Flat Work Posted September 29, 2017 Share Posted September 29, 2017 When I bought the ole' girl, she had spent her life in the Texas oil field. The VGT vanes were stuck. With some penetrating oil and a pry bar, I slowly got it working. The turbo sounds great. It responds perfectly with the throttle. Or seems to. But the truck is sluggish on the low end. The turbo doesn't start building boost until about 1200 rpms. I'm running at about 75,000-80,000 lbs, and it struggles hard on take off and pulling even small grades. I know that 12 liter is no 16L Detroit. But it just seems it's not making what it should. If the turbo in fact does need calibrated, would that help address this issue? Quote Link to comment Share on other sites More sharing options...
Mp8tech Posted October 13, 2017 Share Posted October 13, 2017 What year/engine is it? Quote Link to comment Share on other sites More sharing options...
Flat Work Posted October 22, 2017 Author Share Posted October 22, 2017 On 10/12/2017 at 10:04 PM, Mp8tech said: What year/engine is it? "04 AC 427. Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted October 22, 2017 Share Posted October 22, 2017 Speaking broadly on OEM's (not just Mack), VGT calibration is a fine way to identify a bad variable turbo. If you are not stroking properly it may show itself by an inability to calibrate. Sounds like your getting AI427 performance out of a AC427, not right. They generally respond faster than AI or pre-emissions. Quote Link to comment Share on other sites More sharing options...
Flat Work Posted October 22, 2017 Author Share Posted October 22, 2017 Should I feel power building before 1200 rpm's? Quote Link to comment Share on other sites More sharing options...
ZDB Posted October 23, 2017 Share Posted October 23, 2017 (edited) http://www.macktraq.com/installs/cd/disk1/datasheets/1001408.pdf Edited October 23, 2017 by ZDB Quote Link to comment Share on other sites More sharing options...
ardakota Posted January 3, 2018 Share Posted January 3, 2018 the ac engines fall on their face under 1400 rpm Quote Link to comment Share on other sites More sharing options...
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