92 stock 5speed sonoma STOCK with custom exhaust now sounds like it has a cam in it.

Question

the other day, i let my best friend drive my truck. he went to back down the hill out of his driveway and let off the clutch in 4th gear instead of reverse(popping the clutch). the truck acted like it was going to start then cut off. when he cranked it up, it sounded like it had a cam in it. tons of black smoke, ROUGH idle hardly any brakes and it only acts like that until the check engine light comes on then it smoothes out a little bit. the code thrown is a 33(map sensor range too high). what would drive the MAP up, and how could i stop this? ps-the truck levels out a little bit, but the vacuum still feels like it's lacking in closed loop(hard pedal). the truck ran fine before this, with no codes or anything. i had been driving the truck for 250 miles every week to my job halfway across SC. someone please help! i'm lost on this one

Answer 1

sounds like a vacuum leak.  maybe it was caused by the jerk when it stalled.  MAP sensor means manifold absolute pressure, so if a vacuum line has come off the intake manifold it will suck in air at atmospheric pressure which will increase the pressure in the manifold.  it makes the idle rough because you have extra air going into the motor which is unaccounted for so the ecu doesn't know it needs to increase the fuel to match the amount of air, so the mixture goes lean.

get a can of throttle body/carby cleaner and run the motor.  with the car idling spray around the vacuum lines and connections.  when the idle picks up it means you've sprayed on the leak, so the carby cleaner has mixed with the air and gone into the motor to make the mixture richer.