Engine Performance problem
1991 Chevy Blazer 6 cyl Two Wheel Drive Automatic 12000 miles
Engine lost power in the midst of trying to identify what was causing a sag during the 1-2 upshift. Previous to the loss, engine ran quite well, and especially well in open loop. Here is a list of what has recently been replaced for various other reasons :
Fuel pump(tank like new inside)
Wires, dist cap and rotor
fuel filter/ with new pump
AC O2 sensor
rebuilt injectors(cleaned and flow tested)
dist P/U coil and ignition module, Ignition coil
Here are the conditions and symptoms:
Exh pressure at o2 tap before cat, converter <1/2 at idle, <1 at 2000 RPM and ~3 PSI under heavy load (brake torque at 2000 RPM)
Base timing set at 0 deg. Temp: 190 deg. F smooth idle, fuel pressure 11 psi, Oxygen sensor voltage bouncing between 800 and 200 MV at idle.
During very moderate acceleration, O2 drops to near zero, BLM maxed out at 160 (lean) per WINALDL and my S10 Blazer falls flat on its face. There are no backfires. Fuel pressure during this whole time is 11 PSI before a new regulator. Normal O2 voltage recovers each time at idle always. A known good ECM does exactly the same thing. Both injector spray patterns look good and flow increases when revving in neutral. Neutral revs seem normal. TPS and MAP sensors are in range and voltages are smooth.
ECM grounds read zero from battery and 12 and + 5 volts are OK. EGR is closed at idle and motor displays the same symptoms with EGR hose plugged. Manifold vacuum is 20" at idle and 20" at 2500 RPM in neutral and jumps up briefly when throttle snaps shut.
Open loop ( O2 sensor disconnected) operates equally bad. Vacuum tube thru center of TB and hose to MAP sensor is clear. Gasoline in tank is the same fuel as when truck performed well.
I am out of things to check and could use some help.
have the same problem?
Monday, June 14th, 2010 AT 9:00 PM