New, Intermittent Starting Issue
First off, I'm not stock. I'm running a maggie with a 20A KB BAP and the stock fuel pump, and have been without any issues for about five years.
Here's the problem: about a week ago, after about a 20 minute drive, I turned the car off for about two minutes. When I came back out and tried to start the car, it sputtered a little bit to start with, but wouldn't start. It was turning over just fine, but seemed that there was either a lack of fuel or spark as it wasn't firing whatsoever other than the initial sputter. With that, though, I assumed that there was spark but the fuel pressure dropped off. I tried it a couple more times with the same result. After waiting for another minute, I tried it and it fired up completely normally. There were no issues on the rest of the drive or starting the next 5 or 6 times. Since this sounded like a flaky fuel pump relay, I swapped it with the trunk release relay. No codes tripped at any time.
Everything worked fine for about a week, then a similar issue yesterday. I started the car, but it started to die immediately. I was able to feather the throttle and get it back up to normal idle and it continued to run just fine. I got it home, shut it off, then tried to restart, and it did the same thing as the first time - sputtered a bit, then stopped sputtering and just wouldn't fire. I left it for a couple of minutes again, after which it fired up without issue yet again.
I checked the battery voltage at the battery with the car off, and the voltage was 12.0V, which obviously seemed low. I left it for about five minutes then checked again, and the voltage had risen to 12.2V for some reason. I put the car to the start position without actually starting and the voltage dropped to 11.4V, which seemed very low with minimal load on it. It still started and I confirmed the voltage at idle to be ~13.4V, which suggests that the alternator was still charging ok. After turning it off the voltage was back to 12.0V. I put my ammeter in line with the ground terminal and measured parasitic draw to confirm that there wasn't a faulted diode, and the standing load with the car off was under 1A and dropping over time as everything went into 'sleep' mode. Since the aftermarket battery was five years old, I decided to replace it, even though the old battery did still seem to take a charge with a charger. The new battery started off at 12.5V. I started the car and let it idle for about 20 minutes, after which the battery showed to be 12.65V (i.e., seems like the alternator is working). I also re-seated the fuse for the BAP and replaced the fuses for the fuel pump (20A) and theft deterrent system (2A) that can shut down the fuel pump. I confirmed that the wire splices for the BAP were not damaged, and I haven't driven the car since until I have a proper backup should it refuse to start at some point.
What I'm trying to figure out is whether or not a battery issue could cause a fueling/spark issue if there's still enough charge to allow the engine to crank. It doesn't seem like it should, but maybe the KB BAP was dropping out or something. If I still have the issue the next time I'm at home, I'll be checking fuel pressure to confirm whether it's fuel or spark related. What should the fuel pressure be at the rail within a couple of minutes of it shutting down? Beyond that, I'm wide open to suggestions from anyone and everyone for what to look at.
EDIT: I'm also going to try remote starting next time since that likely handles the security side differently.
2009 PBM G8 GT
TVS 1900 Maggie w/2.8" pulley (9-10 PSI), Maximizer LTs, High Flow Cats, LS9 injectors, Rotofab CAI, LC-2 WB, 40A KB BAP, TR6ix plugs, self tuned [250+ flashes], Camaro Paddle Shifters, UPR catch can, 4300k HIDs, Remote Start Heated Seat Control Module
, Aeroforce Interceptor Gauge, JBL GTO628's, JL 8w3v3's w/JBL P180.2, Bridgestone RE-11 tires