QuestionRecently I have read through Q & A but have failed to find exactly what I am looking for.
My check engine light is NOT on,and I don't have a code reader. But I do have a miss fire. I have replaced spark plugs and wires. I have looked for arching from the coils or arching from anywhere else.Still miss fires idling and acceleration. Thanks for your time.
AnswerAnything that would cause a misfire is suspect if you indeed have a misfire. I feel like I need to ask, however, why you've determined you have a misfire. In most cases, this would result in a check engine light, so it leaves in my mind that there may be some other performance-related issue(s) that aren't misfires. If you're experienced enough that you can easily identify a misfire and are sure that you have one, then I'd say your assessment is correct. If, on the other hand, the engine is simply running poorly, or you have a lack of power, or there's some other symptom that you're presuming to be a misfire, then I'm concerned the information that follows could be sending you in the wrong direction.
Potential issues causing misfires are as follows:
-- Secondary ignition components (you've already replaced the plugs and wires, but you could have a problem with a coil)
-- Fuel injector
-- Any mechanical issue causing low compression in a cylinder
First, let's verify that the check engine lamp operates. It should come on when the ignition is turned to the on position. If it doesn't, I'd recommend checking the bulb and taking your car somewhere that it can be scanned for trouble codes. AutoZone and AAMCO have advertised they'll do this at no charge.
You should be able to feel whether this is a one cylinder, two cylinder, or more than two cylinder misfire based on the frequency of the misfire. If it's a two cylinder misfire, suspect an ignition coil. If a one cylinder misfire, there's no reason to suspect any one possibility over another.
For the purpose of what follows, you'll need to know that cylinders 1,3,5 are in the rear and cylinders 2,4,6 are in the front. The cylinder parings for each coil are 5-2, 1-4, and 3-6.
Next, see if you can identify the misfiring cylinder(s). Start by disconnecting the coils one at a time. One of them, when disconnected, should cause the engine rpm to drop less than the others. So, for example, if unplugging the coil on cylinder number two causes only a small rpm drop while unplugging the others causes a large drop, you should immediately expect that the issue is affecting cylinder #2 or #5. Next, go to the cylinder in question on the front bank and (with the coil connector reattached) unplug the injector. If unplugging the injector causes no change, you should investigate the cylinder on the front bank. Again using the same example, this would be cylinder #2. If it causes just as much change as unplugging the coil, you should investigate the cylinder on the rear bank. Yet again using the same example, this would be cylinder #5.
To see if the problem is component related, you can now switch the components in question with components on other cylinders to see if the misfire follows the component to another cylinder. If you suspect the 2-5 coil, you can swap it with the 1-4 coil and recheck for the location of the misfire. If you suspect the #5 injector, you could swap it with the #6 injector and recheck. (Note that in this case I've purposely selected an injector on the front bank to swap the injector with. You cannot access the rear bank injectors without removing the plenum, and you must reassemble to recheck. Once it's in the front bank, if the injector is the problem, you can replace it without again removing the plenum. To check for a mechanical issue, you'll need a compression gauge to run a compression test. Do this with the ignition coils unplugged to prevent unexpected sparking. If the suspect cylinder is in the front bank, simply compression test each of the front bank cylinders and compare values from the three cylinders. If in the rear, you'll need to remove the plenum to enable readings from the cylinder in question. At this point, there's no reason to not test all six cylinders.
