My 2008 C6 (18K) will run for a few days and then out of the blue it will not start. When it is running it does not miss a beat. I shut it off go to restart it and without warning, it will not restart. It cranks well and trys to start but it sounds sick and stalls out. There is black smoke coming out of the exhaust while it is trying to start and it smells very rich. Eventually, it only cranks and and will not catch at all. I pushed the valve at the end of the fuel rail and gas came out.

The first time this happened, it was towed (3 miles) to the dealer and it started after being unloaded from the flatbed. They kept it for two days and just started it occasionally (started every time) but dd not drive it, said they could not duplicate the problem so there is nothing they could do. It did not throw any codes according to the mechanic.

I have driven it four times since picking it up from the dealer and it happened again today after a 40 mile trip. When it occurred today...same issues. It hardly runs and then stalls. I tried starting it over a period of two hour with no luck (wore out the battery). I disconnected the battery hoping this would reset the ECU or fuel pump issue still did not start. After having it towed 40 miles to the dealer it starts right up...WTH?

So it seems the movement of the vehicle does something to make it start (gas sloshing around?). I am thinking something in the fuel pump, pick-up solenoid, fuel level indicator. Maybe the ECU?? Any thoughts?

 

I dont know all of the components in this fuel system but some cars have a check valve that keeps fuel from going back into the tank after its out. It may be stuck and not letting fuel out in the right direction. I have a buddy with a jeep that has this same problem and thats what was causing it.

 

The check valve is designed to prevent fuel in the rail and line from draining back into the tank. It will not cause flooding. A bad check valve will cause an extended cranking time while the injectors purge the air from the line (returnless system). More than likely, you have a sensor lying to the ecm. If the coolant temp signal is 20 degrees F when the engine is actually 180 degrees, The ecm will command ALOT of start up fuel. The ecm is programmed to deliver a liite extra fuel even a warm engine at start up. If your engine does this again, put the throttle on the floor. The ecm will go into "clear flood mode" and not fire the injectors. If you do this and get it to start, hopefully it will set a code that will help the dealer fix the problem. If you are familiar with scanners, i would keep one in the car and hook it up the next time it does not run. Check the coolant and intake air temp. Also check the maf grams per second.
Hope this helps.

 

absoultely correct !!! good post marty !!!

 

Thanks for the great info. Why do you suppose the movement of the flatbed causes it to start? It has done this twice not and there is apparently some relationship to the movement and it starting. I plan on printing out your comments and taking them to the dealer mechanic. Rick

 

Turned out to be the fuel pump. The car totally died while they were test driving it and had to have it towed back. I guess there is no code for low or no fuel pressure.

 

In this situation, if they had their tech2 hooked up and in snapshot mode, they would have seen a sudden spike in short term fuel trim when the fuel pump crapped out. Then again, cars that don't run at all are easy to fix. It's the intermittant problems that are a pain in the azz. I am glad it got fixed before the problem turned you against your c6 and the dealer!