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2008 F650 6.7 Cummins


doingitall
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I bought a used F650 a few years ago. 2008, Cummins 6.7/Allison auto, pre DEF. This was a real upgrade from my 06 F650 with a 5.9 Cummins. The 6.7 was stellar! More power, the throttle peddle was actually more than an on/off switch, could actually merge with traffic onto the highway, I was happy ... then I had what appeared to be issues with the turbo variable vane system sticking. Common issue, I know. Poor performance, always seemed to be "out of breath", no power going uphill, poor throttle response, back to the 5.9 feel. Replaced the turbo system, could hear the turbo running correctly again, but ever since this happened, nothing has brought back the original performance. So the turbo was replaced, the EGR has been replaced, new injectors, the manifold pressure sensor for the turbo replaced twice, some other stuff, can't remember it all. Nothing has really changed, still poor throttle response, no power going up hills loaded or unloaded. Seems ok in town though not like when I purchased the truck, but getting on the highway, or going up a hill is still a lesson in patience and humility. I do not dare to make a pass at highways speeds unless I can see for at least a mile, even then I usually do not even try. One shop asked if it has ever done a "regen" cycle, and I have never had it do that (I am the only operator), but after asking, he seemed unconcerned. Two different shops have looked at this truck several times and tell me that there are no codes now, and that everything is "within specs". But still the truck does not perform like when I purchased it (at 125K). Now has 170K. There have been slight improvements when things have been fixed, but I am a long way from the performance it used to have. It functions still as it is, but man I wish it would run like when I bought it ...  Any suggestions?

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  • 3 months later...

The calibration of the turbo actuator motor can cause a lack of power.  The actuator arm can be assembled incorrectly inside the turbo, or the actuator can be not calibrated. Cummins software is needed, and actuator must be removed(after draining coolant from block), and installed to get it checked/set correctly.  I would also recommend using DIESEL KLEEN additive in the fuel. It has worked wonders in my trucks, and many of my customer's trucks.  My truck was a turd(no codes) when I bought it, would barely do 65 on the highway.  After a month of DK(double dosed), it will now hit the speed governor at 78, and has stayed that way. It is possible that the DPF is slightly restricted. You can remove it to inspect/clean it yourself. I have had good success using oven cleaner, and a pressure washer. Hope this helps.

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