Using ECU for an RPM activated switch...(experienced, mods, geniuses please =])
 

I am trying to get around buying an MSD rpm activated switch (or any alternative I've seen so far) because they're around $65. I am wondering if I can somehow use the tach signal from the ecu to trigger a relay at a given rpm. I've been using the CEL shift light feature of uberdata for a while, and this is one idea, another idea would be to use the IAB engagement for a gsr, but I don't have a gsr (p72?) ecu, only a P28.

Is there a certain pin that the 'CEL shift light' uberdata script sends 12v+ or ground to when that rpm is reached? The only thing is that I am worried that this might be shared with the actual CEL circuit that triggers the light when a code is thrown, and using it for my purposes would interfere with its normal operation.

Any ideas, thoughts, alternatives? Thanks in advance.

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

Are you trying to make your own Shift Light? ...And just worried that using the Uberdata shift light feature might cause you to miss ECU codes if they are thrown?

Hard to decify what you are asking...

How much have you actually searched on this? I'm sure there are clever write-ups all over the internet on this.

Google is your friend ;)

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

I am trying to get a signal for one of the vtec solenoids on my engine (yes there's 2, one for the 'vtec-e' 12 or 16 valve operation, and one for lo-hi cam. If you want to see more, look at the '3 stage vtec' http://asia.vtec.net/article/d15b/)

If I wire up the one solenoid so it sees a 12v+ constant and runs in 16-valve mode as long as the ignition is on, it idles funny and makes noises sometimes. Currently both solenoids are wired to (pin a6? i forgot) on the ecu, so at ~4400 rpm the motor goes from 12 valve lo cam to 16 valve hi cam. I'd like it to run as it was intended, but the correct ecu (p2j if I remember correctly) is hard to find and from what I understand it has obd-2 style plugs. I'd like the motor to transition from 12-16 valves around 2800 rpms.

I've been researching this for quite some time and trying to go about it various ways (shift lights, the msd switch, any electronic components I could assemble to interpret the tach signal). I figured I'd ask here as someone may know how to do it with the p28.

btw thanks for the very quick response.

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

I think that you could either buy the RPM activated switch or add the components needed to convert the P28 to a P72 and use the secondaries control to do what you are looking to do.

Talk to Projekteg about converting your P28 if it is something you arent confortable doing yourself.

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

hrmmmm, i'm not 100% sure, but about 99% that it would work wired in to iab's. convert teh p28 to a p72 with iab's and use the iab's to activate the 16 valve, then use the regular vtec to activate vtec as intended. so basically you would leave the vtec at pin a4 (if you have it in a6, that's your problem right there ;) ) and wire teh secondary solenoid or whatever it's called for the 12 to 16 valve operation in to pin a17 which would be for the iab's.

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

Would you be able to lead me in the right direction as far as what I would need to add to the ecu to give it the iab capability? And how I could change the iab activation rpm?

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

iab activation is on the rev limits tab of ud right above shift light. here is what's need to convert a p28. Q17(A143)...already present on USDM auto 11F0/1720 (A5x, L5x, etc). Not present on EDM auto 11F0/1720 (G5x, etc).
Q34(D1780 or C3225?)... already present on USDM auto 11F0/1720 (A5x, L5x, etc). Not present on EDM auto 11F0/1720 (G5x, etc). may use PCS trans: Q31(D1780)
jumper from right hole of R135(trans side) to D13(arrow side)

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

http://www.pgmfi.org/twiki/bin/view/Library/AddIABToP28

that might be a little better organized

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

Thanks a million guys.

Re:Using ECU for an RPM activated switch...(experienced, mods, geniuses please =
 

I'll take 1/2 mill...give the other to Projekteg ;)