93 chevy lumina runs choppy!

[stormer22]

i have a 93 chevy lumina minivan and it has started running weird. when driving it shakes like a popcorn machine and makes popping noises.especially at the time you switch from low gear to high gear. what could that be.i have already put a brand new fuel pump and filter in it. everybody keeps telling us to replace the mass air sensor but we dont know were its located.

[Blue Bowtie]

What engine? Many were the Buick V-6. If the "Service Engine" lamp is not lit, I wouldn't immediately suspect the MAF. The ECM monitors the MAF very closely, and if the reading is outside an acceptable range for a given engine RPM and throttle position, the ECM will lock an error code within 600mS.

The fuel pump and filter have been replaced, so we can presume the fuel pressure is adequate. That leaves the ignition system, air intake, and injection as suspect.

The air intake is easy to check. Inspect the air filter, throttle body (where the MAF is located), and vacuum hoses and connections (including the PCV/CCV system and brake booster), and gasketed areas.

The '93 Buick uses a wasted spark system, so one bad spark plug or plug wire can kill two cylinders, causing really rough operation. Verify the coil packs are electrically intact, clean, and not arcing between terminals. The ICM can also become erratic if a cam or crank position sensor is failing, however, either of those will normally set another error code. The ground for the ICM is also suspect, as is the electrical connector on the front of the ICM base.

If the fuel pump failed due to contamination, some of that contamination could have made it past the filter and also clogged or partially clogged injectors. A power balance test of the injectors can reveal any with problems. You might also want to test the injector solenoid coil resistances to make sure they are electrically intact. Since the system is a sequential fire, it would also be good to monitor the injector signals if they still don't respond properly in the power balance test.

If the "popping noises" are due to backfire in the intake, the situation could be from faulty ignition or incorrect mixture. Start with the easy things.