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Variable Intake Manifold

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi Zac,

I can use your help getting a variable intake flap that varies plenum volume on a Suzuki Swift Sport. The car is running a haltech elite 1500 in a piggy back style ecu with the OEM ecu.

We've taken the actuator off the OEM ecu and tried putting it on the haltech but could not getting working for anything. We verfied it does spin with the actuator removed and held in hand and given 12v and ground, but when we install it into the manifold we're not getting any response.

I've done some more digging however and I've found out that this isn't a spring loaded system like most other engines that utlize a variable flap, the Suzuki ecu is actually reversing the polarity to move the motor in both directions hence opening and closing the flap at different rpm.

I've since spoken to another tuner who suggested using a change over relay to get it to work with the haltech. Can you shed some more light on this alternative or offer a better solution yourself?


G'day Chris.

You're already using the drive by wire throttle outputs on the Haltech 1500 to control the OEM throttle I take it?

It would be worth contacting Haltech to see about the capability of their stepper motor drives, as I believe they can drive on the high, and the low side. If they're using a H-bridge IC inside the ECU to achieve this, they should be able to switch from driving on the high side, to on the low side while the engine is running, and that is really what you need. Setting this up in their software might not be possible though :-/.

These flaps are only ever in one of two positions I take it, open, or closed, and never in between? As in, there is no position feedback? If so, then yes, doing it with changeover relays would be possible, see the sketch below. I'm sorry for my messy scrawl! What you're doing here is controlling two changeover relays from a single ecu output. The high power side of the relays is backwards to how it would normally be, we're supplying power into the 87 and 87a pins, and out to the motor via the 30 pin.

Pin 87 of relay 1, and 87a of relay two are connected to an ignition switched 12V source via a fuse.

Pin 87a of relay 1, and 87 of relay 2 are connected to a good power ground.

When the ECU triggers the relays, they will both switch, reversing the direction the voltage is applied to the motor.

Now, I'm assuming you're not going to be switching these relays very fast? Like, you hit an RPM point, and they change over? You'll need a few hundred RPM of hysteresis in the system. If you switch these relays too fast, the inductive kickback from the motor could end up killing them over time.

Let me know how you get on!

Attached Files

Hi Zac,

Yes the dbw is on the haltech, both outputs used.

The first option you're talking about with the stepper motor type output....this is in order to not have to use a relay correct?

Yes valve is either closed or open never in between.

And yes, they will be switching based on rpm and possibly load.

In terms of setting it up in the sortware the other tuner suggested repurposing a VTEC output function in the haltech.

He also suggested using two change over relays one for power and one for ground and both being triggered by a single signal from the haltech. From my understanding this is the same exact thing you're suggesting correct?


G'day Chris.

Yes, if it was possible to do it from the stepper outputs, this would replace the relays

Yes, using the VTEC output function will work, and yes, your tuner and I will be talking about the same setup :-).


Thanks for the input Zac.

Can you clarify one more thing? These "change over" relays, are they different to the regular relays we'd normally use in other areas of an EFI wiring setup?

If so where do you suggest I purchase these?


G'day Chris.

Yes, they're a little different in that they have an 87, and an 87a pin. With the triggering coil not powered, pin 30 will be connected to pin 87a, and with it powered pin 30 will 'change over' and be connected to pin 87.

Any automotive parts re-seller that would sell a normal relay should be able to get them, they're pretty common. For a race-car, I'd try to stick to a name brand relay, like bosch or similar. They stand up to vibration better.

Hi Zac,

Would you mind sending me a link to some you would consider appropriate for what I am looking to achieve? I can then look for something similar on my side of the world based on what I see off the one you selected.

We usually reply within 12hrs (often sooner)

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