So I have finally got my blazer running. Better then ever but I am now back at the original issue. It keeps surging and stalling. It surges between 500-800 rpms and then it stalls. Right before it stalls it makes a high pitch vacuum like noise around the area where the fuel pump is located right before it does stall and if its ran for longer periods of time you can smell almost burning plastic or rubber. I talked to a couple of friends and one mentioned it could be a vacuum line against the exhaust. I don't know how to check my vacuum lines and he doesn't know how either. I am just starting in this field and I don't mean to ask stupid questions but I have no idea what to do or how to even start checking this. I have tried using the Chilton's manual but I really can't find a whole lot of help there. I have this and several other websites for any problems this could be but I can't seem to find any. I redid the timing and I replaced the exhaust (cat was out and I thought it could be an oxygen sensor issue). At higher speeds and rpms the check engine light begins to flash. Since this truck runs an OBD 1.5 I figure its signaling misfire but I have no way to check the codes for sure. I have researched and checked everything I know can be the problem but I am still learning and I don't know it all. I really need help with this, so any advice at all would be very appreciated. I can post pics if asked but I would need to know what you guys have to see. Thank you for your help.