Crank/No-Start With Good Battery and a Fresh Starter
A truck cranks slowly and intermittently fails to start. The battery passed a conductance test at 12.6 V and 850 CCA (rated 900). A reman starter was installed two weeks ago. Cranking voltage at the battery drops to 9.1 V; cranking voltage measured at the starter B+ terminal is 8.4 V; voltage drop on the positive cable from battery to starter is 0.7 V during crank; voltage drop on the ground side from battery negative to the block is 0.05 V. The engine turns over at roughly 120 rpm (spec 150-200). The starter solenoid clicks but sometimes the starter does not engage.
1. Using the voltage-drop numbers, identify the circuit fault and explain why the battery and starter are not the prime suspects.
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The numbers localize the fault to the positive side. Cranking battery voltage 9.1 V is low but not necessarily failed; starter B+ at 8.4 V means 0.7 V is being lost in the positive cable/connections during crank - that is excessive (OEM crank-circuit drop limits are typically ~0.2-0.5 V total, and 0.7 V on one cable is a red flag). Ground side is 0.05 V, which is good, so the ground path is not the problem.
Battery passed conductance at 12.6 V/850 CCA, so it is serviceable; the reman starter is two weeks old, and the symptom is a slow crank plus intermittent no-engage, both consistent with low voltage at the starter rather than a failed motor. The 0.7 V drop starves the solenoid and motor, explaining both the slow crank (120 vs 150-200 rpm) and the intermittent click-no-engage. The prime suspect is the positive cable, its terminals, or the connection at the starter B+ stud.
2. Walk through confirming and repairing the positive-side fault, including how to avoid a repeat, and state what to re-check after repair.
Read the worked answer
Confirm: with a DVOM on the 2 V scale, place one lead on battery positive post and the other on the starter B+ stud, crank, and read the drop (0.7 V confirms). Then split the circuit: battery post to cable terminal, cable terminal to cable, cable to starter stud. A hot or discolored terminal, green corrosion under the insulation, or a loose stud nut will show up as the drop location. Repair by replacing the cable if it is corroded internally or undersized, cleaning to bright metal, and torquing the starter stud to spec - an over-torqued or loose stud is a common repeat failure.
After repair, re-run the crank voltage-drop test (target well under 0.5 V total positive side), confirm cranking rpm returns to 150-200, and verify cranking voltage at the starter B+ tracks battery voltage within ~0.2 V. Also re-check the solenoid engage circuit, since the intermittent no-engage may have been purely the low voltage - if it persists after the cable repair, diagnose the solenoid control circuit separately.