I'm having a constant problem with carbon deposits from my exhaust planting themselves on the back end of my car, rear bumper, and hatch.
Noticeable right after a wash, even driving a short distance.

I have a recently rebuilt (new rings, honed) DOHC ZC, all stock stuff here no aftermarket, not even intake.
Iridium plugs, recently new O2 sensor and cat, PM6 stock ECU, NO CEL's
perfect running order. Ignition timing set at 16 deg BTDC, cam timing dead on, running 90 octane ethanol blended fuel, not burning any oil or coolant
Compression tested good - 185/185/185/180, plugs look good a little carbon on them but not too much, gas mileage pretty good.

Does anyone have any ideas about this;
- running too rich?
- stuck injector?

 

may be its running rich.

may be you still have some stuff in the exhaust from the old motor, take it on the free way see if you can blow it out.

 

Probably coming from buildup in your old exhaust.

What kind of condition is your catalytic converter in?

 

Catalytic Converter in good shape, only about 2 months old.

 

find a pm7 ecu

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by coupej1 &raquo;</TD></TR><TR><TD CLASS="quote">find a pm7 ecu</TD></TR></TABLE>

The PM6 works just fine with the DOHC ZC, so I doubt that's the issue.

Sounds like you're running rich then. I would actually ditch those iridium plugs. Stock NGKs are all you should be using with your setup. You should also do a spray check on your injectors to see if one is stuck open.