Comptech Supercharged S2000 Knock Sensor Problem

[Scott Howard]

I just replaced the Alternator on my 2001 S2K today and after I drove it a little while it started throwing a P0325 CEL code. I cleared it, then it came back less than a mile later.

I took a flashlight and looked at the sensor and it appeared to be screwed into the motor still and plugged into the harness just fine.

I just replaced this sensor when I changed out the clutch 4 weeks ago.:waa:

Can the supercharger itself trigger the light?:think:

I know a few boosted guys still running the stock ECU like me and they say they get this CEL randomly sometimes.

-Scott

[repiv]

The knock sensor is a very simple device, but it's very delicate. In addition to this, putting it in may not always be the easiest thing to do and getting enough torque on it can be a challenge considering the tight quarters in which you have access. Here is a picture of a new one and a broken one:

http://inlinethumb08.webshots.com/21767/2396542690025981935S600x600Q85.jpg (http://good-times.webshots.com/photo/2396542690025981935aAUkTH)

Note that all it is, is a metal core that slips into that hole in the metal base. Also see those 2 little "pads" coming from the core. These pads are only glued onto the surface of the base. If the sensor wasn't screwed in tightly enough, vibration can easily break one or both of those pads loose. Vibration can also shake the connector wiring harness loose enough to not transmit a good signal to the ECU.
It's also possible that in the process of changing the alternator, the wiring harness of the knock sensor could have been interfered with when the harness for the alternator was manipultated during the work.

The above is one scenario. Here's another that may eliminate the actual knock sensor as the problem:
On a supercharged car, knock can be encountered during boost conditions if the air/fuel is not properly maintained. This usually happens during higher boost and thus, during higher rpm and WOT operation. What I suggest you do is the following ................. Reset the ECU to clear the code (since you know what it is). Then drive around for a while (long enough to prove one thing or another) WITHOUT going into a boost situation. Keep your revs below VTEC. Stay away from heavy throttle. This should keep the engine away from a knock situation. If the knock sensor or the harness is at fault, the CEL will likely come back. If you only get this CEL during high boost, high rpm operation, then I would suggest that the knock sensor is "probably" OK, but you had better start looking into the A/F mix during boost. You may be running so lean that the resultant ping (or knock or miss) cannot be compensated by the ECU when the knock sensor does its thing.

PS. Are you using a Comptech kit that was designed for your year of engine? Does it have the ESM? Do you have an A/F gauge?

[Scott Howard]

The kit was for a 2004 but the only thing different was the horn bracket. ( That's what Comptech told me)

I don't have an A/F gauge. shame on me.

It came with a black box thing that keeps the ecu from flipping out when it sees boost. It also came with an upgraded fuel pump and pressure regulator.


Can sudden weather changes trigger it as well?

So basically if it's throwing the light at 45-55mph (6th gear) speeds on the road than it most likely has a bad connection or no connection at all?
If it had no connection at all wouldn't it throw the light before you could even get out of the driveway?

[repiv]

I'm not completely versed in the Comptech. I'm Vortech myself. Did the CT kit for the '04 have a smaller pulley to compensate for the lower redline? The VT does.

Although not impossible, I somehow doubt sudden weather changes would produce the code you got.

It depends on what else you're doing at 55 mph in 6th gear and how you got there. Did you use moderate to high boost getting there? And while you are at speed in 6th, do you give it heavy throttle at any time to introduce boost into the intake? This is what initiates knock -- open throttle plate, onset of boost, high load. Otherwise, I'd guess there's something wrong with the sensor or the wiring connections. Can you reach it from below to check if the wiring plug is on tight? Or if you can unscrew it by hand?
Yes, if no connection, the CEL should come on, however, if you've got a loose connection or a loose sensor, it might not happen right away.

[Scott Howard]

I reset my ECU and I'm going to keep track of how often and when (RPM and Speed wise) this knock sensor code is thrown.


Trip #1: No knock sensor CEL light
-60mile trip
-55-65MPH Speeds
-No A/C
-No Wide Open Throttle (WOT)
-No stop/go traffic
-77 degrees outside

[repiv]

Trip #1: No knock sensor CEL light
-60mile trip
-55-65MPH Speeds
-No A/C
-No Wide Open Throttle (WOT)
-No stop/go traffic
-77 degrees outside

This tells me the engine is not under significant boost. No CEL likely (but assured) that knock sensor and wiring OK. Now try going into high boost. If CEL comes on, you're likely detonating. Time to get supercharger set up checked.
PS. Did you gap the plugs for boost? If not, your spark is blowing out at WOT, high rpm.

[Scott Howard]

This tells me the engine is not under significant boost. No CEL likely (but assured) that knock sensor and wiring OK. Now try going into high boost. If CEL comes on, you're likely detonating. Time to get supercharger set up checked.
PS. Did you gap the plugs for boost? If not, your spark is blowing out at WOT, high rpm.

The spark plugs are gaped properly, how often do they need to be changed in a supercharged setup?

I've driven the car over 200 miles since my last post and the light has not came on. Knock on wood. lol

I still have not put it to the floor yet.:shifter:

[repiv]

The spark plugs are gaped properly, how often do they need to be changed in a supercharged setup?

I've driven the car over 200 miles since my last post and the light has not came on. Knock on wood. lol

I still have not put it to the floor yet.:shifter:

Depends on what type of plugs you're using. If you are using copper plugs, they should be at least checked, cleaned and gapped every 5000 miles. If using the OEM platinum plugs, these can go for 10's of thousands of miles, but check them annually.

Now you need to check for detonation under max boost.