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2011 Chevy Silverado Rough Start HELP

bassmaster

By bassmaster
in Ask A GM Technician

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bassmaster Enthusiast

bassmaster

Posted
Posted

I have a 2011 Chevy Silverado 1500 with the 4.8l V8 and have
recently been encountering a problem with it. When I go to crank the truck, it
half way cranks, then fires and the engine bogs down to about 200 rpm's for a
second or two then jumps up to about 1200 rpm's normally then slowly levels out
like it should. There’s no other idling problems that are happening. It runs
normal after that happens when I first crank it. It's not causing the check
engine light to come on either. It seems to do it worse the colder it is
outside but it only does it when the engine is cold. After the first start in
the morning, it won’t do it unless it sets for about 8 hours or so. It's almost
as if I was letting go of the key too early when cranking but that’s not
possible on these trucks because they have a set cranking time that you can't
control. I run good quality 87 octane gas through it. I have also tried fuel
injector cleaner and fuel treatment but that hasn't changed anything. Could it
possibly be the e85 sensor that adjusts the amount of alcohol to fuel ratio to
the engine? Someone else said it could possibly be the camshaft sensor because
it sounds as if not all the cylinders are firing during cranking. Or could it
be the fuel pressure in the system because after it sets for a couple of hours
it does the same thing. I made sure the fuel pump was working fine by listening
to it as I switched the truck to the on position. Would the battery have any
effect on it because I checked the battery before cranking and it read about
12.1 volts? The meter on the dash reads about 10 volts before cranking the
truck by just switching it on. Once it cranks, it reads above 14 volts when
being charged by the alternator. It has the original battery in it still, and
the truck has a little over 59,000 miles on it. It has really been bothering me
because this is the only problem I have had with the truck, so I will probably
be taking it to the dealership this week to have it looked at. I haven't really heard this issue discussed
anywhere online, so was going to check here to see if anyone knew any
suggestions before taking it in. Thanks!



Here is the link to the video on YouTube that I recorded it
doing the problem.



 



Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

I would take a look at the IAC motor/ports. You may find a load of crap in the port and around the pintle valve. Get some good carb spray to clean it with. Engine almost sounds like IAC is not in the correct position. IAC motors used to use something like a micro switch to tell computer the pintle valve has hit bottom in the port, then computer uses that for its base setting. If you have crap in that area, the pintle may say it is bottomed out, but in reality it could be no where near closed, and that throws the computer off.

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