Hondata

I just wanted to find out why it is that we need to use a relay for the vtec output from the ecu. I hooked up 3 different relays to run from A17 on the IAB output but could not get the Vtec to work. When i wired up the IAB directly to the vtec solenoid it finally worked. The ECU was a P08. So now the car is currently running direct and works perfectly fine. What will be the draw backs or problems arising from not using the relay?

If the VTEC solenoid draws more current than the output can supply then you will burn out the component in the ECU.

when switching from non-VTEC to VTEC or from non-IAB to IAB pretty big current uccur.

for that reason VTEC-ECUs have an amplifier (some kind of transistor, which switches with a small current (digital side) a bigger current (analog side)) to manage this current.

the relais is a bit different from that amplifier, but in fact the effect is quite similar: with a small current coming out from the ECU you can switch a bigger current on the other side of the relais.

worst case is, that you damage you ECU.

best regards Lukas

but in both cases isnt it a 12 volt output? why is it that i could not get the relays to work? i wired it up right, but the solenoid side would never get grounded...

Amp vs volt are two different things. The ecu can handle only so much amperage through the output. A relay has minimal draw at 12v, where a solenoid has an instant peak and drop at 12v.

Think of it as a garden hose. 12v is the size of the hose, the amps equal the water pressure. The more amps you push, the more your resistance becomes a factor. Let the relay do the work, not the ecu.

You should have two circuits going with each circuit having its own ground. It sounds like the switch ground is not present.

if there was no ground, why would it ground when i give the solenoid a direct 12v from the battery or from the IAB from the ECU? I just cant understand why all the relays i tried didnt work... the relay just wont switch... i wired it up just as the diagram in the help file in s manager

my conclusion is, that the relais was wired wrong or you have used a relais, which uses a certain current to switch the primary side to switch the secondary, high current side.

best regards Lukas