Car stumbles in all RPMs

[kenw]

"Dang, thought I had the perfect idea..at least it would verify coil delivery.."

yes, that it would. and do that quite well, too.

But I was muxing your post with the original and failed to see the interim posts that basically voided my thoughts on leaking spark.....confused? so am i.....it must be Monday.....

 

[drifter420]

Well.. the only idea I have with checking coil pack is to unplug each wire off while car is running really quickly with boost cable and the other end grounded on the chassis. If the spark is blue.. it's good.. if it's kinda orange that means the spark is either not enough and or dirty. So is that a good way? This method is good IMO so I can check whether the car is warm, hot, or cold to see if heat saturation may affect the coils too.. keep it coming folks.. I like to share ideas cause I"m sure sooner or later we all may need to troubleshoot these areas

 

[kevm14]

The other problem is, testing at idle won't necessarily prove anything unless the problem is REALLY bad. Increased cylinder pressures and rpms (high throttle/high load) increases the voltage necessary to get a spark (which is why it is recommended to decrease plug gap for nitrous applications, to avoid "blowing out" the spark), which puts more load on the entire ignition system. A weak coil may allow the car to idle fine but once you cram some fuel/air mixture in there and run it up in rpms, the ignition may not be able to deliver the voltage necessary to spark, and you'll get an incomplete burn or a total misfire.