pinging sound while driveing

well i bought a 1994 honda accord ex with the 4cyl vtec 5 speed from a neighbor a few months ago for 300 cash (they need'd drugs or something more than the car) but after i bought it (ran great when i got it) the balance shaft seal went out and oil went everywhere so while i had all the stuff off the motor to fix that i replaced the water pump, oil pump balance shaft belt and timeing belt all in the same job..well that was a few months ago well just recently i have noticed a pinging sound when im going down the road , i only hear it when i give it gas, let off the gas it stops go up a hill i hear it give it gas i hear it...
i have not trouble shooted it yet but since i joind the sit i figured whom best to ask than honda tuners

o and if im parked and its at an idle and i pop the hood and rev the motor it does not ping or rattle only while going down the road with the tranney load on the motor

What's the ignition timing set at? Is the egr system in good working order?

im not sure on the timeing, i know when i reinstalled the parts on the motor i redid the timeing and it was set properly and sounded great..but now thinking about it i could possibly have a bad belt or jumped a tooth on the timeing belt?....
the egr is all in good working order
 
would the o2 sensor cause anything like this or is it more a timeing/ingition problem?
i could replace the plugs rotor and cap retime it
 
just trying to save from doing unneed'd work

I'd double check your oil levels to begin with.  Check the timing (should be fine but it won't hurt).  Are you sure it's not lifter rattle you're hearing? or a loose heatsheild etc.  I just wanted to make sure that it's a pinging noise and not an odd rattle of some sort.  Pull the spark plugs, cap and rotor and inspect those to make sure they're in good working order.  So here's my suggest approach angle

Check Oil
Make sure it's a pinging noise and not something else
Check Plugs, Cap and Rotor (use only NGK or Denso Plugs, if bosch throw them), Check plug wires at night for arcing
Check Timing

 if bosch throw them),
 
well im guilty lol im running the cheap bosch plugs
ill get a set of ngk's
as far as  a hear shild rattle i removed that as soon as i bought the car due to the rust on it made the whole bay look bad
engine oil is as good as possible on the stick.
 
and as far as being a rattle i dont belive that it is, because if i let off the gas it stops but give it more gas when i hear it it stops.
 
 

bosch plugs are notorious for causing problems in honda's.  They have been known to blow a coil or two over time.  that may be your issue

x2 on the bosch plugs.  Chunk em.  Get NGK or Denso.