I think this beast is haunted. Here within the last few days the WOT misfire after 4000 that I've fought for literally months, possibly even a year has mysteriously all but vanished. Could it be the fact that I finally installed a case ground on the coil, I don't know?? There still seems to be some light valve float going on but at least it will pull and isn't acting all sorts of stupid anymore.

So one step forward and fourteen steps back. Its never ever ever ever had a consistent startup. It either busts right off first thing in the morning with a nice little flare up then settles in around 850 and slowly idles down as the engine heats up, or it just starts and stays about 850 and slowly comes down, or when its warm it will hit and die, or start with this big triumphant flare up and bog down and nearly die or die, or when its fully warmed up, startup and idle around 650 to 700 rpms and idle down a touch or barely start and struggle to stay running for the first few seconds before it smooths out. Its very annoying and makes me look like an idiot when it gives this big triumphant flare up and then bogs down and dies and won't restart until I hold it to WOT.

So I've tried everything I know of. I'm running 30 psi on 61# injectors so I set the crank PW vs coolant temp table to 25% less than stock. I've tried stock crank to run and choke tables to no avail. Cold startup seems to be decent but anytime other then that its hit or miss. I've tried playing with crank to run pretty extensively as I know a single plane has some pretty substantial volume to work with and being a high rise there is no heat and the intake stays very cool even on a hot engine so it should take more crank to run on a warm engine to combat fuel sticking to the plenum walls but it doesn't seem to be. More crank to run has lessened the problem on the cold start, its very smooth, busts right off, nice little flare up to around 1100 rpms then smoothly comes back down to 850 and warms up and idles down from there. On a warm start it might fire off fine and then bog down to about 300-400 and then recover or it may just die. Same story on a hot restart. So at this point after messing with just about everything and not really gaining anything this is where I lean on the experts. Specs are a worn 204k mile '95 350 K motor short block with a LT4 hot cam, mildly ported vortec heads otherwise stock, a Victor Jr single plane high rise 2 barrel intake, 454 throttle body and 61# (stock 350) injectors at 30 psi with an external Mallory regulator running the $OD MAF code.

Here is a screen shot of the tables in question in this order: AFR reduction at startup vs CST (choke), Crank to run AFR vs coolant temp, Open loop AFR for idling, and Crank BPW vs coolant temp.

 

Tough crowd.

 

Dont feel bad. I had similar issues a couple weeks ago. Mine would not start period. Then next time it would. Or it would start and I would hold idle at 2000 rpms and it would just die. Intermittant. Once runnin 30 secs all was well. That was at environmental temps of 80dF. Gave up and took to my xpert mechanic and he ways starts every time over 102 week period he had it. He think fuel pump going south/seizing. I had no one to witness spark/fuel during episode at home when it happened. Key on fuel press went to 20 that I know. I guess I would look down TBI and see that is happening fuel wise when it acts up. And then verify spark if fueling looks OK.

 

Check IAC. The inconsistancy of your afterstart idle sounds alot like an IAC problem. Crank to run transition? Im more familiar with afterstart enrichment. I see you can set AFR correction for CT, can you set decay rate? Check IAC first for your idle inconsistancy. Then try fine tuning Crank to run in the temp range where the problem is most obvious. See if you can adjust decay rate. The fact that you have to go WOT to start, after the start and stall, tells me that you may be over fueling at those times. I was having startup issues with my extreme TPI until I set my Afterstart enrichment and decay rate.

 

I just replaced the IAC about a month ago with one for a 3.8 K motor. Its physically identical but with a different part number then what the 454 throttle body calls for and about 65 dollars cheaper. The reason for replacing it was the original IAC would either not go past 88 counts or it would jump to 255 counts and then back to 88. Anything under 88 was fine and I was suspecting it was causing startup issue so I threw one on it. Now I get a smooth steady throttle follower sweep of the IAC but the startup issue is still there.

Yes I can adjust startup fuel decay rate as well.

Here is something else I noticed. If I rev it up in park and let the throttle snap closed it will either stall or dip down to about 300 rpms and barely recover. If it does recover its like it rips the IAC wide open and it flares up to 1500 or so, then slams it shut and back down it goes and nearly stalls but recovers then levels off.

I do have a little excessive MAP AE on part throttle tip in at the moment but would it effect startup too?

 

The dip could be AFR related or it could just be base idle set too low. Monitor your O2 voltage as the dip occurs. Is it going severely lean? If this were an OE setup I would recommend the base idle setting procedure. You might try just a half turn of the throttle stop screw and look for a change. GM's idle ratio is generally 60/40 (60% of idle air through the throttle blade, 40% through the IAC, curb idle speed, no loads). I have dealt with unusually severe sweeping of the IAC counts, with a corresponding difficulty in maintaining idle, on several GMs and generally find it to be a coked throttle. Base idle set too low has the same effect.

 

hey red with my pressure at 25psi my cranking bpw and crank to run are about 50% what stock is. also my choke is almost 0 on a near warm engine. i think your getting way too much fuel on startup IMO