2005 Chevy Express Problem

[Mobile1HVAC]

I have a 2005 Chevy Express work van. It is well maintained, and currently has 97,000 miles on it. It is a 4.3L, automatic trans, and runs great, like new.
However, the vehicle will start and go anywhere with no problems, but once it has been turned off, it has a problem when you re-start it. The engine runs rough like its missing or something. This seems to last 15 to 20 seconds or so. You can push on the accelerator and it will pop and sputter. Then all of a sudden, it will clear up and run with no problems whatsoever. Well, at least till the next time you shut it off and restart it.
I should also mention that I have changed the spark plugs, wires, coil pack, etc, here in the past month and I still have the problem.

[newtofta]

'just' guess, but what you describe for symptoms.
sound to be an injector-bleeding fuel. when eng is off.
'if' this is the problem. you stand a chance of bending a connecting rod-( if enough fuel is there to cause a hydrolock of a cylinder)
as a 'try'-run veh down to 1/4 tank.
add a bottle of'TECHRON' to the tank,to try and clean the injectors.

[Mobile1HVAC]

Ok, I have been adding injector cleaner for the past month or so, as I thought that the injectors could be messing up. Hasn't changed anything yet.
You think that an injector could be bleeding fuel when the engine is shut off then?
Is there a test for that?
Does the fuel rail stay under pressure when the engine is shut off? Maybe something that could be checked with a pressure gauge of sorts.

[newtofta]

in'my' opnion-the 'techron' by chevron, is the only -'tank' additive that actually works.
yes, the fuel rail remains pressurized-to aid in restart.
not much of a test that you can do.
the scan tools that a 'dealer' or other more qualified shops use-can monitor-identify whitch cylinder is - missfire.
you did not state?- no chk eng lite?

[Claw Hammer]

First guess would be MAP sensor - if it has one or a bad throttle position sensor.

next guess would be as the other forum member has stated - that you have a bad injector and no amount of cleaner will solve the problem.

It's time to take it to a garage and have the problem diagnosed.

[DIRTWRKZ]

fuel fire or air as was beat into my head as a young tech, which one is gone when it wont start.
1st 3 things that come to mind are fuel pump (good pressure cold but not enough to fire it up when hot), fuel pump ground circuit (possibly melted in round connector at front of tank on the crossmember), distrubutor cap and rotor (4.3's are horrible about condensation inside the cap, will give you a white chalk like substance) and possibly a crank sensor heading south on ya.

The fuel rail does NOT hold pressure in the rail when you shut it off, the pressure is blead back to the tank via the return line or the feed line. The crank sensor tells the ecm you are cranking and kicks the f/p on. some fuel is in the line but not much and its not under pressure at all after 5- 10 minutes.

I would head down to the part store and but a cheep fuel pressure gage, get the van hot and duplicate the problem, then yank the dog house and check pressure while you are cranking. i will get you the specs tomorrow if you want.