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C7 Cat starts hard.

Logger72

Active Member
Joined
Jun 20, 2018
Messages
27
Location
Pa.
I have a Cat C7 in a FL 80 , after it sits a day or so it is hard to start, it fires but only on a couple of cylinders, when it finally starts it blows blue smoke, after that it runs fine. Any ideas what may be causing this? Thanks
 

Coaldust

Senior Member
Joined
May 9, 2011
Messages
3,471
Location
North of the 60
Occupation
Cargo Tanks, ULSD, RUG, Methanol, LPG
Yeah. The plastic fuel lines and quick disconnect fittings that Freightliner used are horrible. Cat issued a number of Bulletins on the subject. They will leak air, but not leak fuel. Installing a Cat hand-primer pump is a nice addition.

The restriction fitting, fuel return check valve thingy on the cylinder head can be an issue, as well.
 

JPV

Senior Member
Joined
Aug 20, 2015
Messages
756
Location
S.W. Washington
If that stuff checks out ok it could be the temp sensor for the engine ecm is bad. You will have to plug something in to monitor it but if it is reading hot when the engine is cold it will start like that. I have seen that before on a C7 in an excavator. After it started the sensor would snap out of it and work properly. I am not familiar with whether or not Freightliner uses the computer sensor for the temp guage on the dash or a separate sensor, if they use the same sensor just watch the temp guage to make sure it is reading right when cold. Paccar uses a separate sending unit for the dash.
 
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