Question about 1999 Chevrolet K2500

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1993 7.4 liter in a motor home. Runs nicely until

1993 7.4 liter in a motor home. Runs nicely until it hits the 75% throttle mark and goes into open loop mode. (I built an electronic circuit that monitors the oxygen sensor output.) O2 sensor output drops to about .250v and power falls off. 15 seconds or so later, the O2 sensor shoots up to .820v where it is supposed to and the power comes up to where you would expect at full throttle. Fuel pressure is constant at 12 psi. In closed loop mode O2 runs at .420v and runs very smoothly. What could be causing the delay in getting the mixture richened? It has done this since I've owned it, about 5 years. I added the Banks exhaust and cool air package, installed new O2 sensor and nothing changed, except for more torque.

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  • mooneeman Jul 04, 2009

    The symptoms are the same as they were before the Banks system installation and the new O2 sensor. I also installed a new temp sensor and a new MAP sensor with no change. I will look closely at the EGR system.
    Thank you.

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You might start considering the PROM as these values and other parameters could be incorrect within the chip programming especially with Banks add ons.Another item,EGR could be agressive and delivering too much flow causing uncontrollable lean mixtures that put you into open loop.Check all other outboard sensors such as Temp-MAP which could take your system into open loop as well as o2's which you are aware of.It is possible for o2's to be giving false values...good luck

Posted on Jul 01, 2009

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