Light intermittent miss

Tiny
ERE44
  • MEMBER
  • 2004 BUICK LESABRE
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 94,641 MILES
Car has a light intermittent miss, has new plugs, wires, air and fuel filter, coil's test @ same resistance. Fuel injectors? Where do I go from here?
Do you
have the same problem?
Yes
No
Tuesday, November 30th, 2010 AT 5:38 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
If the Check Engine light is on, there should be a diagnostic fault code indicating which cylinder is misfiring. Try switching that injector with one from a different cylinder to see if the misfire follows the injector to that new cylinder.

Only Chrysler uses sets of flow-matched injectors from Bosch and has almost no injector trouble. GM, on the other hand, just grabs a handful of injectors out of the bin and throws them into the engine on the assembly line. All of them are perfectly fine by themselves, but they are not flow-matched. You have to buy a set of rebuilt injectors to get a matched set, and those rebuilders go through a pile of GM injectors. Misfires is the number one problem they cause. Some cylinders will be a little lean and the Engine Computer will enrichen the mixture to all cylinders on that bank. That results in two cylinders on a V-6 running rich. Remember, the oxygen sensor only measures unburned oxygen, not unburned fuel.

Caradiodoc
Was this
answer
helpful?
Yes
No
Tuesday, November 30th, 2010 AT 5:49 PM
Tiny
ERE44
  • MEMBER
No Check engine light
Was this
answer
helpful?
Yes
No
Tuesday, November 30th, 2010 AT 5:52 PM
Tiny
CARADIODOC
  • EXPERT
If it feels like a single cylinder misfire, unplug one injector at a time to see if you can identify one cylinder that isn't working. That's a manual version of the old cylinder balance test.

If you have a scanner that displays live data, you can look at the oxygen sensors and fuel trims to possibly point to which bank has a problem. There should also be a misfire counter. It takes a certain number of misfires before the computer will set a code and turn on the Check Engine light. Before a code is set, the computer will watch a problem that it suspects might continue to act up. Those are called "pending codes", but then you're getting into an area I'm not real familiar with.

You can also measure the resistance of the injectors. Here again, GM seems to have more trouble than anyone else. Look for one that is considerably lower than the other five. That difference could be only a half ohm.

Caradiodoc
Was this
answer
helpful?
Yes
No
+1
Tuesday, November 30th, 2010 AT 6:20 PM

Please login or register to post a reply.

Recommended Guides