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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8628
Experience:  I am ASE Master Truck Certified.
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Weve got a 3406b here, serial #3zj2222, the customer brought

Customer Question

weve got a 3406b here, serial #3zj2222, the customer brought it in for new injectors, so we put a set in from cat, the truck idles fine and runs fine at wot, but between about 1200 and 2000 rpm it misses, pings and blows a bunch of white smoke, once you get past that rpm range it clears out and pulls hard. any ideas?
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.

Thanks for asking your question. I can help you with this.

Was it does not this before replacing the injectors?

Customer: replied 1 year ago.
it ran about the same
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

There are two things I have seen cause this.

The first is the flyweights in the timing advance are hanging.

Second is the flyweights in the fuel system governor are hanging.

When this happens, the engine will run like this. To confirm the timing advance and the governor would need to be removed and inspected. If they are worn, it will be easy to see.

Please reply back if you need more help or have more questions. I am happy to assist.

Customer: replied 1 year ago.
does the injector pump have to come off, or where do I look next?
Expert:  Cat Man replied 1 year ago.

No the pump does not have to come off. Both the timing advance on the front can come off as well as the rear governor assembly. If on is worn, both most likely need rebuilt.

Customer: replied 1 year ago.
should I take that front cover off and take a peek?
Expert:  Cat Man replied 1 year ago.

Yes you can take the timing advance cover off. If you have a C pointed advance you can see flyweights. If you have a true B the advance will need to be disassembled.

Customer: replied 1 year ago.
what am I looking for when I get in there?
Expert:  Cat Man replied 1 year ago.

If the flyweights are worn. The contacts points of the flyweight will have worn a groove or hole in the race it rides on. If there is a groove or race, it will hang

Customer: replied 1 year ago.
ok I got the cover off, I pried the weights forward with a screwdriver, should that assembly move freely? it seems to bind up a little bit. then I started it up and watched, just as soon as the weights move forward the engine runs fine
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

No it will not move freely. You may need to remove and disassemble to see the wear.

Customer: replied 1 year ago.
at what rpm should that start moving forward?
Expert:  Cat Man replied 1 year ago.

Normally between 1000 and 1600.

Customer: replied 1 year ago.
it doesn't move forward till about 1800 rpm
Expert:  Cat Man replied 1 year ago.

Thanks for the information. That sounds like the advance is slipping. When this happens, the carrier assembly in the advance needs to be replaced. When they go bad. They slip.

Expert:  Cat Man replied 1 year ago.

Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.

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