relay. Putting the key in “RUN” and unplugging/plugging the relay to see if it clicks is a very basic test here, but a failed relay can still click a little bit (mine did) and lead you astray. I would recommend you check for continuity by applying +12v to terminal A, grounding terminal B and checking for continuity between terminals C and D. This procedure is detailed in the Enthusiast’s Manual, page 5:42.
        • Depending on the age of your Miata, the old relay may read “B6S8” or “JE16.” The new part number is JE16-18-811
        • If failed, replace. Note that this is a dealer part. Some auto parts stores can try to cross it to another relay, but I wouldn’t risk it unless you know for sure that the guy on the other side of the counter is GOOD, and they can verify that the terminals and mounting will be identical. .
      • If these are good, check for +12V at terminal (X) of the ECU with the ignition in “RUN.”
        • If no voltage, there is a bad connection somewhere in the circuit. Refer to the wiring diagram on pages Z18-21 in FWM.
        • If there is voltage, there may be a problem with the ECU, it would be best to swap it for a known good unit for testing. If the car fires with the known good ECU, you've located the problem.

Step 3: Ignition System Checks

  • First, check for spark at each cylinder. If no spark observed, continue here. If good, strong spark observed at each cylinder, continue to Step 4. Also, while plugs are removed, visually inspect them for damage, excessive buildup, oil in the plug wells, or other obvious issues. Check to see if they are wet- if not, fuel is not reaching the cylinders.
  • Inspect the spark plugs. They should not be fouled or otherwise unserviceable. Check the spark plugs’ gaps- they should be 0.039-0.043in (1.00-1.10mm).
    • While you have the plugs out of the engine, it's a good time to see if they're wet- this is a good initial check for fuel reaching the cylinders. However, the presence of fuel does not automatically mean there are no faults with the fuel system, and while dry plugs are an indication of fuel issues, they do not rule out ignition issues.
  • Inspect the ignition coils.
    • With the key in “RUN,” there should be voltage at the positive terminal of the ignition coil connector.
      • If no voltage here, check the wiring. We have already ruled out the fuses and ECU.
    • Check the resistances of the coils. The specifications are:
      • Primary Coil: .78-.94 Ω
      • Secondary Coil: 11.2-15.2 kΩ
      • Primary Terminal to Case (insulation check): greater than 10M Ω
      • Spark plug wires should be in good condition and securely fastened to the coil packs and spark plugs. While it is highly unlikely that plug wires would cause a sudden failure unless chewed up while the car was in storage, the specified maximum resistance on them is <16 kΩ per meter- the actual maximum allowable resistance for each lead must be determined by measuring each wire.

Step 4: Fuel System Checks

  • If there is a good, strong spark at each cylinder, or if spark plugs are dry after cranking and not firing, check the fuel system.
    • The Circuit Opening Relay is a likely cause of failure here- it is located under the dash. Pull the access panel to locate it (photo, diagram). It will be up under the dash, toward the side of the car (above clutch pedal).
      • To test this relay in the car, jump terminals FP and GND- this will bypass the AFM contact points and the ground group under the brake booster- and turn the ignition key to RUN. The fuel pump will be difficult to hear, so perform this test in a quiet location, and you may want to listen in the fuel filler if you can’t hear the pump elsewhere.
    • If you do not hear the pump, remove the access panel under the rear deck carpet. Check for +12V at the L/R terminal with the FP/GND jumper in place and the key in “RUN.”
      • If no power detected, there is an opening in the circuit to be found.
      • If power is detected, the pump itself is most likely at fault.
    • If the pump is good but fuel is not reaching the cylinders, check the connections to the injectors.
      • Using a stethoscope, or a long screwdriver, listen for injector operation with the engine being cranked- you should hear each injector click on and off.
      • If you suspect a failure, check for battery voltage on the red/white terminal with the ignition in “RUN.” Each injector should show resistance of 12-16Ω.
    • If the injectors are cycling properly, and the fuel pump is operating properly, there may be a fault with the fuel pressure regulator.
      • De-pressurize the fuel system by removing the circuit opening relay and cranking the motor for a few seconds.
      • Install a pressure gauge in the fuel line, where it goes to the fuel rail. The reading when cranking should be 31-38psi. When turned off and pressurized, the system should hold a pressure of at least 21psi.
      • If pressure is low, pinch or clamp off the fuel return line- if pressure increases, suspect a problem with the fuel pressure regulator. If pressure does not increase, there is most likely a problem with the fuel delivery lines, which would most often be present in the fuel filter.
      • If pressure is extremely high, suspect a blockage of the return line.