2004 Impala Only starts on Starting Fluid, but runs fine after

[bigj-dog]

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?

[Tech II]

Last time the fuel filter was replaced? Not sure if this has an external filter or it's in the tank......why they ever did that boggles my mind....

Also, does the knock sensor codes come back immediately after being cleared?

[bigj-dog]

Fuel filter was changed about 36 hours ago. And the knock sensor comes back pretty quickly, but not immediately. The oil level code usually comes back first if I remember right, but that's not immediate either.

[DeltaP]

Have you checked the fuel pressures? KOEO,KOER.

[bigj-dog]

Yep, 52 and 42. I thought that was a little low, even though it was within specs that I found, and I happened to have another similar car around, so I swapped fuel pumps. No change. I also pulled the front 3 plugs this morning when it wouldn't start. They were dry. I swapped the knock sensor with a running car with no code, and the code came back. I did get a new code this morning, P0336B, which related to the 24X crank sensor. Which I read a bunch of different places will not cause a no start situation. This is the first time I have seen this code. Is it possible that it's confusing the PCM enough to not open the injectors enough to start the car?

[j cAT]

Originally Posted by bigj-dog

Yep, 52 and 42. I thought that was a little low, even though it was within specs that I found, and I happened to have another similar car around, so I swapped fuel pumps. No change. I also pulled the front 3 plugs this morning when it wouldn't start. They were dry. I swapped the knock sensor with a running car with no code, and the code came back. I did get a new code this morning, P0336B, which related to the 24X crank sensor. Which I read a bunch of different places will not cause a no start situation. This is the first time I have seen this code. Is it possible that it's confusing the PCM enough to not open the injectors enough to start the car?

this type problem sounds like a bad temp sensor/or wiring of it. if the pcm gets the wrong temp from sensor then the engine will have start issues. if the sensor is open then the temp reported would be -40 deg f .. or if shorted a hot 250 deg f temp that would reduce the fuel injection so that a cold engine will not start.

[bigj-dog]

Scanner says the temp sender is reading correctly. Matches the gauge, and what the temp should be. I also tried disconnecting the temp sender, no change. And it doesn't start fine even when cold, you have 2 or 3 chances to get it to go, if not it stops firing without starting fluid.

[j cAT]

Originally Posted by bigj-dog

Scanner says the temp sender is reading correctly. Matches the gauge, and what the temp should be. I also tried disconnecting the temp sender, no change. And it doesn't start fine even when cold, you have 2 or 3 chances to get it to go, if not it stops firing without starting fluid.

\
so on a cold crank what does the scanner read for engine temp ?

[bigj-dog]

This morning outside temp was around 70, and if I remember right it said the coolant temp was 75 or something. I looked at again after I had ran it a bit, and it said 106, which I guessed was about right for being run for a couple minutes.

[j cAT]

Originally Posted by bigj-dog

This morning outside temp was around 70, and if I remember right it said the coolant temp was 75 or something. I looked at again after I had ran it a bit, and it said 106, which I guessed was about right for being run for a couple minutes.

I would run the vehicle and check temp on cold start and also as the vehicle is operating to see that the engine temp is correct.

with the correct pressures ,no codes , and the poor starting the ECT is most times the problem ..

possible the injector grounds/wiring but once it starts your good so it goes back to the ECT.. one other possibility would be the IAT .. if that reports the wrong temp it can cause a poor start..

so you have engine temp and the intake temp being sent to the computer to provide proper injector on time.

[bigj-dog]

I did watch it on the datastream when it was warming up during a test drive, and it warmed up to about 206, and didn't bounce or anything. IAT sensor was 93 when I was driving, outside air temp was 82ish. I just told them I would guess that it's the PCM not sending signal to the injectors when cranking (since I tried a brand new ignition switch last week and it didn't make a difference), but that I wasn't sure so they might be better off taking it to a dealer or an actual shop instead of me. Pretty sad to have to give up, but at least they can always get it going if they miss the first or second chance with starting fluid. I'll post back if they do end up getting it fixed. I am out of ideas. Thanks for the all the help guys.

[j cAT]

Originally Posted by bigj-dog

I did watch it on the datastream when it was warming up during a test drive, and it warmed up to about 206, and didn't bounce or anything. IAT sensor was 93 when I was driving, outside air temp was 82ish. I just told them I would guess that it's the PCM not sending signal to the injectors when cranking (since I tried a brand new ignition switch last week and it didn't make a difference), but that I wasn't sure so they might be better off taking it to a dealer or an actual shop instead of me. Pretty sad to have to give up, but at least they can always get it going if they miss the first or second chance with starting fluid. I'll post back if they do end up getting it fixed. I am out of ideas. Thanks for the all the help guys.

it was mentioned did you measure the fuel pressure with the key to on engine off... ? if you have no pressure ,then this maybe a relay problem. fuel pump relay. the vehicle runs once you give it a shot of fluid so this is in the crank fuel pump start circuit.

[bigj-dog]

Yeah, key on, engine off was 52, then 42 after being started. Fuel pump primes every time. I don't know if there is a separate circuit that fires the injectors during cranking, but if there is, I have to believe that's the problem, whether the computer isn't sending it, or the wire is broken. If it were my car, I'd have bought a new PCM, given the odd codes showing up and the seeming lack of an injector pulse during cranking, and hoped it worked, but I didn't want to gamble with someone else's money.

[j cAT]

Originally Posted by bigj-dog

Yeah, key on, engine off was 52, then 42 after being started. Fuel pump primes every time. I don't know if there is a separate circuit that fires the injectors during cranking, but if there is, I have to believe that's the problem, whether the computer isn't sending it, or the wire is broken. If it were my car, I'd have bought a new PCM, given the odd codes showing up and the seeming lack of an injector pulse during cranking, and hoped it worked, but I didn't want to gamble with someone else's money.

so is there an injector pulse when cranking ? also with the key on you have injectors with 12 volts on all ? PCM would be a good guess . I would remove the PCM and check for damaged corroded pins on the connectors even chafed wires with the harnesses to the PCM.

[bigj-dog]

When I last had the car I didn't have a good enough diagram to know which wires were which at the injector harness plugin and I was under another time crunch, so I didn't have time to locate one. I just picked a couple of the wires and I did have a flickering led test light at a couple of those wires, but I don't remember which wires.