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Your melted terminal on the Headlamp Switch (C269) is C269_I. C269_I feeds Instrument Cluster lamps and other lamps used on the dash. Do the other lamps work normally (ex: ash tray lamp, fog lamp switch lamp, PRNDL lamp, heater/AC panel lamp etc etc)? Don't understand why they work on HI BEAM.

Page 78 shows C203 pinout. 88 Electrical Manual

IP Cluster uses two (2) pins for grounding Illumination Lamps (C203). Check both C203_5 and C203_10 for path to ground from the connector.

88 Electrical Manual

That's exactly what STFT/LTFT is all about. RENIX seems to be working just fine and as intended. Good thing you got that MT2500.

Numbers well within the O2S range of authority.

How's your 3rd O2S doing?

Looks good, very clean. Wonder how white would've looked like.

Start with battery, battery terminals, battery cables and then all the grounds.

Your signature doesn't say what engine. I'll take it as a 4.0L by your fuel pressure posted above.

Single wire, single bullet connector is cruise control ground. The other four (4) wires are engine block grounds.

That one photo with the cracks on the bottom, if that a bubble it could have been cause by excess of heat and it look like something blew up inside.

I think that tap was used for ICM production, certain types of Tachometer could be connected there.

C103 is a inline connector (Engine harness to Engine Control harness) and C103_B (RED) goes to fuse link G.

If CPS is assumed good, the injector within the throttle body should spray fuel. Does it? Two pin (C214_A) should be empty. C214_B goes to the ECU for timing control.

Ignition module only has two connectors. One is a 3 pin and the other is a 2 pin. Loss of spark can be caused by a faulty Crank Position Sensor (CPS).

Welcome to CC. This 88 manual could help with most of your questions. 88 Electrical Manual

Check secondary ignition for possible crossfire or carbon tracking under distributor cap.

Could be leaky injector(s). Check fuel pressure. Gauge should hold pressure after cycling KEY ON, then KEY OFF.

What seems odd to me is the loss of 1.3 lbs/hr should cause LTFT (go above 128) to increase INJ PW time (ms). But so many other factors come into play here. Throttle bodies, exhaust systems etc, etc. But O2S switching (RICH LEAN) will always try to find 14.7 to 1 (stoichiometric fuel ratio).

Good read.

Its just you and JMO413 that's tracking LTFT. These numbers are real world stuff. Random, I don't know, but yes it could be ECU characteristic.

Too me, LTFT of 91 means O2S sees RICH and LTFT 91 is taking fuel away (decreasing INJ PW time (ms)).

Must have some kinda memory, possibly KAM. Yours is a 90 ECU?