4 Wheel Drive/SUVs: problem with 94 diesel suburban, freeway drive, long distances

Question
When I travel long distances at speeds over 70 I get the check engine soon light. It does not come on in town driving or at speeds under 65-70. Nor does it come on when the engine is cool. Usually 2-3 hours into a long freeway drive.

Answer
Clyde,

the fuel system may be overfueling setting  a code for being too rich or too lean depending on if it is over or under fueling. if the light is coming on ot means it is setting a code so first i would get it scanned at the dealer to find out what code is in the ecm and go from there

Matt