Jeep IAC Valve Limitations

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dll67
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Jeep IAC Valve Limitations

Post by dll67 »

I am using a Jeep iac on a custom mount and seem to be running into a limitation on the amount of air it will flow. It seems to be functioning correctly from the test mode results but it doesnt change the rpm.
From open to closed I see a 2 point change in the AFR's but not a noticable change in the rhythm of the rpm.
At first I adjusted the throttle plates thinking I could use the IAC for all my idle air and when that didnt work I put the throttle plates back to their original idle position and all my settings. That was when I got into the test mode and realized what was going on.

Are there others out there that have run into similar problems with iac valves? Because MS's are so problem free LOL

Am I correct in deducing this is a problem with the iac not moving enough air?
Or is the cam so large its masking the rpm change?

Are there any IAC out there that will move enough air for a large displacement engine to have a fast idle at low coolant temps?

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MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
billr
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Re: Jeep IAC Valve Limitations

Post by billr »

When you use test mode, do you have the IAC valve out in the open, so you can actually see the pintle moving? I doubt it is the IAC size. Can you feel a lot of air going in the IAC port when the valve is supposed to be fully open? My BBC (427) isn't nearly as big as your engine, but even an 1/8" hole can affect its idle a lot.
dll67
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Re: Jeep IAC Valve Limitations

Post by dll67 »

Update ..
After fiddling with it some more I realized at idle I was in my "idle VE table" when making adjustments where my fuel is at a constant for a 400 rpm range in an effort to steady my idle.
Every day theres a new lesson with this tuning.
MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
dll67
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Re: Jeep IAC Valve Limitations

Post by dll67 »

billr wrote:When you use test mode, do you have the IAC valve out in the open, so you can actually see the pintle moving? I doubt it is the IAC size. Can you feel a lot of air going in the IAC port when the valve is supposed to be fully open? My BBC (427) isn't nearly as big as your engine, but even an 1/8" hole can affect its idle a lot.
I had the valve out in the open to design my mounting block. I needed to figure out how deep to make the pintle seat.
Side Note ...
Those pintles have a spring under them and when they are not in thier housing the pintle will come out and launch across the room.
Go ahead .. ask me how I know that ... I had to learn that lesson twice.

Anyway I think I will be able to make it work.
MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
Yves
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Re: Jeep IAC Valve Limitations

Post by Yves »

I have the same issues : the valve only ups the rpm with about 150 rpm, which is not enough. I tried using the valve to push against the throttle lever, but it's not strong enough.
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Re: Jeep IAC Valve Limitations

Post by turbo conversion »

What size are the lines going from and to the valve?

I had the same issue with 3\8" lines and fittings.

I am using a DIY manifold and 95 Jeep 4.0L IACV.

I changed the lines and fittings to 1\2" and I can now get 500+ rpm with valve fully open.

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
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Re: Jeep IAC Valve Limitations

Post by jsmcortina »

Yves wrote:I have the same issues : the valve only ups the rpm with about 150 rpm, which is not enough. I tried using the valve to push against the throttle lever, but it's not strong enough.
This sounds like a mechanical problem for sure. A normal idle valve will give 2-3000RPM when wide open.

James
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Yves
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Re: Jeep IAC Valve Limitations

Post by Yves »

What mechanical issues are you thinking about ?
DaveEFI
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Re: Jeep IAC Valve Limitations

Post by DaveEFI »

turbo conversion wrote:What size are the lines going from and to the valve?

I had the same issue with 3\8" lines and fittings.

I am using a DIY manifold and 95 Jeep 4.0L IACV.

I changed the lines and fittings to 1\2" and I can now get 500+ rpm with valve fully open.

David
Really do need an answer to that. If the airways in and out of the valve ain't big enough no software tweaks will help. The Bosch PWM valve commonly used here for conversions is 3/4" in and out, and will cope with 5 litre engines happily.
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dontz125
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Re: Jeep IAC Valve Limitations

Post by dontz125 »

Yves wrote:What mechanical issues are you thinking about ?
The ports are simply too small to flow enough air.
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Re: Jeep IAC Valve Limitations

Post by Yves »

dontz125 wrote:
Yves wrote:What mechanical issues are you thinking about ?
The ports are simply too small to flow enough air.
the ports of the Jeep iac valve body ?
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Re: Jeep IAC Valve Limitations

Post by dontz125 »

The ports, and the fittings, and the lines. This fellow posted a few days ago that swapping to 3/4" lines allowed much higher idle speeds.
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Yves
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Re: Jeep IAC Valve Limitations

Post by Yves »

I'm not sure. Seeing how far the valve only comes off the seat I wouldn't expect it to flow that much. Maybe an alternative valve with larger openings ...only which one ?
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Re: Jeep IAC Valve Limitations

Post by turbo conversion »

dontz125 wrote:The ports, and the fittings, and the lines. This fellow posted a few days ago that swapping to 3/4" lines allowed much higher idle speeds.
I am running a remote IACV manifold from DIY plumed with hard wall vacuum line.

The IACV is a 95 jeep 4.0L stock part.

My lines from intake source to IACV manifold are 3 feet total.

There is a major volume difference between 3/8" and 1/2".

I am assuming when you say custom mount you are using some type of hose correct?

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
Yves
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Re: Jeep IAC Valve Limitations

Post by Yves »

I don't think Don uses the valve. He was replying to my question.

I'm using the barb fittings that came along with the IAC block van DIY. These are intended for a 3/8 hose. My hose is about 3 feet long as well.

The volume inside the hose is larger I agree, but all of the air that enters has to pass through every piece of it, including the valve. So if the valve itself is too small, it won't flow much more no matter what size hose you put on it.
My additional problem is that all fittings for these items are npt, which is not readily available here. So I cannot just run out to a store and buy some of those.

At the moment I can see 2 solutions : either try a larger hose setup, with larger barb fittings in the hope this will solve it or use a second IAC block.

BTW : all threading in the manifold for this connection is 3/8 npt as well.
Last edited by Yves on Wed May 27, 2015 3:52 am, edited 1 time in total.
jsmcortina
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Re: Jeep IAC Valve Limitations

Post by jsmcortina »

For fittings, try a hydraulics place. In the UK at least they seem to be a source for NPT. Otherwise BSP is the common threadsize here.

As a test just remove the idle valve block totally and see what RPMs you can get with open hoses. 3/8" sounds far too small to me. The Bosch valve sitting on my bench has 15mm internal diameter fittings. That valve was fitted to a wide range of small engines. So using 3/8" on a large engine sounds like it won't work.

Also, why such long hoses? That will likely cause a restriction too.

James
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Re: Jeep IAC Valve Limitations

Post by Yves »

Yes, bsp is common, but the angle of the threads is different.

The valve is mounted on the side of the engine against the firewall. I use 2 airboxes due to the stacks. The air is drawn from both of them so that (when going to maf) the airflow is the same on both sides.
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Re: Jeep IAC Valve Limitations

Post by turbo conversion »

What valve are you using?

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
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Re: Jeep IAC Valve Limitations

Post by Yves »

The DIYautotune block and the required Jeep valve.
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Re: Jeep IAC Valve Limitations

Post by turbo conversion »

I am using the exact same set up.

The valve and block flow more than you need.

If you go with 1/2" hard wall rubber lines and 3/8" npt to 1/2" barb fittings it will flow all you need. :D



David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
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