fe1rx

Does anyone have experience with the J&S SafeGuard Knock Sensor on a TII?

Various threads have reported that the stock knock sensor is ineffective at higher rpm. Various people have reported partial throttle and full throttle knocking that the stock ECU is not capable of dealing with. Is this just a lean running/excessive boost issue?

In any case the SafeGuard's ability to a) retard timing beyond the stock ECU, b) indicate inaudible knocking to the driver, and c) potentially save the engine seems worth while.

I had a case where I had a full throttle blast through a tunnel one time and was astounded to hear knocking due to the reflected sound. I couldn't hear it on the open road. How much damage is the knocking we don't hear doing?

Aaron Cake

iTrader: (1)

I have no first hand experience with the J&S unit, but I have not heard anything good about it. Apparently the sensor does not respond fast enough.

If you are exeriencing detonation, my first suggestion is to check your fuel mixture. It would help if you posted your mods.

Digi7ech

iTrader: (1)

Yeah the knock system is kind of a very last resort.

If your AF is set right then you should never have to worry about detonation.

First try searching for the cause of the detonating instead of just giving it a make shift fix.

fe1rx

My mods have evolved like this:

1) 3" custom downpipe, test pipe instead of presilencer or cat, RB 3" Y-pipe and mufflers, no fuel cut defenser. (Sound with this setup is antisocial for street driving above 3000 rpm.) I ran this setup for one track season. I ran into fuel cut only at the top of 4th and 5th, which was not generally a problem on the tracks I run. Boost crept to about 14 psi only in 4th and 5th. Knocking a problem after about 1000 miles on new plugs, but replacing the plugs fixed it.

2) At the end of that season I added a fuel cut defenser. On the first time out, a cool evening I blew the engine at the top of 4th gear. I guess the fuel cut was doing its job.

3) The next season I added a 3" Random cat instead of the test pipe. (The car sounds fantastic with this setup and passes emissions.) Boost was dropped a bit and changing plugs with each oil change generally kept knocking at bay. I blew the engine at the end of the season on a cool afternoon (fuel level was a bit low and could have contributed, I was cornering under power at the time).

4) This season I added a rising rate fuel pressure regulator and ported the wastegate. I tuned the regulator to give 60 psi fuel at 10 psi boost (which incidentally was the limit of the stock pump). This means that I start enriching at about 8 psi. The porting holds the boost to 10 except in 5th gear on very cold days (I was surprised on one track day at 32 deg F). I have almost completely eliminated knocking with this setup, but still need to change the plugs at every oil change (2000 miles).

5) For next season I have installed a Walbro GSS-341 to give me a bit more tuning range on the fuel pressure. I have never had the car on a wideband but I have an A/F gauge. I realize that the output of a narrowband O2 sensor is strongly dependent on EGT so the A/F gauge is a very dubious tuning aid (how many green bars is enough). My goal is to safely run 10 psi boost. To effectively use the fuel pressure the Walbro gives me I will need to get on a wideband and see what's happening.

I agree with Digi7ech that fixing the problem is job 1. I think I now have the means in place to get the AF right up to 10 psi. The safety net provided by a knock sensor with the power to retard the timing does seem appealing though. I am not too keen on replacing another engine.

RETed

It's a waste of money.  Unless J&S makes a proper rotary application one that can handle 3 channels, retarding just the leading will not prevent you from blowing your engine up.  For $150, you can get an MSD unit which is just a strict display - that's what the J&S unit ends up doing for $500!


-Ted

fe1rx

Ted,

I assume by 3-channel you mean 2 for the leading ignition and 1 for the trailing ignition. You are right that the SafeGuard only addresses the leading ignition. It does also provide an adjustable fuel cut controller function and boost retard feature of up to 2 deg per psi also (of course only on the leading ignition).

Idle timing is 5 deg ATDC leading and 20 deg ATDC trailing. Does teh ECU maintain the 15 degree difference between leading and trailing at all times? If this is the case the SafeGuard has 15 degrees of effective retard available. Is this not enough to be useful? The standard retard ranges for the SafeGuard are 10 degrees max or 20 degrees max.

Regarding the stock knock sensor - although I have heard knocking, I have never felt the ignition retard in response to it. The sensor is working according to the test in the service manual. I am forced to question the effectiveness of the stock system.

RETed

Actually, both leading fire at the same time and only constitute one channel.  The trailings take up two channels.

Our research via SAE papers on split trailing by Mazda R&D show that the split goes to zero when load rises,  Thus, the leadings and trailings fire at the same time at WOT.  Retarding just the leadings will still allow the trailings to "push" the engine.


-Ted

fe1rx

The information about the timing split is very interesting but unexpected Ted. I see your point now. Thanks.