reference voltages
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reference voltages
I've been trying to find the gremlin in my truck (85 F-150 302 FI) without much luck. I replaced the knock sensor (3rd one from the junkyard) and i still get a code 25 for the knock sensor. I checked the KOEO voltage to the sensor which should be at or about 5 volts but I have 2.51 volts. I've changed several sensors that I had codes for without any change, sometimes I get a code for it sometimes not. It runs fine some days and others it will hardly run. It has a crate motor in it with under 9k on it and freshly tuned up. I can't figure it out unless it is the computer malfunctioning. When cold it runs good, after its been driven a while it begins to act up. Does anyone have any ideas?
Thanks
Dan
Thanks
Dan
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Joined: Jan 2001
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From: Virginia
There is one of those oddball trucks again with the knock sensor. Do you know much about the code tests you are running? After it gives you the KOER tests, it will wait a little bit, and then the scanner or the testlight/meter(whatever you are using) will give you one blip. After this it gives you a couple of seconds to goose the throttle. It looks for the rpm to go over 2000, and that is when it checks the knock sensor to see if it's working. The guy in the fuel injection book says if you keep getting a code 25, when it gives you the blip(they call it the goose test) take a hammer and hit on the exhaust manifold. This will simulate a knock, and if the sensor is working, it will pick it up and not give you a code.
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I"ve done the full throttle on the one flash, theres too much crap in the way to really hit the manifold without hitting other stuff. The plug has 2 wires, the book says to check the voltage across these with the key on / engine off just like the other sensors. I get 5 volts (4.somthing usually close to 5) on all the sensors that should be 5 volts (ECT, TPS, EVR) but the KS is only 2.5 volts. If the PCM isn't giving it the correct reference then when it returns the signal voltage it will be wrong even though the sensor may be good. I've cleaned the connectors and unplugged the PCM and checked the connection there. What else could make it give a wrong reference voltage?
