This just started happening today.
My 2004 LeSabre, L36, no engine mods, 117k on her.
I got up, left for work about 230am. (Yeah, I know, overnights suck..)
Started up fine, ran as normal 18 miles to work.
Left work at about noon. Started up fine, ran as normal.
Drove about 4 miles down the road to wally world, and parked her.
She sat there, probably 20 minutes.
Came out, got in, and went to turn the key. Cranked but no start. Tried again, crank but no start. I could turn the key to on, and hear the fuel pump prime, then shut off. Still wouldn't start. Mashed the gas pedal to the floor and cranked it, and started right up.
Turned around, went back down the road about 3 miles to stop and get lunch. Drove fine. Got my food, parked, and listened to my satellite radio and enjoyed the weather and watched cars go by on the main road. Probably sat, 20 minutes. Same problem happened as before. Crank, no start. Crank, no start. Mash gas, starts.
I decide to head for home on the main roads, instead of taking the scenic route around the lake I had planned on.

I get home, hook up my OBD2 scanner. No codes, no pending codes. Started right back up. So I go inside for awhile, look at my FSM for ideas.
Go back out, hook up the scanner, starts up, and I'm watching the data stream for anything unusual. Nada.
So I shut her off, and go work on my other car for awhile. Again, probably 20 minutes go by. I go to start the LeSabre, and same deal. This time, I kept going without touching the gas. Crank, off. Crank, off. Took the third time before it decided to grab..barely.
Was scanning the whole time. Nothing unusual.

The car has new plugs, new wires, new filter, good gas, I've cleaned the MAF, IAC, TPS, all out within the past 2 months with a safe cleaner. No problems until today. Battery reads good both sitting and charging, its less than a year old. I've checked the coils, and they all spec out ok.

Only started acting up this afternoon, and seems to be repeatable for the most part.
I have 1/2 tank of gas, only been in there 4 days.
Its not even all that warm out. Its only about 60 here. If it were more like 90-95, I could see heat soak being an issue, but not at this temp. She doesn't even really get over 190, not even enough to turn the fans on.
Again, it runs normally. If I'm driving along and put my foot down, she goes! (For an L36 anyway..). If she was starving for fuel, I would think WOT would sputter and hesitate. She doesn't even pause for a split second.

I'm baffled. Something this easily repeatable should be easy to track down, but beyond what I've checked already, I don't know where else to look.

Anyone have ideas? Dan?

Almost sounds like a flooded condition. when that happens you floor the gas and it shuts down the fuel system. I wonder if you have a leaking injector(*)

Wow. Thanks for the fast response, Dan! You rock!

That would make sense. But if I start her up, shut her off, and try to start back up in a couple minutes, shes fine.
I even setup the scanner to watch O2, and the fuel trims. (fewer values update faster on my scanner). If anything, I was seeing trim values in the positive side, by around 2-7% on short term, and <2 long term.

If I hooked up a fuel pressure gauge (its a schrader valve, correct?) I should be able to verify that the pump is pushing enough. But, how long should it hold pressure in the rail? Or does it just dump back into the tank too quickly to tell?

Or is there an easier way.. can you measure resistance of the injectors to see if one is going bad?

Can honestly say I haven't had a leaky injector problem before, but it makes sense.
If that is the case, where do I go from here? I've replaced injectors before, swapped out my stockers for some much bigger ones in my 87 Regal with the LC2, so that part isn't new. But actually testing them is another story...

Scanning wont find that. The engine does not run off the O2 sensor for the first 20 seconds or so. It'* in open loop. Once it goes to closed loop the O2s will go up and down. By then, any flooding will be gone.

If it happens every time, you can run the engine, then shut it down, wait what ever time is needed and try to start. Once it fails you can pull the plugs and see if they are wet, or which ones are wet.

Actually, going back through the testing procedures in the FSM, it doesn't look too hard to test the injectors. I should be able to isolate one or which ever ones are staying open. Heck, right in the opening explanation, it says that the injectors resistance is affected by heat, and can be the cause of a misfire or bad running condition. I think you saw my other thread about it running rough, long before it got this bad. I think you're spot on with this one. I haven't gotten any misfire codes at all, but I imagine a leaking injector could do it without setting a code.

This is why I love this site! I've been working on cars a long time, but I can always learn something new.

Post up your findings, that information will help others.

