Lovely, now it threw a p2135 while driving, limp mode had to reset the car

 

Well I’m ready to use a volt meter and track this down but idk how to start with it being so intermittent.
Cleaned all my grounds again and applied solder this time. G105 is solid.
Cleaned my OBD port, all my obd cables.

it’s gotta be my PCM..

 

Well I watched Voltage very attentively today. Noticed on my lunch break voltage started at 12 and some change, drove around was charging around 14.5. Parked my car looked back up and it was at 12?!?! Turned on some accessories wondering if it would bump back up to 14, nope. Cycled key and it was back to 14.
Going to pull the positive wiring bridging the alternator and starter tonight I suppose.
Also noticed my dash lights were extremely dim but I don't think that's an issue, just read it takes a minute for the sensor to determine false light from real light and I think that checks out.

 

Just went for lunch, and again battery read 12.9 over the course of a 20 min drive mix of highway and city.

okay so we might be getting somewhere, maybe belt tensioner, alternator and again pcm possibly.
Pulling out the volt meter today

 

Hmmm. So after a little while of no codes.
I decided to try getting a start up scan again to collect some data for this hesitation on start up.
VCM communicated, car looked OK, fuel was a little lean and cranking timing seemed low. So with a tune update and flash, started the car, seemed a little better, little less hesitation. Next cycle it threw codes.

So not the tune, afr, or timing. It’s not missing when this happens so I can rule out it being an engine hesitation. I was speculating fuel pump going out (no I can’t hear it over the sound of my Intercooler pump)

I’m tempted to throw a PCM at a it as it looks like the majority of people who experienced these codes ultimately leads to a complete no crank no start and they replace a fried PCM..
again u0073, u2105, u2107, u2100, p0700, p1501, u2106.

After work today, thinking a snap on tool could individually pin each module. (It could not) I went through every page and the only other thing worth noting is from the BCM the theft déterrant system voltage was reporting out of range.
car could connect to Bcm, tcm, pcm, ebcm and pscm. However I could not connect (get data) from the theft déterrant module or the vehicle interface module.

Odd? My first thought is, these modules might not be large enough to give out their own data, and maybe they actually just send info to the BCM and it’s suppose to be read there?

I deleted Vats previously, however I turned it back on yesterday. I attempted to relink vats in my scanner yesterday, however it reported failed. Did a quick google search and people said if your car started, it relinked vats, ie, the relink can be forced but it also happens on its own with a single key cycle.


so the fact that my theft and vehicle interface modules aren’t communicating, and voltage is being reported irregular at the theft module, could this mean my vats is truly still off possibly?

Snap on gave no codes, and it was running for 25 minutes. Tried both on/off several key cycles..

maybe worth noting: for about the past 9 months, almost the same time I bought an aftermarket key fob my car everyday tells me I have a low key fob battery. I’ve replaced it several times, the battery is fine and my other two fobs are not in the vehicle. Pretty confident that’s just the aftermarket fob operating slightly out of spec then the oem ones but maybe it’s an indicator of a module malfunction.


so I have tomorrow off, I was thinking, despite confirming twice g105 is fine, was thinking of cutting the terminal off and rewriring the ground a few inches back. Eliminate the possibility of the wires being broken under the sheathing at the eyelet terminal.

but I think I may start with an ohms test on the obd before shooting in the dark after today. Been putting it off, am no wizard with a multi meter but maybe it’s time to learn. Part of me thinks it’s gonna give out perfect values but oh well.

 

Okay! So after finding a fuse and cleaning off the corrosion in my antique multimeter lol.. DLC tests 61.5 ohms.
so I’ll do another test tomorrow morning before starting it make sure that’s consistent.

So I’m going to try to test fuel pressure at the rail next. But I think tonight, after reading a little more on how to tell if Vats is turned on or off, I’m going to switch back to my summer tune, turn vats off and try that for a little while.
MAF is a little different because I run methanol with this tune, cranking timing is higher and everything on my Cam page is disabled. Which was another thing noted for failed cold starts, VVT solenoids. & I happen to notice it engages at -10C which seems to be the tipping point for this to issue to start happening. Odd but worth a shot.

after that, I think I should try bypassing my VICM and if that doesn’t yield anything look at my theft module more closely maybe.

 

At this point I’m really hoping it’s too separate issues. Bad fuel pump and minor communication mishap that just seems like it appeared around the same time. Because if it’s not wtf

 

So vats off, write entire, vats light comes and goes and the same speed of it being on… maybe onto something? Probably not lmfao
—
updated hptuners from version 4xxx to 5xx, disabled started fault check, vats light still comes on. That’s super strange..

