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.
Injectos, Inj. harness, ECM replaced. Still problems.
Discussion in 'Trucks [ Eighteen Wheelers ]' started by RepoweredRookie, Aug 7, 2025 at 5:22 PM.
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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?Rideandrepair and RepoweredRookie Thank this. -
I'm assuming speed is not limited? If it is, to what speed, and is fuel economy incentive turned on in the ECM?
Rideandrepair and RepoweredRookie Thank this. -
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Big Road Skateboard Thanks this.
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Rideandrepair Thanks this.
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Or just forget the pedal and run it with the cruise control to test it.
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