In 1998 I bought a Triumph Herald 13/60, here you can read about it's restoration and share in a few photo's from it's travels. Please feel free to leave comments to any of the posts, of even email me if you want to.

Saturday, August 19, 2017

Converting a Triumph Herald to EFI (Part 7 - IAC Valve Update)

Back in an earlier post I mentioned that I was having trouble getting the Bosch IAC Valve to function correctly, not wanting to be beaten by this I started re-reading all the articles when the penny finally dropped as to why I was struggling.

The valve I was using only has 2 wires, one a 12v supply the other goes back to the ECU so simple enough, but I had missed the instruction which said that I needed to put a 1N4001 diode across the 2 wires, once this was done the valve started to operate as I'd expected.

These valves only need to open a very small amount to make fairly large differences to the amount of air coming into the plenum, so I decided to restrict the airflow by inserting a short piece of rubber hose on the intake side as I figured this would give me more control, I also fitted a small cone filter.

To control the valve you need to work out at what Duty Cycle % it is fully closed and fully open, mine seemed to be at around 33% for closed and 75% for open, once you have these figures you can start to experiment. There are 2 ways to set up these valves, Open Loop (Warm-Up) which is based purely on coolant temperature or Closed Loop where yo can set a target RPM. Most people start with Warm-Up only as it's much easier to set-up, so this is where I started.

With all these things it involves trial and error, but after a couple of days I ended up with with the settings below, which work pretty well. This provides an idle speed of around 1100rpm during warm-up, with a gradual reduction in the duty cycle, then I tail it off quickly just before it's fully warm.

Idle Air Control / Warmup Duty Cycle

I may revisit the settings and experiment with Closed Loop at some point, but for now it's working well so I'm going to leave it alone.

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