Starts very rough then smooths out nicely

[BigRedWeather]

WHEN IT HAPPENS: sometimes in cold weather, but many times in cold weather it does not happen. It just seems to happen when it wants to, not because of any set of confitions.

WHAT HAPPENS: The truck will start and run kind of rough, like it is missing 2 cylinders, or very rough, like it is missing 5 cylinders. The amount of power it has corresponds to how many cyliners (imagine that!) it seems to be running on. When it is very rough, I have to put it in 4 wheel Lo to back it out of my gently sloping driveway.

WHEN IT STOPS: After I have driven for about 5 minutes at up to 2000 RMP it will run smooth as silk with all the power it normally has. It will do 90 on the interstate easily.

My injectors have 150k to 200k miles on them. I can't understand why they would operate so poorly and then run so smoothly.

It only runs rough for 5 minutes after I have started it.


Any ideas?

Thanks,


BigRedWeather

 

[Tim4R]

I have an idea that your oil is too old/too cold/too thick. Rotella T6 5w-40 cured that in mine. Yeah, it stinks to pay $25.00/gallon for motor oil but my truck is happier.

 

[BigRedWeather]

Hmmm. I run Rotella 15W40 (certainly thicker), and it is at 3500 miles. I change it every 5000. Since cold weather would make it thicker, I would think I would have this problem every time it gets cold, but I don't.

I have thought like you did, that this problem sounds like the fuel or oil (and hence the fuel) not getting to the injectors at the right pressure or volume. That could make it put only 20% of the fuel in the cylinders that was needed and cause the very rough running. But I don't know what would cause that under the conditions I mentioned. If this is the scenario when the engine heats up, or oil thins out or the stars line up, it runs smoothly with full power again.

Thanks for your post.


BigRedWeather

 

[94f450sd]

Your oil is fine.shouldn't being running anymore but 15/40.try cleaning the fpr screen if you haven't already.

 

[BJS]

I'm going to hazard that you have some poor connections at either the VC gasket or in the UVC Harnesses going to some glow plugs or possibly the injectors and once it warms up those poor connections make contact