1998 Renault Laguna Black Smoke & Stalling

Our 1998 Laguna operates well most of the time, but then unexpectedly putters and and stalls while driving. I can feel the engine puttering, and I rev it to try to avoid stalling. Black smoke starts to come out of the tailpipe. After the putting and revving it, the car usually stalls. It is often hard to restart and usually have to push hard on the accelerator to get to get the engine to turn over. If the engine turns over, it will putter out again with black smoke comes out of the tail pipe. I have to leave it for some time, usually 30 min – 1 hour before the car starts again.

Then the problem can reappear or dissapear for days at a time. We notice that the engine seems to have this problem in the late afternoon when it’s hotter (we live in a warm climate). The engine can stall after driving after both short and long distances.

We have cleaned the gas tank, cleaned the fuel lines, changed the fuel filter; checked all the vacuum tubes, changed the air filter; cleaned the MAF; changed the spark plugs and changed the ignition coil. The problem is starting to get worse with more black smoke. The car computer was tested and does not show any errors, but the car computer doesn’t have any memory on it. The check engine light does not appear. My mechanic says it could be the fuel pump. Is he on to something? Could it be sensor connections to the MAF? Sensor connections to other parts of the engine? Could it be the fuel injection or fuel regulator? Any thing else?