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Ford Ranger '86 2.9L Knock Sensor replacement questions


pcsstoll

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Hi, I'm pretty new to fixing vehicles but am learning fast. I've had this 86 ranger XLT 2WD for a little under a year and been fixing small things here and there.

I noticed recently that my knock sensor had been unplugged. Truck has been running well but I have no comparison. I plugged it back in and didn't notice a difference in how the engine performs. I did an error code test and received a 25 error code. I traced this down to be a knock sensor issue.

I tested the knock sensor and can't tell if it is functioning or not. I tested for resistance and I tried to do a knocking test looking at Volts AC response. Either this thing is tricky to test or I'm doing it wrong.

I read in the ranger forums of people suggesting the sensor may be too sensitive and pick up unwanted noise. Some one mentioned replacing the computer with an '88 but I'm not sure what other aspects can be affected by this. Also I can't seem to find a replacement for less than $200?

Question: Should I replace the knock sensor for $200? Any tests I should retry or do? Are there better questions I should be asking?

Thank you for your help in advance,
Paul
 

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franklin2

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When you pull the codes, after they are all spit out it should give you the pulse to tell you to goose the throttle. When it does this, take a small hammer and peck on the exhaust manifold near the sensor. If that makes the error code go away, the sensor is ok.
 

pcsstoll

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Thanks Franklin! I will give this a try tomorrow evening and get back with the results.

Paul
 

RonD

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Outside of the code there should be no engine operation issues
The Knock sensor is not needed in most situations
It would tell the computer to advance spark timing if pinging/knocking was detected, usually from sub-87 octane fuel, i.e. blow Regular gas, lol

And you can HEAR if that's happening, so can back off the gas pedal, sound like a Diesel engine

If you have a timing light you can hook that up to warmed up engine, and look at the spark timing at idle, SPOUT connected, should be 18-22deg BTDC
As said above use a metal hammer and tap on the exhaust manifold, should see timing jump when you do
 

pcsstoll

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Thanks Ron,

I'm not experiencing knocking so it makes me think that I don't even need this sensor and to just keep it removed.

I'll test the part again using the manifold tapping method. If it doesn't work then I may just let it be without the sensor attached.

If this doesn't make sense to anyone feel free to chime in.

Thanks for the help!
Paul
 

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