San Diego Miata Club

Setting Engine Timing

Submitted by John O'Hara

Miata 14-Degree BTDC Timing Adjustment

I wrote this "how-to" after my first adventure in advancing the timimg on Mickey, my '94 Laguna Blue -- thanks to some encouragement and moral support from both the San Diego Miata Club and Keith Tanner of The results are pretty much as advertised -- much smoother torque and free-revving up to redline.

Since then, I've had the Jackson Racing Cold Air Induction system installed, and note that JR includes the 14-degree timing advance as part of their standard set-up.

As a complete novice at Miata mechanics, this procedure was a pretty big deal for me. The Workshop Manual was helpful; the Ignition Timing FAQ from even more so. But I ran into a few details and surprises that I had not seen covered in either. So I thought I would share the experience with other "mechanophobes" who might be considering the timing trick. I hope it is helpful!

The following descriptions assume a familiarity with the information in the timing FAQ (included at the end of this description).

Tools and supplies used:

  • SunPro inductive timing light (Pep Boys)
  • Craftsman offset ratcheting box wrench (Sears)
  • Small paper clip (Gem style)
  • Alligator clip (Radio Shack)
  • Terrycloth towel
  • Plastic electrical tape
  • Flashlight
  • Bandages (oops)
  • 1994 Miata Workshop Manual (Helm)
  • Ignition Timing FAQ ( "Garage")
  • Supply of favorite beverage (optional)

Practice makes perfect

As a novice Miata mechanic, I find that my biggest obstacle to confidence is usually the fear of a) forgetting some important procedure; b) not being able to react quickly if something unexpected happens; c) simply screwing something up. A few days of "rehearsal" made a big difference -- making sure I could do all the individual steps; getting familiar with the tools and how they behave; and knowing I could put everything back if necessary. Oh, yes -- the "favorite beverage" also helped :-)

Preparing to avoid injuries

The lip edge of the metal firewall near the cam position sensor is VERY SHARP. A length of plastic electrician's tape along this edge, below the rubber molding, helps to avoid a severe cut. Or do as I did, and make sure you know where your supply of bandages is :-).

Setting the timing on the warmed-up engine, the cam cover is warm-hot, and gets hotter as the engine runs. Placing a small towel on the cover, on top of the spark plug wires, provides a convenient, insulated arm-rest while attacking the cam sensor bolt.

Jumpering the Diagnostic pins

A standard small Gem-style bare metal paper clip makes an good jumper between the TEN and GND pins on the Diagnostics block. I bent the clip completely straight, then down at the ends to form an inverted V. Gently inserting the ends of the clip about 1mm into the TEN and GND connectors gives a good connection.

Removing the cooling fan fuse

Disabling the cooling fan is recommended both to avoid injuries and to prevent accidental electrical loading of the engine while setting the timimg. I popped open the cover of the main fuse block and removed the 30 amp fan fuse (pink on my car) located at the "upper right" of the block. For easier access to opening the cover, I first disconnected the wires to the windshield wiper motor, located on the rear firewall immediately behind the fuse block. Don't forget to replace the fuse and reconnect the wipers when done!

Connecting the timing light

The metal "tongue" in the blue 12V power connector is recessed too far into the connector housing to be able to attach the large (+) clamp-type lead of the typical timing gun. Attaching a bare metal 1-inch (2.5-cm) alligator clip to this tongue provides a convenient "extension" for easy connection. Be careful not to allow this exposed (+) connection to ground against any of the nearby metal parts.

The cruise control actuator brackets make convenient attachment points for the ground (-) lead of the timing light. Alternatively, the bare bolt which holds down the end of the air intake tube also works fine.

Finding the cam sensor lock bolt

Locating the right bolt on the cam sensor was one of the most confusing parts of the whole procedure. The 1994 Workshop Manual refers variously to the "lock bolt" (page B-9) and "lock bolts" (page G-17). There is, in fact, only ONE bolt, as described below. The Manual also suggests first removing the entire ignition coil and bracket for access. This is COMPLETELY UNNECESSARY with the correct tool.

