I have two issues with my 2000 6.8L gas excursion. Neither seem to be causing any harm, but I'm hoping someone has experienced this and knows the solution.

1st issue - While its raining, or even just really humid, on a cold startup, my truck runs rough. it almost feels like it wants to die, but doesn't. After about a 1000 feet down the road, it runs normal.

2nd issue - I've started noticing that almost always, I here a whirring type of sound coming from the back. It is not from the brakes, as they are new and the sound is best heard at a complete stop. The sound lasts for about 3 seconds and then repeats after a few more seconds. At first I thought it was the coolant circulating through the pipes that run to the rear heater unit, since the sound sounds a lot like fluid flowing through a pipe. However, my coolant level is normal and the system is tight and I have not had to add any since the only major overhaul in January. At idle, the engine sounds like it isn't idling at a constant rpm, but more like a slight up and down in rpm, but the amount is so slight, it doesn't register on the tach. The only other thing that comes to mind is the fuel pump. Is this sound a sound of imminent failure of the fuel pump? Or is it normal? The truck otherwise runs great at any speed and pulls my boat as well as I would expect it to.

Thanks for any guidance.

 

The whirring could be the blower motor back there.

 

Even with the blower motor off, the noise is still there.

 

Not that this is any help...

My truck has the same "irregular heartbeat" with the rpm going up and down slightly.

I always figured it has something to do with the 400k+ km on it.

It seems to smooth be somewhat smoother when it's warm

 

1. Have you checked the Idle Air Control valve? Ours smoothed up to the point it's hard to tell it's running when I changed the IAC. When it's humid does it feel like a distinct misfire or just running rough? If the spark plug boots haven't been changed in awhile (50k) you may have one that is deteriorated. You can see misfires in the raw OBD data when a code is not set to help isolate down to a particular cylinder/boot.
2. When the A/C is ON the engine coolant flow to the rear should be shut down by the heater control valve. You may be hearing A/C refrigerant being metered thru the expansion valve in the rear lines. Is the A/C ON/OFF when this is happening?

 

1. I'll have to look into the IAC valve. However its not the plug boots or the coils. I recently replaced the head gaskets. New plugs, boots and coils were put on. This issue existed both before and after replacing those ignition parts.

2. Living in Alaska and all, I never thought to check the A/C, I never use it. On my way home yesterday I tried it. When the **** for the directing the air was turned off, the sound when away. However the sound was present whether the A/C or other positions were selected. My experience with the heating and air systems is limited so Ill have to look into that. I don't suppose you know what the name of the part that controls the flow of coolant to the back is, do you? Ill probably disconnect the A/C all together since I don't use it to try and eliminate it from the equation all together.