I've searched around here on the forums for the answer and I haven't seen this issue. I am trying to stop my fuel pump from running so I can disconnect my fuel lines safely and cleanly. Per the inside of the fuse box cover and the owner's manual, I pulled the fuel pump 15amp fuse AND the fuel pump relay above it. The car still runs. I've had it running for a good 3 minutes with no signs of stalling. When I've done this with other cars in the past the engine would run for maybe 10-15 seconds before stalling. I've triple checked that I am pulling the correct fuse and relay. What am I missing here???

 

You need to be careful if you have never touched a DI system before. You do not want to run the injection pump dry, and the fuel pressure on the other side of the injection pump is well over 12,000 PSI. At that pressure, it will shoot thru your skin and out the other like a knife. IMO, dont touch it.

 

You need a bleed tool, some fuel pressure gauges have the bleeder installed on them..
snap-on tools injection fuel pressure gauge has the bleed system on it..

 

The OP is following the GM procedure for relieving the high side fuel system pressure. You're supposed to remove the fuel pump relay and let the car die. Also, max PSI on the Ecotec's fuel system is in the 2,500 PSI area. Normal idling is between 400 - 600 PSI that I've noticed. 12k PSI is diesel territory.

OP: I've noticed this on more than just Cobalts. The same thing happens when you remove the fuel system control module fuse on the LLT equipped cars. My thought is that the high pressure pump is actually able to siphon enough fuel from the pump to continue running.

My suggestion would be to shut off the car and let it sit overnight. Fuel pressure will be 0 when you go out the next morning.

 

I just read my post, one too many zeros. Thats still more than enough to cause some damage.

 

So pressure will reduce very low over time? Maybe I'll go this route. Thanks guys.

 

I just did this myself. Once the relay and fuse are disconnected, fire up the car, let it run for 30 sec or so, then shut it off. Fire it up again and run it for another 30 sec and shut it off. Repeat this process until the car can no longer fire up. Mine took about 4 cycles.

 

on vw and mazdaspeed hpfps i just crack the line and let the pressure bleed out while holding a rag underneath the line. idk if the cobalt hpfp is similar.

 

Yes. My friends and I have disconnected the HPFP from the high pressure rail several times on our various cars. Just let it sit overnight and no pressure will be in there.

On a side note, it's possible for the car to still run and limp around on only the low pressure fuel pump. Perhaps you pulled a fuse for only the HPFP.