I've replaced (literally) every sensor known to B18C, & I'm still in open loop mode. O2s reads ~0.7v consistently, a little lower on WOT.
I'm pretty sure it's a coolant system error, but I would assume someone here would know more than I would about engine management. Here's my recent findings:

ECT checks out at the sensor, 0.35 ohms (around 200 deg) at operating temp, constant 4.99v feed. However, at the ECU side I get 0.47 ohms & a feed of 2.1v... Normal? I don't get how that's possible actually. I've never been sure how to test for shorts though either.

The radiator fan Coolant temp switch (just replaced) reads ~0.7 ohm. When I remove & bridge the temp switch connector, the fan starts, but never automatically. I'm wondering if this is because the A/C was removed? (Not sure if this affects fuel control) or, if this is just due to a thermostat malfunction & why.

The upper radiator hose is always hot, lower hose is always cold. Just replaced thermostat (190 deg), not really sure if there's a way to check if it's opening or closing.

I think the ECU is not getting accurate readings & defaulting to open loop, but I'd like some help if anyone could direct me here. I'm at a loss, & too frustrated to think about it anymore. Anything is appreciated.

Thank you.

Post more info of your setup so we know what were working with.

Here's the mod info:

* '93 Del Sol chassis, '94 B18C1 harness & block (10:1 comp w/ lightweight pulleys & flywheel), B18C5 head (stock) adjustable cams set back to 0deg.

* 310cc injectors @ ~55psi WOT (adjustable), insulated fuel lines, stock pump.

* Custom intake manifold, medium runners / large plenum, 60mm TB. New IACv, new FITv, new MAPs, new IATs, new TPs, all vacuum components and evap system replaced (pressure @ -12psi idle), IABs system removed.

* Ported B18C1 3-2-1 headers (heat wrapped), stock cat, 3" resonator to 1.5" y-pipe dual exit (sounds like a raccoon crawled in it, for the record. Not recommended.)

* Gates timing belt, hi-flow water pump & new tensioner, stock oil pump.

* Optima Gold batt w/ ground stabilizing kit, iridium 4 plugs, 8mm wires, stock dist.

Thanks for your help

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