Honda Fuel Injection and Turbo History

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Rednaxs60

Rednaxs60

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My next installment will be on the idle air control valve and the system. Information on the reed valves that Honda has installed is scarce at best. The idle air control valve (air valve) is connected in parallel with the fuel pump and has a 12 VDC signal going to the valve - confirmed that today. The coolant connections must be the controlling aspect of this valve. The sensor where the bike wiring harness connects is integral to the valve and from what I can see cannot be removed. It is not identified in the parts fiche either. Here is a picture of the internal configuration from the CX500-650 forum:
Air Valve Taken Apart.JPG
I have an understanding of how the idle air control valve works in present day, as well as a rationale reason for having the reed valves in the system.

Now for my question, anyone able to wade in on this with a plausible explanation?

Cheers
 
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Rednaxs60

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I have found an explanation on how the IAC valve works including a test procedure other than a resistance check. I will be digesting the information and putting together a Reader's Digest version for this thread.

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Rednaxs60

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This installment has really tested my sleuthing abilities; however, it has been very rewarding. Hope you enjoy the read.

'85-'86 Air Valve System

References:

A. https://ricksfreeautorepairadvice.com/ho ... alve-work/
B. https://www.ej9.ru/civic/book/chpt_23.pdf

The '85 and '86 fuel injected GL1200 models have an idle air control (IAC) valve and air valve system that is actually quite complex for its day.

Carburetors and fuel injection (FI) systems differ in how the engine gets combustion air at start, idle and during operation. Carburetors have idle screws to set the idle. There could also be two idle screws, one for hot operation and one for cold starts – fast idle. I remember these. Turning these screws in opened the throttle plate such that air was admitted into the engine for combustion. This was need so that air would enter the venturi of the carburetor to draw fuel into the engine.

FI engines do not work like a carburetor and do not have a venturi. When you close the throttle you close the throttle plate almost completely. To accommodate this, design engineers incorporated the IAC valve to provide combustion air by bypassing the closed throttle plate during cold starting and during periods of deceleration where the throttle plate is closed.

The IAC valve air valve bypasses air around a closed throttle plate so the engine can get additional air on cold start ups, during deceleration, and at idle. Since it bypasses air, it is sometimes called an air bypass valve.

The operation of the IAC valve is controlled by the ECM or PCM (power control module). Parameters such as engine coolant temperature, ambient air temperature, barometric pressure (on some engines) are used to determine how much air and gas is required to start the engine.

The IAC valve works at idle and during deceleration only. When starting an FI engine, it is recommended not to press on the gas pedal. Pressing down on the gas peddle is, IMHO, a throwback from the days of carburetors, not necessary for FI engines. Once the car is started the IAC valve is actually a bypass valve allowing additional combustion air to go around the throttle plate hence the use of “idle air bypass valve”. During deceleration, the ECU reduces, or cuts off the fuel injection to force the engine to slow down - lose RPM; however, the engine still needs an air supply. The IAC valve is opened by the ECU allowing air to bypass the throttle plate.

The idle air control valve does not fine tune the air/fuel mixture when driving. This is done by the ECU adjusting the fuel injector operation.

Looking at the electrical schematic for the idle air control valve there is a ground and a signal wire from relay number 5 in the fuse block, and the IAC valve is wired in parallel with the fuel pump.

Reed valves are also incorporated into this air system on the '85-'86 FI models. Reed valves are one way valves and are actuated in a variety of ways.

One of the issues that these reed valves take care of in this air system is intake reversion. This is basically where there is overlap in the exhaust and intake stroke and a small amount of exhaust and intake gases are forced into the intake port and manifold during low to medium speeds. This occurs because the air/fuel mixture enters the cylinder at a low velocity and the piston is trying to push it back before the intake valve has fully closed. Since the idle air control valve is being used during deceleration, the air bypassing the closed throttle plate(s) keeps the fuel/air mixture from reversing its flow, thereby keeping more of the fuel/air mixture in the combustion chamber to be burned. I have not confirmed this as yet, but the premise is sound based on the engine design information I have read on this subject.

Reference B is well worth the read. It provides additional and more detail about the idle air control system that Honda has employed over the years.

Honda uses, has used, two and three wire IAC valves in its FI engines. The '85 LTD and '86 SE-i use the two wire IAC valve.

The IAC valve can be a rotary idle air control valve or a pintle style air control vale. I submit that the IAC valve installed on the '85 LTD and '86 SE-i is a pintle style air control valve because of the valve design. If I am not exactly correct, both styles achieve the same aim.
idle air control valve schematic - 1.jpg
idle air control valve schematic - 2.jpg




I mentioned that the IAC valve is wired in parallel with the fuel pump and as such, is powered at 12 VDC. The power provided activates an internal coil that opens the internal pintle valve to allow air from the air intake plenum to be supplied to the intake manifold after the closed throttle plate(s) for combustion air on start, and during periods of deceleration.