Well,
I did test the resistance of all injectors at a fairly cold start. All were in the ballpark of about 13 ohms, give or take .3 or so.
Since it seems to act up when its warmer, I started up, and got the coolant temp to top 200, where it runs kinda rough as it is, starting problems aside.
Resistance measurements were quite a bit higher, some nearing 15 ohms. But not one in particular seemed to stick out. But, with it being in the low 40s, keeping the injectors warm enough to affect them was difficult. Not to mention getting a good reading off the small pins, especially on 6 with the fuel lines in the way.
I do believe that a leaking injector is the likely culprit though. Reading through the FSM and especially in depth about how the PCM reads parameters, and the clear flood mode. It sounds like the PCM is in clear flood mode when I try to start it up.
Especially since I was watching the difference in fuel trims from a cold start through 200 degrees. Around about 185, it started pulling long term fuel like crazy. Short term values were hitting over 10%, and long term was holding steady at about 3.5%. Giving it throttle reset the values, but they soon settle back into those parameters. So, something is definitely dumping more fuel than the PCM is expecting.

I think my next steps are:
Get an injector pigtail, and cut out the safety clips, and wire it so that I can easily test the resistance of the injectors at cold and hot settings easily, and do it on a warmer day, because the heat trapped in the engine bay disappears quick when its only 42 out.

I think I will pull the plugs and see what they look like. They haven't been in for more than 2 months, so I should be able to see a definite result if one cylinder is getting flooded.

To go with that, I'll grab my fuel pressure gauge out of my Regal, and see just how quickly the pressure drops, both as a cold start and hot start situation.

Upon reading the first post, I felt the same stuff you guys have thought and done. Exactly.. the same.

Technically the pressure reading should hold and not drop down when you turn the key on. However there'* a check valve on the pump that frequently goes out and you can't 100% count on that.

All your symptoms do point to an injector though. Especially since you can consistently put the pedal into flood mode and it starts.

I have seen a fuel pressure regulator do the same thing you are describing

Ok gang, gonna need a bit more help here.

I managed to get a new set of injectors, thanks to ZZPerformance. Put them in last night.
The old ones coming out, well, at least 2 leaked, and they were gunked up pretty bad. No surprise there.
Got them in and seated. Still couldn't build pressure in the rail, cycling the key on and off.
Started right up. Ran good, the bit of lopey idle was gone, pressure gauge was reading steady instead of the needle waving a lot like it was before. Fuel trims, once in closed loop were back in the normal range.
I ran it up to temp, all the while checking for any signs of leaks. Everything looked good, and pressures were right on spec.
However, when I went to shut it off, the pressure instantly dropped to 0 again. Just like before. It wouldn't hold any pressure in the rail.

I figured I would test the hot start problem. I left it about 12 minutes. Sure enough, had to jump on the gas to get it to start.

Where to next? I did talk to the local GM dealer. And they are full of crap. They suggested that since my injectors were clogged, and my car had 118k, I should just replace everything, tank, pump, lines, fuel rail..etc. They wouldn't even listen to me about trying to test the system to isolate the leak. They just wanted to sell me parts, or they were also pushing me to just flat out get rid of the car and buy one of their new ones..

So, since I don't have the fuel return and feed line shut off tools... either I have to start just throwing parts at it, or find a shop that does have the tools and will actually listen.

What troubles me though, is why it should be a hot start only problem? Right now, the car has been off all night. I could go out there and it would instantly start without touching the gas, and hardly having to crank it for more than a split second. There is still no pressure in the rail, there never is at a cold start up. So, why would it have a problem starting with no pressure in the rail, when the only difference is the temperature of the engine? Unless the brand new injectors I got are leaking down somehow, I don't see why having the pressure drop in the fuel rail is any issue? Even if its still warm, and I shut it off but restart within a couple minutes, its fine, even without pressure in the rail.

I'm desperate at this point. I start a new job this week, and the last thing I need is more problems with this stupid car. I'll be driving 60 miles a day for this job, and the thought of the problems just frustrates me. I don't want to spend 100s of dollars and waste countless hours to get a shop to tell me something I can find out on my own.

I'm assuming, since I've done the injectors, and since the regulator maintains correct pressure when running, that the check ball in the pump is shot, and dumping pressure back to the tank. But, again, how is that a hot start only related problem? What don't i understand, what am I missing here?