The lock bolt is the large, silver-colored 12-mm bolt located at approximately the 5-o'clock position when facing forward from the cockpit of the car. The exposed hexagonal head of the bolt is long -- about 1-inch (several cm), and is accessible from above.

Access to the bolt is, unfortunately, made more difficult by the harness for the cam sensor wires, which is attached to the cam sensor bracket at several points by what appear to be expanding locking pins. Anyone know how to remove these?

Finding the right tool

If finding the bolt was the most confusing part, finding the right tool to turn the bolt was the most frustrating. A standard socket wrench was too bulky to fit into the narrow space between the bolt and the firewall. The correct angle to seat the socket on the bolt was also impossible, and an articulated head was even bulkier. A standard six-point box-end wrench did manage to fit -- awkwardly -- but the extremely limited lateral movement (less than 60 degrees) made it impossible to turn the bolt enough to be able to re-seat the wrench for another turn. *Sigh*

After a week of desperate hunting, I was just about to give up when I stumbled across the "Magical Mystery Tool" -- a ratcheting box-end wrench with a 25-degree angled head. It's perfect! The angled head is ideal for positioning on the bolt (angled toward the bolt), and it's long enough to provide both clearance above the hardware and adequate leverage. The ratcheting action makes it possible to turn the bolt in small increments (20-degrees per ratchet stop) within the limited lateral clearance without having to re-seat the wrench after every pull. And the mating surface is quite large to help prevent damage to the bolt. With this wrench I went from complete frustration to being able to loosen or retighten the bolt easily in a matter of seconds.

The magic wrench is a Craftsman 11/12-mm model from Sears (catalog part #43663), at a cost of US$8.50. Highly recommended.

Shooting the timing dots

On the '94 there are actually two timing dots on the crankshaft pulley, located 10-degrees apart. With standard factory timing, the first dot lines up with the 10-degree mark on the timing scale, while the second dot lines up with the "T" (zero-degree mark). At advanced timing, these dots line up at 14-degrees and 4-degrees respectively.

I was surprised to find two dots, since the Manual and other references only ever mentioned one. But the two reference points are actually quite helpful in lining up the correct timing under the slightly jittery motion of the strobe.

Moving the cam sensor

None of the references I have seen mention the direction or degree of cam sensor rotation in order to move the timing up or down. On the '94, rotating the top of the sensor toward the center of the car advances the timing, while away from the center retards the timing. This is, in effect, the same direction as the movement of the dots under the timing light. Only very slight movements are needed to affect the timing. The difference between 10-degrees and 14-degrees amounts to only a few millimeters of rotational displacement of the cam sensor. For this same reason, retightening the bolt after setting has to be done carefully, to avoid accidentally moving the cam sensor in the process.

Adjusting idle speed

I seem to have lucked out in not having to make any significant adjustments to idle speed. I was surprised to find that the idle speed dropped from normal 950 to around 750 with the TEN/GND jumper in place. But according to the Manual, this is within spec with the jumper connected. After removing the jumper, the idle returned to normal with the timing dot steady at 14. I understand that others may have to "shuttle" back and forth between timing and idle in order to achieve the right combination. In any case, on my '94 there is no "cap" on the idle adjust screw, which is easily accessible with a short flat-blade or Phillips screwdriver.

Hope this is helpful!

Miata Timing Adjustment FAQ ( Garage)

Checking Timing

Tools required:

  • Inductive Timing Light
  • Jumper or paper clip
  • External Tachometer

Begin by locating the diagnostics connector (close-up view) on the driver's side of the engine compartment near the air intake. Connect the jumper (or paper clip) from pin TEN to GND. (This puts the on-board computer into the proper mode for setting the timing.) Connect the timing light power cable to a source of 12volt power. Since the battery is not in the engine compartment, you should use the auxiliary power connector provided for this purpose. There is a blue connector which is not connected to anything located on the driver's side of the engine compartment close to the side of the car about halfway between the diagnostics connector and the headlight motor. Remove the dummy connector to expose the conductor. This is where the timing light can be powered from. Connect the timing light ground connection to a suitable grounding point. Put the inductive pickup around the number 1 spark plug wire.

