2013 Denali rough start and poor acceleration

[DaninOK]

I’ve scoured the internets for solutions and been to 3 local mechanics and spent almost as much as I want to spend. Wife’s Denali XL developed a lifter tick last winter. Suspected collapsed afm lifter. Found a guy who talked a good game on knowledge and cost and dropped it off. Replaced camshaft, lifters, VLOM, valve guide seals, intake manifold, then pulled engine to fix rear main seal leak, replaced torque converter, and I a purge line. Drove fine for 3 months, then developed a spot around 1,000 rpm’s where it would “get stuck”. Apply more pedal, and nothing, until you apply enough pedal for a downshift, then it screams like normal. Took it back and got a new gas pedal, replaced front left wheel hub bearing (only code it had) and no fix. Took it to the local guru, had it for 4 days and called to report he couldn’t figure it out. Fuel trim, pressure, everything seems great. First shop replaced VLOM with Delco unit, replaces oil pressure relief valve, and installs second melling high volume oil pump. Does plugs and wires, catalytic converters. Another pedal. Tried a new throttle body. And still, same driving characteristics. It’s been sounding rough on first startup in the morning but but no blue smoke. Today, first time ever, it took 5 tries to start. I was set on torque converter lockup problem until this. What in the world is left??

 

[DaninOK]

I’ve scoured the internets for solutions and been to 3 local mechanics and spent almost as much as I want to spend. Wife’s Denali XL developed a lifter tick last winter. Suspected collapsed afm lifter. Found a guy who talked a good game on knowledge and cost and dropped it off. Replaced camshaft, lifters, VLOM, valve guide seals, intake manifold, then pulled engine to fix rear main seal leak, replaced torque converter, and I a purge line. Drove fine for 3 months, then developed a spot around 1,000 rpm’s where it would “get stuck”. Apply more pedal, and nothing, until you apply enough pedal for a downshift, then it screams like normal. Took it back and got a new gas pedal, replaced front left wheel hub bearing (only code it had) and no fix. Took it to the local guru, had it for 4 days and called to report he couldn’t figure it out. Fuel trim, pressure, everything seems great. First shop replaced VLOM with Delco unit, replaces oil pressure relief valve, and installs second melling high volume oil pump. Does plugs and wires, catalytic converters. Another pedal. Tried a new throttle body. And still, same driving characteristics. It’s been sounding rough on first startup in the morning but but no blue smoke. Today, first time ever, it took 5 tries to start. I was set on torque converter lockup problem until this. What in the world is left??

Oh yeah, he also installed a new fuel pump.

 

[petethepug]

1st verify what brand of fuel pump was installed. If the f/p is OEM, GM or Bosch that’s covered. If not, it’s should be on the lookout for what generic Chinese knock offs are known for, creating havoc in situations like this.

Did the shop replace the carbon canister? If not, replace it now and verify if it has exploded all its carbon pellets into the fuel tank. Regardless, blow out the vapor and fuel lines and inspect for carbon pellets.

Did the tech wipe out the fuel tank and check for carbon pellets when it was out?

 

[j91z28d1]

wow. I got nothing.

At this point, they have thrown so many parts at it, you can't rule out that one of the replacement parts are bad.


and you make it do the stuck at one rpm thing? I'd be curious what the fuel pressure is doing at the point.

 

[Fless]

Today, first time ever, it took 5 tries to start.

Can you describe the "no start" condition a little deeper? A lot of questions (some spitball...) and assumptions here, so please correct or clarify as needed.

I assume it cranks over fine, but for how long is it cranking each time? I assume that the operator stops cranking, then start cranking it again? 5 times?

I would definitely recommend a complete fuel pressure test and monitoring: KOEO and monitoring while running, especially at the rpm point of issue as @j91z28d1 noted.

If the purge valve is stuck open or is intermittent, that can cause flooding / hard start. If the fuel pressure tests are good, next time it has the crank-no-start try using the clear flood mode by flooring the accelerator pedal when attempting to start. That turns off the fuel supply until the pedal is let up.

You might also look at individual cylinder misfires with a good scan tool. Maybe do an injector balance test.

Also, to rule it out, have a CASE relearn done (crankshaft correlation). Quick procedure.

Have you looked at fuel trims to see what they look like?

 

[petethepug]

It’s a lot easier to go for a drive with the person who has the diagnostic tool in their lap while they are in your passenger seat.

Until then, ya got nothing. Everyone could be right or no one could have the answer to what’s going on. That’s forum diagnostics for you. This far in you need data and someone who can correctly interpret it.