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waverlybus
Senior Member

89 Posts

Posted - 01/28/2019 :  06:47:12 AM  Show Profile  Reply with Quote
I have been having an intermittent problem with one of my freightliner/Thomas bodied buses with a c7. It started randomly loosing power and not wanting to go over 20mph but if you would stop the bus and put the throttle to the floor it would creep up in Rpm then power through and come out of it. I Replaced the fuel filters, f/w separator and made sure the turbo actuator wasn't freezing up and it didn't do it for a while. now today after sitting over a cold weekend it started dying when the driver would come to a stop. It did that 5 times this morning but by the time he got back to the barn it was running fine. No check engine lights have ever came on ever for the problem. It has to be fuel related in my opinion but I do not have any way to check pressures. Does anyone have any insight for me? thanks

Bluenozer
Senior Member

Canada
103 Posts

Posted - 01/28/2019 :  08:27:51 AM  Show Profile  Reply with Quote
fuel pressure will be low(except for what comes out of injector) due to it being a huei engine( hand primer(if equipped) could have bad o-rings but it should be a hard start issue if these were bad) other than that its all oil that does the rest you have to check the IPR and see what your ICP is doing , if you full field it the pressure should be about 5000 psi
What is engine oil pressure doing? stable - all over the place- low when throttle is depressed? If it gives you all 6 injector driver codes your ECM is toast (IDM internal)

OEM trained in wiring and all engine platforms for 20 years
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RonF
Top Member

714 Posts

Posted - 01/28/2019 :  08:43:33 AM  Show Profile  Reply with Quote
How cold it is? Do you have a fuel gelling issue? Is the fuel heater working in the separator.

US Army retired CMBT
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waverlybus
Senior Member

89 Posts

Posted - 01/28/2019 :  1:20:29 PM  Show Profile  Reply with Quote
No hand Primer. Oil pressure holds steady when I have it here, but I cannot ever get it to act up here. I don't have any way to test fuel pressure so it would have to go to the dealer at that point. No codes have ever popped up for me or the driver. this morning it was 5* but other days it has been above freezing when it happens, no real rhyme or reason to when it decides to act up.

I did tell the driver that if it happens again to stop the bus and apply the parking brake then try to bump up the idle with the cruise control and if the RPM's would go up doing that but not the throttle pedal that it would tell me if it is a problem with the TPS/throttle pedal.
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Tb4020
Senior Member

United States
82 Posts

Posted - 02/01/2019 :  03:50:07 AM  Show Profile  Reply with Quote
If it has a water separator check the aluminum head where the oring makes contact. I had one that the driver swore the trans was slipping, when the bus was loaded and got any hill it would slow down. The aluminum filter head for the separator was corroded at the sealing surface allowing it to suck air on heavy fuel draw.
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Cal Mc
Advanced Member

295 Posts

Posted - 02/02/2019 :  7:01:40 PM  Show Profile  Visit Cal Mc's Homepage  Reply with Quote
Fuel pressure regulator at the rear of the head is a common problem.
PITA to get to in an FS65.You can sometimes reach over the rear of the engine on top or go at it from the inside. It looks just like a fitting. We sent one into a truck dealer for a warranty head problem and they lost the regulator. They replace it with a fitting. ..idle was fine, but would not pull.
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Bluenozer
Senior Member

Canada
103 Posts

Posted - 02/04/2019 :  03:50:26 AM  Show Profile  Reply with Quote
easy test for that valve or the valves in the cummins engines is a Infrared Thermometer the valve itself will become hot(warmer than rail temp) good sign that fuel is bypassing and flowing back to tank

OEM trained in wiring and all engine platforms for 20 years
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Cal Mc
Advanced Member

295 Posts

Posted - 02/04/2019 :  1:44:43 PM  Show Profile  Visit Cal Mc's Homepage  Reply with Quote
On the 2005 Cat engine they do a hot fuel return to the tank. I would think that you will find the valve hot in any case.
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waverlybus
Senior Member

89 Posts

Posted - 02/11/2019 :  12:01:57 PM  Show Profile  Reply with Quote
It did it again this morning, died twice. Using the high idle switch when it was acting up did not change anything so I am assuming the tps sensor is good. I will try replacing the fuel pressure regulator since it does it so intermittently. Thanks for the advice!
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Dvorak
Senior Member

United States
78 Posts

Posted - 02/12/2019 :  04:28:20 AM  Show Profile  Reply with Quote
If you haven't checked it already, make sure your fuel tank vent isn't plugged.
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