Extended engine crank time on my 2017 6 liter

[SierraHD17]

So far it's intermittent which is why I don't want to be bothered with GM..... they are just going to say it's "normal" or "cannot replicate customer condition" unless I do the leg work for them.  So please refrain from the "take it in" comments...... thanks!

 

In recent times every once and a while the truck will crank a lot longer before starting.  Usually it's maybe 2 revolutions and it's running but then this sounds like the direct injected trucks and it will crank 6 or 8 times to get going.  I added fuel pressure to the scanner and it builds 550 kpa and holds it engine off but key on.  However taking it to start it will crank the longer duration before it lights off.  I thought it was only after sitting overnight but I just got it to do it with the truck just running, shut off and then restarted.  The scanner showed normal looking fuel pressure the entire time.  

 

Has anyone else had an issue or is there a TSB floating around for it?  

[SierraHD17]

For reference this only has occurred since the weather has warmed, not that I think it's related.  This morning the coolant temp when I got the truck to do it was sitting at 50 C or 122 F so it's not a "cold start" issue per say.

[Logan Lanfear]

Well if you have good fuel it must be a spark issue or fuel delivery issue.  How many miles are on the truck?  I had a similar issue when my fuel pump was putting out too much pressure.  Once it does start, does it sputter or does it light right off?

[SierraHD17]

Truck has under 20000 miles on it.  Fuel pressure drops on engine crank to around 400 kpa which is basically 60 lbs.  It fires normally just sometimes takes longer than others.  Talking with others they are mentioning the cam phaser being out of position on start... but that should set a code which i am not seeing.

[bgbdwlf2500]

5 minutes ago, SierraHD17 said:

Truck has under 20000 miles on it.  Fuel pressure drops on engine crank to around 400 kpa which is basically 60 lbs.  It fires normally just sometimes takes longer than others.  Talking with others they are mentioning the cam phaser being out of position on start... but that should set a code which i am not seeing.

DId you go from 87 to E85 recently? only time my truck has acted like that was when I hadn't read the ethanol content correctly

[SierraHD17]

Truck runs 94 octane premium and is custom tuned.  Ethanol % is around 11% like it should be with that fuel.

 

[bgbdwlf2500]

5 minutes ago, SierraHD17 said:

Truck runs 94 octane premium and is custom tuned.  Ethanol % is around 11% like it should be with that fuel.

 

gotcha, just a thought as mine had very similar symptoms when it calculated the % wrong

[SierraHD17]

This one's physical alcohol sensor seems pretty bang on.  No such thing as e85 here so the most it sees a swing of is null to 10%.

[Colossus]

I had shorter crank time when running 91 octane vs 87 octane here at 5000ft.  (would be 93 vs 89 down at sea level) 

[redwngr]

Alcohol sensor on a 6.0??

[SierraHD17]

Yeah it's under the cab in the fuel line.  It's not a gmt900 with its inferred bullshit.

[4x4Pete]

Have yoy tried it with a stock tune?  I doubt it would make a difference but rule it out anyway.  

[SierraHD17]

It's not tune related considering i have rewrote it and it's been on the truck since I bought it 8 months ago.  It's like the ops at work blaming a plc program lol.... they don't just go bad.  Hasn't done it in a couple days now so who knows what it's problem is or was.

[mjm-1957]

If your truck is a 2017 l96 it is flex fuel correct? Read document ID #4518520 . The second paragraph details the fuel delivery system and yours does not have a fuel composition sensor.

[i82much]

Maybe it's not related to the tune, but once you dork with it, there's a good chance the dealer will blame it on the tune.