Real detonation?

[jeff1234]

I have had an ongoing problem with my CEL. I have read many of the posts concerning detonation and have tried most everything except running a hose from the engine to a stethoscope or similar set up. That is next, but for now... I have tried timing the engine as low as 2 degrees (sensor unplugged) but it doesn't make any difference. It still sets off the CEL right about 10 psi in every gear regardless of timing or fuel pressure settings. I have tried fuel pressure from 55 psi to 48 psi. 48 seems to be the best. I have +40 injectors and three different Shelgame chips, all of which do the same thing. I am running lower fuel pressure based on how the plugs look. By the way, RN12YC or RN9YC or the Autolite equivalent, no difference. I presently have about 8 degree's initial and although the CEL is lit, i only hear knock at the high end of the rpm range. Here are a couple of questions. 1. I measured my compression ratio at 9.2:1, I have the 782 head, could this be overly knock sensitive? I have decarbonized the combustion chambers by spraying water into the intake, no help. 2. I have Wiseco forged pistons, I have heard they are noisy, could this be the source of the CEL? 3. My engine has a noisy valve train, could this be coincidently resonating at 10 psi? I'm about ready to use Roachjuices teflon tape solution or remove the CEL lamp from the circuit. Would alchohol injection solve this? Any ideas?

[wallace]

Do you see any signs of detonation on the plugs? I had a problem with the CEL indicating knock and I found worn out alternator bushings to be the culprit. Are all the engine mounts in good shape?

[tryingbe]

Get a OTC 4000E then you can really monitor knocks and tune from there.

[roachjuice]

I have had an ongoing problem with my CEL. I have read many of the posts concerning detonation and have tried most everything except running a hose from the engine to a stethoscope or similar set up. That is next, but for now... I have tried timing the engine as low as 2 degrees (sensor unplugged) but it doesn't make any difference. It still sets off the CEL right about 10 psi in every gear regardless of timing or fuel pressure settings. I have tried fuel pressure from 55 psi to 48 psi. 48 seems to be the best. I have +40 injectors and three different Shelgame chips, all of which do the same thing. I am running lower fuel pressure based on how the plugs look. By the way, RN12YC or RN9YC or the Autolite equivalent, no difference. I presently have about 8 degree's initial and although the CEL is lit, i only hear knock at the high end of the rpm range. Here are a couple of questions. 1. I measured my compression ratio at 9.2:1, I have the 782 head, could this be overly knock sensitive? I have decarbonized the combustion chambers by spraying water into the intake, no help. 2. I have Wiseco forged pistons, I have heard they are noisy, could this be the source of the CEL? 3. My engine has a noisy valve train, could this be coincidently resonating at 10 psi? I'm about ready to use Roachjuices teflon tape solution or remove the CEL lamp from the circuit. Would alchohol injection solve this? Any ideas?

I know quite a few people that have had the same problem. My current knock sensor in the race car doesn't work. I know this. It never reads knock. Plugs look good. Timing is stock. Plenty of fuel. It shouldn't knock. I don't trust it when it works. Hasnt blown up yet. I don't know what could be causing this issue. Hell my 2.5 Omni would be flashing the cel at 10:0 afr and less than stock timing! It was losing power real bad. Sometimes after a run it would pick up knock just driving!!!! Engine wasn't knocking or making any noise! I don't know if the voltage was wrong or what. All I know is I hated it. One day it would be fine. Next day knock city with no other changes. Same weather same boost same timing same fuel.
Personally I think the factory knock sensor sucks. It's not accurate. Check the plugs. No salt and pepper. You're fine. Teflon tape just one or two rounds of it on the threads should work to deaden it a little. Rob Mercer (force fed mopar) is having this problem as well with his lebaron. Removing the cel lamp won't work. It will still pull timing. As long as that knock sensor sees "knock" it will pull timing.
Also ask Rob Lloyd (shelgame) to burn you a mopar stage 2 tune just scaled for your setup (injectors map etc) and dont touch the timing in the cal. See what happens. That tune is the tune I've had the most luck with.
Also what's your reading on the wideband?