With the idle set to factory spec, check the timing by observing the timing marks on the crankshaft pulley in relation to the fixed marks on the timing belt cover. Each mark represents 2 degrees of timing advance. If the timing is outside of the factory specification, 10-degrees before top dead center (10-degrees BTDC) you need to set the timing.

Setting timing

Tools required

  • 12mm socket
  • Socket wrench with articulated head (if possible)

For 1.6 liter engines locate the crank angle sensor (close-up view) at the rear of the passenger side valve cover. It is a circular metal unit that sits right on the rear of the valve cover. Locate the locking bolt for the sensor. This is on the lower side of the sensor bracket nearest to the passenger side. Loosen this bolt only enough to allow you to rotate the crank angle sensor. As the crank angle sensor is rotated (only a small amount at a time), you will see the timing change with the timing light. When you get the timing back in spec, tighten the lock bolt.

You can find the cam sensor on your 1.8 liter Miata by following the driver's side hump in the valve cover to the back of the head. On the rear face of the head you will find a round unit with a multiplug on it. This is the sensor. There is one bolt with a twelve mm head on it that is the hold-down. If you were sitting in the driver's seat looking at the back of the head, the bolt is at about five o'clock. Don't forget to jump the TEN and GND pins in the diagnostic connector (close-up view) before setting. Use the yellow painted dot on the crank pulley.

Jared Stack points out: It's best to set the timing when the car has warmed up to the point where the idle has settled and the engine is up to operating temp, but is still relatively cold. The motivation for doing this is to make sure that when you check your timing that the radiator fan is not running. If it activates, the timing will be retarded by 1-2 degrees. The consequence of setting it at this point is when you are on the open road at speed the fan usually won't be running as much and the timing will be higher than what you thought it was set to. There should be a fuse for the radiator fan... just make sure you put it back when finished. :-)

If you tweak the idle this will affect the baseline value of the timing. Tweak idle with jumper in place and correct the timing. After adjusting the idle (improperly, without the jumper) to compensate for the current draw of the Hella H4's, my timing was retarded by about 3 degrees!

Rick Fischer ( helps clarify Jared's statement:

Timing must be set with the motor in a no load condition at the specified idle speed. Electrical loading of the alternator sucks horsepower, drag on the motor - slows it down. Therefore the revs aren't right. The timing mark may move when the motor drops revs but that is a function of the rev drop not the electrical load.

The Hellas did not affect his timing by 3 degrees the current draw and motor slowing did. Advancing the timing to compensate will have just advanced his timing - period.

This may cause problems if the person doing the retiming is not across the general principles of ignition timing, and accepts Mr. Stack's comments on their face value. Someone advancing their timing to the 16 or 18 degree marks and then compensating for what they think is another factor may well over advance the timing to the point where detonation may occur; i.e. 16-18 plus 2 for the fans and 3 for lights = 21 to 23. The Pinging may well be a very expensive noise, breaking rings and cracking pistons in extreme occurences.

Very simply, time any motor - no load. No A/C, no lights, no fans.

Extra power by advancing

Many enthusiasts have found that they gain a few extra horsepower by advancing the timing to 14-degrees BTDC. If you do this, you may experience some pinging when running on regular gas. If so, try switching to premium. If you still get pinging and it isn't caused by one of the other problems described above, then back the timing down to the point where the pinging is no longer an issue. (Pinging is usually experienced under hard load driving - not idling in your driveway. So you'll have to set the timing and drive it for a while before you really know the effects.)

Timing for Modified Intake Tract

If you've modified your air intake with the installation of a turbocharger, supercharger, Cold Air Intake, or other type of upgraded high flow intake system, the timing rules may change. You should follow the advice given by the manufacturer of your unit.


Please note that these tips and pointers are not reviewed or approved by Mazda Motor Corporation or any other corporation or entity other than the originator. The San Diego Miata Club does not accept any liability for damage or injury as a result of utilizing these tips and pointers. Please use common sense and always remember safety first.

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