1990 GMC 3/4 ton 350 engine floods every time I start it warm or cold then after the excess gas clears out it runs OK until I shut it off and have to start it again. For a couple minutes after I start it, I get black or blue smoke out the exhaust, backfiring, stalls, and rough running in general. If I unplug one of the two injectors, it smooths out somewhat. Sometimes when cold it doesn't even start and I have to take out a few spark plugs and clean them up. They are all wet and black. #8 is the most soaked. When I crank with it out, the gas pours out.
This started happening after I put a '91 engine in it. I don't suspect the fuel pump or filter because it handled the old engine quite well before I blew it up. I strongly suspect the problem is due to something I (not an expert) screwed up while doing the engine switch. What could it be though? I had to put the throttle body from the old engine on the new because my linkage wouldn't work on it. What could I have scewed up there? I put new plugs in it gapped at .035 like the parts salesman said and plug wires. I tried putting several parts from the old engine in the new....dist.cap, rotor, coil, O2 sensor. The EGR valve on the new was shot. It ran much better when I removed the vac hose from it, so I put the one from the old engine on it.
I'm guessing fuel is getting into the intake manifold after I shut it off, but I don't see any leaking down from the injectors when I shut it off. Is there somewhere else that fuel can leak in other than the injectors? I switched injectors from the old to new and back again, plus injectors from another TBU I had...no help. no difference.
I don't have anything to look for codes with and I don't know where the ECM is anyhow. The SES light stays on all the time though. I don't know if it's because of the flooding or something else.
Any ideas, anybody? I'm all out of them!
Jim