Ωhm Posted July 17, 2023 Share Posted July 17, 2023 Both 2.5L & 4.0L use a B+Latch relay, thanks for pointing that out. When you get a chance, can you do some preliminary voltage checks? Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage (B+) on the following pins (use battery_negative terminal for ground): D1_2: B+ (Hot during KEY ON/CRANK). D1_5: B+ (Hot at all times) D1_6: At KEY ON (B+ (Hot for 2-3 seconds)) or CRANKING (B+ (Hot during CRANK)). With KEY ON, measure for voltage at D2-4. Determine if flipping the KILL SW changes the voltage reading on that pin. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 11 hours ago, Ωhm said: Both 2.5L & 4.0L use a B+Latch relay, thanks for pointing that out. When you get a chance, can you do some preliminary voltage checks? Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage (B+) on the following pins (use battery_negative terminal for ground): D1_2: B+ (Hot during KEY ON/CRANK). D1_5: B+ (Hot at all times) D1_6: At KEY ON (B+ (Hot for 2-3 seconds)) or CRANKING (B+ (Hot during CRANK)). With KEY ON, measure for voltage at D2-4. Determine if flipping the KILL SW changes the voltage reading on that pin. Absolutely! I will do that as soon as I get home from work. I appreciate you taking the time to help me with this Last night I took it easy, was hot and humid. Noticed the tail lights were thrown on with whatever they had laying around. The driver side only had one screw holding it on and the passenger side had three deck screws in it! So I went through my tub of jeep hardware and found some proper screws to install Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 20 hours ago, Ωhm said: Both 2.5L & 4.0L use a B+Latch relay, thanks for pointing that out. When you get a chance, can you do some preliminary voltage checks? Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage (B+) on the following pins (use battery_negative terminal for ground): D1_2: B+ (Hot during KEY ON/CRANK). D1_5: B+ (Hot at all times) D1_6: At KEY ON (B+ (Hot for 2-3 seconds)) or CRANKING (B+ (Hot during CRANK)). With KEY ON, measure for voltage at D2-4. Determine if flipping the KILL SW changes the voltage reading on that pin. Using your preferred test light. All of those check out good. And yes, the kill switch made the light go out. I also tested for voltage on D2_4. Key on it has 12.08v and when I turn the kill switch off I get 1.82v Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 D1_2, D1_5 & D1_6 testing are all good readings. D2_4 testing shows that we're dealing with the B+Latch Relay. Why? IDK. Let me look for my next question. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 5 minutes ago, Ωhm said: D1_2, D1_5 & D1_6 testing are all good readings. D2_4 testing shows that we're dealing with the B+Latch Relay. Why? IDK. Let me look for my next question. For what it's worth, I noticed the shift indicator flash and was able to hear the fuel pump prime when turning the toggle switch back on Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 Determine which Relay is the B+Latch Relay. Check for HOT AT ALL TIMES on PIN_1 (RED). PIN_4 & PIN_5 should have PINK wires. Pink should help with relay ID. Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 7 minutes ago, GrandBoost98 said: For what it's worth, I noticed the shift indicator flash and was able to hear the fuel pump prime when turning the toggle switch back on Somehow, I think the toggle SW shuts down the ECU. Anyone else got a understanding for the B+Latch Relay circuit. It's a strange circuit. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 1 hour ago, Ωhm said: Determine which Relay is the B+Latch Relay. Check for HOT AT ALL TIMES on PIN_1 (RED). PIN_4 & PIN_5 should have PINK wires. Pink should help with relay ID. Pin 1 hot key on or off. And the toggle switch made no difference Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 Turn KILL SW OFF. Remove B+Latch relay. Jumper wire between PIN_1 and PIN_4. See if engine STARTS and RUNS. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 17 minutes ago, Ωhm said: Turn KILL SW OFF. Remove B+Latch relay. Jumper wire between PIN_1 and PIN_4. See if engine STARTS and RUNS. Kill switch off. B+ relay removed and pins 1 and 4 jumped. It started up and ran for a couple mins and I revved it up a few times. Should I run it longer or is that good? What really surprised me is that doing this "fixed" the two crank start! I was able to start it on the first crank 3 times. So then I removed the jumper wire, reinstalled the relay, turned on the kill switch and it went back to two crank starts Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 Oh and I forgot to mention, with the jumper wire in and kill switch off, I can't hear the fuel pump prime like I can with the relay installed and kill switch on Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 6 minutes ago, GrandBoost98 said: Kill switch off. B+ relay removed and pins 1 and 4 jumped. It started up and ran for a couple mins and I revved it up a few times. Should I run it longer or is that good? That's good. Proves we don't need the kill switch. Next question is "will ENGINE START and RUN with KILL SW OFF and B+Latch Relay reinstalled? Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 4 minutes ago, Ωhm said: That's good. Proves we don't need the kill switch. Next question is "will ENGINE START and RUN with KILL SW OFF and B+Latch Relay reinstalled? No, does not start just cranks Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 1 minute ago, GrandBoost98 said: No, does not start just cranks I think having the KILL SW answered my own question and that proved it. Do you have a known good relay? Swap them out, Try START and RUN again. I'm thinking faulty relay, relay (Coil) ON circuit or ECU not controlling B+Latch Relay function. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 12 minutes ago, Ωhm said: I think having the KILL SW answered my own question and that proved it. Do you have a known good relay? Swap them out, Try START and RUN again. I'm thinking faulty relay, relay (Coil) ON circuit or ECU not controlling B+Latch Relay function. I have a drawer of used relays and fuses. I tried 3 different relays and they all acted the same. No start with kill switch off. I did notice that I can turn the kill switch off after it starts running and it will continue running Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 2 minutes ago, GrandBoost98 said: I did notice that I can turn the kill switch off after it starts running and it will continue running Interesting. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 2 minutes ago, Ωhm said: Interesting. Not sure how long it would take to run out off fuel though if that indeed kills power to the pump. But it ran for a min and I revved it a few times with no hiccup Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 KILL SW OFF. Relay installed. Jumper D2_2 with D1_3. Try START & RUN again. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 18, 2023 Author Share Posted July 18, 2023 5 minutes ago, Ωhm said: KILL SW OFF. Relay installed. Jumper D2_2 with D1_3. Try START & RUN again. No start, just cranks Link to comment Share on other sites More sharing options...
Ωhm Posted July 18, 2023 Share Posted July 18, 2023 KEY OFF. KILL SW OFF. Remove Relay. Continuity test between D2_2 and B+Latch Relay PIN_2 between D2_4 and B+Latch Relay PIN_5 between D2_4 and B+Latch Relay PIN_4 Looking for 0_Ωs. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 19, 2023 Author Share Posted July 19, 2023 7 minutes ago, Ωhm said: KEY OFF. KILL SW OFF. Remove Relay. Continuity test between D2_2 and B+Latch Relay PIN_2 between D2_4 and B+Latch Relay PIN_5 between D2_4 and B+Latch Relay PIN_4 Looking for 0 Ωs. D2-2 to pin 2 =4.3ohms D2-4 to pin 5 =1.5ohms D2-4 to pin 4 =1.5ohms Link to comment Share on other sites More sharing options...
Ωhm Posted July 19, 2023 Share Posted July 19, 2023 I'm calling that as circuits are NOT open. Next two tests involve the ECU connector. Looking for continuity. Same conditions KEY OFF. KILL SW OFF. D2_2 and C200_7 D2_4 and C200_19 If both test good, all wiring test good. Suspect ECU. Link to comment Share on other sites More sharing options...
GrandBoost98 Posted July 19, 2023 Author Share Posted July 19, 2023 @Ωhm Ugh, I just had that out too lol Had to rig up an extention. That by itself ohmed out at 1.4ohms D2-2 c200-7 =4.2ohms D2-4 c200-19= 1.5 ohms So you're saying a new ECU would fix all my problems? This would give power from pins 1 to 4 on the B+ relay and I could eliminate the kill switch and related wiring? Which in turn would fix my two crank start as well? If so, do I need a specific 2.5l ECU or is one from any mj/xj okay? Link to comment Share on other sites More sharing options...
Ωhm Posted July 19, 2023 Share Posted July 19, 2023 13 minutes ago, GrandBoost98 said: So you're saying a new ECU would fix all my problems? I'm not saying, I'm hoping. 13 minutes ago, GrandBoost98 said: This would give power from pins 1 to 4 on the B+ relay and I could eliminate the kill switch and related wiring? If B+Latch Relay worked properly (relay jumper test) you should be able to get rid of kill switch. 13 minutes ago, GrandBoost98 said: If so, do I need a specific 2.5l ECU or is one from any mj/xj okay? @eaglescout526 ECU request help here. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 19, 2023 Share Posted July 19, 2023 Any 2.5L Renix ECU will do just fine. Since you have an 89, I highly recommend you stay within 87-90 ECUs. You can use 86 if you absolutely have to. Link to comment Share on other sites More sharing options...
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