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Converting 3 plug MPFI-T to 4 plug Spider XT Turbo .

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Hi all , I have an 85/85 RX Turbo and am having an Australian spec XT4 Turbo engine being rebuilt for it . I managed to get the complete loom and all engine control gear with it acc cable pitch stoper etc .


Now my car is a 3 plug computer flap style AFM type and I need to convert to 4 so the XT's electricals can run the engine inc its infernal screwy backwards TPS .


My plan was to get a 4 plug L loom and seperate out the wiring from the CAS/transister/coil back to where the engine loom plugs are (opposite side on RHD cars to USDM) and then also the MAF wiring and resistor wiring back to the computer . Basically I'm trying to make a seperated engine control loom all the way to the 4 plug ECU then figure out how to patch power to it - possibly by 2nd fuse panel and fusable link box .


Sadly all I have to play with is a 4 plug auto non turbo L loom but it could form an ok basis .


Another thing is that engine looms will be different from Spider XT to garden variety L MPFI because the two large plugs (black and white) head towards the XT's firewall where the RHD L goes through the LHS (looking from the front) inner gard .


Can anyone spot any holes in this plan ? I realise I'm gonna have to run knock sensor wires .

Also on the computers wiring diagrams it shows a couple on pins used to differentiate between turbo/NA and auto/manual . Does anyone know if they are earthed/not earthed and for wich of two combinations ?


My brain hurts , cheers A .

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I think you are going about it the wrong way. You would be much better off finding an 88+ MPFI sedan or wagon and using its loom. It will then match up to your vortex engine (you will have to use the MPFi engine loom, but thats no hassle)


The MPFi and Turbo looms are identical for 4 plug systems. there is no grounding pin to tell the ecu its turbo mode, or man/auto ect.


Just 2 ecus, turbo or mpfi


Fire me a PM on AUSubaru, im Suparoo over there.

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