Hi All..
i have a 96 2wd astro 4.3 vortec about 175,000 miles .. and its just won't idle smooth..runs great at speed.. keep coming up with random miss fire.. or cylinder 3 misfire..
compression is good 130-150 on all cylinders .new plugs,wires.Cap,rotor ..still the same . Maf, O2 , Injectors .. still crap..

Any ideas?
Help
Dan

 

It's possible you have a vacuum leak.

 

check your entire intake hose from filter to intake manifold. sometimes the intake takes air behind the MAF and it causes miss fires. the seal on the intake manifold could be damaged. if possible, hook up a scanner and monitor live data from MAP sensor and MAF. if there is a leak you will notice pressure differences in the MAP when the car misses. check all vacuum lines.

 

It idles like a mean v8 with cams ? and you can smell fuel from the mufler tip ?

 

Hello new here to the forum. I am haveing the same problems. started off as a cyl 1 and 2 misfire, replaced coil, plugs, wires, cap and rotor (acdelco), maf, tps, distributor, checked for vaccum leak by spraying every inch of the motor, cyl 1 was misfireing at 96 misfires per cycle and cyl 2 was 79 misfires per cycle, now i have a cyl 3 misfire at 185 per cycle, checked fuel have 64 psi with key on and 55-60 with it running, also did a injector test and all the injector pressure to 65 and go to 30psi t the same time, replaced with new cam sensor, new egr reading on my scanner at 1500rpms my cam would go to -17 degrees so i resat the timing at 0 degrees and it seems to running a little worse. Starts with no trouble but has a small rumble like he said above seems like it has a radical cam , If you go to pull out i stumbles a bit but runs fine with higher rpm. misfire counter goes down between 20 and 65 at higher rpms




here the specs from my scanner,.

rpm 700
tps 0.57
b1s1 495-600 MV fluctuates constantly
B2B1 200-550 MV fluctuates constantly
B1S3 200-740 MV fluctuates constantly
A/F RATIO IS 14.7
MAF 7.5
BARO (KPA) 95
MAP 2.05 V 49(KPA)
COOLANT 94DEG CELSIUS
INTAKE AIR 16 DEG CELSIUS 2.66V
IAC 84
DESIRED IAC 84
DESIRED IDLE 650
IGNITION 13.5 VOLTS
MISFIRE CYL 3 184 PER CYCLE
KNOCK 4.65
SPARK ADVANCED 22
KNOCK RETARD IS 0
CAM RETARD 0
CAM RETARD CHANGES TO -17 AROUND 1300 RPMS AND SLIGHT TO NO MISFIRES AFTER 1200 RPMS
B2S1 SWITCHING FROM LEAN TO RICH CONSTANTLY
egr 0.76

 

It was a bad injector spider, it was leaking on the right side