Q: Misfire at hard thottle, rpms either dont go up when accelerating, or slowly drop as i accelerate

asked by on

My grand prix has began to hesitate and misfire under hard throttle, im unsure as to why which is why im asking here. This is whats been fixed and whats new on the car:

  1. Mass Airflow Sensor
  2. Manifold Absolute Pressure Sensor
  3. Spark Plugs- NGK TR6
  4. Spark Plug Wires- MSD Street Fire 8mm
  5. Ignition Coils- all 3 of them
  6. Vacuum lines running to map sensor and supercharger bypass solenoid
  7. Supercharger Bypass Solenoid
  8. Supercharger Bypass Valve
  9. Accelerator Pedal Sensor
  10. Fuel Pump- Airtex E3700M

After all this it still acted strange so I removed the fuel injectors and manually cleaned them aswell, and reinstalled with new o rings. Im at a loss as to what it is. It ran great for a long time, and I miss being able to run it like I used to. I am thinking maybe a camshaft position sensor but theres no codes to reflect that. "on a side note, I checked tps with a scan tool, its ok, but the fuel trims are a bit erratic. Thank you for your help

My car has 187000 miles.
My car has an automatic transmission.

Hi - check your vehicle’s fuel pressure when running, and under load. Your comment regarding "fuel trims ...erratic" gets my attention. If the pressure is not correct, check the fuel pump relay (possible burned contacts) and fuel pressure regulator. If the pressure is correct, I would suspect the injectors need professional cleaning and testing - given your mileage. I would recommend having an Engine is Misfiring Inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Misfire at hard thottle, rpms either dont go up when accelerating, or slowly drop as i accelerate

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Car hesitates when accelerating, plus lurches & stalls

When faults are intermittent such as this, they can be much harder to diagnose. Especially if they do not leave a code of some sort. A few different components can cause this fault. The most likely would be a fuel...

Q: #3 Misfire engine light

Yes, it can be an electrical issue. A misfire at a particular cylinder can be caused by ignition, fuel injection, mechanical issue, or vacuum leak. I'm curious why none of the dealership techs repaired it. Faulty sparks plugs, coils, or...

Q: Trying to install LED dome lights

This is a tough question to answer over a message. I really need to see what you have purchased and what the original looks like. From my experience, installing an LED light should be the same as installing another bulb....

Related articles

How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.