2005 yukon xl denali 6.0

[Yukonxljake]

Looking for info! Have a 2005 yukon xl denali with the 6.0. It has been in and out of the shop for misfire on the initial startup and after sitting for a bit. Once started it runs perfect. Not throwing codes either. The shop replaced the fuel pump, cam sensor, crank sensor, new intake seal, new plugs, new wires, rewired the ecm. They gave it back to me and said they couldn't figure it out! Any ideas? I'm assuming it's a fuel pressure issue, but besides the fuel pump it doesn't have a Fuel pressure regulator, so what else could it be? Thanks!

 

[ks03]

Sitting for a bit mean hot soak for 5 minutes, or parked in tall grass?
Could the shop duplicate the concern?
Misfire one one cyl only? Dead miss, or a lil rough? for how long after started?

 

[Yukonxljake]

Sitting over night, or for long enough for the fuel system to lose pressure some how. It's not a misfire when running only when going to start. It will turn over for 3 or so seconds without firing, then once I stop and turn it over again it fires right up.

 

[ks03]

If you turn the key on for a few seconds before cranking, does it start smoothly, or do the same thing?

 

[Yukonxljake]

Does the same thing unfortunately.

 

[ks03]

Connected a fuel pressure gauge and know if it is a fuel pressure issue?
Does it do this every or almost every morning?
Keep an eye out on the behavior of the security light.
Any modifications?
Pretty much grasping straws after that unless you get a code to come up sometime

 

[Yukonxljake]

Yeah pressure drops after sitting, I cut the security system out all together to see if that was the issue, but was not.

 

[ks03]

Tried leaving the fuel pressure gauge on to monitor when starting? Does the pressure come up from keying on?

Some vehicles seem like they don’t fire up the pump until you try cranking, I was thinking you could try to bump the starter and stop, see if the fuel pressure then came up, and then started normally… but I was thinking at some point they made a change and they’ll crank for a few seconds or until they start, even if you let off the key

 

[Yukonxljake]

Pressure does increase when it starts, then when you shut it off and go to start it up right after it starts fine. It only happens when it loses fuel pressure

 

[ks03]

I mean, have you left a fuel pressure gauge on overnight to see how it’s responding. Does keying on bring fuel pressure up, but then still starts hard?