2003 7.8 loss of power

[riverrat]

Hi Brand new to your forum hope you can help.I have an 2003 C-6500 Chevy. It has about 115000 miles on it. I got it 86000 on it. It always has been hard to start only when it has been sitting more then 5 days or so. No fuel leaks serviced every 6000 miles with oil change and fuel filter. Lately it has loss of power not at take off but after 65 miles per hour. It has Duel 45 gal. fuel tanks on it that draw independent and when we fill them up the drivers side tank always needs about 15 gal. more than passenger side. Is there lifter pumps in the tanks or maybe a valve where they come together? No check lights on. Thanks for your help It has 7.8 Durmax

[Mark Rinker]

I would first rule out intake air or exhaust restrictions. If none, then its a fuel supply problem.

Could be pump is weak, fuel flow is restricted, or both.

What happens after 65mph? Does power flatten, shudders, chugging, please explain.

Any black smoke under acceleration? White smoke at idle? Is mileage lower than normal?

[riverrat]

Thanks for your help troubleshooting. After 65 MPH. It just flattens out and hard to get over it on flat road. Before no problem cruising at 75 MPH. Air cleaner has been replaced. There is a flat spot on exhaust pipe right before muffler but not to bad and has been there since it was bought. No smoke black or white no coolant loss no running hot.

[Mark Rinker]

Sounds like lack of fuel. Pump on the way out? Sprays not spraying like they used to? What is mileage doing?

[deepblue hawaii]

did you ever figure it out ? mine is doing same little by little over last year im looking for injector pump