Skip the auto shop - Our mechanics make house calls

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.

A: Hi - check your vehicle’s fuel pressure whe...

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?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: My car he got power and everything but I feel like he's plugs something hold it

You need to begin with checking the necessities. If your car is missing, you will need to check all of the following. Internal combustion engines (ICE) require spark, fuel pressure, injector pulse and camshaft timing to run. All of these...

Q: Random misfires

Hello. There are several possibilities that could explain why you are having this problem. One possibility is that you could have one or more faulty fuel injectors, or the fuel injector wiring is damaged. Another possibility is...

Q: Car windows not going up or down

Being that none of the windows roll up or down, its more likely that the fuse controlling the main power supply to the windows could be blown. If the fuse is blown, it blew out for a reason. An electrical...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...