i drive a 94 ls/vtec with quite a bit of work. i just rebuilt it about 2 months ago and ever since i have a rough idle and when vtec comes on black smoke comes out the exhaust. i took it to the dyno to see if hp was the same but i lost about 18hp. i was hoping to fix it my self but not sure what to check. could my valve lash have anything to do with it? any replies is appreciated.

 

Black smoke means you are running rich. What kind of fuel management do you have? If you don't have anything but an ECU chip, I'd suggest getting a Hondata or something tunable.

 

i have no fuel management but i didnt before the rebuild either. i have a mugen ecu. but y would it only do it only in vtec?

 

The mugen ECU is notorious for running rich, especially in VTEC. That's your problem.

 

maybe so but it didnt before the rebuild. it had perfect idle and ran great with no smoke before.

 

I would say the valves. I mean if it's only in VTEC then I would check valves.

 

I got similar problems with my LS/VTEC, but after tuning the ECU engine run perfectly. I suggest You reprogramm the ECU. BTW, what Ecu are You using. Is it true Mugen or it's stock Ecu with "Mugen-like" chip installed?

 

its a true mugen ecu. i was really thinking valves or somthing like too but i sent the head off to a machine shop to get all seals and a couple of valves replaced cause they werent in perfect shape and a 3 angle valve job done so im not sure...

 

Save your motor and your ass some money.. Get hondata .. it'll solve it.

 

My point from the get go.