1987 gmc v1500 idles but will not drive

[Georgiasquare]

So first some background. It is a 1987 gmc it has been swapped to a carbureted 350 from the stop TBI 305. the truck has a MSD 6al box and MSD distributor. When I bought the truck I knew it had problems but I got a good price. I was driving it and it literally just died not stumble, sputter or anything like I turned the key off. First at the guidance of people far smarter than me I suspected it was a fuel Issue so I just went ahead and redid the fuel system (new tank, pump, filters and carb). This did not fix the issue It would still idle but not drive. Then I began checking the ignition system It has spark at the coil and at the plug. I checked the Distributor cap and rotor and they were terrible (corrosion and cracks in cap) so I ordered some and they arrived but I am at college and can not work on it at the moment. I will be going back home this weekend to work on it some but I am looking for any other ideas you guys could have for this problem. I have been reading some forums and people are saying it could be the fuel pump relay or the ignition switch. Any other ideas would be greatly appreciated.

also, As a test I plugged all vacuum ports on carb to ensure it was not a vacuum leak, the problem was still there.
Thanks in advance.

 

[John Nes]

Heyo, welcome! for the sudden loss of power, if you lost all power, I’d tighten up them battery cables, if the engine just straight up shut off but you still had power, I’d make sure that your 87’s ecu and O2 sensor aren’t still active.

You said a forum led you to believe it’s maybe a bad fuel pump relay,… you running the tbi fuel pump with a fuel pressure regulator? Mechanical fuel pump? External/in-line or in-tank pump?

If it’ll crank, fire up, and then sit at idle,but won’t move, it’s clearly getting fuel and there’s enough spark getting to the hei…might sound dumb, but have you checked your trans fluid? If it’ll run but not move while in Drive, add a quart or two of dex merc 3 ATF and see what that does for ya