POS chevy uplander

[91stranger]

So I have a 2007 uplander and it seems to start whenever it wants. It did that once before and I cleaned the throttle body because it was black on the inside and didn't have any more issues for about a month. Now it will shut off while driving and not start back up for 10-20 minutes. Only code that has came up is PO449 code which shouldn't cause this issue. So today I have it scheduled to get looked at and low and behold it doesn't start. tried for about 10 minutes before giving up so I'm not late to work. I can hear the fuel pump turning on but still wont start. I've replaced the fuel pump relay. cleaned and tightened the battery cables. cleaned every sensor I can reach. Added a better ground to the motor. So I'm at a loss on this. This is the family vehicle and it is not reliable so this is a big issue for me. I don't have money to throw at it or money to tow it 25 miles to the shop. Does anyone have ideas on this or what I could do??? I need help on this bad. It is a 2007 uplander ls with the 3.9 liter and 131,000 miles.

 

[RonD]

Hold gas pedal down to the floor and then crank engine, it should not start with gas pedal to the floor, it should not fire, fuel injectors would be off
Thats called Clear Flooded Engine Mode, all fuel injection computers have it
RPMs at 0
WOT(wide open throttle)
= shut off injectors
Spark is still on

If it fires then you have fuel leaking in from an injector, which is flooding out the engine on normal startup

If engine doesn't fire then do 50/50 test
Spray gasoline or ether into the intake and then try to start it
If it starts and dies then injectors are not working, assuming fuel pump is
If it doesn't start then spark is the issue, crank/cam sensor maybe, not sure which is Primary on Chevys

 

[91stranger]

Hold gas pedal down to the floor and then crank engine, it should not start with gas pedal to the floor, it should not fire, fuel injectors would be off
Thats called Clear Flooded Engine Mode, all fuel injection computers have it
RPMs at 0
WOT(wide open throttle)
= shut off injectors
Spark is still on

If it fires then you have fuel leaking in from an injector, which is flooding out the engine on normal startup

If engine doesn't fire then do 50/50 test
Spray gasoline or ether into the intake and then try to start it
If it starts and dies then injectors are not working, assuming fuel pump is
If it doesn't start then spark is the issue, crank/cam sensor maybe, not sure which is Primary on Chevys

Well it has and hasn't started while doing all those start up tests. It seems like it just starts when it wants to. I've got it to start while giving it gas, not start while giving gas. Sprayed starting fluid in and it started up. Sometimes it stays running, sometimes it sputters and dies and sometimes (like today) it just wont start at all with starting fluid. So I'm still at a loss on this. Normally I am pretty good at solving the riddle but not with this. This may be why I don't normally own chevy's. Posted this on a chevy forum and got 90+ views and no answer.

 

[RonD]

No spark is why its not starting, because it is intermittent.

If fuel supply was intermittent then it would start every time by adding fuel, it doesn't so spark issue for sure.
Compression is off the table since it does start even if intermittently

Not well versed in GM but all newer systems work pretty much the same way.
If an engine is Distributorless there will be a Crank sensor or Cam sensor or both
If there is a Crank sensor then it is the Primary sensor

Engine computer is not connected to starter motor, so it doesn't know when you want to start the engine, and doesn't care, lol, its a computer

What it "sees" its a timing pulse from a Crank or Cam sensor when starter motor is engaged, and engine is turning over, and it uses that timing pulse to start spark and fuel injectors in time with the engine.

So I would look for info on 2007 3.9l crank or cam sensors

I have had 2003 Cadillac CTS, since new, on 3rd crank sensor, they seem to last about 5/6 years, not hard to replace so not a big deal, but does cause that unreliable no start when it starts to go, and no code right away, just slow start sometimes

 

[91stranger]

Well started messing with it again and it would start. was looking at fuses under the hood and saw the power wire for the fuse panel was corroded. So I figured what the hell and I cleaned those power connections and it started right up. Has start up numerous times now. So hopefully that was the issue. I don't own newer vehicles so it didn't even occur to me to check that when I cleaned the battery terminal and cables.

 

[RonD]

Good work