1991 Cummins ISM (350 HP) - Road Speed Governor

[Mopar1973Man]

Hey Gang... I've got a local guy here in Idaho that owns a semi-truck without trailer that has a issue with the Road Speed Governor. It limits the truck out to about 60 MPH and that's as fast as the truck will go. Does anyone know how to fix this issue on a Cummins ISM? Also the truck is for sale $4,900 bucks, fresh rubber and looks good... It's a old Food Service of America truck.

[fire176969]

Happen to have the engine serial number?

[Mopar1973Man]

No I didn't write it down... As a matter of fact I didn't happen to see the plate on the gear case like the ISB's... Is there another location?

[fire176969]

They are usually located there but can also be on the rocker housing just under the valve cover also.

[fire176969]

The only way to change the road speed limit is through the ecm with either Insite software from cummin or something like a prolink diagnostic tool with the right cartridge in it. I wondered what the serial number was so I could look up the fuel system. Then I thought about it again and realised it didn't matter since if it has an ECM stuck on the side of it the only way to change it is through the ECM or to trick the speedometer to make the truck think its going slower than it actually is, which could actually cause problems with setting other codes and possibly causing it to derate the amount of available power.