1997 Pontiac Grand Prix 97 Grand Prix GTP MISFIRES UNDER LO

BIGGS-22

MEMBER
1997 PONTIAC GRAND PRIX

Engine Performance problem
1997 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic

I have a 1997 pontiac grand prix gtp with a 3.8 supercharged motor it was rebuilt internaly only but has 185,000 miles, was rebuilt at 95,000 miles. The car ran okay when I bought it. I imediately got a fule injection cleaning and an oil change done on it, then did my own tune up. After completing the tune up and driving it its misifiring badly causing the supercharger boost to skyrocket when it misfires. I checked the wires and got top of the line bosch platinum 4 plugs, the old ones were covered in black soot. Wires are correct and plugs are pre gapped nothings loose. I have magnaflow dual exhaust if that makes a difference, most of the hesitation comes at heavier load or steady around 40 mph. What coulda caused this? It also seems to lose power when I come to a stop the lights dim as well?

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.