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Miata Fuel and Engine Electronic systems interchange Guide

Miata Fuel and Engine Electronic systems interchange Guide

By Randy Stocker

*** !!!UNDER CONSTRUCTION!!! ***

First, please check the Miatapower archives for detailed discussion about Miata fuel systems and the ECU. It is alphabetically sorted by topic and contains much more information than the general highlights found on this page

Fuel pump:

Altough there are performance fuel pumps available on the aftermarket through Holley (Walbro) and Bell/BEGI (Pierburg), the 93+ RX-7 TT, 95+ turbo DSM and the 93+ Supra Turbo are reported to fit. Minor mods to the electrical connections and pick-up tube might be required.

Catalytic converter:

The 1.6 catalytic converter has smaller input and output openings than the 1.8. The 1.8 catalytic converter has the input flange rotated about 30 degrees more vertical so it will not directly fit on a 1.6 header without cutting off the flange and having it rewelded in the proper postion.

Input, 1.6 on left cat1.jpg (46 KB) Output, 1.6 on right cat2.jpg (52 KB)

Ignition coils:

The 1.6 ignition system uses a separate ignitor while the 1.8 uses a coil pack with an integrated ignitor which makes them incompatable. The 1.6 coil pack assembly uses a single connector and the 1.8 has two connectors to accomidate the ignitor. The coil brackets are also different between the 1.6 and 1.8, only the large center head bolt is usable for a swap. In March of 1995 (VIN 61493) when some of the ODB-II electronics were implemented (i.e. Still OBD-I but the cam angle sensor has an extra pulse for the "limp home "mode) the coil connectors were again changed to a 3 wire connector instead of a 4 wire one (The tachameter wire was removed) If using the later coil in a 94-3/95 car then it requires splicing the earlier connector on and derermining how to tap the tach signal. The coil versions are 90-93, 94-3/95, 3/95-97, 99+

The 1.6 coils are marginal for boosted apps above 15 psi. The long run from the ignitors is to blame. A performance ignition upgrade for 1990-93 1.6 motors is to use the 94-95.5 coil pack or a MSD DIS. Frank Devocht gives step-by-step instructions to install the 1.8 coils here http://users.pandora.be/miata/english/techie/coil_swap.htm and here http://www.sonny2.com/Miata/CoilSwap.htm

1.6 on left coil1.jpg (44 KB) 1.6 on right coil2.jpg (73 KB)

Throttle Body:

Although the 1.6 and 1.8 TB share the same 55mm butterfly valve diameter they are not much alike after that. The mounting bolt pattern if wider for the bottom two bolts, IAC is controlled differently and the TPS is variable for the 1.8 and on/off for the 1.6 5-speed (the 1.6 automatic is variable). The two TB's are not directly transferable. A 1.8 swap using the 1.6 ECU requires an adapter plate to be fabricated.

1618TBcompare.jpg (55 KB)1.6 on left, 1.8 right.

When using an aftermarket programmable fuel injection computer such as a Haltec or Electromotive on a 1.6 the use of a variable TPS is usually recommended. The 1.6 5-speed used a on-off TPS but the automatic did have a variable TPS. The whole TB must be swapped as the mounting for the TPS is different in the casting.

Miata-TPS-comparison_TN.jpg (38 KB) automatic on right.

TPS

UNDER CONSTRUCTION 5/11/04. The 90-93 TPS is a simple on.off/on type. . The switch us used to tell the ECU the var is at idle and at WOT. To use a variable TPS in the 90-93 1.6 5-speed TB you only use the bottom two wires of the variable TPS to get the ECU expected idle on/off circuit. The top two wires are for the variable signal (pentiometer) but are not designed to give a ON when WOT is reached so they will not work for the ECU signal - use those for your other piggy computer. The 5-speed ON/OFF TPS cover just pops off so you can see the power connector and the idle connector and know which wires are which. I personally just cut and reconnected my harness with insulated blade terminals onto the variable TPS plug.

Variable TPS .

Injectors:

The Miata uses high ohm injectors (saturated type, 12-16 ohms) and has a fairly unique rounded injector connector. The 205cc 1.6 injectors can be directly replaced with the 94-97 230cc 1.8 units. Many other makes injectors are also a direct fit, including the late 87-89 Toyota injector from the normally aspirated MR2 (4AGE) 1.6 DOHC at 213cc (Beige top), 89-91 B2200 truck at 224cc, 89.5-92 Toyota Supra non turbo at 305cc (light green top) and turbo 430cc (black top), 89-91 B2600 truck at 326cc and the 89-92 Mazda RX-7 non turbo at 440cc. Most OEM injectors of ealier vintage or larger capacilty either have a different shaped connector requiring swapping the pins to the Miata connector or soldering a new connector on. Examples of this are the 88-89 323 GTX/91-95 Capri Xr2/88-92 MX6 2.2 turbo 300cc injectors. Many larger aftermarket and some OEM injectors like the 86-88 RX-7 440cc are of the low ohm variety (Peak and Hold type, 2-6 ohms) which requires a balast resister in line to work with the factory ECU injector drivers. FYI, if you are running at 150 rwhp or over then the factory 94-97 1.8 230cc injectors are at full duty cycle.

Cam angle sensor:

The cam angle sensor was changed from an optical type to a magnetic type when the 1.8 was introduced. The cam drive and mount is the same from 1990-1997 and the signals are compatible so they interchange (i.e. a 1.6 sensor can be used on a 1.8 engine for the purposes of a engine swap). Starting in 1999 the cam angle sensor is gone and replaced with a crank angle sensor mounted behind the crank pulley. The camshaft drive and CAS mount are still there so the sensor can be retofitted for the purposes of a 99-05 engine swap into an earlier car.

The optical unit reads holes punched in a disk while the later unit is magnetic based. In theory the later style is more accurate and offers potentially less spark scatter. Without removing the rear cover they can be recognised by the optical has a flat rear cover and the magnetic has a convex rear cover.

In the Miata the ignition trigger signal rises 70 deg before each TDC (the 4 equal holes) and uses the other two to determine cylinders #1/4 and #2/3 (the primary and waste spark).

Miata16CAS_TN.jpg (23 KB) 
Miata16CASdisk.jpg(5 KB) Miata18CAS2_TN.jpg (29 KB)

Flowmeter:

Wiring harness:

The fuel injector wiring harness was slightly altered for the 1992 model year by changing the connector for it. If you will be installing a 92-93 engine in a 90-91 car then just make sure to use the whole harness from the recipient car. The wiring harness versions are 90-91, 92-93, 94-3/95, 3/95-97, 99+

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