Isuzu Repair: injector coil, electrical tester, question thanks

Question
QUESTION: My Isuzu jerks when in 3rd and 4th gear. I was told I had a bad ignition coil(injector coil?. What is the easiest way to single out the 1 out of 6 that is bad? Can I switch one out at a time to systematically find the bad one? I have an electrical tester but am not familiar with it.

ANSWER:  a common way is to individually detach each of the spark plug coil-overs one at a time and if a power decrease occurs on that cylinder,it is good. But when you pull off the bad Ignition coil and power decrease is not present. Then that coil would be at fault. If this is confusing to you let me know and we will work at it more okay? Also did your mechanic tell you injector or coil-over/plug?

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QUESTION: Thanks for quick reply. I unplugged each coil as you suggested and each one showed a decrease in power.Does that indicate each coil is 100% functional or can there still be a faulty coil when getting in the 3rd and 4th gears or when trying to accerate fast? Could it just be a bad plug? I forgot to mention I have a 2000 Trooper.

Answer
Yes although was there one that did not show a decrease in power even slightly? Yes it could be a bad plug or faulty/clogged fuel injector. A fuel system cleaning only costs about 45-60 dollars so it worth it Dave. If you need anymore help let me know okay?