Hey Guys, 1999 Freightliner Century 12.7 DDEC 4, pre-emissions. All injectors, injector harness, and ECM replaced. I have done 2 identical loads. The truck will not go over 67 mph top speed, but has moments where it will go 72 mph for 10 minutes, then drops back to 67 mph. You can feel it at the pedal driving 67, and then push the pedal hard and you can feel acceleration. Anyone got any ideas? Thank you for any help.
I'd start with driving with pro link or laptop viewing TPS % and counts. If anything changes on the laptop you'll see it. If nothing there, any faults? Don't overlook a fuel supply/return issue. Any smoke?
I'm assuming speed is not limited? If it is, to what speed, and is fuel economy incentive turned on in the ECM?
No smoke, and no faults. The TPS sensor is a great idea. Gonna try replacing it since I don’t have the DDDL software. Great idea, thank you Skateboard!
That’s the only problem, they didn’t ask me about top speed preferences or limits. Getting about same fuel economy as with old injectors at 6 mpg at 67 mph. Lets try TPS and I’ll report back. TY.
TPS aren't cheap anymore. Dealership might tell ya you'll have to but a new pedal assembly. I'd grab a test one from a junk yard first
