This Buick began stalling,then difficult to start. We have replaced fuel filter,fuel pump and sending unit. It will start sometimes and either run smoothly for a few minutes or run rough stumble and backfire through the throttle body. It has not thrown a code thru any of this. can anyone offer advice as how to procede?
Was there any work done that led you to (or mechanic) to focus on the fuel system? In other words, why were the fuel pump/filter/sender replaced? If it was just on guessing then say so. If not provide the details for how a fuel system problem was detected and what was found.
In the midst of that was the fuel pressure regulator checked?
How old are the spark plugs and wires? Has anyone checked out the ignition coils?
Has anyone actually put it on a scanner to check for pending codes? Or hidden GM codes, since GM seems to like to “hide” some of its codes from the check engine light.
Has it been checked for vacuum leaks?
I would suspect a bad crank sensor. Then tend to fail when warm and will work once they cool down.
Has anyone checked the idle air control valve (IAC) and mass airflow sensor (MAF)?
The problem might be with a leaking fuel pressure regulator.
If the fuel pressure regulator is leaking, gasoline will leak into the engine via the vacuum hose. This gasoline will settle in the intake area. If there’s gasoline in the intake, it will be ignited by the wasted spark ignition system used on the engine. And this causes the engine to run rough and the backfire out the throttle body.
Turn the ignition switch to the run position for a second or two and then turn the ignition switch off. Locate the fuel pressure regulator on the fuel rail and remove the vacuum hose. If gasoline leaks out of this connection replace the fuel pressure regulator.