Can I use a 305 TPI harness in a 350 TPI setup? Also, do I have to swith the harness from the firewall into the passenger compartment? The car WAS a 87' LT and now will have a guage cluster WITH tach and a 350 TPI ECM. So again, what to do harness wise?

 

Yes, a 305 TPI harness will work on a 350 TPI motor. The only difference between the two setups is the fuel injector flow rate (19 lb/hr for 305 cid & 22 (or 23?) lb/hr for 350 cid), and the PROM in the ECM.

The '87 LT is probably carbureted, so the entire harness from the passenger side ECM connection needs to be swapped out. Also, you will need the pinout of the dual connector next to the ECM that goes connects from the ECM harness to the dash harness, because the pinouts will be somewhat different between the two harnesses. You will also have to add 3 fuses under the driver side kick panel - two for fuel injector power (ign power) & one for the VATS (Vehicle Anti Theft System) module (battery power) if the ECM uses the VATS system.

If the ECM uses the VATS system you may also buy an ign key tumbler for a '92 that accepts a VATS resistor ign key, if you want the VATS system to work. You will also need to figure out which of the 15 resistor values the VATS module needs to work - I have the values, if you need them. Another option is to disable the VATS function in the PROM.

You will also need to connect the new harness to some of the wires on the drivers side, where the harness goes through the fire wall.

Also, if the car needs electric fan hookups, you will have to add a 30 amp fuse from the battery to power the fan relays.

If the car is carburated, you will need to add a fuel pump in the tank, or an external aftermarket pump for the TPI system & run power from the fuel pump relay to it.

You will need wiring diagrams for the existing harness and the harness you will be installing.

Tim

 

Tim, thanks for the info. My 87' is a 2.8 MPI I believe. I have the whole harness out now. Only what connects from the dash to the inner firewall remains. If I'm putting in a COMPLETE 87-89 350 TPI setup will I need to still do the VATS and wire splicing you described??

 

The VATS system is not used in that setup. Easier to install!

Tim

 

The knock sensors are different btw 305 and 350 applications, very much non-interchangeable.

-Kevin

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1982 Z-28

See http://www.mycar.net/mafb/registry/detail.cfm?id=276 for details

 

Thanks for pointing that out. Different knock sensors were used for the 305 & the 350 in some years, but the same knock sensor was used for both the 305 & the 350, in others:

'87 VIN F TPI 305 & VIN 8 TPI 350 use the same knock sensor GM10456287.

'92 VIN E TBI 305 uses GM10456287.
'92 VIN F TPI 305 uses GM10456126.
'92 VIN 8 TPI 350 uses GM10456031.

Tim

 

SO, in my project 87 LT I HAD a 2.8 MPI, no power options except rear hatch motor, dash guages had no tach...a big *ss fuel guage existed. I've pulled the entire engine harness out. Can I plug in a 87-89 350 TPI ECM and engine harness? The LT dash harness is still in there.