A brief history of the "tech 4"

A bit of History

GM built Dukes as cheap and light as possible, mainly for commuter cars like Monza Fiero etc.

Why?

GM used Aluminum 2300 engine for Vega and Opel. Vega with Aluminum engine is good on paper but many didn't last, resulting 30,000 to 50,000 miles the engine eats oil etc. and is a big reason why many think Vega = Junk even today. To "fix" that problem... GM introduced the Iron Duke in 1977.

It's a weak engine

Again, GM built Dukes as cheap and light as possible. GM had to make trade-offs for a "strong" engine vs. "economy" engine. That's why GM used a simple Cam Timing Gear instead of a Chain. Later years, 1991-92, GM switch to a timing chain and increase HP.

Remember that GM and others Publish HP are often under rated for many reasons. Real HP can be and often is more then Publish data. Transmission type and gearing will have an affect on overall Torque and HP values measured at the wheels. Also, Make sure that TBI can reach WOT. Many Fiero can't do that and owners think/says just weak engine. See Throttle Cable.

For more, see: (Both from Wikipedia)

GM 2300 engine

GM Iron Duke engine

Versions used in Fiero

There are 4 factory engine configurations all based on the GM/Pontiac cast iron 2.5l block. Here's a short list of the major differences.

Function	84	85	86	87	88
ECM # (Cruse?)	1226156 (No)	1226864 (No)	1226864 (No)	1227748 (Yes)	1227748 (Yes)
MAT sensor	No	No	No	Yes	Yes
Ignition	HEI with external coil	HEI with external coil	HEI with external coil	DIS II	DIS II
TBI Type	300	300	300	700	700
Cam	Flat lifter	Flat lifter	Roller lifter	Roller lifter	Roller lifter
Balance unit	No	No	No	No	Yes
Oil filter	Under intake	Under intake	Under intake	Under intake	In oil pan
PTO belt(s)	Multiple V	Multiple V	Multiple V	Serpent	Serpent
PCV vent	Under air cleaner neck.	Under air cleaner neck.	Under air cleaner neck.	Separate vent to air cleaner side	Separate vent to air cleaner side

Erratum

84 Indy may have came with roller cam setup as part of Indy's Option Package(s).
85 might have roller cam setup or had mid-year change.

Engine Versions as Software Versions...

Another way to say is if you think Software versions and Major.Minor numbering a program or OS. Majors versions can be big problems and "Break" some to many part interchanges. That's why switch 87 Duke in an 86 is same job as switching in a V6. Minor version cause less problems but often can work around the problem, like switching a Coil plug on an 84 to use an 85+ coil.

So if we say Carburetor Dukes are 1.x...

Fiero Dukes: 84 are maybe 2.1, 85/86 is 2.2, 87 is 3.0, 88 is 3.1.

Later VIN R engines are 3.2 etc. Final Version rated around 115HP.

Service & Upgrade notes.

NOTE: This table is the "Official" GM data that I have for cars as built. Due to "rolling changes" and engine replacements you MUST verify your motor before ordering parts for it. For example it has been reported that some 85's have roller lifters. Because many 84 cars had the motors replaced it is entirely possible they have them as well.

To check Roller or Flat Cam setup, TopNotch said:

Remove one push rod and measure it. If it's less than 8 1/2" long, you have roller lifters. If it's almost 9" long, you have flat lifters.

Source: He used Melling catalog (to get the part numbers), and Melling Push-rod identification chart (to get the lengths from the part numbers).

To move a motor across the 86/87 boundary you must also move the engine wiring harness, throttle cable, TV cable, fuel lines, and ECM unit. You will also have to fool with the AC and Cruse Control with those options. Treat 87 & up L4 as a different engine and needs same work as a V6 swap. Using 87+ engine in 84 car even more so... 84 moved C500 and used a different version that connector. Wires for Alternator output and sense go thru 84 C500. See Alternator Sense.

86-88 4 cylinder does NOT use the same AC compressor as previous years or all years with V6. See AC Service.

84-86 motors may be used with either 1226156 or 1226864 ECM units. They are interchangeable.

1227748 has Cruse Control build in. ECM will report cruse control in the data stream. Older models have a separate cruse control module and will not report the system.

The roller lifter setup may not have started until 86 1/2.

87+ engines are NOT compatible with the Holley redesigned 300 TBI. See 700 TBI article.

MAT sensor. 87+ 4 cylinders gain an additional sensor. The MAT (Manifold Air Temperature) sensor is located in the intake manifold to the right of the TBI unit. DO NOT over tighten the MAT sensor or you may split the intake manifold. See DIS and 700 TBI articles.

After market coils and ignition enhancements are available for all years. See the MSD and Mr. Gasket web sites for details. (Read the article about DIS before altering that system.)

The 87+ PCV system uses different parts than the earlier cars. Be careful looking up these parts that you don't get parts for the earlier years. Many parts books are wrong for 87-88.

87+ motors usually do not use the air preheater, "thermac," system.