won't stay running

I have a freshly built 5.3 drive by cable truck motor. when is cold it will start up and run some what ok as it warms up ot gets worse. put n it in gear it just dies. ive added some air flow to the base running air also added some advance at idle no real change that I can see. its got a mild truck cam shaved heads and flat top pistons. Ive never tuned one from scratch like this so if some one could give me some direction that would be great lol.

Hello sorry but you will need to give us more information what ecu, what software etc

Regards ross

Assuming your running a GM computer, can you watch your IAC steps on your logger? Fuel trims?

it is the p01/411 ecu. the iac counts stay around 160 and domt move when it stalls

Check for air leaks, the PCV, and try disconnecting and plugging the brake booster/servo' line.

It sounds not unlike a problem with it drawing in air somewhere - at worst you'll eliminate a potential cause.

What happens to the mixture as it warms up? What does your wideband Lambda or AFR reading show. I'm betting it runs lean -- so it may just be the fueling in the idle area that needs to be increased. The extra fuel normally added to compensate for low coolant temps is just enough to keep it running initially, but when that extra 10 or 20 % is removed -- too lean.

yeah I put the stock tune back on it seems to do a little better starts super rich then goes a little lean but fuel trims show its pulling fuel even when wideband showing lean. It has long tube headers on it so I don't know if that may be messing with the narrow bands

yeah I put the stock tune back on it seems to do a little better starts super rich then goes a little lean but fuel trims show its pulling fuel even when wideband showing lean. It has long tube headers on it so I don't know if that may be messing with the narrow bands

Depending on how well they're made, and your exact setup, could there be cracks/leaks in those headers tahat's allowing air in when cold, or hot, that are closed/sealed in the other condition? It may seem counter-intuitive because the exhaust is pressurising the headers, but there can be pulsations that result in low pressure areas that may be drawing in air. This is a problem because the lambda and ECU will regard that as a 'lean' condition and, worse, it may only show up under certain conditions.

well I was messing with it yesterday and got the p0300 random miss. When I checked it with the scanner all cylinders are showing high miss fire counts but to hear it run you would never know its missing. so I think I'm having some other issue entirely. Its not showing any other codes so I'm thinking I possibly missed a ground wire I know some of these ls style engines are finicky with the grounds

Misfires can cause problems as the unused oxygen is registered as a lean condition, and some ECUs will keep dumping fuel into the engine in a vain attempt to remedy this. So your problem, if electrical, is going to cause both a rich and lean indication at the same time.

yeah that seems to be what I'm experiencing plugs are black and sooty and widband shows lean at least i have a direction to look in that at least makes sense now