View Full Version : Knock sensor?

03-06-2017, 06:59 AM
Pulled codes on my '90 XR7, with no check engine light. KOEO I got canister purge circuit failure, and KOER got #25 (if I recall) knock sensor not recognized during dynamic test. Little suprized I'm not getting light? How does the computer respond to the no knock sensor? I would think it would go into a limp mode with regard to timing and set a base time and not advance? Is this correct? The car runs pretty well, but just sorted out some other issues, so don't know how it "should" feel with full advance at proper times?


sam jones
03-06-2017, 09:23 AM
Good morning

Here some information on the knock sensor as it pertains to the Ford 3.8 SC.


03-06-2017, 12:31 PM
Also, light bulbs burn out ... I'd replace that light with a 194.

(While the cluster's out so you can, I'd consider replacing ALL the bulbs)


03-06-2017, 01:03 PM
Ford seems stingy when it comes to throwing a CEL in some cases, I think...takes a long, hard, consistent fault, I guess.

Did you try running a code test and whacking the block with a hammer to simulate knock to give the sensor something to sniff? Is the harness and body ground ok on that side of the engine?

03-06-2017, 06:23 PM
Thanks guys.

I get what the knock sensor does, although not exactly what kind of signal is generated. I understand the ecc pulls timing when it detects knock. What I'm wondering is what does the eec do if it does not see the sensor at all? Gas mileage has always been worse on this car than others in the stable, and I am wondering if the ecc has pulled timing to some base "safe" number. Even during low load cruise (where it spends most of its time, highway DD to and from work). Then also I would be losing performance as well (on ramps r WONDERFUL things :D). To my thinking that would be the "safe" response in ford engineer think.

I currently have a break out box plugged in but have not had the time to determine which pin is in from knock sensor to try the "hammer" test, it's on the to-do list, but I am pretty sure the ecc is correct, and the sensor is shot. Just may be a while b4 I can get to R&R.

I know the CEL light works, and all grounds have been cleaned and worked as part of the "other" issues. 1st try I had to use the jumper/CEL flashes to get codes as it would not talk to scanner (however the top left of the speedo is a little dark so lamp R&R is ALSO on the list :rolleyes:). Amazing what a GOOD battery can do! LOL! Was pulling down to as little as 3 volts on crank, and I think blowing out the keep alive memory on start up, as I was getting #15 code ONLY (KOEO) when this mess started.