My problem started with my lights flickering on and off in the cab as though it was an electrical short or a bad relay or something. That was months ago, but it stopped doing it for a while and I have been ok. Yesterday they started again but now the engine is majorly chugging along with it. The 2 problems must be related. Maybe there is a relay that runs the cabin lights and supplies the fuel or something important in the engine that makes it run. We also just replaced the fuel pump 3 weeks ago, but it has ran great since then as far as the fuel pump goes and I don't think that has anything to do with it. Also, it was chugging real bad yesterday and the lights flickering, and then both problems just went away all at once and it ran great the rest of the way home. But this morning the problems are back. My truck is a 1999 GMC Sierra 2500.

 

Hey,
Id be checkin the alternator. Doesnt make sense for the lights/electrical to work then not work but id start there.

Hope this helps.

 

Yea, it sounds like a voltage problem. Either altenator is bad, or the conector is shorting out, or the battery and alternator is bad. Use a volt meter and check batt when not running should have at least 12.8 volts and check either alt. or bat. while truck is running and it should have 13 -14 volts. if your not getting over 12.8 at batt. while running check at alt. If you get it there then its the wires. Ifyou don't get it at the alt. its the alt but you can also take the truck to autozone or discount, ect. and they will check it for free.

 

Thanks for the responses. It sounds logical and I will start from there.