Over the past few weeks I have gotten quite a few emails on this subject concerning the Fiero swaps. Personally, I use the 94-95 OBDI 3800 PCM on all of my 3800SC swaps, but it does have its limitations. With that being said, there are pros and cons to both types of systems so allow me to describe your options with each:
OBDI
The 94-95 OBDI computer is a passenger compartment mounted computer with a removable mem-cal (chip) assembly. It does NOT require any OBDII-specific sensor monitoring capability, which in plain english means there is less wiring involved. This computer will fit in the stock Fiero ECM mounting location and it accepts the common ECM wiring connector terminals like those used on the stock 2.8L Fiero computer (although the plastic connectors are different). This computer was designed to control the 3800 Series I and II n/a engines, as well as the 3800 Series I SC engine. I have also successfully reprogrammed this computer system to work with the 3800 Series II SC and 3800 Series II Turbo engines. This computer can be reprogrammed to run the 3800 Series III engine so long as you use a cable-operated throttle body.
With that being said, it does have limitations. First and foremost, this computer is not compatible with the 4T65-E transmission. However, it will control the 4T60-E transmission, as well as work with any non-electronic auto or any manual transmission. This computer also has a tuning limitation concerning the rev limiter. Currently, I cannot set the rev limiter any higher than about 6400 rpm (this could change as I and others do more research into this computer system). However, I do have the capability of disabling the rev limiter altogether if you wish to rev the engine higher. Concerning other tuning aspects, the sky is pretty much the limit as far as timing and fuel amoung other things. I like using this computer because it allows me to switch out the chips easily. This can be very useful in tuning on the dyno or at the track, or if you want to be able to swap in a race gas chip for racing use without having to reflash the whole computer.
OBDII
There are a number of different OBDII computers for the 3800. First, the 1996 computer is designed to only work with the 4T60-E transmission. I am sure it can be reprogrammed to work with a manual or non-electronic auto but I am not aware of many aftermarket tuners who are tinkering with this system. The 1997 computer is designed to operate the 4T65-E trans, and like the 96 unit it can be reprogrammed to run the other transmissions as well. The 98-up L67 (3800 Series II SC) computers have the same capabilites as the earlier units, but these newer systems are designed to work in conjunction with a body control module, ABS computer, and possibly other components that share the Serial Data Line. If you plan on using this system in a Fiero without these other components you may have to have the computer reprogrammed to delete these other systems or it may not function properly. Not all of these computers work the same and this depends on year/make/model of the car in which you get the computer from.
GM released the 3800 Series III engines in 2004. These engines used fly-by-wire throttle control which works in conjunction with a gas pedal position sensor to determine optimal throttle opening for minimal emissions during all driving aspects. If you want to use fly-by-wire throttle control you MUST use a compatible 2004-up computer system, no earlier computer will operate the electronic throttle. However, as I stated before, there are adapter plates available for about $100 that will allow you to use an earlier LS1 or L67 cable-operated throttle body on this engine. The earlier computers can easily be reprogrammed to work on the Series III engines.
The biggest issues I see with the OBDII systems are as follows: These computers must be reprogrammed (flashed); there is no removable chip. This means that if you don't have the ability to flash your own computer, you must send the ENTIRE unit off to someone to have it done. These computers are also physically larger than the OBDI computer which puts limits on where you can mount it. However it is a sealed unit which means it can be mounted inside the car or outside in the engine compartment. These computers also have more wiring involved, depending on year/make/model they are. You can have these systems reprogrammed to disable all of the OBDII sensor monitoring such as the post cat-converter O2 sensor, enhanced EVAP emissions monitoring sensors, etc just to name a few; which means you don't necessarily need all of this extra wiring.
So basically to boil it all down the only thing an OBDII computer can do that an OBDI computer cannot do is control a 4T65-E transmission. As far as performance and drivability there is virtually no difference between the two types of systems and there capabilites. In fact, some of the fastest 3800 powered Fieros here on PFF are running OBDI systems. But to be fair, that doesn't mean you can't do the same with an OBDII system. Just depends on what trans you want to run.
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