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Just Some Dude in Jersey
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Discussion Starter · #101 ·
From Facebook:

<<< I had to take a leap of faith drilling the holes in my air box to mount the IACV, loose fitting and measuring showed that it should just barely fit where I wanted to put it, but I had almost zero room for error. I really didn't want to screw up my air box, it was a PIA to make and shape to the curvy awkward shape of the car. I had to grind away some of the fuel rail and a bit of the casting seams between the throttle bodies to get the IACV to fit more or less comfortably. I still have to fit the tiny barbed fitting for the hose for the MAP sensor.

Where to put the barbed fitting for the MAP sensor is the question right now. This is my first experience with one of those sensors, but having that form of air flow sensing is super important to me to make this mod worthwhile. The older Opel and aftermarket systems used AFM's and MAF's and they take up space right where you don't have much space in a GT. Holy Cow, that MAP sensor uses a tiny hose! Like a 1/8" inside diameter and it simply goes straight from the manifold, or other high vacuum location, straight to the circuit board of the ECU itself. With only an 1/8" hose going to a pretty darn small circuit board, the actual sensor on the board must also be really tiny. But, before I fit it I have to check to see if it will work accurately by sensing only 2 cylinders worth of air. The big flaw of this manifold is that it doesn't have a common plenum to unify the vacuum from all 4 cylinders. It is a "siamese" configuration manifold, which is kind of rare in the car world. Each of the 2 runners only service 2 cylinders and the 2 runners are not connected together via some sort of common plenum. When the manifold had it's intended single side draft on it, a guy in Australia(GT Alex on the .com site) suggested that I drill a hole through the flange that the carb mounted to, to help unify the vacuum to the brake booster to eliminate pulsing of the brake pedal. I drilled a 10mm(3/8") passageway between the 2 runners through the side of the flange and plugged off the hole I made to do it. It worked great. I repurposed that passageway to mount the 4 IAC hoses I chose to install. I can only hope that they provide enough air. The 4 port air manifold that the hoses go to only has a 10mm(3/8") outlet and that, supposedly, is all that a 4 cylinder engine requires to supply enough air at idle to keep the engine running. So, the question remaining is: Is my passageway in the flange unifying the air flow or relative air pressure in the manifold enough to provide accurate sensing of the Mass Air Pressure(MAP)? The manifold only has one outlet for vacuum and that is for the brake booster. So, I put a series of T-fittings in the brake booster hose to operate my auto tranny's modulator and a super small hose to operate the vacuum gauge that I like to put in my cars. That set up works great for those 3 items, when I had a carb, so, can I simply add another T-fitting to the brake booster hose to operate the MAP sensor? Or should I maybe remove the passageway plug in the manifold and try to put the MAP sensor hose there for slightly more accurate sensing. I need to contact the seller of the system for his opinion. >>>
 

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Just Some Dude in Jersey
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16,728 Posts
Discussion Starter · #102 ·
For Fuel Injection Nerds:

I had a few discussions with the guy in England over the past couple of days about a couple of things. It started out with me just wanting to know about MAP sensor hose barb positioning. He refers to barbed fittings as "tails". In the conversation, he mentioned concern about where my idle air flow enters the system in relation to the injector spray pattern. This is "fuel injection nerd" stuff that most of us would never think about, especially an FI rookie like me. As it turns out, just by dumb luck, my idle air flow intersects the injector spray pattern just about perfectly. THIS sort of thing is EXACTLY why I wanted to buy my operating system from a place that would give me tech support. I'm sure that the other 2 American companies I had bought systems from wouldn't have given me this sort of advice. Not too many American guys make weird, 2 injector/4cyl, custom from the ground up, systems utilizing repurposed single side draft manifolds.

As a synopsis, I gave him 2 pictures showing the flow of idle air and another showing the angle of the injector spray pattern in regards to where the idle air enters the runners of my manifold. He approved how/where the air/fuel intersect each other. Here are those 2 pics:

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What I really wasn't expecting, as the conversation developed, was him saying that you really want most of the idle air to come from creeping by the throttle blades and NOT come mostly or entirely from the idle air circuit and passageway. I thought that, ideally, you would want all the air at idle to come in through the computer controlled idle air control system. But he said: "Best results on pretty much any car is to let the throttle blades do most of the work and just use the IAC as the fine tune for the airflow. For example - when the car is fully hot and if your target idle speed is say 850 then let the throttle give enough air for say 800 rpm and just the extra 50 via the IAC."

