Cranks but slow to start

[alvocado]

2011 GMC Yukon 5.3l, 194k miles. Recently started exhibiting long crank time and slow to start. The engine is cranking indicating the starter is working and the battery is  charged. If I back off the key then try again, the engine starts and runs fine. I did notice that the starter continued to crank without rotating the key past ON and I had to return the key to off for it to stop. 
 

it’s either air, fuel or spark. I don’t have a fuel guage to check pressure at the rail but will pick one up if that’s an appropriate troubleshooting step. Does this sound like a fuel pump that is going out based on the mileage? I’m not aware of a fuel filter on this gen Yukon.
 

Any advice on troubleshooting sequence would be appreciated. 

[Jsdirt]

The problem with this generation truck is, there's a computer in the mix. Nothing simple like the earlier days of just power, ground, a relay, and the control side of said relay. That was too simple for automakers. They wanted to save a buck on fuel filters and return lines. Now you've got a FSCM - fuel system control module which varies output based on demand, which eliminates the return side of things.

 

Same things still apply to the pump - still needs good power, ground, and functioning check valves in the pump itself, but the computer throws a whole other world of possible failure modes. If the FSCM fails, you can't just replace it - it has to be programmed to the vehicle with a J-box and subscription (More $$$ to GM).

 

All that said, a long crank / slow-to-fire symptom is usually a check valve in the pump that can't hold fuel pressure when the vehicle is off. So, every time you turn the key to start, the pump has to refill that whole line again - that's why the long crank time. Air and spark have nothing to do with that issue.

 

On the point of what mileage things fail at, today, it's a complete crapshoot. Some don't even make it off the lot, while others go longer than the engine or transmission does. Nobody knows. It's the luck of the draw as to what you'll get. On my '07, that was one of the few things on that truck that lasted. Everything else failed during warranty, or before 100k.

 

Get a pressure gauge on there somehow and see if pressure is bleeding off whenever you kill the engine. If it is, you've found your problem, and the only fix is a new pump assembly.

 

EDIT: Just remembered on this one you can use the scan tool for fuel pressure, so long as the sensor is reading correctly. 

Edited July 30, 2023 by Jsdirt

[alvocado]

The condition is consistently occurring on cold start and there is a noticeable gas smell inside and outside the truck. I think this indicates a fuel pressure loss while sitting since it starts fine when warm. There is no sign of fuel leaking.

[Jsdirt]

Any codes? If your smelling fuel, there should be an EVAP code either pending, current, or history in the PCM.

[alvocado]

Confirmed: cracked plastic on the fuel pump assembly. Replaced the entire assembly and it's resolved. 

[Jsdirt]

Good deal.

 

Would be nice if GM could make a friggin pump that lasts. They used metal, it rusted. They use plastic, it cracks! You can't win today.

 

Meanwhile, my '86 Grand Marquis just turned over 300,000 miles on Wednesday morning, on the ORIGINAL in-tank electric fuel pump (and the ENTIRE driveline, minus the u-joints)! Was the 1st year of multiport injection. 37 years, 300k, ZERO LEAKS!!! Proof that it can be done. Automakers just refuse to.

 

Lately GM can't even get their 6.2 to make it to the first oil change without spitting rods out the oil pan!!

Edited August 4, 2023 by Jsdirt

[Princess]

I have a 2013 Yukon gmc Denali 6.2 L my Yukon will start for a little bit then turn off can u please tell what is really wrong with my car

[Jsdirt]

Could be any number of things from a fuel pump problem to the security system, and anything in between. If you recently had a new key made, that would be where I'd start. If not you'll need to get someone to do some diagnostic troubleshooting and then post what they found here. Too little info to even guess at the problem here. 

[Grift_40]

I have a 2013 Denali having similar issue long cranks after sitting. Have replaced fuel pump twice plugs and wires twice and still have a long crank to start. Runs perfect once started and  I’ve noticed that if I press the pedal to the floor when cranking will fire right up. 
 

I need some other opinions on possible causes. I’m almost convinced that it could be a bad injector leaking but don’t want to keep throwing money at it. 
 

also just to add I do not have a gas smell outside or inside the vehicle. Just smells like it runs really rich. 

Edited March 7, 2025 by Grift_40

[CamGTP]

Hook the truck up to a nice scan tool and see what the alcohol content is reading. If that value is way out in left field, it will start hard.

 

If all you run is regular unleaded fuel it should be reading right around 10% alcohol content. If the reading is way up around 30 or 40%, the alcohol percentage needs to be reset with a scan tool so it can relearn. I've seen this happen many times.

 

Not saying that this is the exact issue but you really should check in it because it will cause those same problems on the first start.

[alvocado]

You have three variables: air, fuel, spark. Based on the quick start with the pedal comment, I would focus on fuel delivery first. Put a gauge on the fuel rail. 

[Jsdirt]

Flooring a GM vehicle puts it in "clear flood mode". Meaning it kills power to all the injectors. That tells me you've got too much fuel at start up - in other words, probably a leaky injector.

 

If you can get ahold of a bi-directional scan tool and a pressure gauge, you can perform an injector drop test to figure out exactly which one isn't holding.

[Silverado4x4]

Just to add to the above comments pull out the dipstick and smell the oil to see if it smells like gas a gas smell lean towards leaking injector or could be a malfunction fuel pressure regulator. Get it scanned for any code as said.