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Old 12-29-2015, 04:00 PM   #1
codermyers
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Member#: 382196
Join Date: Feb 2014
Chapter/Region: NWIC
Vehicle:
1994 Impreza L
green

Question ej18 -> EJ25D swap question (theory)

Background - I'm doing the popular EJ18 to EJ25D swap. 96 LGT motor in a 94 L Wagon. I have read many threads in preparation and have both shop manuals. The swap is finished except for the emissions stuff, I will be starting the engine today or tomorrow.

Here's what is puzzling me:
The older EJ22/EJ18 grey top injectors are supposedly 240cc. The EJ25D red tops are 280cc. The fuel pressure spec is the same, 36ish psi. Therefore, the EJ25D injectors flow 17% more fuel for the same pulsewidth. The EJ25D has 39% more displacement than the 1.8, so at low throttle openings it should need 39% more fuel assuming similar volumetric efficiency.

Running the 2.5 with the 1.8 ECU, if 39% more fuel is required, but the injectors only provide 17% more fuel, I would expect that the engine would run a bit lean, as the 1.8 ECU base fuel map should be programmed for shorter pulsewidths than the 2.5 ECU.

However, all the threads I've read say that this swap runs slightly rich with the 1.8 ECU. Maybe that's not such a bad thing with higher compression and no knock sensor, but I'm curious why it would run rich. Any ideas?
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Old 12-31-2015, 02:35 AM   #2
codermyers
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No one cares to speculate. Guess I'll try RS25.
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Old 12-31-2015, 04:18 PM   #3
Einimas
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maf and knock sensor will take care of everything
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