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Saturn Ion won't start after sitting

I have a 2003 Saturn Ion-3 that I bought a few months ago. It has 157,000 mile and runs great when it will start. Here is the issue: after the car has sat for several hours it seems to flood and starts hard. I end up putting the accelerator to the floor and this seems to help. I have to crank the engine repeatedly and when it catches I hold it to the floor until the engine clears (lots of chugging and white/blue smoke until it clears) and then runs just fine. If the car sits for a short period, it starts ok. the longer it sits, the harder it is to start (i.e overnight or a whole shift at work). If the car sits for several days it starts just fine. It acts as if it floods while it sits so I cahnged the Coolant Temp Sensor, still acted up. I then checked the fuel pressure at the schrader valve (55 psi) and noticed that it lost pressure as it sat. I assumed that the injectors were leaking and had them rebuilt (by Mr Injector). The flow bench results did not show and leaking. I reinstalled them along with new spark plugs and the car started up immediately and ran/drove great. This moring was the first morning of sitting all night and it would not start again. It tries to fire but will not catch. I tired to have the CEL code read at autozone but they told me my lighter wasn’t wrking and the couldn’t do it (although it runs my GPS just fine). I am out of ideas and a car! Please help!!!

Check your fuel pressure again. It could be a bad pump. Are you loosing any coolant? White smoke is why I ask.

I have checked the fuel pressure a two occasions and it is good both times. I had thought perhaps the head gasket was leaking into the cylinder but the cooling system holds pressure even after sitting for a week without running. So i am assuming that is out as a possible cause. Is there anything that would cause a rich condition at start othe than the coolant temp sensor? I have been told that the O2 sensor doesn’t even come into play until after start up.

@MarkG you took a very drastic step in having the injectors rebuilt. When fuel pressure doesn’t hold after shutting off the engine, the fuel pressure regulator is often the first suspect.

Another possibility is the fuel pump. When the check valve fails, pressure drops instantly after shutoff. Check valves can be tricky to diagnose. Even though you may have hard starting, the pressure is often normal at idle.
Of course, the entire fuel pump may be on the way out. You’ve got the miles.

My advice: replace the fuel filter/regulator assembly and take it from there. Since you seem to have the fuel pressure gauge, hook it up before you replace the regulator. Replace the regulator.
Start the engine, note the pressure at idle. Shut if off and note the pressure and how long it holds.

Good luck!

Assuming the CEL isn’t on and routine engine maintenance is up to date. Like you say, it sounds like too rich a mixture. The ECM is supposed to be reducing the gas according to coolant temp and air temp. The coolant temp sensor was a good item to check. On some cars there is an intake air temp. If your car has one, worthwhile to check it I suppose.

But the ECM assuming the fuel pressure is adjusted correctly too. I concur w/@db4690 that given what has already been done, this seems more like a fuel pressure regulator (or its vacuum control) or a faulty check valve. It might be more economical at this point to take this car to an inde mechanic, as diagnosing these gadgets takes some special skills.