Hey all, I just bought a 1994 GMC Sierra 1500 with 190,000 miles. Its a 4x4. Extended cab. Real nice condition for the year etc. I have owned it for 3 days and every time I take it out on the highway doing about 65 it will buck and lose power. It doesnt stall and at low RPMs it seems fine. It also takes two cranking sessions to get it started in the morning. So my thought is that the lift pump is on its way out or already out.

When I test drove it, it didnt have either of these symptoms. It felt real strong. The guy I bought it from seemed to take good care of it. So the first time it started bucking I called him to see if he knew about it and he said no (of course). We kept talking and he told me one time he put a gallon of gasoline in it, caught himself, topped it with diesel and kept going. He said it ran fine. I wanted to slap him silly, especially bc i just bought the damn thing. I think that is definitely having a part in this too. I dont know though.

I havent taken it to see if there are any codes stored yet, but I am tomorrow morning. Its got S&B intake. PMD relocation. Strait pipe. He said the PMD was just replaced and relocated too.

Anyways, if any of you have an idea on where to start that would be great. Ill probably start by testing the lift pump but I am not too familiar with the 6.5s so if theres anything that sticks out Ill take any help I can get. Thanks

Chase

 

To test the LP you need about 6 ft of heavy gauge wire insert it into the G terminal in the ALDL port under the dash open the t-valve next to the top radiator hose take the other end to the positive terminal on the driver side battery this will make the LP run if it is not bad