My Blazer's history... Friend owned it and the fuel pump went out. He is NOT mechanical at all so it sat for almost 4 yrs. Because I knew it ran great I bought it and replaced the pump. It STILL runs great... until you put it in gear.. then it pukes. Reverse or Drive it dies. The ABS warning light is also lit up and the RPMs drop briefly when brakes are applied. Don't have a clue where to start. ANYONE??

 

I would start with the entire fuel system. Gas sitting in lines, filters, injectors, etc for four years does nothing to help anything. You could try dumping a cleaner into the tank and start it up to get it through the entire system and then let it sit for a while.

That would be the best case scenario.

As for the RPM's dropping when you apply the brakes, take a look at all of your vacuum lines. Again, sitting for four years didn't do any help.

As for the ABS light, pull the code and see what the problem is. Most scanners can't pull ABS codes but a few can. Might bet would be one or both of the sensors on the front hubs, but getting the code will tell you where to look.