Well, that's a revelation. He is basically saying that 90% of the air at idle should enter via the throttle blades and only 10% via the idle air control system. Sheesh! That idle air contraption and the ducting of air takes up a fair amount of space and requires some engineering acrobatics to fit neatly in place. On my Motronic system, it involves huge hoses and outlet/inlets, plus the big valve contraption. He is implying that only a very tiny amount of air coming from the idle air circuit is required and only to supplement the much larger amount of air creeping by the throttle blades. Well, golly, how many people know that? I would have tried to start and run my car with the throttle blades dead closed, thinking that the IAC would do virtually all the work of letting air in for idle. Now, a lot of things make sense that had perplexed me before. I had always wondered how all those tiny passageways and hoses could possibly supply 2.4 liters worth of air at idle. Now it makes sense: The idle air circuit only supplies a little bit of extra air at idle to fine tune the idle speed and smoothness and most of the air comes in via creeping by the throttle blades, almost like a normal carb set up.

Here is the edited conversation. The earlier part of the conversation is at the top, the most recent is at the bottom:

Him:
<<< I assume from the pictures that the 4 x clear pipes all run to a common point on the modified manifold ? If so, then you could have probably got away with just 2 clear pipes, but no matter if you have 4. However ( if it is all common ) what you can do is use 3 pipes ( blanking the 4th pipe on the IAC Jenvey manifold ) and use the 4th union for your MAP sensor.
Since your idle pipes are forward of the injectors make sure you do not allow the idle valve to supply too much of the idle air ( otherwise air flow my bypass the injectors ? ). So set your throttle stops so they do most, if not all the idle work at hot idle, that way any extra air is only a small amount and hence hopefully no bypassing the fuel squirt. >>>

Me:
<<< The 1st attached picture is from a few months ago and the blue lines show the air flow through my original IACV and the passageway. The IACV air enters the runners SIDEWAYS through a 10mm passageway in the mounting flange located just after where the TB's bolt to the manifold. I envision that the air coming out of the passageway intersects the middle of the fuel squirt or slightly below it(see 2nd pic).
I'm leary about this. I thought that the IACV was supposed to control ALL the air coming in at idle, if possible. If I let some air creep past the throttle plates, would I have to calibrate or recalibrate the ECU to that new throttle position? How would I determine if my IAC set up is providing too much air? If it runs rough or stalls, try tweaking the throttle stop to see if it smooths things out?

Could I put the MAP hose tail in one of the FAJS barrel's air bleed holes? Would it read accurately in that location? >>>

Him:
<<< Your air flow and injector positioning looks like it will work OK - I just mentioned as on a couple of cars ( with different set ups ) I had the IAC hose tail too far forward of the throttle blades and it gave me all kinds of head aches. I think yours will be OK as is, but if you do get lumpy idle running then that is s symptom of too much air out of the fuel flow stream, in which case crack the blades a touch further open, which will in turn force the IAC a little more closed. For best results on pretty much any car is to let the throttle blades do most of the work and just use the IAC as the fine tune for the airflow. For example - when the car is fully hot and if your target idle speed is say 850 then let the throttle give enough air for say 800 rpm and just the extra 50 via the IAC. This way stops the IAC shutting down too far when on a long throttle closed decel - because it will not necessarily know you are on a decel and will be trying to shut the IAC to bring the RPM down. Modern cars have a vehicle speed sensor and they do not do anything with the IAC when the road speed is above say 5mph - but having a classic car you do not have a vehicle speed sensor.

I think the FAJS air bleed maybe too close to the throttle blades, meaning you may see throttle edge vacuum rather than proper manifold vacuum. You could put the MAP hosetail on one of the idle hose tails ( if you do not use them all ) or probably just as good would be to drill your 10mm passage plug and put the hose tail in there. >>>
 
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