Have a problem that's got me stumped. Working on a 2004 Impala with a 3.4L, that will start sometimes, usually when cold. Then may or may not start otherwise. When it won't start, it'll usually fire and die, fire and die, and maybe fire and die once more, then just turn over without firing. If I put the throttle down about 1/4, the chances of it starting the first or second time are greatly increased. And if I pull the nipple in the air intake duct (the hard line that goes to the rear valve cover) and spray a second of starting fluid in it, then put the throttle down 1/4 or so, it'll start just about every time. When it does, it runs perfect. No power loss, no misses.
I have no idea what could be causing this. Fuel pressure is good, swapped in a borrowed ignition switch, verified spark is present always, security system is not tripped, maf sensor swapped with good known one, as well as IAC, TPS reads correct with pressing of gas pedal, map sensor passes electrical tests, owner swapped a new Fuel pressure regulator (which I don't think was bad). I am wondering if for some reason the fuel injector pulse is getting cut off when it's cranking for some reason? There are no BCM codes related (that I know of, only for interior dimming high and low, and driver's side door lock issue). It does throw 2 engine codes, though. P0327B, Knock Sensor frequency, and P0520C, Low Oil level (If I remember right). This car doesn't have an oil level sensor that I can find. I can see where someone polished off some what I'm guessing was junkyard paint on the upper intake, so it's certainly possible that the engine has been swapped and they forgot to change pans, but I didn't see a pigtail for it either. I'm assuming the knock sensor can't cause a no start, but maybe I'm wrong. Anyone have any ideas?

 

fuel pressure was good but did you check for leakdown? the fact that starting fluid and changing the throttle position increases likelihood of starting makes me think its flooding. did you inspect the spark plugs?

 

Yep, I left the gauge on, and it drops 5 lbs or so in 5 minutes, and then remains pretty steady. I only checked one plug yesterday when it wouldn't start, and it was dry. I will go try again here in a bit.

 

All 3 front plugs are dry when when it won't start. I also got a new code this morning, P0336B. Which pertains to the 24X crank sensor, but all my research says that it won't cause a no start.

 

Ended up being a broken wire to the camshaft sensor, in the intake valley. No idea how it could cause the symptoms the car was showing, but I guess it doesn't matter since it's finally fixed.

 

bigj-dog - I'm glad you found the problem. How did the wire get broken? Was there some recent work done on it in that area? My brother had a similar problem with broken wires, except he had some chipmunks get in there and raise havoc with multiple circuits.