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Cookie63
New Member

United States
1 Posts

Posted - 11/22/2008 :  04:56:47 AM  Show Profile  Visit Cookie63's Homepage  Reply with Quote
Hi everyone! I am in dire need of advice regarding the engine speed caps that have been installed on some school buses, and so I am turning to you, the experts, for help. Yesterday, I witnessed a school bus that was driving 70 mph on the expressway, in a 45 mph-limit construction zone. The bus sustained speeds between 63-70 mph for at least 5 miles. (I drove with my heart in my throat, as the crowded bus had three 10-year old children per seat, and was extremely crowded, and at times it was snowing outside.) When we reached our destination, I asked the driver to slow down on the way home. He told me that it was impossible for the bus to travel at 70 mph, because the bus has a speed cap installed that will not allow it to surpass 58 mph. Because I know nothing about bus engine speed caps, I am struggling to understand. I know what I witnessed, since I remained directly behind the bus for the entire 5 miles, and I know that my vehicle's speedometer is accurate, since after speaking with the bus driver, he did the speed limit on the way home (with me driving directly behind him again). Can drivers choose to surpass the speed cap? Are the service levels of these computerized caps reliable? Any insight you can give me would be helpful, as I struggle to decide whether I should ask that the bus be checked out for mechanical failures so that future groups of children aren't affected. Thank you, in advance, for your expertise!

origcharger
Top Member

United States
619 Posts

Posted - 11/22/2008 :  05:54:11 AM  Show Profile  Reply with Quote
I am familiar with Internationals maximum road speed limiting feature built into its electronic diesels. I very recently adjusted one of ours down to 60mph after reports of driver doing over 65mph on his route.
On Internationals system you have to hook a computer to the bus with Internationals Fleet diagnostics program, enter a password, and make the change. It cannot be driver over ridden and the buses ECM tracks how many times the parameter gets changed.
I believe the driver is trying to convince you that you are mistaken in what you witnessed by claiming the speed limiter is programmed at 58mph, the bus I turned down had been programmed with a 68 mph max. for interstate road trips.

Operating; Seven T444Es, One MaxxForce 7, One VT365, Four DT466s, One E-450 6.0 and one Mercedes in a C2.

Edited by - origcharger on 11/22/2008 05:57:10 AM
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Thomasbus24
Administrator

USA
4544 Posts

Posted - 11/22/2008 :  05:58:09 AM  Show Profile  Reply with Quote
I won't get into older buses with goveners (speed cap as you call them) because I don't know much about their operation, I'm sure somebody else will chime in on that subject.

As for newer model buses...

Many 1995+ and all 1999+ school buses have electronic engines with offer "road speed limiting". These engines are run entirely by computers so there is no physical member than can be altered on the engine or accelerator system to make the bus go faster. Unless the driver has access to a computer with the proper software to acces the bus engine programming (very expensive), then there is no way he or she can surpass what the bus is set up to do.

Now--what that limit is set to is up to the person who spec'ed that bus new, or whoever hooked up to the vehicle with a computer and the proper software to interface.

My point is--it is possible that the top speed was never programmed (Caterpiller engines default to 127 MPH ), or that it was programmed to a value high enough for that bus to run at the speeds you witnessed, but it is not possible for the driver to overcome the top speed programmed.

This setting can be password protected to ensure that only authorized persons can alter it. (No unscheduled stops at a buddy's truck shop for a "tune up" hey--it happens.

You're best bet is going to be to contact the transportation supervisor of the school or company in question. Present the facts as you've done here, clear and calm. What they do with that information is up to them, but it warrants attention.

Hope you found this helpful!
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