Question About My 2007 Freightliner 14L 60 Series Detroit

Can anybody tell me why my 2007 Freightliner with 14L 60 Series Detroit runs perfect in good weather & when its rainy it starts running rough & burns more fuel? This has me stumped?

First thing to check would be the wiring. It could be a bad ground or an exposed wire that once exposed to water is causing issues. Check the main harness at the firewall to make sure there's a good connection and nothing cracked to allow water in, then do a quick check of sensors for the same. You might also have the egr checked, sometimes moisture due to the weather will cause them to stick, hence the poor performance and fuel economy.

Thanks. I bought the ugly fix for the egr and have installed it. Does this truck by chance be known to have a issue with the wiring harness?

I wouldn't say an actual issue with the harness but it's an 8 year old truck and I'm guessing at least a half million miles on it so far? Vibration, weather, age, it all wears on parts.

Obviously something is getting wet. I would check anywhere there is water when it is doing it, crank sensor, map or maf, and electrical connectors, loose or frayed wiring etc. It might be that some sensor or wiring to a sensor gets wet thereby giving a false reading to the ECM, which cause the ECM to make improper adjustments to the injector timing. Does your check engine light come on when it does this?? If so have the code read while the check engine light is on to see what the error is. I would also try spraying each connector with a garden hose and see if I could cause the problem thereby discovering what is getting wet that causes it.

Phil