The IAC valve has two controlling aspects. The first is the 12 VDC power supply that fully opens the internal pintle valve. The second controlling part is the engine coolant.

The 12 VDC power supply opens the internal pintle valve by energizing the internal coil of the IAC valve. This allows for additional combustion air to bypass the throttle plates aiding in combustion on start. Once the engine comes up to operating temperature, additional combustion air is not required, and there is a need to reduce the amount of air bypassing the throttle plates.

Once the engine is at operating temperature, idle is controlled by the IAC valve. The required combustion air is regulated by the ECU that operates the IAC valve. To do this the ECU controls the current in the IAC valve by controlling the amount of time the IAC valve is grounded. The amount of current that flows through the IAC valve internal coil determines the pintle valve opening force is that opens the pintle valve against spring tension.

It must be noted that the IAC valve does not fully open and close, but is held open a certain amount by the current in the internal coil windings. The ground is turned on and off so fast that the plunger does not have enough time to fully closed.

The IAC valve is supplied heated water, via two small coolant hoses, to keep the valve from developing ice during cold operation. The IAC valve is not sensitive to the temperature increase from the heated water. The position of the IAC valve's plunger is totally dependent upon the amount of time the ground is on, which is controlled by the ECM. This is a direct quote from reference B and may be the most plausible answer as to why coolant hoses are hooked up to the IAC valve.

The IAC valve can be tested to cause the IAC valve to fully open or close.

To cause the IAC valve to fully close, temporarily disconnect the power supply. When this is done, the engine idle should drop to “base” idle, and the idle is controlled by the idle bypass screw. If the idle is somewhat erratic, the idle bypass screw may not be adjusted correctly, or thee is another source of air entering the system.

To cause the IAC valve to fully open, temporarily ground the ground wire going from the IAC valve to the ECU. When you ground this wire, the idle should increase.

The OEM service manual also recommends testing the IAC valve resistance. The spec for this valve is 60 to 100 ohms.

A good research project this instalment. As always, it is a Reader's Digest version of information I have gathered and my understanding of this information; however, I am getting a better understanding of the FI system on my '85 LTD.

Will be delving into the reed valves and try to get some additional information regarding the function and operation of this item.

Cheers
 
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Rednaxs60

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Idle air control circuit update. The research I have done regarding the FI systems on the '85 LTD and '86 SE-i has been extremely beneficial. This research has increased my understanding of the items/components such that I am more comfortable and better at troubleshooting issues. Diagnosed a failed IAC valve. Ordered, received, installed a new IAC valve. Got the NOS valve from Burgers Motorcycles in NJ.

Have had idle issues at start, excessive fuel smell, having to keep the RPM higher than normal for some 45 to 60 seconds then the system would idle, and disconnected the IAC valve from the system with no change in RPM. Read everyhting I could regarding the operation of this valve and the issues with a faulty one. Did the resistance check and when warm it was out of spec, and at the high end of the spec when cold.

Had to drain the coolant because of the coolant hoses going to the valve.

Socrace over on the NGW forum found this description and it is exactly how the valve works: "There are valves that need no control other than a 12V supply when the fuel pump is on. These heat up a bi-metalic strip that rotates a plate inside the valve and shuts the air down as the engine heats up, these are known as Extra Air Valves. They are becoming rare and hard to get hold of, they were fitted to various early efi engines. The Idle Speed has to be controlled with the throttle stop when using these type of valves, as the valve is only used to add air when the engine is cold." The stock Honda unit works the same as this, except it has additional coolant warming that this one doesn't need. These coolant lines are to prevent icing up in colder weather. The FI system is based on the auto industry and hence the same prinicples were applied to the early Honda FI systems. I would also surmise that this was a valve that worked in the Honda FI cars and so it was used in the '85 LTD and '86 SE-i.

Before I installed the new valve, I blew through the valve on the air and coolant sides. The valve is not fully closed when cold as air went through with no problem. The information I have is that this valve is never fully open/closed, and this short test confirms this. The coolant side is flow through as well.

Here is the valve in question:
idle air control valve.jpg

Here is a look inside the working end of this valve. Pim205GTI over on the CX500-650 forum posted this picture of the internals:
Air Valve Taken Apart.JPG

Here is a diagram of how the valve works:
Internals of IAC Valve.jpg


After I installed the new IAC valve, started the bike without changing any idle settings. I put the shelter and others items I removed to do this work and let the bike warm up to operating temperature. Interestingly, the idle climbed to 1450 RPM whereas before it would stay at 1040ish RPM. This leads me to conclude I was having to dump a lot of fuel into the engine at idle, cold or operating temperature - hence the excessive fuel smell. I adjusted the idle, went for a good road test and have now adjusted the idle to suit. The telling of how well the idle system is working will be tomorrow morning when I do a cold start.

