Odd starting behavior....

[96whitetahoe]

Hey all, fairly new to the forum, so bare with me on this. i've searched the forum thoroughly concerning the infamous P0300 CEL, which i unfortunately have. I've cleaned the egr, checked for vac leaks, changed plugs,wires,cap and rotor and even had a gm tech check timing, all good there. Now, what's odd, is that when the truck is cold, it starts right up. decent idle, nothing crazy lumpy etc etc. but if i drive around for a while, get up to temp, and shut her off for say 15 min, it takes about 3-5 seconds for her to fire back up. now, here's the ringer. if the truck is up to temp, and i go to get gas, and take say 5-10 min shooting the breeze with the tech while filling up, the truck will fire up right away.

weird.

i decided to experiment on this. drove for the week, and when it came time to fill again (little less than quarter tank) i went to the gas station, took off the gas cap like normal but didnt fill it at all. waited 5 min or so, put the cap back and went to start it up. 3-5 again. drive around the block really quick, back to the station and shut her down. fill it this time to about half full or a lil more, and she fires up right away. wth....drive 10 min home, turn it off, try to start it. 3-5 again. oh and i do have a new fuel filter too, but im wondering if its the pump or the regulator/injectors?

any insight/advice would be great.
-Pedro

 

[FunFordCobra]

Mine is the same.

1997 with over 200k miles.. Cold'ish start fires right up but when it's normal operating temp it takes a few secs to fire. I was gonna tune it up (coil, wires, plugs, cap'n'rotor) and see where that took me. Maybe PCV, EGR, MAF next.

I don't think it's a fuel issue because other then a 2 sec longer start....it runs like when I bought it.

 

[96whitetahoe]

Mine is the same.

1997 with over 200k miles.. Cold'ish start fires right up but when it's normal operating temp it takes a few secs to fire. I was gonna tune it up (coil, wires, plugs, cap'n'rotor) and see where that took me. Maybe PCV, EGR, MAF next.

I don't think it's a fuel issue because other then a 2 sec longer start....it runs like when I bought it.

Now that you reminded me. 1996 199k miles... lol veerrryyy similar....

 

[FunFordCobra]

@ start up, mine back fired today..through the carb and out the back..alittle smoke for a sec and now it's been starting up fine all day..I think these vortech get sick and "cough" to get better?

 

[our97ho]

we had similar issue and after going thru the same check list as you finally changed the fuel pump and OMG what a wonderful difference it made!!

***Also (ours) it happens more when you have about 1/4 or less of a tank it will make it even worst!