MartinS Posted June 30, 2023 Report Share Posted June 30, 2023 Strange event yesterday: after filling at gas station, went to restart and noticed tach jumping around, no start. I have since turned off Ign 7 (tach driver) so as not to damage tach needle. Checked ECU for faults and noticed at that my O2 sensor had failed 'to ground' which is a relatively new sensor and had been working fine moments before. I also noticed a clicking sound coming from the engine bay. This was the fuel pump relay cycling at about 2 Hz and with this the e-throttle was oscillating at the same frequency. The only commonality in my setup is the e-throttle and O2 controller are powered through the same relay; all engine related items have a common power supply through 5 relays from starter (direct from battery) and alternator. The 2 fuses for power to the engine (sensors, ignition, solenoids, etc) were blown but do not blow since replaced nor do they get warm with cranking. Only the O2 sensor seemed to have had a problem but is not on the fused line . Towed home thinking perhaps a faulty relay was oscillating. Changed the relay and now, with ignition on, the relay chatters for the 2 sec of fuel pump run but then stops (no 2 Hz oscillation) and chatters when cranking (pump on) as does the e-throttle at the same frequency. Fuel pump tested, runs fine. O2 sensor still dead. Initially, when cranking the ECU would kick my computer offline but once I changed the relay and the fuses, I could log while cranking and have included 2 crank logs below. E-throttle appears to work ok except for chatter with turn on. With cranking, I get trigger errors and the computer tach jumps around. Is an almost new crank sensor and the wiring is correct (was working fine until this event). No other apparent problems. Only electrical anomaly I can find is the fuel pump relay ground switch line from the ECU has 7V (terminal 85) when measured. Continuity and ground faults tested with ECU unplugged and this line appears fine, the 7V seems to be coming from ECU. Power perhaps is the cause of the chatter of the fuel pump relay but am not sure. Terminal 86 12V at FP relay. I'm at a loss. Help greatly appreciated. https://drive.google.com/file/d/164drUJHm2gpRMDuoTap0CvGQYXeUM1rc/view?usp=sharing https://drive.google.com/file/d/1aqSimJmH6PEfAjdG60JP64TVZZfvD08I/view?usp=sharing Quote Link to comment Share on other sites More sharing options...
MartinS Posted June 30, 2023 Author Report Share Posted June 30, 2023 Tested crank position sensor, exactly same ohm readings as used item with no ground to body from pins. Tested system with e-throttle unplugged at intake: no change (except of course no throttle plate chatter with FP relay chatter). Note about switched ground line from ECU to fuel pump relay: only reads 7V when ECU turns pump on. Quote Link to comment Share on other sites More sharing options...
MartinS Posted July 1, 2023 Author Report Share Posted July 1, 2023 Ok, despite all of the symptoms being related to the ecu and engine management systems (found more this morning when began more trouble shooting), the problem turned out to be either a faulty valve or its' relay in my fuel management system (used to fill reserve tank) which only shares a common power supply with the engine systems but is before the fuses for the engine and ECU. How it blew the fuses for the engine and ECU systems, not it's own, and continued to throw off the ECU when the fuses were replaced, I do not know or understand. Some kind of weird resonance in the system? However, with this valve disconnected, the engine runs perfectly again! Whew! Happy I posted on a Friday here in Canada, solved it before Adam looked at this post on Monday morning in NZ! If only I could understand how this worked so I can avoid it in the future... Quote Link to comment Share on other sites More sharing options...
Adamw Posted July 2, 2023 Report Share Posted July 2, 2023 Its hard to follow all you mention but most of what you describe with relays clicking and the odd voltage coming out of the fuel pump aux means the ecu had lost its main power supply (pin A5), but everything else connected to the ecu was still powered up. So instead of the ecu being powered via its intended pin A5, you instead get current back feeding through one of the aux relays. The 7V you measure is coming into the ecu from one of the other auxes. Quote Link to comment Share on other sites More sharing options...
MartinS Posted July 3, 2023 Author Report Share Posted July 3, 2023 Oh! That does make sense of it. I think this is what happened: Fuses were blown but I found the initial 2 and replaced them before I began the troubleshooting process. When the ECU was powering up and connecting to the computer, I assumed the ECU power relay was fine and didn't even check it's fuse until later. When I did check it, I'd already found the primary issue so assumed I'd blown the fuse during the diagnostic process by inadvertently shorting it. Lesson learned. Would also explain why I got a 'low voltage' message from the ECU early in the process and why it was dropping offline when I ran the starter initially. I assumed it was from running the battery down trying to start the engine but, in retrospect, I didn't run the starter all that much; more likely the ECU was already at marginal voltage and when I did run the starter, the current draw dropped the voltage below the 'ECU on' threshold. Replacing the 2 fuses which were blown fed more current to the ECU through aux circuits and I could stay connected when cranking but the supply pathway was wrong causing all the ECU symptoms as you note. Good news: got everything back together and buttoned down today and went for a good test drive. Ran perfectly, no issues. No damage done as far as I can tell. Useful information if I ever have a similar chain of events. Thanks Adam! Quote Link to comment Share on other sites More sharing options...
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