tom jelly

knock sensors gone WILD! (help w/ J&S)

Looks like the rotorsports motor mount for my reman gives a bit of a resonance at low rpm, which , though not bothersome to me, is giving my J&S knock retard unit fits, and causing ig retard at low load low rpm. What I need to do to solve the problem is hook up the yellow arming wire from the J&S to the map sensor so it will only operate under load. problem is, the map sensor has three wires and I don't know which to tap. if anyone does, please let me know...

Thanks Tom

r0t0rhead

iTrader: (12)

Tom,
While we haven't experienced or seen any increased knock signals as a result of our motor mounts-its possible the J&S system is sensitive enough to read the vibrations. FWIW Our experience with ALL knock sensor systems-(including J&S) is that if the tuning is correct then a knock sensor is redundant- the problem is knock sensors are reactive -something bad has to occur BEFORE it can retard the ignition. Another problem is that none of these retard systems can reduce spark knock effectively enough nor do they retard both leading and trailing ignition equally.

So if the system is connected to the leading igniton -and retard occurs then you can have a potentially more damaging situation when the trailing ignition leads the leading.
On a side note-Virtually every ignition problem we have seen on RX7's that come into our shop has been as a result of some form of "high powered" igniton box being installed to try and gain power. The factory coils are quite good and we've used them on many applications exceeding 23psi of boost with no failures.

tom jelly

I just changed out the motor rebuilt turbos, replaced motor mount, removed ac and ps, did a hose job and OMP supply bypass. I have stock ignition. I had no such activity with the old motor, I know there is more vibration, and figure that this is the issue. Its not objectionable to me, only occurs just off idle, and I would buy the mount again if faced with another broken OEM one. I spoke to j&S and they designed the unit to use the "map/tps sensor wire "for just such an issue. with the old motor I never saw more than one light on the j&S (and rarely and only under heavy load) and never really fooled with it much. I have an M2 unlimited chip and I know the car runs rich. BTW J&S said to tap the middle wire of either the tps or map sensor, which will delay arming of the unit till sensed voltage is 2.7, which on the map sensor is about 0psi. I'm going to try it again with this map voltage sensing wire connected and see what happens, then decrease the sensitivity if I still get retard or try with the tps tapped. I THINK there is also a switchable max retard level of 10 deg/20 deg, which I will switch to 10 (anybody know if this will reduce the max retard enough to eliminate the possibility of retarding the leading back beyond the trailing?)

r0t0rhead

iTrader: (12)

Tom,
Virtually all the reprogrammed ECU's we've seen retain at least 13-15 degrees of timing split under full boost- so if you have the J&S set to retard only 10 degrees of leading ignition timing you will avoid firing the trailing ignition prior to the leading-you will not have as much ignition split, but our testing has shown this is NOT always necessarily bad IF you have a good ignition curve. Our racecar runs simulataneous ignition (firing both leading and trailing at the same time) at up to 22 psi of boost- the key is we have mapped the ECU to optimize ignition advance, versus dumping excessive fuel in to try and control detonation. Using a reprogrammed stock ECU and the J&S knock sensor you are a bit limited since you can't "see" exactly what's happening. If your knock sensor keeps reading high and cutting back the Leading ignition then you might have some other issues (fuel delivery) to consider. Its also still possible that the J&S sensor is picking up the vibrations from the urethane motor mounts-if so then the knock sensor sensitivity should be adjusted to compensate.
Hope this helps.
Bryan Smith
RotorSports Racing Inc.