how hard is it to swap out a tbi for a tpi in an 89 firebird. do i have to change the hole wiring harness or just the motor half? any help would be appricated  

You have an opportunity or a problem depending on how you want to look at it. The 89 Camaro/Firebird TPI was the last year of using Mass Air Flow (MAF) as a means of measuring the engines air flow requirements. Starting in 1990 TPI changed from MAF to Speed Density sometimes referred to as Manifold Absolute Pressure (MAP) systems. TBI systems like the one you have are also MAP systems.

Sensors between MAF and MAP TPI systems and MAP TBI systems have differences in location even when both systems are MAP types. Also, in the case of the MAF systems compared to MAP system, the air measurement sensors function differently. This drives you to obtaining the appropriate engine wire harness or modifying the harness you have, which I don’t recommend unless you’re very familiar with the electrical engineering behind these systems.

The same goes for the computer, the MAF system’s computing requirements are much simpler than those of the MAP system.  MAF systems measure air flow directly and simply take the input from the sensor and look up the appropriate amount of fuel from a table (it’s a little more involved than that but for clarities sake I’ll leave it there). The MAP system takes a number of sensor signals, the Manifold Air Pressure signal being one of the most significant, and calculates the engine’s air flow requirement, then goes and looks up the appropriate amount of fuel from a table. So the computer must be matched to whether it’s a MAF or MAP system.

There are differences in the TPI MAF systems from various years. The period of 1985 to 88 used a separate cold start injector. 85 also uses a different computer and some other components from the other years, it’s more of a Bosch design where later years are DELCO. These differences extend to details within the wire harness, type and location of certain relays, etc. These yearly differences extend to the intake manifold and EGR system. These need to be matched with the appropriate cylinder head and exhaust system by year. For example 85 and 86 manifolds bolt to pre 87 heads where the center 4 bolts are at 90 degrees to the machined intake port surface. 1987 and later TPI manifolds have the center 4 bolts positioned at 72 degrees to the intake port surface of the head. The LT-1 engine with the L-98 head throws another curve as the L-98 head has no exhaust heat crossover provision; therefore, these TPI systems require special exhaust manifolds with unique plumbing to connect the EGR valve. This situation would also apply to the ZZ3 and ZZ4 crate engines of the era.

Now it would appear that using the MAP sensed TPI system from 1990-92 would be simple choice since your TBI computer is appropriate for that type system and unless your trying to fit a LT-1/L-98 system, the manifold bolts up to your 89 engine without any headaches. My experience here with the TBI computer running the TPI system is a mixed bag, sometimes these work with nothing more than an adjustable fuel pressure regulator to trim the system and other times a new chip was required. Note that TPI requires a higher base fuel system pressure; therefore, you will need to replace the TBI pump in the fuel tank with the appropriate TPI pump.

Backing up a bit from the previous paragraph’s recommendation of a 90-92 system, if you intend to hop up the engine over time, rather than all with this mod, you will find the earlier MAF sensed systems are much better at accepting cam, compression, and cylinder head modification than MAP systems. Especially where the cam is concerned, this is because the MAP systems look at engine vacuum to throttle opening as a prime relationship toward calculating air flow requirements. A different cam (for argument a hotter cam) will change the engines vacuum to throttle opening relationship. The MAP system can only deal with about a 10% change here before the computer requires a new chip with new relationships burnt into it. For example an engine that idled at 18 inches of vacuum with the factory cam can only accept a new cam that reduces idle vacuum to 16.5 inches before a custom chip with new relationships is required, and these chips are rather expensive so try to do this only once.

In summary you need to select a TPI that’s compatible with your engine’s design (i.e. heads, etc.) and any configuration changes you’re contemplating. You are best off with a complete system from the air cleaner, manifold, runners, injectors, fuel rail, wire harness, computer, fuel pump, etc. These can be had from your local auto wrecker and sometimes off E-Bay. I highly recommend that you have the Helms manuals for your 89 as well as the manual for the year and model of the TPI you’re using if it’s not covered in your 89 manuals. You’ll need the factory Helms manuals, simply because the off the shelf manuals at the local parts store are not sufficiently detailed for where your going with this swap.

Bogie