Knock sensor CEL - Honda Prelude Forum

ludebeginnings · 02-06-2004, 02:47 PM

recently got my motor rebuilt & was running through the break-in period. done that & going to get VAFC II installed & dyno'd up next week.

I'll list just the stuff that might affect the knock sensor: crower stage II cams, head milled .040, skunk II high comp valves & valve train. CC'd the head prior to all the work & should be running about 10.5:1 comp.

from the beginning i've been throwing the code 23, knock sensor code. ONly seems to happen when I hang in the 3200 RPM & up or cruising over 60mph. Prior to the cell there is no odd sounds or actions and the car seems to run just fine. once it's on I'm assuming it's retarding the timing as it goes into limp mode.

spoke w/my shop and they stated that there shouldn't be any pre-ignition happening so it's either a faulty knock sensor or possible the work I've had done is duplicating the tone the knock sensor is listening for (my interpretation).

Is there any other possible issues that would throw this code?

It's not bad gas, I run 93 octane tried several reputable places and had the same issue

if it is possible that the engine is duplicating the tone the knock sensor is looking for, and it is doing it, how do you resolve w/out dissabling the knock sensor?

NXLude · 02-06-2004, 06:52 PM

Knock sensors get broke sometimes when pulling the motor apart, Ive had it happen to friends of mine.....

ludebeginnings · 02-07-2004, 09:39 AM

yeah, i'm hoping it's just a f'd up knock sensor...

marcucci · 02-07-2004, 11:26 AM

Uhhh... head milled .040 and high comp valves? You are NOT running 10.5:1 unless you have some extra-thick gasket in there. I believe you will be well beyond 10.5, probably 10.7+ with JUST the mill, you will be past that with the valves. That is, unless you got some massive headwork done and deshrouded, etc.

The knock sensor is likely not bad unless they jacked it up during the work. They can go bad but that's not terribly common. It is worth investigating, though.

Try a bottle of NOS Octane boost before you write off "real" knock.

Do you get a flashing CEL or a static code? Something to keep in mind is that when it happens (if at part-throttle cruising), that's when you are leanest. I wouldn't write off a fuel, tuning, or compression issue (genuine knock).

ludebeginnings · 02-07-2004, 11:36 AM

Marcucci> yeah, had a good deal of head work done. I spent some time figuring out what the compression would be & had him CC the head. Actually, everyone on here helped out a ton when I was trying to figure the right formula. Unless he screwed up when CC'ing the head (did it three times), or I screwed up a calculation, it should be right around 10.5:1. Is there a way to test this now that the engine is assembled?

I'm not sure what a static code is. The engine light will pop on when cruising and stay on until the car is shut down. Please explain a little more & I'll try to answer better.

ludebeginnings · 02-09-2004, 06:04 PM

well, I tried a bottle of octane booster and couldn't get the cel to come back on for the life of me. Guess that may have been the issue...

thanks again for the input

marcucci · 02-11-2004, 12:33 PM

Sounds like it.

"Static" is my term. Your light stays on which means that the ECU detected a misfire. This is MUCH less severe than when the light comes on and flashes which means it has detected a series of misfires. Something is VERY wrong in that case.

There's no way to test the CR other than to reverse-ballpark it off of the compression it blows. That is VERY unreliable, though, since you are essentially assuming your engine is 100% good and you're just going to compare to other peoples' values...

ludebeginnings · 02-12-2004, 07:59 AM

got ya'. Yeah, light was coming on and staying on. I started running 94 octane so I don't have to worry about buying a bottle of octane boost each time...

when I get dyno tuned, will it make sense to run down there on 93 octane? or am I stuck paying 1.80 per gallon?