jeff48

I am posting a file of the latest of several runs, all which
show some phantom knock spikes that occur for just a fraction of a second. I chart these files showing

1. Basic Boost (with a verical range of from -750 to 15)
2. Basic InjDuty (with a vertical range of from 0-100)
3. TPS Volts (with a vertical range of from 0-5)
4. Basic RPM (with a vertical range of from 0-8000)
5. Knock (with a vertical range of from 0-150)

You can see that the "phantom spikes" occur after hard acceleration and boost but, not where you expect to see them (during prolonged WOT). Instead they occur seconds after the throttle has been released and Injduty cycles are at 0. The attached screen capture is an example of this phenomenon. These phantoms continue to occur in this way and after days of charting I still can't figure out what is going on.

Things I have checked:
1. No noises corresponding to the spike
2. No loose connections
3. No loose bolts
4. Ground is perfect
5. The logged spikes are similar to the peak hold numbers registered on FC Commander with the logging hardware disconnected.

I am going to post this in the Single Turbo forum and ECU forums also. Any ideas would be greatly appreciated.

Jeff

680RWHP12A

the noise its picking up is apex seal chatter.....try switching the knock sensor to the other rotor housing.... see if there is a difference...

Resource

Now that I think of it.I do remember hearing about 3mm chattering.

Hmmm.

680RWHP12A

the apex seal size dosent matter as much as apex seal material , and the condition of the rotor housings... if very minor chrome is missing it can cause spikes in the knock sensor...also the oil injection may not be enough , try adding more oil..

Resource

Jeff48 has a brand new motor with less than 2000 miles on it so I highly doubt the housings are damaged.


My question is.Why is the knock sensor picking up sound 5-6 seconds after he lets off the throttle?

680RWHP12A

if the motor has BRAND NEW rotor housings my guess would be lack of oil injection... what kind of apex seals are in the motor?

jeff48

This is an interesting, but unsettling theory. The seals are Mazda OEM. The OMP is injecting a lot of oil since the vacuum lines have been removed. Based on oil consumption, my best guess is that the OMP is injecting twice as much oil as normal.

I am very interested in why I would see chatter appearing seconds, not microseconds, after throttle cut. Also, the chatter, if that is what it is, appears to be occuring for one brief instant instead of a recurring pattern. I am also confused as to why the chatter might appear during a period of level RPMs instead of during a period of rapidly decreasing Rs.

I like the theory however and I am going to add some 2 stroke oil to the gas next fillup. I am also going to swap the knock sensor if the spikes keep occuring.


Thanks for the reply
I am still interested in all theories so if you uys can keep them coming I would appreciated it.

setzep

Maybe it's because you are running fuel cut durring decel? I've herd that rotary engines don't like this.

fdracer

maybe your injecting too much oil. are you using synthetic? synth's leave a residue for lubricating, maybe some of it has built up at the injection hole and causes your apex seal to chatter when it goes over it.

jeff48

Setzep: Could you give me a little more info on what you mean by fuel cut during deceleration? If you are referring to instituting fuel cut at different RPMs dependent on the on/off character of certain electrical loads... then the answer is yes. Depending on the load, FC is instituted at anywhere from 1000-1800 Rs.

fdracer: No, I am not using synths. Just plain old Castrol 10-40 or 20-50

Yes, because deleting most of the vacuum hoses effects the ability of the OMP to control the rate of oil injection, there is probably too much oil going in but would you explain your theory that knock spike might be result of too much oil

Thanks

javrosario

iTrader: (5)

What kinda of knock sensor are you using?

jeff48

bone stock knock sensor......didn't want to confuse the ecu

fdracer

have you tried higher octane gas to rule out that it's not really knock?

Lost Time

You're not the only one. I've seen the exact same thing on mine. Are you using an engine torque brace? I noticed that after I installed mine the phantom knocks went away. When I took it off, they returned. Coincidence? Probably not. May have something to do with the engine rocking over when you drop the throttle. Just a thought.

setzep

From what you say you are running fuel cut durring deceleration (throttle has been released and Injduty cycles are at 0). If you didn't run fuel cut you would have some fuel being injected in the engine while off the throttle coasting in gear.

jeff48

OMG
I think we have a winner!!!!!
I am going to try this ASAP----Thank you, I will let you know here and via PM in a week or so.

jeff48

Not yet but I am running 93 octane exclusively. I will either try to find a load of something better or add some of STP's Orange can enhancer (I know that would only get me to about 94 but it may be the best I can do locally).

Thanks for the suggestion

jeff48

That seems accurate. Can you suggest a procedure to rule this out as a cause for the spikes. I thought that with an FD, fuel cut was always on until the Rs returned to the presets, so unless I put it in neutral or push in the clutch on decel, the fuel cut (0 Injduty) would occur until the engine speed would reach the preset.

setzep

Can't you simply turn off fuel cut during decel or is that not a option on the Power FC?

Lost Time

You can adjust the fuel cut on decel with the PFC.

jeff48

As far as fuel cut on decel, I will give that a try by setting fuel cut to begin at 0 RPM but I am afraid that will have the different (negative) effect of causing idle problems.

Resource

The whole engine brace seems logical to me.I'm very anxious to see if this cures it!

nocab72

Most of my "phantom" knock numbers show up during "shifts", so the rocking motor could certainly be causing this... I always thought it was probably drive train shift noise the knock sensor is picking up...

I've got a set of urethane motor mounts I'll be installing soon, will let you know if that helps out with the phantom knock as well...

K

jeff48

jeff48

Lost Time

Thanks for the option but I installed my torque brace last night and I am still experiencing the knock. However, I don't feel like I spent the money badly......I now have one of the tightest shifters ever!!!!!