[Gmecm] Cold start with 1228746

[Jared Ryan]

> Jared, it sounds like as the engine warms up it leans out too quickly and dies, or like you suggest the IAC is closing too quickly and killing the engine

I'm thinking more the latter, since it doesn't really get a chance to warm up.  When it's very cold outside, it runs for maybe 10-15 seconds before dying.

Occasionally, when it is warm (80 or higher), it will start and run strong, then start to sag and almost die, and keep doing that for a while.  It sounds to me like it's hitting the stall saver routine.  Once it has gone through a few cycles of almost dying, then revving very fast and settling down, it runs fine.

> As a matter of fact, the car runs quite remarkable given the relatively poor tune I am running.

Same here.  Once warmed up a little bit, mine idles very well, does not ping audibly, has more than enough power, and can break both rear tires loose on any surface (PosiTrac rear axle).

> I eliminated the AIR pump as well as the EGR valve


Mine does have an EGR valve.  It is finally exempt from emissions inspections in Texas, so it no longer really matters.  The AIR pump went away when the engine was changed from the original 305 to the new 350; I have an idler pulley in place of the AIR pump (serpentine belt system from an '88-'92 Camaro/Firebird).

I picked up a 1227747 ECM with a PROM that is supposed to be for a '91 C1500 with 5.7L L05 engine.  As I understand it, my block is basically an L05 except for the camshaft and intake manifold (heads are the TBI swirl-port heads).  I'm going to give it a try out of curiosity and see if it behaves differently from the ANLU PROM with the 1228746.

> Your car may perform well as-is, but once the ecm goes into closed loop it's going to alter the fuel curve to maintain the proper AFR and therefore you may not realize how far off your VE tables actually are.

That's sure to be a major factor.  A serious impediment is that I have not had a good laptop to do real logging with.  I don't currently possess a Windows laptop.  I have had some luck with my old Mac iBook G4 running a Windows emulator with Win98 in it, running WinALDL, with an ALDL cable connected through a USB-to-RS-232 adapter... but as you can imagine it's very slow and WinALDL in that configuration is prone to suddenly shutting down.

What I'm going to end up doing is getting a used or refurbished Eee PC or similar and try to really do some logging.

Something I have noticed while logging with WinALDL: I can drive for quite a while, but very few of the cells in the BLM table are ever populated.  Is this a function of how slow the ALDL interface is?  What I'm really asking is, just because I don't see a value in the BLM table in WinALDL, does that mean the ECM has not updated it in its memory?

Does anyone know if WinALDL works in Windows 7 with a USB-to-RS-232 adapter?  If not, is WinXP a safe bet? I use only OS X and Linux at home and at work, so I am out of the loop with Windows software.