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so i just got a 94 civic ex coupe and it seems to backfire. has a d16z6 engine but it was barley put in. can some one tell me what is causing the backfire?

 
Rep Power: 188

What does this mean?

backfire could be a lot of things, can you expand a little?

<---is it on?

 
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The original motor(d16z6) that was in it started messin up, so I found a used motor(d16z6) and put it in!

I put the car on neutral and step on the gas and heard the backfire!

 
Rep Power: 188

Does it backfire when driving down the road, does it do it a lot, a little, when was the last time you check your spark plugs?

 
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i really cant hear anything when im in the car

 
Rep Power: 188

what about your check engine light -->

If it only does it in neutral the it might be semi normal since when you rev the car in neutral the cylinders are being loaded with fuel. When the rpm comes down the exhaust valve causes the excess fuel to burn causing the backfire.

Otherwise it may be time for a tune up...(vacume leak,timing..or 100 other things)

so if it drives smooth, and you cant hear it in the car then maybe things are good...