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Won't Go Over 50 mph, Cummins 400

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7 replies to this topic

#1 jgscott01



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Posted 23 October 2012 - 09:59 AM

What would cause the coach not to go above 50 mph.

Not getting any warning lights.

Thanks for your help.
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#2 rossboyer


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Posted 23 October 2012 - 10:36 AM

Possibly you need to change your fuel filters. I have had this happen in that I could not go 65. 55 was max and then intermittently I could not get above 35. Stopped at a campground for the night and the next morning changed both the Primary and Secondary filter. I always carry two spares of each. I could quicly accelerate to 75. If you have not ever changed your filters, ask the service tech to show you how so that you can do it on the road. My tech suggested that I buy a special strap wrench that works with a 3/8ths extention. I think it was $5/6 at Auto Zone. Please let us know what the solution is to your problem.
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Ross & Melanie Boyer

2006 Fleetwood Expedition 37U

Cat C-7 300HP

Allison MH3000




#3 aztec7fan


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Posted 23 October 2012 - 01:38 PM

Probably not your issue, but something to think about: We originally had a 1991 Tiffin Allegro Bay (gas, Ford chassis). We took it out on it's first test drive and it would get up to 55 mph, then die back to 50 mph, and the engine ran really loud. I called Tiffin, asking if there was a governor on the engine and they said no. I checked with Ford and local mechanics and they confirmed, no governor. I took the coach on the highway again and noticed that the shifter seated itself in 2nd gear very easily, and you had to back it up slightly to get it into 3rd gear. No more problems.
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Chris Guenther
Westminster, CO
1989 33' Southwind (Gas 454 Chevy)


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#4 wolfe10


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Posted 23 October 2012 - 01:50 PM

Ya, Chris, not their problem, as they have the electronic controlled Allison 3000.

I second the "replace fuel filters FIRST. That is both an inexpensive step and one that causes by far the most issues where power is limited, but engine runs fine at lower throttle settings (when less fuel flow is demanded).
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Brett and Dianne Wolfe
2003 Alpine 38'
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#5 cmarq


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Posted 23 October 2012 - 08:46 PM

Check the connections from turbo to charge air cooler and to intake if a clamp broke or is loose you loose turbo boost which will reduce power and no warning light. The charge air cooler could also have a leak, this needs to be tested in a qualified shop.
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#6 jc21014


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Posted 24 October 2012 - 09:58 AM

We had a similiar "reduced speed/power" situation last week while enroute to Branson, Mo last week on our ISL 370 Cummins. There is only (1) combo fuel/water separator filter on our rig and the general consensus of most was a filter issue.(Wolfe10 was one of the responders on another forum :) ) This filter was supposedly changed 8-9000 miles ago but I replaced it with a new one at the cg and it seemed to run fine on the way home. Will be taking it to Cummins-Onan and have them check the fuel pump specs to make sure it is working correctly.
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2004 Newmar DSDP 4015-370 hp Cummins ISL-08 Saturn Vue-ReadyBrake-FMCA 402879-SKP 120487

#7 mayordave



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Posted 24 October 2012 - 05:22 PM

Almost guaranteed its something with the Turbo, either a leak or the turbo itself. CMARQ suggestions are good.
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#8 desertdeals690


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Posted 24 October 2012 - 08:22 PM

When my cooler hose clamp broke, I couldn't run above an idle.
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