MY #4 IS MISFIRING AND I WAS TOLD TO CHANGE THE PLUGS. I DID, AND IT DIDNT DO ANYTHING. WHAT ARE OTHER THINGS THAT CAN BE CAUSING THIS?

 

Wires...coil...fuel injector. You can get an inexpensive spark tester at the auto store that connects between the plug wire and ground. Run the engine (will be running on only 7 cylinders) and you can watch the spark tool to see if you have a strong consistent spark or not. If it checks ok, look at the injector, either electrical connection or the injector itself. Sometimes a sharp rap on the injector with the butt end of a screwdriver handle will clear it up. Try some injector cleaner in the tank too, your injector(s) could be gummed up.

 

AsCamaro 69said. Three things in the proper amount and timeare needed to get ignition. Fuel, compression, and spark.
Causes of misfire:
1) Bad or no spark: plugs, wires, coil, distributor, ignition module, timing sensors, etc..
2)Excessive fuel: carb problem, stuck injector, bad pressure regulator, regulator maladjusted, dirty air cleaner, etc..
3)Insufficient fuel: bad fuel pump, fuel filter, pressure regulator, clogged injector, damaged fuel line, etc..
4) Mechanical damage: Adequate compression is required!!! Leaky valve, blown gasket, damaged valve gear, broken piston, etc...

 

He's good.

 

So, here is the trouble shooting guide from GM for Cutting out and missing engines. It is from the 2000 3.8L engine troubleshooting guide, if you want more info I can provide it, just pm me... Good Luck...



Cuts Out, Misses





Checks

Action


DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases.


Preliminary

[*]Refer to the Symptoms .[*]Search for bulletins. [/ul]


Fuel System

[*]Test system fuel pressure.[*]Refer to Fuel System Pressure Test and Fuel Pump Electrical Circuit Diagnosis .[*]Test the fuel injectors.[*]Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Between 10-35 Degrees C (50-95 Degrees F) .[*]Refer to Fuel Injector Coil Test - Engine Coolant Temperature (ECT) Outside 10-35 Degrees C (50-95 Degrees F) .[*]Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .[*]Test items which can cause an engine to run rich (long term fuel trim significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich Bank 1 .[*]test items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean Bank 1 .[*]Inspect for fuel in the fuel pressure regulator vacuum hose. If fuel is present, replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement . [/ul]


Sensor/System

[*]Inspect for conditions which cause an incorrect idle speed.
[*]Throttle body tampering, excessive deposits, or damage.[*]Restricted air intake duct or dirty air cleaner element. Refer to Air Cleaner Element Replacement .[*]Large vacuum leak. [/ul][*]Test the Electronic Throttle Control and inspect the related circuit wiring.[*]Test the EGR system:
[*]The EGR pipes and adapter for vacuum leaks.[*]Remove the EGR valve and inspect for a sticking pintle. Refer to Exhaust Gas Recirculation (EGR) Valve Replacement . [/ul][*]Inspect the PCV valve for proper installation.
[*]Refer to Crankcase Ventilation System Inspection .[*]Test the transaxle range switch input with the vehicle in drive and the gear selector in drive or overdrive.[*]Inspect for the following conditions:[*]Bent harmonic balancer interrupter rings.[*]Damaged crankshaft pos

 

Oh yeah, the links that are in the post will not work... Sorry if that is confusing...