dark grey smoke on cold start up only. lost millage. any 1?

[nothingFancy]

every time i start my car dead cold it smokes dark greyish smoke or almost black , more on the grey side.. only does it on dead cold start up..

also im noticing loss in gas millage. my car is a 97 240 with the ka motor.mods are header,home made short ram intake *passenger side* ,2.5 in cat back. 300zx fuel filter. denso iridium plugs. timing bumped all the way. i dont know if these mods will hurt me in any way.

would any 1 know what causes these problems?

[1991S13]

Maybe you are running rich?

Im not sure, but maybe the timing has something to do with it. Set the timing correctly and see if that does anything.

[p00t]

definately does sound like its running rich...

Could be an injector leak or faulty injector. Measure resistance of each injector where the harness plugs into it. They should all measure near 11 Ohms. If one or more are out of spec they need to be replaced.

Take out the fuel rail, but leave the injectors on it. If you turn the key to the ON position the fuel pump will run for 5 seconds and presurize the line. You will be able to spot a leak past the injector seal. If you try to start the motor the injectors will spray. It should come out as a mist. If one injector is just shooting fuel out of it, it needs to be replaced.

If you are unsure about working on the fuel rail you could also just check the plugs. The cylinder that is running rich will have the plug fouled or wet with fuel.

If all injectors are fine, or all plugs are the same it is something else.