 

OKAY!!!! SO hooked up a pressure tester,
Reaches about 50psi with one prime after bleeding pressure at the rail.
Run car, boom 58-60 psi ,
turn car off, quickly drops to 40psi, maybe 5 minutes later its at 30psi and about 45minutes later its at 18psi now, and still appearing to slowly be going down.

so it is fuel related?

 

it would be great if i could get it to no start just before the end of the day while I have someone watching the gauge, idk if ill get that lucky though

 

Held at 18psi for quite a while, now at 15psi

 

So does anyone know if the "valve" to prevent bleed back is in the actual pump? or in the assembly?

 

So I think before replacing the pump, I'm going to put a check valve on my rail, should be here January 4th, and we will go from there, see what happens ! do another pressure afterwards!

 

Nope. That test can’t be trusted. Upon starting it before leaving work. Rail pressure read 12.5psi priming and running. Shoot.

I read a little more on vats, decided to turn of starter diag under system. No change to vats light.

so I decided to read the car, confirm it was actually taking my changes. It was thankfully, however it threw p0606 and p0607.

and I should note writing entire, to my ecu, takes about 8 minutes.. it never use to take that long, maybe 3-4.
ugh! Hahaha. All things concerned maybe more likely to be ECU.
the techs suggested at work to pull the rail and do a visual test to see if injectors are loosing pressure and I just might too.
i think it might be time to get a PCM coming, at least be able to rule it out. And I should try to take a video of this cold start hesitation/ stall.

and maybe I’m crazy but I think I want to check trans fluid too, although a reach, maybe I have low trans fluid and it’s slipping intermittently on start up allowing me to stall for the first key cycle.

 

I'm super stumped.
Again the problem at hand, cold start first thing in the morning, car cranks, fires for a few seconds than the rpm's just drop and dies. Restart is super healthy.
Did an oil change over the weekend, cleaned starter wires.
Sounds like a vats problem to me, however the vats light is not on or flashing when this occurs. I ordered a PCM today, I cleaned my MAF, resealed TB gasket, grounds are clean etc.
Going to have to test fuel again here, speculating it'll come out fine, but I'll have to source the shop a new adapter that fits my shredder valve better and try nonetheless to rule it out.
Maybe read up on how to disable vats from BCM

 

any luck?

 

Not solved yet, I think I'm gonna figure it out this month though.
I rewired my fuel pump, much better fuel mileage I've noticed so far, cold starts did get a little better but not fixed. I ordered a new fuel pressure tester adapter for my work and that should be showing up any day now.

So my plan, likely in this orderh
-is to test fuel again, If it is back bleeding I'm going to try a one-way check valve before dropping the tank
-Swap ECU's (got one in today)
-Tear up G105 and rewire it entirely.
-Swap out MAF

Honestly at this point my gut is saying ECU.

However I did notice something slightly concerning over the weekend, I have a methanol tank in my trunk and keep a additional 4L in a windshield washer jug.. now, not sure how, but there was water all over my trunk area and if that windshield washer fluid jug was full I likely lost 2.5L.
I'd love if that was my smoking gun, it would explain some odd behavior but again, doubt it is my problem... cleaned it all up and should probably check on it again. ODD thing, in the morning's I swear I can hear fluid spitting out and onto the ground near the fuel tank but when I look there's nothing there, must just be my exhaust making noise

 

i would say PCM (same year model) but see if it will start with before you license it with HPtuners

 

The one I got here is 2010 G6 2.4L,
I have 8 gm Hptuner's credits and don't care if I use em

That wont be an issue eh?

 

Kinda sounds like your thought logic there is, if you tried a same model year, without programming, if it didn't start, if you could then associate the issue to be a vats problem?

 

if it doesnt start, then it isnt a pcm issue. also i dont believe VATS will allow it to crank. but check out this thread as well a no-start issue - Cobalt SS Network

 

Hmmm, interesting I'll have to read up then.

Might try grounding the control moudles directly tonight, that should be easy enough

 

I relocated my ECU and TCM under my PDC. Otherwise I would've swapped the ECU already
I'll post the answer at the end of the month lol

 

Okie, grounded both tcm and ecu directly. Still wasn’t all that easy to run a bolt through….

Place your bets now haha.results in the am.

almost sounds like ecm relay is making a harder click off now

 

NGL, had a little faith that was gonna do something. Fired up this morning, but I could tell, it was on the verge of stalling for a few seconds. No dicey