cobra2411
01-05-2008, 06:26 PM
Had a 92 Van in the shop last night, 165k miles, rebuilt heads (10k) 3.0 v6, auto.
It was in three weeks ago for a bad cat, if you tap it, you can hear the innards were all broken up.
It was back for state inspection and the owner complained of an occasional miss. It took a while, but we were able to recreate the problem. It seemed to do it more in reverse for some reason.
Anyway, in reverse I brake torqued it and hit the gas. It would start to stumble and cough. At the same time I had the scanner hooked up and noticed a couple things. The fuel trim was -22, but the 02 volts where 0.02. It was like this the entire time it was stumbling, then you would see the trim go positive, the stumble would clear up and the 02 rose to .88v
TPS was steady 50%, temp was steady 204, Stall RPM was 2200-2300, but while it was stumbling it was only able to hold 1400-1500. Manifold vacuum was about 1.7hg while stumbling and about 4-5hg at stall normally according to the computer.
02 sensor is brand new and the problem was observed with both the old and new sensor. Fuel pump is also new, but I didn't get pressure readings during the test.
What would cause the computer to pull fuel when the 02 is showing dead lean?
Thanks,
David
It was in three weeks ago for a bad cat, if you tap it, you can hear the innards were all broken up.
It was back for state inspection and the owner complained of an occasional miss. It took a while, but we were able to recreate the problem. It seemed to do it more in reverse for some reason.
Anyway, in reverse I brake torqued it and hit the gas. It would start to stumble and cough. At the same time I had the scanner hooked up and noticed a couple things. The fuel trim was -22, but the 02 volts where 0.02. It was like this the entire time it was stumbling, then you would see the trim go positive, the stumble would clear up and the 02 rose to .88v
TPS was steady 50%, temp was steady 204, Stall RPM was 2200-2300, but while it was stumbling it was only able to hold 1400-1500. Manifold vacuum was about 1.7hg while stumbling and about 4-5hg at stall normally according to the computer.
02 sensor is brand new and the problem was observed with both the old and new sensor. Fuel pump is also new, but I didn't get pressure readings during the test.
What would cause the computer to pull fuel when the 02 is showing dead lean?
Thanks,
David