Engine light has turned on

[compasser]

Hi Guys
My 2007 jeep cvt 2.4L benzine was converted half year ago to work on CNG natural compressed gas.

anyway 2 weeks ago after I have contacted the NGK spark plugs company inn the US, they advised me to switch to a different number of spark plugs, instead of the ZFR5F-11, to buy one degree colder which is ZFR6F-11

after I bough last week, car worked and between time to time made some gaps though it feels better with the strength of engine and burning way, but I recently got my engine light on, I guess its because of it. so I removed the plugs and put the old ones, removed the positive battery connector for 10 min, then driven the car for a while then turned of the engine, again turned on the error disappeared,
yesterday was driving and almost after 40 km the error light started again, now I don't know what to do? any advice please? should i use these error code reseters, or some other advice?
our dealer in Finland is a money sucker, so would charge me alot for anything.

any advices are appreciated

[liggettj]

The 1st thing I would do is find out what code is coming up. it should be PO something. Like if it is PO420 it is a oxygen sensor. I don`t know about where you live but my local auto parts store will scan the codes free. That is going to be your best bet.

[Cherokee]

I have to agree, best thing to do is not to clear the code(s) but to find out what they are. If you can do that and post the codes here, we can help troubleshoot better from that point. Am I correct in reading that even after you put the old plugs back in, the light is still on?

- Cherokee