Pete_89T2

iTrader: (4)

Hey guys, my S5T2 was running fine a few weeks ago when I parked her on my 4-post lift, but this morning when I tried to take her out for a ride, I was greeted to a failure to start, and a bunch of electrical gremlin symptoms that I'll describe below. My FC must be jealous that I took the FD to Deals Gap this year and have been spending more time with her. Anyway, here's the specifics & symptoms - looking for any advice/suggestions on what to check next:

- Car was running fine before I parked her on the lift; no indications really that anything electrical was amiss then. Wiring harness along with the AEM Infinity ECU was installed in 2017, harness was built by a pro, so I have no reason to suspect wonky wiring, at least with regards to the stuff what we touched to install the ECU. Also, all of the car's mission critical prime power circuits, grounds, relays (i.e., ECU, Fuel Pump, Coils/Ignition, E-fan, etc.) were all new top quality parts with all new over-engineered wiring - no cheap crap and I'm not relying on ANY of the 30+ year old factory wiring with the exception of the ignition switch itself, and the switches/relays associated with the starter interlock circuit to run the car.

- Upon keying the ignition ON and attempting to start, I noted that the tach would sporadically jump around bit (normally doesn't budge until the engine fires up), and I could hear the fuel pump TRYING to run. Otherwise, it was pretty obvious I had a major electrical problem - dash lights barely lit, motor mouse seatbelt was ultra slow moving in its tracks and my BTI CAN bus gauge was completely dark, indicating no power to the gauge and that its CAN connection to the AEM Infinity wasn't active yet - which could mean the ECU didn't boot up due to a lack of voltage.

- Stuck a voltmeter on the battery, it was down to 8V, which explains why the AEM Infinity wouldn't boot, along with all the other dead battery symptoms.

- Got the jumper cables & hooked up the FC's battery to my daily driver's battery. Ran the daily driver for a bit to charge the FC's battery; let it charge at a measured 14.3V for about 20 minutes (DD running obviously) before the next step.

- While the DD was running & still charging the FC, I attempted to key on & start the FC again. This time when I keyed the FC to ON, the dash lights all illuminated normally, but I still had the bouncy tach needle. The BTI CAN gauge looked like it was about to become operational again, but only displayed its splash screen and then went dark - this indicates the gauge had 12V power, but had no CAN communications with the AEM Infinity ECU. Also, I can hear the fuel pump running at full speed this time - which means the AEM Infinity is at least partially booted up, as it has to energize the fuel pump relay in order to run the pump. Also, the motorized seat belts were faster too. When I tried to start it, the engine cranked, but it was cranking way too slow to possibly start, so I called it quits for now. I suspect the battery may be too sapped out at this point, will try getting it charged first before trying again, or just swap in my FD's fresh battery.

- Next thing I tested was to see if there is a current drain on the battery with everything shut off. Hooked up my ammeter between the battery's negative terminal and the battery ground terminal. Measured approximately 25mA, which would sometimes spike up to an over-range condition (over 200mA on my meter). Those over range spikes may just be an artifact of my less than great DVM I'm using, but that 25mA reading is kind of high. So I suspect I have a parasitic drain or short somewhere in the car's electrical system. Normally you should measure something significantly less than 10mA or so - constant power current used by the clock, radio & other electronics for memory and such.

So now my strategy is to try to hunt for the short/drain current one circuit at a time. Idea is to use a spare 12VDC computer power supply in lieu of my battery for power, and measure current draw as I sequentially remove fuses and trip circuit breakers one at a time. When the current measured drops significantly below 25mA, that would be the circuit I'd need to troubleshoot further.

