Skip the auto shop - Our mechanics make house calls

Q: 1999 gmc pickup, acts like it is not firing on all cylinders randomly

asked by on

Car acts like it is not firing on all cylinders randomly

My car has 149000 miles.
My car has an automatic transmission.

Engine misfires can be caused by many different problems and are generally caused by either a spark or fuel issue or in some cases, a combination of both. Spark related problems generally will result from things like ignition coils, crankshaft position sensor, spark plugs, spark plug wires or ignition modules not working properly. When the misfire results from a fuel related issue, this is commonly related to a lean fuel condition (lack of sufficient fuel supply to the motor). Fuel related misfires can be caused by many different things such as low fuel pressure, faulty or dirty fuel injectors, a faulty O2 sensor, a dirty or failing mass air-flow sensor, a faulty or dirty idle air control valve or a vacuum or intake leak. When the fuel supplied to the combustion chamber is insufficient, this results in an ignition (spark) that is igniting a less than balanced load of fuel and air. This results in a misfire or an explosion in the cylinder that is much less powerful than the other cylinders. This creates a loss of power that resonates throughout the motor additionally causing other problems with ignition and fuel timing. Due to the number of different things that may cause an engine misfire, the quickest and easiest way to diagnose this type of problem is to hook the vehicle up to a scanning tool which will download any potential fault codes that may have registered in the vehicle’s computer as a result of the poor running condition. I would recommend having an expert from YourMechanic come to your location to diagnose your misfiring problem.

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!
  • Home
  • Questions
  • 1999 gmc pickup, acts like it is not firing on all cylinders randomly

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: Wiring issue when ABS Light does not work - 1997 GMC Jimmy

Hello. You may be having a problem with fretting corrosion in the vehicle harness connections to the ECM, BCM, ABS, TCM or other modules. You would need to have the battery disconnected and module connections disconnected inspected for any problems...

Q: Engine chugging at low speeds when the weather is bad

It is very possible that moisture is getting into the connectors of the engine control module. The connectors should be checked and cleaned if necessary. Di-electric grease can be used to help seal the connectors and keep the moisture out....

Q: wen brass compression or copper compression ? for battery terminal repair 1966 5.7liter?

Hello. The appropriate gauge cable for that vehicle would be a 2 gauge, however a 4 or even 0 gauge could be used. In regards to the terminal I would recommend using a copper terminal, as it is more conductive...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
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...