1994 GMC C1500 smoke signals

94SLESIERRA

MEMBER
1994 GMC C1500
V8
4WD
AUTOMATIC
183,924 MILES

My 1994 GMC sierra SLE z71 has been having a few problems lately, when I rev the engine when it is warmed up it emits black smoke and when I start it I get a blue smoke from the right hand side of the engine (it has dual exhaust), I also get a egr trouble code every once and a while. I have also been getting poor mileage when a few months ago I was getting 14 in town and 17 on the highway (not bad for a 4x4 with 33 inch mud tires). The engine has headers, a cold air intake, a throttle body spacer and the throttle body has been smoothed out. It has a new distributor cap, rotor, accel super stock wires, AC Delco plugs gapped at 0.35 and an MSD blaster coil. There is also a motorvation chip in it. THere is a new fuel pump, tank, IAC, TPS, MAP, O2, EGR control, temperature sensor, all have been replaced over the course of a year and a half. I made my own adjustable fuel pressure regulator but did not change the diaphram. What to you suggest that the problem could be?

1 Reply

PEAR69

MECHANIC
1,482 POSTS

I assume the engine is a 350. Is the engine a vortec? Does it have a TBI or CPI fuel injection system? What is your fuel pressure?
Blue smoke is oil being burned in the combustion chamber--Black smoke is a fuel rich condition or too much fuel squirting into the combustion chamber. Oil can get into the combustion chamber two ways--through the valve seal or through the piston rings. The valve seals are not as much as a problem as the piston rings. Do a compression test on all the cylinders and let me know what you find?
BTW--check the plugs tell me what they look like?

Oh yea, try opening the gap on these plugs to 45 or 50 thousandths. A high power coil and ignition system usually needs a bigger gap.