jaradt2013

03 silverado 4.8l procharged msd ignition long tubes stock bottom end stock 862 heads with stock intake the problem started out of no where when i start the truck it runs fine for about 45 seconds then according to my plx wideband it bottoms out running lean as hell and just a harsh idle and sluggish after i set and rev it up a few times for a minute or two not nothing major just playing with the throttle it lines out and starts idleing at 14.5 where it has always idled and then under wot it runs between 10.5 and 11 but what i need to know is what would cause it to lean out when i start the truck and then line its self out after playing with the throttle a lil bit and throwing no codes someone please help its my daily i drive it everyday to work so i seriously need to get this figured out and get it fixed thanks

kelsey_canard

iTrader: (5)

Is it running a speed density tune? Possibly maf calibration being off during open loop(when you first start it). Although, I would not think it to be an intermediate problem. Does it do it on hot starts? Fuel trims may be an indicator of this as well.

Maybe a vacuum/boost leak that the fuel trims have covered up.

jaradt2013

yes it does it on hot starts as well and its granatelli mass air and to be honest i dont now nothing about the tune on it i baught the truck back in jan. of this year and hadnt had any problms out of it untill now so i know nothing aboutu the tune on the truck and when it happened it just happened out of know where i was driving down th road it was raining and out of know where the truck just went lean and started missing i took it home checked all the plugins and everything on injectors i changed the fuel filter and run a bottle of fuel injector cleaner thru it and let it set for a day and now it just runs lean and misses about 45 seconds after i start it and like i said it then lines itself out after a few minutes of playing with the throttle

jaradt2013

as for vacume leak im not sure my vacume gauge has not changed in what it reads so but i dont know alot about this stuff i just figured if i had a vacume leak it would show on my vacume gauge and as for boost leak wouldnt that leavme o boost i still pushing 10lbs which it has always had

kelsey_canard

iTrader: (5)

Have you had the air intake or maf off recently?

jaradt2013

no sir havnt had anything off untill today i did take the maf off just to clean it thinking it could be dirty but it was clean as a new one

Mangled03gmc

iTrader: (95)

My truck does just the opposite on really humid or wet days, is intermittent also. Runs rich as hell, then if I blip the gas a few times it goes away. Havn't logged it yet, but suspect a bad 02 or possibly bad MAF. Hope ya get it figured out.

jaradt2013

i jus wasnt suspecting o2 sensors or really any sensors considering its not throwing any codes last code i had was ast month and it was p0300 and it was caused by two bad msd coil packs changed them and erased codes and light hasnt been back on

kelsey_canard

iTrader: (5)

Try unplugging the Maf and then clearing the fuel trims. You can do this by disconnecting the battery. Then start and see if it will idle in speed density. This will help you diagnose if your maf sensor is the problem.

jaradt2013

so if i unplug maf and then disconnect battery and then reconect battery and start it and it runs fine then it is the maf bad ? sorry to sound so stupid but im new to ls based engines hate to say it but ive always had mustangs so im kinda lost in tying to figure this out never had anything like this happen... but if its not the maf then fuel pressure regulator maybe or i just dont understand what would causeit to start and idle perfect for 45 seconds and then drop off lean and the line back out after playing with the trottle and not throw any engine codes im just lost