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Jeep Wrangler YJ
YJ General Discussion
Non starting after new thermostat and heater core flush
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<blockquote data-quote="deadpool1" data-source="post: 441162" data-attributes="member: 21229"><p>FYI old ECU go dead below 10vdc battery some can run at 9. but most can not this old. (a general statement)</p><p>the ecu internal regulator goes dead at 10v. but..</p><p>the FSM starter test pages claims 9.5vdc is the lowest voltage cranking, most cars do 11vdc, for sure a tiny 2.5L with 550 CCA battery. </p><p>yours is 9.9v.</p><p>the starter uses 100 to 200 amps max.</p><p>the one way to see this failure, that is the 5vdc pin in the MAP sensor is dead. key on. ( loss of power to ECU or its grounds or voltage is too low)</p><p></p><p>newer cars can to to 8v. with far better regulators inside the ECU. (called LDO,low drop out regs) none existed in 1989, not yet.</p><p>why is there 11.9vdc there not cranking,, my guess is cranked the battery flat or battery is bad. </p><p>also starters do short out inside (rotor coils or field), even partially shorted, and use way too much current. and overloads the battery. easy.</p><p>I must say if the starters sounds good, it is.</p><p>the starter solenoid goes berserk at 8.v chatters like mad., so is moot point there. we have 9.5.</p><p>if battery shows 12.6vdc across the terms now, the wiring is bad in the car and easy to find using voltage drop tests, ask how. (dmm voltmeter simple tests)</p></blockquote><p></p>
[QUOTE="deadpool1, post: 441162, member: 21229"] FYI old ECU go dead below 10vdc battery some can run at 9. but most can not this old. (a general statement) the ecu internal regulator goes dead at 10v. but.. the FSM starter test pages claims 9.5vdc is the lowest voltage cranking, most cars do 11vdc, for sure a tiny 2.5L with 550 CCA battery. yours is 9.9v. the starter uses 100 to 200 amps max. the one way to see this failure, that is the 5vdc pin in the MAP sensor is dead. key on. ( loss of power to ECU or its grounds or voltage is too low) newer cars can to to 8v. with far better regulators inside the ECU. (called LDO,low drop out regs) none existed in 1989, not yet. why is there 11.9vdc there not cranking,, my guess is cranked the battery flat or battery is bad. also starters do short out inside (rotor coils or field), even partially shorted, and use way too much current. and overloads the battery. easy. I must say if the starters sounds good, it is. the starter solenoid goes berserk at 8.v chatters like mad., so is moot point there. we have 9.5. if battery shows 12.6vdc across the terms now, the wiring is bad in the car and easy to find using voltage drop tests, ask how. (dmm voltmeter simple tests) [/QUOTE]
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Jeep Wrangler YJ
YJ General Discussion
Non starting after new thermostat and heater core flush
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