[Force Fed Mopar]

2.2 or 2.5? Stock lifters or 2.4 lifters? How did you determine you have 9.2 compression? Is it a new knock sensor or an old used one? How much clearance on the forged pistons? I am assuming you are running at least 91 Oct fuel and that it does it after its warmed up?

[shackwrrr]

I had to raise my knock threshold a lot below 2k to filter out noise. Then ramped it up. I'm automatic with a high stall torque converter though so pretty much any throttle input takes me over 3k. The newer sensors are extremely sensitive and either need a resistor or the threshold adjusted.

[shackwrrr]

Also find some octane booster or race gas, add that, if knock goes away or lessens you know its real.

[Reaper1]

I've also had the issue. I haven't put the Shel-Game cal back in yet. I think I might try it this weekend. I tried the Teflon tape trick, no luck. I had alcky injection on the car when I first ran it. I tried all kinds of settings, mixtures, and fuel settings as well as fuel pressures. Nadda, it always showed knock.

I don't have a way to log knock, so I don't know if it really was, but the plugs always looked good. I run NGK BPR6ES plugs gapped at .028 with the ground strap modded and they are indexed.

[jeff1234]

Wallace, here is what I see on the plug, the porcelains are white, no salt or pepper, the ring that the ground strap is attached to is black with no residue, plugs just installed. Alternator, just replaced, motor mounts brand new.
Tryingbe, that OTC 4000 is cool, where do you get them and what is usual price.
Roachjuice, I am going to consult with Rob and see how much different the cal you mentioned is than the one I presently have from him.
Force Fed Mopar, 2.5 roller cam from TU stock style lifters from Autozone. I determined my compression ratio by measuring chamber volume with liquid and calculating from there. Probably .002 clearance on pistons, machine shop didn't log everything and I didn't ask. My bad. 91 octane, all the time. It does what it does anytime. I have used octane boost, no help.
Shackwrrr, I cant change threshhold, I guess Shelgame would have to. By the way, Using race gas will damage you AEM uego, as per their instructions. I called them about spraying water into the chambers, they said no problem.
This thing does what it does regardless if it is 10:1 or 15:1 f/a. I really seems to be rpm or boost oriented.

Thanks for the replies, it has shown me that others are struggling with this as well and gives me more confidence that what i'm seeing is BS until I actually hear a knock.

[roachjuice]

OTC 4000 on eBay. About 50-150 dollars.

[bakes]

Most of the false knock i have come across is cam/ valve train related .

[jeff1234]

I believe that, my valve train is really pretty noisy . Jeff

[zin]

The problem isn't so much the sensor, as it is the routine that analyzes its output. It seems that it needs a "band-pass" filter, something that will limit the frequency of the signal to filter out the non-detonation noises...

Can be a tricky thing, and is no doubt why so many new engines will have two. With two one can isolate the location of the sound, not just that there is a sound, so if a noise originates in the cylinder, take it seriously, if it's coming from the heads or bottom end, ignore it! Though I'd hope if it picks up on noise from the bottom end it'd let you in on the secret!

I think Ian's suggestions are the most practical, given what we have to work with... But an electronic stethoscope would be quite informative.

Mike

PS Race gas won't kill your sensor, at least not right away, it will cut down its life-span, but so will running it rich, so a bit of testing shouldn't cause any problems, especially if you let it warm up before starting the car. If you wait until you see the display go full lean, you're warmed up.

[shackwrrr]

Also you can get unleaded race fuel that won't kill the sensor.

How quiet is your exhaust? I can hear real knock over my 3 in exhaust at 5k rpm before the knock sensor picks it up. It takes a well tuned ear to hear it. Think cellophane tape hitting fan blades, best I can describe it.

[jeff1234]

shaackwrrr, I have 3" into 2.5" into Magnaflow straight through. I can hear it about 5K, just a couple of staccato like clicks.