Sputtering and Coughing at Start

[LTZ C20]

This is about my 03 Tahoe because I need help and I don't know what to do next. I have an 03 Tahoe, 4.8L Vortec. It was having trouble starting and the carb cleaner spray trick pointed towards bad intake manifold gaskets. Chevrolet after consulting them, they said I should replace the intake gaskets and that should stop the crappy rough start. So I took apart the entire top of the Vortec engine, wiring harnesses, fuel rails, vacuum, all that stuff, I replaced the intake gaskets and put it all back together again. Everything I took off was labeled and I paid careful attention to how things were, I followed every step in my Chilton's Manual for Intake Manifold removal and installation. Now the entire thing is back together and when I start it it sputters, coughs, burps and dies. Sometimes it will high idle then drop and burp and die. I expected it at first because there was no fuel pressure and I had to take the fuel rails partially apart. Well after 20 or more attempts to start it, it still won't smooth out, I don't understand why and I need to get this thing running again because my family needs it. Thanks ya'll.

[454Man]

Sound like a vacuum leak. Did you use any sealant when you put everything back together? Did you leave off any vacuum hose or electrical connectors?

[Irish_Alley]

did you clean or mess with the M.A.F. sensor? can it be put on backwards. other than that i would look for a vacuum hose off or something not connected

[bake74]

Sound like a vacuum leak.

     x2

[zieg85]

Or it could be low fuel pressure due to a weak fuel pump....

[454Man]

True

[LTZ C20]

I used sealant yes and I labeled everything and put it all back the way it was, I don't know what the MAF sensor is but everything is connected. After I was finished I double checked everything to make everything was plugged in and stuff. I thought it would be low fuel pressure because of air in the line, but after cranking it 30 times, it still won't start and idle normally. I have no idea.

[454Man]

Is there a port for you to check the fuel pressure? If so you can push down on it and see if any air comes out. Becareful gas might spray out

[LTZ C20]

I will investigate that tomorrow.

[Irish_Alley]

m.a.f. mass air flow sensor its after the air filter and has a screen

[LTZ C20]

Oh got it. OK.

[mattgood]

I also think it may be a vacuum leak. I would triple check everything including hoses, electrical connectors, make sure all the plug wires are on tight....etc. But if you say the problem was occurring before you took it apart, something like a plugged fuel filter (if it has one) or a weak pump may be the cause. Good luck and please post what you find out.

[jaredts]

Autozone's tool loaner program has a fuel pressure gage.  I would start there.  Make sure you have the injectors seated back into the intake all the way.

[LTZ C20]

I replaced the intake gasket as before, new spark plugs, new plug wires, new fuel pump which returned the right fuel pressure. The truck is miss firing so its at the Chevy dealership getting fixed. I don't have the equipment or knowledge to fix the miss fire. My work I did was good, but as the truck has a lot of miles on it, it needed a good service. Thanks ya'll.