My 92 GMC 1500 Automatic runs strong from a stop in 'Open Loop'. In "Closed Loop' it runs very lean, low power and stuttering. If I keep my foot in it, at about 2500 RPM it pulls strong again.


Asked by Mar 09, 2015 at 12:08 AM about the 1992 GMC Sierra 1500 C1500 SLE Standard Cab SB

Question type: Maintenance & Repair

I have replaced the O2 sensor, MAP sensor, TPS, EGR valve, plugs, wires, cap & rotor. I measured the Temp sensor & its in range cold & hot. I also added a performance chip to the ECM. If I disconnect the temp sensor once warm, it goes rich and will die at idle as expected. At idle the O2 sensor voltage swings from 0.1 V to 0.8 V. I tried adding a 780 Ohm resistor to the Temp sensor ckt, it will raise the idle and lower the strong pull to about 2000 RPM but it bogs even worse when initially flooring it. If it were fuel pressure, it wouldn't pull strong above 2500. BTW the old plugs were clean, a light tan colored insulator.

1 Answer


Turns out I was wrong about it being lean. One injector was leaking. I disconnected one injector at a time. On the good one it would hardly move the truck, but on the leaky one it ran almost normal. a new injector fixed it.

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