Anything else to try? I was also thinking perhaps it could be an issue with the ignition switch, just given its age - an intermittent/permanent short there could cause a multitude of issues.

j9fd3s

iTrader: (3)

its this for sure

um i think the next step would be to plug in the laptop and see if you can connect to the ECU, and then maybe crank the car and make sure the ECU is seeing rpm and such

Pete_89T2

iTrader: (4)

Good idea, and I can do that while it's still on the charger to verify the ECU is alive & booting up

UPDATE - Just plugged in the laptop & tested with ignition switch ON - AEM Infinity boots and shows no indication that anything is amiss (diagnostic page says all is good to go for starting); BTI gauge is fully functional and commincating over CAN with the ECU. Didn't try to start the car yet, as battery voltage is still a bit low - barely hitting 12V.

So I think more charge time or a new battery and she'll fire up and run... BUT I'll still have to hunt down that short/parasitic current to find out why the battery died in the first place.

Pete_89T2

iTrader: (4)

After a few hours on the charger yesterday, the FC battery reached about 12.6V. Someone on FB suggested the battery may have a dead cell, so I took the battery to my local Advance auto to have them test it - result was no dead cells; the battery experienced a pretty deep discharge (almost a month sitting with a ~25mA parasitic current drain will do that), but it's taking a charge now and just needs to spend more time on the charger.

As a test, I swapped the fresh battery from my FD into the FC, and she fired right up and ran. Measured 14.3VDC at the battery posts running at idle, so I know the alternator is working. After letting it run long enough to reach operating temp, and get it off the 4-post lift to switch parking spots, I shut it down and repeated the current draw test with everything off - result there was the same, still drawing 25mA. As a point of reference, doing the same test with my FD and any other electrically healthy car results in a current drain of about 3~6mA max.

So now I swapped the batteries again, but left the FC's battery disconnected until I figure out where the short/parasitic drain is coming from by testing one circuit at a time until I find it.

Pete_89T2

iTrader: (4)

With the ammeter connected between the battery negative post and the negative/ground battery terminal, I was measuring the expected ~25mA current draw with everything off. Step 1 was sequentially switching off all the new circuit breakers associated with my aftermarket ECU wiring. None of them when switched off (ECU Main, Fuel Pump, ECU/FIs, Coils) changed the 25mA current draw, so that means all the new ECU wiring is good. Next it was on to the OEM fuses. Started with the main fuse box by the battery, and when the BTN fuse was pulled, current went to zero. Now we're getting somewhere! From the FSM diagram below, the next branches to try that are fed by the BTN fuse (after replacing the 60A BTN fuse, highlighted in yellow) will be all those fuses highlighted in light blue. A bunch of those individual fuses branch off to power multiple circuits, so it may take me a while to sort this out - e.g., the "Room Light" fuse feeds non-switched battery power to no less than 8 different circuits according to this diagram! WTF were you thinking Mazda, and why can't you do electrical stuff right?

UPDATE - It's that damned 7.5A "ROOM LIGHT" circuit. Removing that fuse dropped the current draw from 25mA to about 1~2mA. Sequentially removing all of the other fuses did nothing to reduce the current drain. So now it's on to find out which of those 8 UN-FUSED circuits that branch off of "ROOM" has a problem.

Pete_89T2

iTrader: (4)

Yesterday I had some time to try to digest the FSM wiring diagrams, and started to tackle isolating which of those 8 un-fused branches off of the 7.5A ROOM fuse is causing my problems. Since the Audio system is among the easier ones to get to, and since I have an aftermarket JVC head unit, that's where I started.

So with the 7.5A ROOM fuse removed, recall that the parasitic current drain measured between the battery ground terminal and the negative battery post drops from about 25mA down to 1~2mA. The ROOM fuse was replaced, and after verifying that the drain went back to ~25mA, the next thing I did was unplugged the 2x OEM connectors that connect to the JVC head unit, via an adapter harness. Doing so disconnects the L/R wire that carries the constant +12VDC that branches from the ROOM fuse circuit. The ~25mA current dropped to only 14~15mA. Which tells me a couple of things: (1) The JVC head unit is consuming about ~10mA, which may or may not be normal for that radio - something I'll be reaching out to JVC to find out, and (2) I still have a parasitic drain of roughly 14mA in one or more of those other 7 circuits that branch off from the ROOM fuse that I need to find.