[T2] 78 harness into 75 FI bus

[Jon Stiles]

The ‘78 computer and the 6-pin ‘78 AFM are the two big pieces you will need for the ‘78 FI conversion. You can use your ‘75 throttle body, just block off the EGR port. The old throttle switch and EGR switch are not used and are abandoned.

Be sure to check Ratwell’s vacuum diagram for the ‘78 bus for correct vacuum routing. Your intake plenum has the vacuum line on the left side but still will give the correct signal to the FPR (fuel pressure regulator) and to the Decel Valve.

http://ratwell.com/technical/VacuumHoses.html

Options:

I find the ‘75 only TB (throttle body) with EGR tends to wear faster than the later style TB because of exhaust gas contamination. If you have a later TB, you should use it.

Using the ‘78 airbox is also a good idea. It omits the pre-heat valve and flapper assembly and allows better airflow to the AFM. It also incorporates the charcoal canister return into the emissions bypass valve.

I also try and use a later SVDA (single vacuum dual advance) distributor with the ‘78 FI map. Bosch 205s or 205p. Remeber the timing map is different on the SVDA, 7.5 degrees BTDC (before top dead center).
The original ‘75 DVDA (dual vacuum dual advance) will work with the retard port on the can blocked off.

With the elimination of the intake pre-heat, the thermotime switch is also different on a later bus allowing the motor more enrichment time during cold starts. Using a later one will help in overall idle and drivability when it is cold. 

Hope this help!

Jon
Aircooled Outfitters



> On Nov 2, 2017, at 7:08 AM, MUTS <muts at verizon.net> wrote:

> Has anyone had experience putting a later FI in the 1800cc bus??  I assume the later AFM will still meter the fuel based on the air sucked in??...I have extra 78 ECU and AFM.
>