sharkcohen

I use a switched ground auxilliary port on my engine management (EFI PMS) to control when vtec engages. However, this custom wiring makes no provision for the VTM signal (vtec pressure switch), so sometimes I get a CEL for code 22. What I want to do is fab up something using electronics parts to fool the ECU into thinking that it is still connected to the vtec solenoid and the pressure switch, and that the system is functioning normally.

To review how the vtec system works, at low RPM the pressure switch is closed, running the VTM wire to ground. The ECU activates vtec by applying a 12V signal on the vtec solenoid wire, which activates the vtec solenoid. Oil pressure does its thing, the vtec rockers enage, and the oil pressure switches the vtec pressure switch, opening it. Thus, when vtec is engaged, the VTM wire is open, which tells the ECU that vtec engaged successfully.

Here's an MS Paint of what I think would work, using the appropriate resistors, diode, and transistor. I'm pretty sure this would work correctly, but I'm an electronics n 0 0 b and could use some input from people that are educated in the subject.

TimeRacer

Shark, after thinking about it I opened up the Helm's and looked at the troubleshooting section. From what it seems, the VTM (ECU side) is always putting out 12v and is grounded at the switch. When the switch reads 55 psi it switches on and sends the "ok" signal (allows voltage to pass though) to the VTEC solenoid. At least this is my speculation. So putting a relay on the wire won't work unless you have a connection to ground when the circuit is open, and the connection to the switch when it's closed. At least that's my speculation, as I'm an electronics n00b as well!

Though then again the issues of the off throttle (at least for me) readings will screw with the ECU as well. I'm not sure how it'll interpet it if the ECU sees the engine at 6000 RPM and the VTEC pressure switch reads "too low" when you get off the throttle.

prelittlelude

ok so let me get this strait, are you basically trying to make your own vtec controler without having the ecu cause you problems?

its obvious that you can switch the vtec solinoid on or off when ever you want using the auxilliary ground with your engine managment.

im not sure what type of engine managment you have but if you are concerned about the vtm signal what not use another output if you have it connected to a relay. when below the STOCK vtec engaugement point have the relay closed so that the ecu sees ground thinking that the presure switch is still closed, and then when the appropriate STOCK engagment point is reached you cut ground to the relay which causes the relay to go open which causes the ecu to see an open on the VTM wire. i just don't know what type of control you have with you EMS or if it is even a piggy back ??

sharkcohen

Dammit, I've got the VTM signal backwards, the pressure switch is open when vtec is not engaged, and closes when vtec is engaged. Funny thing is, I already had this epiphany 18 months ago, and forgot

sharkcohen

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by prelittlelude &raquo;</TD></TR><TR><TD CLASS="quote">ok so let me get this strait, are you basically trying to make your own vtec controler without having the ecu cause you problems?

its obvious that you can switch the vtec solinoid on or off when ever you want using the auxilliary ground with your engine managment.

im not sure what type of engine managment you have but if you are concerned about the vtm signal what not use another output if you have it connected to a relay. when below the STOCK vtec engaugement point have the relay closed so that the ecu sees ground thinking that the presure switch is still closed, and then when the appropriate STOCK engagment point is reached you cut ground to the relay which causes the relay to go open which causes the ecu to see an open on the VTM wire. i just don't know what type of control you have with you EMS or if it is even a piggy back ??</TD></TR></TABLE>
Yup, I have 2 switched grounds on my EFI PMS that have throttle and RPM settings. I'm already using one of them to work the vtec solenoid, and the trouble caused by the VTM issue is rare but annoying.

prelittlelude

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sharkcohen &raquo;</TD></TR><TR><TD CLASS="quote">Dammit, I've got the VTM signal backwards, the pressure switch is open when vtec is not engaged, and closes when vtec is engaged. Funny thing is, I already had this epiphany 18 months ago, and forgot </TD></TR></TABLE>

yeah i thought your VTM idea sounded backward.. i was like ehhh its shark im sure he has it right. but none the less the idea with the relay will work. what have you come up with if anything?