problem with 1994 gmc jimmy

when the service engine light comes on the vehicle wont go faster than 10 mph it does it very erraticly one day it'll run like new the next day i cant even drive it does anybody have any ideas

the service engine light is setting trouble codes that are saved in the truck's computer. Go to Autozone or any car parts store and ask them to read the codes-they'll do it for free. Report back here with those codes-make sure to get the exact number code - they'll give you a paper printout, Keep it and report back.

Also, search the following on this forum and see if you have similar symptoms:

cpi
nut kit
washing


when the service engine light comes on the vehicle wont go faster than 10 mph it does it very erraticly one day it'll run like new the next day i cant even drive it does anybody have any ideas

i had the codes read and it came up code 42 and code 12 the guy at autozone was very helpful and more or less pinpointed it to a problem with the speed sensor

42 is for the ignition control.

The ignition module in your distributor could be gone.

Also, you really need to inspect your CPI injector for leaking. We had a guy just ruin his engine in the Blazer section seeing the fuel destroyed his bearings.