Troubleshooting Engine Driveability Problems: Surging or Misfiring

How To Diagnose Surging or Misfiring Engines

car troublsehooting DIY
An engine misfire can be traced at home in many cases. Getty

The article will help you troubleshoot an engine that is misfiring or surging up and down while you're driving. Uneven engine revs and misfiring can affect drivability, but can also cause error codes to appear in your OBD-II Diagnostics system. These codes can cause you to fail your local vehicle inspection, or at the very least can result in that very annoying orange glow to appear on your dashboard: the Check Engine Light.

The good news is that, in many cases, an engine that is running poorly can be repaired for very little money. Performing maintenance tasks like replacing worn spark plugs, inspecting plug wires, or even replacing an old, partially clogged fuel filter can make a huge difference in how well your engine is running. This can also save you a bundle of money because even an hour of diagnostic time at your local repair shop can put the smackdown on your wallet.

The list of symptoms and possible causes below should help you get a better idea of what's causing your engine to act up. If you see a symptom that looks familiar, read on to find out what a possible fix can be. Nothing is in stone, of course, but a cheap fix is always preferable to an expensive repair bill. Be sure to look over all of the symptoms and fixes to be sure you're working with the one that most closely describes your situation.

 

Engine Symptoms and Causes

Symptom: The engine surges or misfires while moving.
The engine seems to start fine and will normally accelerate fine. As you are driving and maintaining a steady speed, the engine seems to "speed up" slightly or it seems to miss and buck.

Possible causes:

  1. If you have a carburetor (there are still a few out there), the choke may not be set properly, or the choke may not be working correctly.
    The fix: Check the choke plate and make sure it is opening completely.
  1. The engine may be running too hot.
    The fix: Check and repair cooling system.
  2. The fuel pressure regulator may be operating at low pressure.
    The fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)
  3. The ignition timing may be set wrong.
    The fix: Adjust ignition timing.
  4. Ignition system problem causing a weak spark.
    The fix: If your vehicle has them, check and replace distributor cap, rotor, ignition wires and spark plugs. Otherwise have the coil packs looked at.
  5. There may be a fault in the computerized engine control system: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)
  6. The fuel filter may be partially clogged. This is an easy fix!
    The fix: Replace the fuel filter.
  7. Torque converter (automatic transmission only) may not be locking at the right time, or it may be slipping.
    The fix: Check lock up circuit or replace torque converter. (Not a DIY job)
  8. There may be a vacuum leak.
    The fix: Check and replace vacuum lines as required.
  9. Possible internal engine problems.
    The fix: Check compression to determine engine condition.
  10. EGR valve may be stuck open.
    The fix: Replace EGR valve.
  1. Drive axles may be loose or worn.
    The fix: Check and replace CV/universal joints as required.
  2. The fuel injectors may be dirty.
    The fix: Clean or replace fuel injectors.