Loping idle on a 3406 A Cat.......

[mjstef]

What do i need to adjust to stop a loping idle? It is an early 70's Cat Engine in a W900.

 

[Ak HDM]

Does it have any other problems? Is it getting air into the fuel line from the tank to the transfer pump? Have you checked tansfer pump pressure? It should have about 35 psi at full rpm, minimum 25 psi @ full rpm & 10 psi @ low idle. How many miles on the engine? If it has alot, say6 or 700,000, the injection pump/ governor may need to be rebuilt. Hope this gives you a starting point.
Mike

 

[mjstef]

Does it have any other problems? Is it getting air into the fuel line from the tank to the transfer pump? Have you checked tansfer pump pressure? It should have about 35 psi at full rpm, minimum 25 psi @ full rpm & 10 psi @ low idle. How many miles on the engine? If it has alot, say6 or 700,000, the injection pump/ governor may need to be rebuilt. Hope this gives you a starting point.
Mike

doesn't seem like it's getting air. Fires right up at 40* with no aids. Runs 95MPH!! Fun truck to drive. Odometer says 936,000, Don't have any engine history but no leaks or blow-by and 60# oil pressure.....

 

[PackRat]

Does it do it all the time, or just when it's cold? One of our O/O's has a B model that lopes pretty good, until it builds a little heat.

 

[camara]

I see that you said it has 60 # oil pressure. I would suggest that you do the bottom end.....main & rod bearings. That engine likes about 90 psi. That engine is also very expensive to replace. The contractor I used to work for learned the hard way. A bearing roll was about $2100.....The whole engine cost him 14,500......TWICE!.....within a month. Think of it as cheap insurance.

 

[mjstef]

I see that you said it has 60 # oil pressure. I would suggest that you do the bottom end.....main & rod bearings. That engine likes about 90 psi. That engine is also very expensive to replace. The contractor I used to work for learned the hard way. A bearing roll was about $2100.....The whole engine cost him 14,500......TWICE!.....within a month. Think of it as cheap insurance.

60# is at idle, Runs 80-85# going down the road. My grandfather always said the difference between oil pressure at idle and operating speed tells the health of an engine. Kinda funny as a lot of the Detroits in heavy equipment i ran have been less than 10# at idle and around 60# at speed. They seem to run forever though! The Cat lopes when it is warm more than cold.

 

[DmaxEter]

When its running at idle, take a small hammer or wrench and tap the back side of the injection pump with it. If the lope stops then its the gov. in need of repair.

 

[Ak HDM]

You may have a weak or broken spring in the governor, maybe the dashpot spring. It can cause loping idle. if you can get your hands on a service manual, it will show how to adjust the dashpot. if you can't get a manual, I'll try to scan the page & post it for you. I would try adjusting the dashpot first, before tearing the governor apart.
Mike

 

[mjstef]

You may have a weak or broken spring in the governor, maybe the dashpot spring. It can cause loping idle. if you can get your hands on a service manual, it will show how to adjust the dashpot. if you can't get a manual, I'll try to scan the page & post it for you. I would try adjusting the dashpot first, before tearing the governor apart.
Mike

If you could find a manual that would be great!!

 

[DBogo]

http://cgi.ebay.com/ebaymotors/ws/e...ory=6032&item=7967382233&rd=1&ssPageName=WDVW

 

[Ak HDM]

mjstef, it will be tomorrow before i can get the info to you. My scanner went TU., damn thing was old. they never break til you need them.
Mike

 

[Ak HDM]

What is the serial number of the engine? Does it start with 92U, 4MG, or another number/letter combination? There is a difference in the governors, depending on the S.N.

 

[Ak HDM]

I got the info on the dashpot adjustment scanned.If the back of your governor doesn't look like this one, there is no adjustment for the dashpot,& the problem is internal. Hope this helps. The file is too big to be attached here, so I'll e-mail it to you.
Mike

 

[mjstef]

Sorry, Been on an out of town job for a few days. I'll try to get to the shop late this week to look at it. Thanks...