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IAAC Valve Wiring Woes - 1994 D21 VG30 to 1997 VG33


alco3
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Hello everyone. I have a 1997 based VG33 (actually a VG34, but that's a whole other story) intake and IAAC valve I'm trying to get to work in my 1994 VG30 D21 that has stock wiring and ECU (actually a JWT ECU, but the basis is the correct MEMC). Has anyone been successful at this? Maybe someone has proved it can't be done and I'm just wasting innumerable hours. I have the factory manuals for both including the electrical supplement and access to both alldata and mitchell so the answer is probably right in front of me ... Thanks in advance.

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The problem begins with the disparate design of the two engines control systems: The VG30 is OBD1 and the VG33 is OBD2. The IAC systems differ physically as well: The VG30 uses two parts: 1) an IACV-AAC valve with a two wire connector and 2) an additional IACV-Air Regulator with a two wire connector. The VG33 uses a single IAACV valve with two connectors with 2 two wires each. The best I can do is to have a excellent cold start and an excellent hot restart with a smooth idle at 800 RPMs if the restart is within 10-20 minutes... after 20-30 or so the engine starts with a really low idle - 300-500 RPMs and has almost no throttle response. It doesn't matter if I nurse it down the road or if I keep it running parked after about 20 seconds it acts as if a switch has closed and the idle instantly goes up to 800 RPMs and it has all the power it normally has. Maybe this is as good as it gets.

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The swaps I've seen just bolt the stock VG30 intake manifold to the VG33 (or 34 in your case), thus retaining the truck's original sensors and idle controls and whatnot. Everything the computer cares about plugs in and works like it was always there.

 

That said, your description of the wiring differences makes it sound like the two idle setups may not be that different, and I don't see how an idle air circuit could screw up throttle response off-idle. (If it's not idling, the idle air control should make little to no difference, right?) This leads me to suspect that your wiring on the IAC is not the issue here.

The twenty second cutoff on the problem is interesting as well. You say it's like a switch closes. I'm wondering if it's not a solenoid that's closing. I'd have another look at your vacuum lines, particularly the line for the fuel pressure regulator, and make sure nothing's crossed up that shouldn't be. Compare the VG30 and VG33 vacuum diagrams, maybe try and figure out what system is supposed to kick on for twenty seconds on a warm start, and verify that it's rigged properly and you don't have, I dunno, the charcoal can purge solenoid robbing vacuum from the fuel pressure regulator, or the wrong connector in the EGRC solenoid, or something else supplying vacuum to the EGR valve when it shouldn't be. Or maybe the VG33 IAC has some relationship with a vacuum component that's not present on the VG30. I don't know either system well enough to point at anything in particular, and I don't know how much of either system is in your rig at this point, but that's where I'd start.

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Hello. First off thanks for the response and thoughts on this strange problem. I was hoping that someone else had fought the same battle because that often occurs and I spend hours reinventing the wheel. Yes it is a complex interrelated system ... in my case it also has relatively low vacuum given the JWT S2 cams and my 4750' elevation 17 - 18" is the highest I see ... and then there is the 10.5:1 compression, ported heads and intake manifold, VG33 throttle body & MAF , the VG33ER injectors and fuel pressure regulator etc. etc. JWT has taken the injectors and other mods into account after I sent them some recordings from my innovate wideband. To determine what I could do to get past this stumbling off idle I completely blocked off the EGR system. The fuel regulator and PCV system are the only devices attached to vacuum ... the canister is blocked off and the gas cap is off ... I adjusted the IAACV to maximum which is about 2 1/2 turns out from the seat. After this the problem was still with me. If the TPS was unplugged it would start fine cold but when fully warmed it would barely idle at 250 rpms. So I got brave (or foolish) and broke the paint seal on the top throttle body screw and adjusted the speed to 800 rpm warm with both the IAAC and TPS unplugged. Then I adjusted the IAAC to the 2 1/2 turns out and adjusted the TPS. Wow! what a difference! The cold start is still great and the warm start problem is almost completely gone ... I've got a livable ... heck almost not noticeable ... flat spot off idle on a warm start and it's gone within 15 seconds. I suspect the IAACV is operating as good as its going to give the mismatch between all the components ... I'm good with it! Thanks Again!

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  • 4 weeks later...

The power is pretty good ... I've installed an Aquamist meth/water injection system recently and that helps both the power and the cooling that can use some assistance when it gets to be over 100 degrees and I'm running the air ... I've got the largest radiator possible ... a custom copper crossflow and that Spal twin fan setup and the gauge would creep up to 3/4 running up a long highway grade at 80... I've installed a 10 gallon water meth tank so I can set the injection curve low enough that the long pull on the grade gets the power boost as well as enough cooling that the gauge sits in the middle. On the idle issue I just can't leave it alone. I've got the ported VG33 manifold off and I'm modifying it to accept the secondary idle control valve from the VG30. That coupled with a stock VG30 IAAC valve should allow the Wolf ecu to be within parameter and maybe ... maybe the idle problem will be fixed. Another question for you guys: Do you know what the butterfly in a stock VG33 throttle body is set at from the factory? Mine is new but has been adjusted back and forth so many times I've no idea where to set it to be back at a factory starting point.

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