Sam Loffler

2006 stock lq4 in 1500hd Silverado

Alright, this is where I'm at.dum

Had to rebuild my 6.0 after a piston blew up. Everything is back together and runs great. The only problem I have is this:

Truck can sit all week and start normally the first time. If I shut it off to get gas or something that takes less than about 30 mins, it starts fine. If I drive it, and it sits for any more than about 45 mins, it will do one of two things. It will either crank and crank and crank until I stab the gas and it starts or it will give me a slow crank and catch and sputter for a second. After the gas stab or sputter, it runs great.dum

I have cleaned the maf and the throttle body. The injectors were cleaned and flow tested for the rebuild 3500 miles ago. Plugs are new. No vacuum leaks.dum

I have been turning the key to let the pump cycle before starting, but that doesn't seem to make a difference.dum

I read it could be the starter getting hot and weak, so there's a heat shield on there now that hasn't changed anything.dum

I put a gauge on the fuel rail and it was right at 60 psi with key on engine off. It bled down to about 45 psi after 20 mins or so. I was told this is normal. What do you guys think?

I even considered something with my rebuild expanding with the heat and not turning as well when warm, but that would mean it would be harder to start right after shut down.dum

Does anyone have any insight? This on an 06, so thedumfueldumfilter, pump, regulator, and check valve are all inside the tank, correct?

thunderstruck507

iTrader: (18)

My truck has been the same thing since I replaced the fuel pump and tuned it.

So I'm in for ideas. My car sometimes does the same thing.

Sam Loffler

I got all excited when someone replied. Haha

I keep thinking through scenarios like leaky injectors or bad pump but eventually get to where those don't make sense.

I've had other suggest a bad sensor, but I don't know which could cause this kind of thing....

I'm close to dropping it with the dealer, but I'm sure they miraculously wont be able to reproduce the issue...

Let me know if you figure something out. I'm gonna double check my injectors and rail pressures tonight after work.

thunderstruck507

iTrader: (18)

My thoughts are leaky injector or low IAC counts at warm cranking. If I figure out I will post.

sweet99ss

iTrader: (41)

Very weird. Looks like you checked everything important. Did you have the fuel pressure gaige on ot when it was having the problem?

Sam Loffler

I haven't had the gauge on while the hard start has been happening. My plan is to double check pressures and leak down tonight. Clamp off the fuel line and see if it leaks down on the rail side or the tank side and go from there.

I'll go drive it for a bit and try to replicate the hard start with a gauge on it too.

Old Geezer

iTrader: (3)

"I keep thinking through scenarios like leaky injectors "
How many miles on the injs? I occasionally get injs that have hi miles, that do what you are describing...

Sam Loffler

Could be up to 135k. I got the truck at about 130k so I don't know if they have ever been replaced.

When I did the rebuild I had them cleaned and tested and the test looked good. The results are in the glove box at home. I'll put a picture up this evening. As I recall though, they all passed the test.

I appreciate the ideas, guys! I'll get back to you with results tonight or tomorrow morning.

Sam Loffler

Progress so far...
Injectors are not leaking.
Key on engine off rail psi is 58.
Engine on psi was at 60-62ish

Pressure drops down to 30 in 45 mins when its off. Is this normal?

I went on a short drive and let er sit for a while but couldn't reproduce the hard start this time, of course. Psi was back up at 58 imediatly when I turned key to on.

I did relocate the main ground, as I had it on the waterpump/salt bracket instead of the block. Its on the block now. What a pain in the *** with all the oil cooler crap...

The ground that hooks on at the same place is for the injectors, I think... Anyway, that got moved too. And broken. And fixed.

Long story short, I can rule out the injectors leaking.

If the fuel pressure leak down is normal, I'm confident the pump assembly is fine.

Maybe a sensor? Maybe I'll get really lucky and the grounding gymnastics fixed me...

robsblown427

Just throwing this out there but are you sure its not your cam sensor? Your rail/fuel pressure looks good...

Sam Loffler

I'm not sure its not the can sensor. I don't know how I would test that.

It looks like it's narrowed down to something along those lines though...

kpeters59

I don't know if this will help and am way not any kind of expert, but I found this info while researching for a returnless 'upgrade' on my 5.3l:


Clear Flood Mode: If the engine floods, the engine can be cleared by pressing the accelerator pedal down to the floor and then cranking the engine. When the throttle position sensor is at wide open throttle, the PCM reduces the fuel injector pulse width in order to increase the air/fuel ratio. The PCM maintains this injector rate as long as the throttle stays wide open and engine speed is below a predetermined rpm. If the throttle is not held wide open, the PCM returns to the normal starting mode.


My injectors seem to be leaking along with an 'unfinished' fuel system so that is kinda why I'm (considering) doing the swap. It also smells bad (rich) and occasionally won't restart properly.

HTH

-KP