i have 3.4,volts to coil,no spark

You will need more than 3.4 volts to the coil. You should have 12v @ the positive side with the key on. If you attach a wire with a grounded spark plug to it and ground the signal side (-) you should get spark from a good coil.

thank you very much so'''i had baught a comp,scanner hooked it up and im getting a ererr message its saying it can't read my computer,im at a block wall,should i change the main ''cpi'' computer again?im lost..

Check your cigarette lighter/radio fuse(s) first. If the scanner doesn't pick up vehicle power from this circuit, it often will not do anything. Could still be a computer issue, but don't jump the gun.

i will check them ,i also just other day replaced the grey fuse center junction box with all new fuses,but the computer under hood bolted to firewall was used i think it could be bad,

Try this: http://www.topix.com/forum/mesa/TTC3KFC4OII4HPC1G.

Just had a 98 Grand Cherokee with no spark and no fuel pump. There was 3.6 volts coming to the ASD relay and fuel pump relay... There was a bad AC CLUTCH relay leaking voltage back through the CPU. Pulled it out and it fired right up. ... Got lucky, hope this helps you poor Jeep owners...