On my '97 3.0L with 106K I'm getting what feels like a bad misfire only in the 700 rpm range. If I bump the throttle to 800-900 rpm it goes away. The check engine light hasn't come on. The plugs were just replaced, but not the wires. Had the same problem a little while back and the dealer was never able to totally fix it (replaced a couple plugs and wires, but there was still a slight miss). Should I go ahead and replace the wires or is there something else I should consider first? Thanks...

Is this a Duratech or vulcan? A bad coil on a Duratech will do that sometimes because of heat buildup in the back 3 plugs.

Even though the check engine light (CEL) has not come on, a scan tool that can display component parameters or enter the I/M readiness mode should be able to display if there are any misfire counts on the individual cylinders, even if the counts are not high enough to trip a code.

If there are no misfire counts, but the knock sensor goes wild around 700 rpms, you may be looking at a torque converter that is out of balance or something similar.

-Rod

Sorry, this is the Vulcan 3.0L. At the moment I don't have access to a scan tool, but I recently used one at an auto parts store, there didn't appear to be any stored info. There has been a slight miss at idle for a long time, but this is the second time it has gotten worse. Is it worth going ahead and replacing the wires, or should I spend the money to get a scan tool?

It won't hurt to replace the wires and just might solve your problem. Most auto parts stores will let you use the scan tool for free because it sells parts :wink:

To address the purchasing of a scan tool, If you are going to buy one, you need to find one that will read and store PIDS (Parameter Identifications for the sensors). These readings are what is needed to address concerns with a failed emission system. A code reader is just that, it displays and erases codes. Code readers go for around the 50 to 100 $ range. A scan tool that reads PIDS goes for about 300 to 900$. All depends on what you are wanting to do with it. I have about 15K invested in just scan tools and use all of them daily.

To address the engine misfire, as far as the miss going away at higher RPM's, the engine speed is probably covering up the misfire. It should still be there. A good quality scan tool will be able to read the engine misfires under thwe mode 6, 53 series tests (I think). I usually use the Ford PDS system on Fords and have no use for the mode 6 tests. Good luck and have fun repairing. Oh, also check for vacuum leaks.