2013 LC9 problem

[BarryKH]

2013 GMC Sierra crew cab 4X4 with LC9 engine. I am pretty sure the previous owner had the AFM programmed out of it since it has never been in 4 cyl mode. I can't even get it to go into it. The problem I'm having is sometimes when I start it, the engine starts and sounds like it's flooding out, never smell fuel, just barely runs for 2 or 3 seconds then idles normally. Sometimes I turn the switch off and restart it, sometimes it does it again, but mostly it starts and runs fine. Other times I've been driving and stop at a light, or for other reason and it won't take off, just barely runs, but I put it in neutral or park and turn it off and restart it and it's fine. I've checked it for codes and there are none, I disconnected the TPS and cleaned the throttle body, which wasn't bad at all, compared to a lot of them I've cleaned. Reconnected the TPS and drove the truck and it seemed better but still does the same thing. This is not happening every time I drive it, maybe once a week, maybe twice, if I drive it everyday. Could the TPS cause this without throwing a code or any lights flashing or coming on. I just bought a new TPS and spark plugs, but haven't installed them yet. The truck has 156,000 miles on it. I've only had it about six months.

 

Edited November 23, 2020 by BarryKH
More info

[newdude]

Codes?  Check engine light on?  Have you hooked a fuel pressure gauge up to it?

Edited November 16, 2020 by newdude

[MaverickZ71]

Check fuel pressure and scan for oxygen sensor/other codes?

[swathdiver]

5 hours ago, BarryKH said:

2013 GMC Sierra crew cab 4X4 with LC9 engine. I am pretty sure the previous owner had the AFM programmed out of it since it has never been in 4 cyl mode. I can't even get it to go into it. The problem I'm having is sometimes when I start it, the engine starts and sounds like it's flooding out, never smell fuel, just barely runs for 2 or 3 seconds then idles normally. Sometimes I turn the switch off and restart it, sometimes it does it again, but mostly it starts and runs fine. Other times I've been driving and stop at a light, or for other reason and it won't take off, just barely runs, but I put it in neutral or park and turn it off and restart it and it's fine. I've checked it for codes and there are none, I disconnected the TPS and cleaned the throttle body, which wasn't bad at all, compared to a lot of them I've cleaned. Reconnected the TPS and drove the truck and it seemed better but still does the same thing. This is not happening every time I drive it, maybe once a week, maybe twice, if I drive it everyday. Could the TPS cause this without throwing a code or any lights flashing or coming on. I just bought a new TPS and spark plugs, but haven't installed them yet. The truck has 156,000 miles on it. I've only had it about six months.

 

Sounds like a vacuum leak.  Got to get a scan tool on there and check the Long Term Fuel Trims and you can spray a water bottle or ether or propane or whatever along the intake ports at the heads and watch the trims or upstream O2 sensor readings and see how they react to it.  Mine is cranky if it hasn't been fired up in a few days but quickly settles down.  It has a minor vacuum leak somewhere.

[BarryKH]

On 11/16/2020 at 9:45 AM, BarryKH said:

2013 GMC Sierra crew cab 4X4 with LC9 engine. I am pretty sure the previous owner had the AFM programmed out of it since it has never been in 4 cyl mode. I can't even get it to go into it. The problem I'm having is sometimes when I start it, the engine starts and sounds like it's flooding out, never smell fuel, just barely runs for 2 or 3 seconds then idles normally. Sometimes I turn the switch off and restart it, sometimes it does it again, but mostly it starts and runs fine. Other times I've been driving and stop at a light, or for other reason and it won't take off, just barely runs, but I put it in neutral or park and turn it off and restart it and it's fine. I've checked it for codes and there are none, I disconnected the TPS and cleaned the throttle body, which wasn't bad at all, compared to a lot of them I've cleaned. Reconnected the TPS and drove the truck and it seemed better but still does the same thing. This is not happening every time I drive it, maybe once a week, maybe twice, if I drive it everyday. Could the TPS cause this without throwing a code or any lights flashing or coming on. I just bought a new TPS and spark plugs, but haven't installed them yet. The truck has 156,000 miles on it. I've only had it about six months.

 

I recently cleaned the throttle body and it seemed to help my problem. It seems as if the harder I drive it, the better it runs. Maybe it just likes to be hot rodded a little. I'm 72, but still like to feel that power and listen to the exhaust rumble and the roar of the throttle. I'm not as up to date on these engines as I was with the old 327, 350, and especially the 396 I had in the red on red 1966 SS396 Chevelle.