# 3126 Cat engine: Knock and rough Idle.



## jakegypsum (Jan 25, 2002)

Anybody have an F-650 with a 3126b Cat engine? This morning when the truck was started, there was a nasty knock and rough idle. It seemed to clear when the gas pedal was pressed down but continued back to the knock and rough running at idle. After the truck ran for several minutes, the enigne knock and roughness cleared up. The truck ran fine all day. 
Anybody else ever have a situation like this? It's kind of similar to the way a diesel would run if it had air in the lines. (I have had situations like this in the past with other diesels with air in fuel). The truck is under warranty and I will probably have to persue it. Just curious if anybody else has had this happen? Sounds like it could be a minor thing and hopefully not major. Thanks Jake.


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## Brickman (Jun 17, 2002)

Sounds like water or air in the system.

Try changing the fuel filter. Or take it in for warranty. Good luck.


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## jakegypsum (Jan 25, 2002)

Thanks Brickman. I have to agree. It did it again the other day. I shut the truck and pumped the gas pedal several times. I started the truck back up and it ran fine. I think the truck is loosing prime. The fuel filter is not old at all but I agree that that could also be a problem. 
One thing I noticed and am not happy about is that this truck did not come through with a primer pump. There is a place for a typical CAT primer pump but there's nothing but a plate bolted in the place where one should be. I do have a new pump and pump gasket for a 3208 on the shelf and it looks like it will mount right up. I will probably mount the pump when I do the filter. Thanks for the reply. Jake.


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