Ωhm

You can PASS the continuity test, but each wire should also be tested for Short To Ground (STG). ECU disconnected. Take measurements at CPS connector, also disconnected.

Knock sensors are piezoelectric in function. Knock or EMF can cause the same reaction (both being high frequency). Knowing this should take away any worry.

No. KNOCK Sensor (KS) shielding prevents or attempts to prevent the KS circuit from becoming activated by outside EMF. Examples of EMF include High Tension wires, near airport radio waves, illegal CB radios (wattage), etc, etc. Sudden EMF without shielding, will cause vehicle to stumble, hesitate usually for only a short period of time, the time it takes to drive under the wires or during a transmission signal, as examples. ECU is fooled by the KS and retards timing very suddenly and quickly. Generally speaking, this is not a problem, but it can/has occurred. Yes

Odd it finds knock during WOT, yet no knock control, while in CL, for the other modes of driving.

Looks like ECU is in OL only. Correction: OPEN LOOP = OL, not OP

Not sure here but KNOCK might only come into play here during WOT when ECU is in OP.

When pinging occurs is ECU in OPEN LOOP (OP) or CLOSED LOOP (CL)?

Check Instrument Cluster (fuel sender) page in the Electrical Manual.

Check Instrument Cluster (fuel sender).

Wouldn't the black wire enter the tank using that grommet used by the other two wires? If so, then pump and gauge are finding ground thru the metal tank & straps.

Not sure on the 2.5L if the electric fan is ON when the AC clutch is engaged. Since heavy duty cooling was an option needed for Dealer Installed AC, might not have all the necessary wires. Not sure here.

The 4.0L uses a Fan Diode Assembly (C246) which allows the electric fan to kick ON when the AC clutch is engaged but will not allow the AC clutch to kick ON the electric fan.

Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage on the following pins (use battery_negative terminal for ground): D1_5: Battery_Voltage (Hot at all times) D1_6: At KEY ON, (Hot for 2-3 seconds). During CRANK, (Hot at all times). D2_4: At KEY ON, (Hot at all times). During CRANK, (Hot at all times).

Drawing matches the stuff I/we have. _mj1988electricalmanual_1.pdf

Shifting the CPS either CW or CCW only fools the ECU to thinks a cylinder is at TDC when it is not. Shifting will also shift, for each cylinder, when KNOCK looks for ping and when the INJ fires. The ECU seems to be able to handle CPS ADVANCE, not sure on CPS RETARD. I'd pin it out, back to the ECU just to make sure.

Welcome. One more thing to look into, it's about grills. Click Here

Anyone with a REM hookup. Do you see the same voltage (VLT) as listed below? This displays the current voltage of the Battery. Note: On 4.0L this may be the Fuel Pump/o2 Relay Circuit which will normally read 0v after 3 seconds when the engine is off. This will read correctly when the engine is running. – Engine Off (~12.4-12.8) A healthy battery will rest around 12.6 Volts – Engine Idle (~13.5-14.5) A healthy Alternator should supply 13.5-14.5 Volts

Click here: Check connector C102.

What is Battery Voltage (VLT) on the REM?

Pump prime is a two-fold process. 1. Allow fuel pump to run for 2-3 seconds. 2. Check valve to prevent fuel drain-back through the fuel pump to the tank when fuel pump is OFF. Question is ‘Does fuel pressure drop once the pump is turned OFF?’ Faulty check valve. I’m not saying this is your cranking issues, but it sure could help here.

Battery Voltage with ENGINE RUNNING. This is a quick test. If GOOD, need to check O2S heater on the component itself. Disconnect C229 and on the component side connector check for resistance between pins C229_A and C229_B. Looking for ≈6 Ω's. If TRUE, circuit is GOOD. Note: This view is harness side.

With ENGINE RUNNING, check for Battery Voltage on D2_9 (O2 Heater Circuit).

225 PSI refers to when the pump deadheads (ON but no flow). IDK what SPEC is, might say with the pump's paperwork.

Might be off base here but doesn't the ground wire for the sending unit on the pump, ground at the bottom of the resistor for RENIX and at the top of the resistor for SBEC. Can't tell from the photos. Gauge still should work with half tank of fuel. Does Coolant Temp Gauge peg pass 260° when KEY is in the CRANK position? If NO, check GAUGES FUSE (7.5A). If GOOD, look for voltage on C203_6 & C203_18.