fired up then stalled out now won't fire up

ok now I've got a big problem with my 2005 3500 GMC Duramax I started up just fine but then it just stalled out like it ran out of fuel. tried cranking a bunch of times with it just cranking away. checked the fuel filter bleed screw pumped it up might have been some air but I think I loosened the bleed screw to much at first. it had a fuel filter change a couple of months ago. but it pumped up well. so I couldn't find my scan so I rented one from Autozone. it gave a P0090 trouble code.one place said to clear the code and see if it starts up so I did that through the scanner. by know the batteries were getting low so I disconnected them and charged them up. When I hooked up the batteries it seemed like a healthy arc power jump happened when I attached the power positive lead. and when I tried stating the truck up the dash lights start flickering on and off. I've tested the fuel pressure regulator it showed 29 ohms . and didn't see any sign of it being shorted out with a meter. not sure were all the grounds are at any body got a diagram. which lead on the FICM do you test and which on the ECM do you test a good description would be helpful as my eyes are getting very old a tiny number are hard to see. . anybody know of a good repair place in Vancouver Washington, if I can't get it running. was thinking DSU as they are a GMC fleet Dealer. but really don't want to pay dealer repair prices so if I could. check off as much as I can before going that route. and can the FICM and ECM be tested by them selves at the dealer or some where else.

Welcome aboard!

P0090 indicates an FPR control circuit 1 communication error (non-specific).
Flickering IPC during a start attempt indicates poor battery connections, failed battery(ies), loss of proper ground contacts, or a failed ignition switch (very rare on late models).

If you have any electronic power/tune modifications, remove them completely and try again (cures many communication errors, and can be reinstalled once you move past the issue, often with no further problems). From your description, I see no reason to suspect PCM/FICM issues. An inability of the PCM to control the FPR will prevent a start/run, in any case. If the start fuel pressure window can't be achieved (too much or too little), there will be no injector firing. This is a communication/control error, not a pressure window error. Simply being unable to maintain the desired pressure window won't prevent a start/run, but will set different code(s), likely limp mode, and the SES lamp.

well it's a no run issue hear that's why I wanted to know where all the grounds where at as I've read hear and else wear that bad grounds can cause issues to. going too have the batteries load tested too. think they might be the original batteries or if not it was a Canadian truck moved into USA. and the batteries say some thing like Canadian power and have a foam wrap around them. some one also said some thing about checking the starter connection . as to the flickering the batteries where well connected. nice and tight used my side post tool to tighten them. also someone told me to reconnect the batteries and turn the headlights on and try to start it if they don't dim then it's the starter connection. but their familiar with Fords they also said some thing about primary and auxiliary battery. told him their wired in parallel. he said what I said their in parallel he said they can't be told him the are so he said well one still has to be primary and the other secondary. guessing that's the way their on Fords.

Battery connection is simple.
Parallel: 12V+12V=12V
Series: 12V+12V=24V

The system has no isolator and the batteries are continuously connected, therefore, neither battery is primary. Each battery has in independent ground to the block, but the Batt+ terminals are connected via a single cable (daisy) chain. So, if there were a "primary" and "secondary", figuratively, I don't know which would be primary. The battery at the end of the cable, or the battery in the middle of the cable (closest to the starter). It's irrelevant, in any case, but they can call it whatever they want. With healthy batteries, cables and terminals, the system doesn't care which is which. Failed/failing battery(ies) will affect the system the same, regardless of their position.

A bad connection at the starter solenoid lug that may cause other "flickering" issues, will also not allow continued cranking.

Going back to the original post, if the DTC is still present, it will not start. This is not a pressure issue, which most often allows for a start. This is a loss of communication issue, which prevents a start. The engine may crank, but the injectors won't fire. The PCM isn't satisfied with the conditions while cranking, and doesn't command an injection event. If this were a ground issue, that code wouldn't be the only one, and likely wouldn't be the first you'd see (you would likely not see it, at all). Either the regulator has failed, or the connection between it and the PCM has failed. The flickering IPC is a separate issue, as you said it began after messing with the battery cables. Maybe. Failed/failing batteries, one or both, have caused worse issues. If you believe they are original (highly doubtful), or of questionable health, work the problem from there. A 2005 truck should have had the batteries replaced at least once by now, likely more. The truck was original with AC/Delco batteries, US or Canada. If they look old, they probably are. Regardless of what the problem is, bad batteries won't help you to a solution.

well both batteries are bad one had 60CCA's the other had 150cca's after charging the 60cca batteries had 99cca's and the 150cca battery actually got worse 110cca's out of 600 for both. might not be the AC/Delco batteries but their old anyways considering the truck was originally sold in Canada. 570 dollars later got two Odyssey AGM 850cca batteries suppose to be better then Optima batteries guess I will find out had an Optima in an old 81 SWB with a454 it was a great battery. but looks like going to have to do some more testing or take it some where. once I get them hooked up, working 12+ hours a day. five days a week plus weekends don't leave much time for fixing it. anyone know of a good very good shop in the Vancouver Washington area.

While bad batteries isn't necessarily good news, it's good to know. If you haven't installed them yet, do that when you can, and start the diagnostics over. It may be more simple than you think, considering the condition of the old batteries. In the meanwhile, before you install ANY batteries, ground the Batt+ cable(s) to chassis ground for at least 30 minutes (no limit on longer, incidentally). This will default the PCM, and should clear out any erroneous diagnostic data. If you're lucky, when finished, you'll only have to reset the clock.