NEED HELP Rough idle after parked on incline

[Sp00nix]

Hello all!

I'm new to the trailblazer community and I have my first question for you guys.

When ever the TB is parked facing down hill for any longer than a couple of hours the truck will start and have a rough idle for a minute or two. It clears right up and goes back to it's buttery smooth operation. I don't notice and smells or smoke, and no CEL or codes.

I have already taken the into apart and cleaned everything, including the throttle body.

Attached is how I usually park it.

2006 LS, 4.2, 4X4 245,000 miles.

Thanks!

 

[Maverick6587]

Welcome to GMTnation!

Do you have a scanner with the ability to view misfires or a fuel pressure gauge?
I assume you do not have this issue parked in the other direction?

I'm thinking (guessing) that it's a fuel issue. After a few hours your fuel lines will lose fuel pressure. Your fuel pump is at the back of the fuel tank. With your vehicle pointing downhill, that puts a lot the fuel in the front of the tank.

I'm guessing that the fuel pump is losing the quart or so of fuel that sits in the pump itself and it would take a few seconds to refill that once the trailblazer is restarted. Again, totally guessing here.

When you're parked facing downhill. What level does the fuel gauge say that you have left?
I see that you don't have any CEL on now. Have you had any recent CEL codes though, maybe vacuum?

Edit* Was this happening before you cleaned the throttle body? If not, did you unplug the battery for at least 30 minutes before you started the trailblazer back up? If not, I would unplug the battery for 30 minutes to reset the computer.

 

[Sp00nix]

Hey Maverick,

Thanks for the reply.

I have Torque with a Bluetooth adapter that I use, with all the GM PID extensions. I never tried monitoring it during a start, but i should try that next.

As for stored codes, none at all. No current, snapshots or any in history.

I usually keep at least a half tank in my vehicles at all times. That was one of my earlier thoughts, either that or maybe some oil was sitting toward the front of the head and maybe getting passed valve stem seals?

Just another thought, maybe oil is settling in a way that it is getting into one of the columns for the spark plugs? But i feel that would have a longer lasting effect.

Welcome to GMTnation!

Do you have a scanner with the ability to view misfires or a fuel pressure gauge?
I assume you do not have this issue parked in the other direction?

I'm thinking (guessing) that it's a fuel issue. After a few hours your fuel lines will lose fuel pressure. Your fuel pump is at the back of the fuel tank. With your vehicle pointing downhill, that puts a lot the fuel in the front of the tank.

I'm guessing that the fuel pump is losing the quart or so of fuel that sits in the pump itself and it would take a few seconds to refill that once the trailblazer is restarted. Again, totally guessing here.

When you're parked facing downhill. What level does the fuel gauge say that you have left?
I see that you don't have any CEL on now. Have you had any recent CEL codes though, maybe vacuum?

Edit* Was this happening before you cleaned the throttle body? If not, did you unplug the battery for at least 30 minutes before you started the trailblazer back up? If not, I would unplug the battery for 30 minutes to reset the computer.

 

[Mooseman]

A check of fuel pressure would be good also.

 

[Kelly@PCMofNC]

I second the fuel pressure check. You can rent a gauge from autozone. Hook it up and tape it to the windshield so you can see it from the truck. Park it in the position that triggers it, and then watch the FP when you try to start it. That is what it sounds like to me!

 

[Sp00nix]

I have a gauge, so I'll hook it up and set up my phone to data log this weekend and see what I get.

Thanks!