DOD Noise? Strange noise when starting cold.

[oesman]

Hey Guys,

So I noticed a noise when starting the car cold in the garage. I can't hear it when starting outdoors (other than a lifter noise for ~1 second on a cold start, before oil runs up). This is like a very very very light very high frequency rattle, think spray paint rattle, but very quiet and super high frequency. It seems to happen while it's idling at high RPM in open loop before the ECT and oxygen sensors reach operating temperature. I can sometimes find the same noise at about 850rpm with the throttle at idle when warm, in fact I can probably record it later by using hptuners/vcmscanner to hold the throttle open at that RPM while I go record under the hood. The interesting thing is, if you start the car remotely, it does it and quiets down, but as soon as you put the key in and turn it, it makes the noise again for maybe 1/2 second. Exactly at the moment you turn the key. I know our overhead

So the only things I can think of:

1. DOD / DOD lifter related. Is AFM triggered when key is turned?
2. Some sort of power draw and noise may be related to the alternator.

I know pushrod / OHV engines make all kinds of slight sewing machine noises, so maybe I'm being overly sensitive, but it's just rubbing me wrong. This combined with the alternator whine that all these cars seem to have on startup really grinds my gears.

[GeeAte]

Sounds like the fuel pump based on your description....some pumps are more noticable than others.

[oesman]

Ok so I made a video of this noise here:

http://www.youtube.com/watch?v=vRO6v9oM74Q&hd=1

I don't think it's the fuel pump, since I would hear it prime before the car started, not after it started. I'm just curious wtf that noise is. In this clip I couldn't get an extended instance of the noise, each time its real short. When the car starts the noise blends into the whine of the alternator, and when I put the key in it's just like 1/4 of a second blip of it.

[norm8332]

Could be the electric fans is my guess.

[johnbell2]

Sounds like climate control cycle on start up. Doesn't sound like anything bad in your video. Have you changed your cabin filter yet?

[Crazy Paul]

Is AFM triggered when key is turned?
No.
"The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications."


Other reasons V4 mode will not happen while driving.

Cylinder Deactivation Inhibit Reasons
Listed below are the powertrain conditions that will inhibit V4 mode, while operating under light load driving conditions:

• Engine manifold vacuum low

• Brake booster vacuum pressure low

• Accelerator pedal position rate of increase too high, electronic throttle control

• Accelerator pedal position too high, electronic throttle control

• Ignition voltage out of range

• Engine oil pressure out of range

• Engine oil temperature out of range

• Engine RPM out of range

• Transmission gear incorrect

• Transmission range incorrect

• Transmission gear shift in progress

• All cylinders activated via scan tool output control

• Minimum time in V8 mode not met

• Maximum V4 mode time exceeded

• Engine oil aeration present

• Decel fuel cutoff active

• Fuel shut-off timer active

• Minimum heater temp low, HVAC system

• Reduced engine power active, electronic throttle control

• Brake torque management active

• Axle torque limiting active

• Engine metal over temperature protection active

• Catalytic converter over temperature protection active

• Piston protection active, knock detected

• Hot coolant mode active

• Engine over speed protection active



• Fault Active or Fault Pending--cylinder deactivation is disabled for the following faults:

- Brake Booster Vacuum Sensor

- Manifold Absolute Pressure Sensor

- Engine Oil Pressure Sensor

- Engine Coolant Temperature Sensor

- Vehicle Speed Sensor

- Crankshaft Position Sensor

- Engine Misfire Detected

- Cylinder Deactivation Solenoid Driver Circuit

[oesman]

Could be the electric fans is my guess.

I can hear when those start up, it's a different sound and are real loud, they shouldn't be starting up at that temperature yet. But thanks :)!


Sounds like climate control cycle on start up. Doesn't sound like anything bad in your video. Have you changed your cabin filter yet?

I think that's what it is actually. Because I realized I had my climate control off when I parked the car (cool night, i like driving with windows down) and the remote start turns it on, so the key would be turning it off when you put it in. I think it's exactly what it is. The cabin filter was one of the first things I replaced :D.


No.
"The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications."

That's awesome info, thank you!

[johnbell2]

Yep, if you have a fresh cabin filter the climate control can pull more air and it's pretty loud. Every so often I guess one right :)