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· Registered
55 Posts
Discussion Starter · #1 ·
Hello and seasons greetings to everyone.
Black death has killed my 87's EFI 3.5 engine.
I fitted a 3.9 cam and for a short while it ran great. It is an early injection car with the simplified hotwire injection.
I have been offered a good used 3.9 engine from a '93
Can I simply use the 3.9 engine (al the mechanical bits) with my inlet manifold, plenum chamber and all the injection system without having to revert to the 3.9's loom, ecu, plenum etc?
How different are the ECU settings? My car ran great with the 3.9 cam and the 3.5 ecu, would the increase in bore make that much difference and require a different ecu?
I need to decide quickly for the engine, so if you have any experience here, please let me know!
Many thanks, Philippe

· Premium Member
3,225 Posts
The 3.9 will be a direct bolt-in swap. You should try and get the ECU from the 3.9 as it is a newer version called 14CUX. The mapping is slightly different and improved low end torque, also, 14 CU (used on your old 3.5) requires TPS adjustment in addition to IACV setting. 14CUX is self calibrating and does not require any TPS fiddling. You will still have to set your base idle. I wouldn't swap the intakes, because the throttle body is slightly different (TPS mount). You don't have to swap out the wiring harness, as it is the same, but the tune resistor (taped to the side of the harness connecting the airflow meter, and then on to coil) isn't likely to be the same.
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