MIL29 IACV Intermittent problem

[veloman]

It’s been a while but even though there isn’t yet a positive conclusion I thought I’d give an update for the interest of those who have given advice and are interested.

I bought a bunch of cheap pin removal tools off eBay, found the one I needed which was basically just a thin strip to poke down the side of the pins and which in theory should have pushed back the plastic locking catch and released the pin. I couldn’t release the pins! I was reluctant to push really hard on the tool or pull too hard on the wire in case I did irreversible damage. In the end I gave up, put everything back together and with the fault now permanently there took the bike off the road.

The other day I generated enough enthusiasm to strip the bike down and access the IACV on the throttle body. I disconnected and reconnected the 4 pin plug and the fault went!! It has remained off so far since. The logical conclusion is now that the problem lies at the IACV end rather than the ECU end which seemed the logical conclusion earlier. As the saying goes “it’s doing me ‘ead in”

I’ve removed the IACV and it seems to be ok. Its clean and the motor spins as it should. My understanding of how the IACV works is that one pair of the 4 wires from the ECU drives the IACV piston all the way down and covers an airway to the throttle body. The second pair of wires then drives the piston back an amount depending on the temperature of the engine. Is this an accurate description of operation?

I also assume that the ECU only returns an error for an electrical problem. If the IACV piston was sticking for some reason the ECU wouldn’t return error although the bike may not idle correctly. Is that too an accurate assessment?

I will persevere!

 

[rc_heli_nut]

Interesting, the pins failed to contact at the IACV? Glad you got it fixed. Any signs of corrosion on those pins?

To clarify how the IACV works, all 4 wires are active to make the motor move. In basic terms, each pair of wires is fed a square wave by the ECM, and depending on which square wave leads or lags the other one, the motor moves the air valve to meter the air bypassing the throttle blades. The motor inside the IACV is commonly referred to as a stepper motor, that is it rotates as commanded by the square waves, with the leading square wave determining which way it rotates, and it steps its way through full rotations. Hope that made sense.

 

[veloman]

Thanks for the explanation of how the IACV works, I kind of understand but am still thinking about it! Although, at the moment the problem seems to be fixed in that all is working OK I haven't yet found a definite cause of the problem. I'll hopefully find the reason for the problem but think it may take time. At the moment I think I'll put the bike together again and if the problem has shown itself again ride it until it does. Then start again!! Thanks for your input which has been helpful.

 

[mikesim]

Keep in mind that the control voltage is typically quite low (~5VDC) thus any corrosion/oxidation on the connector pins can cause problems. You may have unknowingly fixed your NT's problem.

Mike

 

[veloman]

You could well be right about low voltage signals being more susceptible to high resistance caused by oxidation etc. It might explain the elusiveness and difficulty I am having in locating the problem. At the moment the problem seems to have disappeared after removing and replacing the 4 pin plug from the IACV even though previously everything pointed to it being the ECU plug.. I've ridden the bike a short distance and its perfectly ok. I'm just a bit concerned that I haven't actually found a problem and that at some point the problem will return.

 

[mikesim]

You could well be right about low voltage signals being more susceptible to high resistance caused by oxidation etc. It might explain the elusiveness and difficulty I am having in locating the problem. At the moment the problem seems to have disappeared after removing and replacing the 4 pin plug from the IACV even though previously everything pointed to it being the ECU plug.. I've ridden the bike a short distance and its perfectly ok. I'm just a bit concerned that I haven't actually found a problem and that at some point the problem will return.

Time will tell. Based upon what I've learned about the environment in the UK is that corrosion/oxidation is much more likely than on this side of the pond. I've seen some pics from the guys on the UK forum and the corrosion is horrendous.

Mike

 

[veloman]

Just to wrap this one up, since putting the bike together I have rode it all summer without the slightest problem. My younger brother now has the bike as I bought a 350 Classic Royal Enfield (love it), acquired another Velo and don't have enough room in the garage! Within a month of having the NT my brother has problems with it! Nothing to do with the IACV. I've posted the problem on UK site without any response so will start a new post here on my brothers behalf as I am trying to help resolve the issue. I'll trawl through for any previous posts first though that might help.

 

[ST1100Y]

Keep in mind that the control voltage is typically quite low (~5VDC) thus any corrosion/oxidation on the connector pins can cause problems. You may have unknowingly fixed your NT's problem.

Likely, disconnecting and reattaching simply scraped off the oxide layer...
ACF-50 has proven as a good treatment, it's on my annual service regime...

 

[DirtFlier]

"...I've seen some pics from the guys on the UK forum and the corrosion is horrendous...MikeSim"

The one photo that shocked me as regards corrosion in the UK was taken years ago and it was from a NT650 Deauville. The shock mount on the swingarm bridge had completely rusted away! When you're surrounded by salt water, it can't be good!