here is what happenned , on each full tank of gaz ,there is about 50-100 k where the check engine light goes on. 5 sec before it happenned , i can ear the engine going weird than the light goes on. Is anyone know what is it ???

 

I think if you want anyone to even try to help you, you may need to be a little more specific.

First, what kind of vehicle are you driving and what exactly does an engine sound like when it goes "weird"?

Second, are you closing the gas cap properly?

 

sorry about it , Its a jeep TJ sports 2003 with 70 000 k on . Whats happenning is the RPM go down and up a bit and its like if the engine turn square , hard to explain the noise ,it last between 3-5 sec and than RPM stabilize and the light go on. Once the light is on it stop making that(weird) noise .

 

Sounds like you need a good tune up. Check your owners manual and do what's needed.
If you don't have an owners manual let me know and I'll point you in the right direction.
Tune ups are money well spent, because it takes care of the basics you will get rid of a lot of little headaches.
And make sure to your throttle body is clean.
Sure doesn't sound too serious to me.

 

i dont have the manual ,i bought the jeep not too long ago .thanks appreciate that

 

This is where I bought my Owners Manual.
Bishko Automobile Liturature available for 2003, Jeep, Owners Manual
You can often find a pdf version on the net, but it's just not like the real thing.