There are similar IAC valves available for FI bikes. This one from SMP: Standard Motor Products AC356 Idle Air Control Valve Here is a site for it: https://www.amazon.ca/dp/B000C7UMJK/ref ... XzbCH0TPVZ Don't forget to look at your local auto wrecker as well, lots of good used products available that may fit the bill.

I do not believe the coolant hookup is necessary because the coolant is to prevent icing and I for one will not be doing any riding in weather that would test this.

Will update tomorrow after starting in the morning.

Cheers
 
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Rednaxs60

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Now that I understand and have rectified a deficiency in the operation of my bike, I have been wondering about other components in the idle air control circuit, specifically the "reed" valves.

Air does not move from one area to another just because you enlarge the discharge hole, in this case open the blocking plate. Air needs to be moved by a push or pull method. There is no "push" per say, so there must be a "pull" aspect to this circuit.

I remember back a few years when I worked on the older snowmobiles, carb models all of them, and in tinkering with the fuel system and carbs - put an external vacuum operated fuel pump on the sleds. I am thinking that the "reed" valves may have this functionality as well. I have some homework to do on this.

As an aside, HD had a sled back then - not a bad machine; however, it never gained much in notoriety and did not have the following that its motorcycle cousin had/has. My father sold them as well as the Skiroule brand.

More to follow.

Cheers
 

DaveKamp

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I do not believe the coolant hookup is necessary because the coolant is to prevent icing and I for one will not be doing any riding in weather that would test this.

I realize this is darned-near 'necroposting', but this is a historical gem of information, so I'm gonna add a note about this aspect...

Icing occurs as a result of Combined Gas Law and Venturi Effect pressure changes... Weather is basically irrelevant... it's about pressure change, relative humidity, and air velocity. At 78F, there's enough pressure change going through the air pathways to cause local freezing right at that valve. The coolant heating keeps frost from sticking the valve, and even accumulating and blocking the airway shut.

Aircraft have 'carb base heat'. Automobiles, even fuel injected ones, have coolant passages that bring engine heat to the plenum areas susceptible to internal icing. Cars from the 40's through the mid 80's had 'heat risers' on the exhaust, and the cylinder heads were fitted with exhaust passageways across the carb base, and into opposite side ports, for the express purpose of bringing up enough heat to compensate for temperature drop through the plenum.

What happens, is that the temperature drop is enough for frost to form on the internal surfaces in low pressure areas. As this frost builds up, it forms a more considerable (longer, and narrower) passageway and in effect, becomes a self-forming venturi, which then extends the icing pathway further. It will eventually reach a point where it's constriction prevents adequate flow to the engine, and power drops off rapidly. In an aircraft, this puts you back on the ground, and usually, it does it somewhere in a field not far downrange of the departure runway... and frequently, it happens really fast, when you're doing everything you can to get airspeed and altitude from about... a thousand feet or so... and your aircraft falls like a rock.

Even my boat (cooled with river water coming in at 78F on an 85F day) forms frost on the OUTSIDE of the intake... which is integrated into the exhaust manifold... so it's very, very real.
 

joedrum

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I agree ...but airplanes and bikes are 2 different things as altitude comes into play ...as I’ve said many times ...icing happens big time in a lot of SCC set ups for one reason ...there idle is way to rich and they can ice up fast ..to me it’s a sign of not dial in period ...I’ve found when the idle and rest of the carb is dial in right icing is no problem at all ...I’m sure if conditions got bad enough it could be a problem ...but I actually go completely the other way and cool charge going on ..insulating the entire induction system from head heat and have been caught in blizzards and had to ride hundreds of miles in these conditions ...personally I’ve had more icing condition in 40 degree temps and very high humidity conditions but nothing that stops the bike ...
 
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Rednaxs60

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Good morning - "necroposting" is good. Lets one revisit what has been done and maybe an update is required.

I had the heads done this past winter and I renewed the hoses for the IAC system. When I installed the air chamber one of the reed valve hoses came off and the noise from the reed valve sucking in air was considerable. I would surmise that the speed of the air being ingested, combined with the air temp could result in "icing", but without instrumenting the system, cannot say for certain. Concern with "icing" may also be for the reed valves as the reed valves have the smallest components. The IAC valve and system air hoses are larger and probably not susceptible to "icing" per say.

If "icing" were to occur in the reed valves, it would impact on the engine operation, specifically when the throttle plates are closed. The IAC system provides combustion air to the cylinders when the throttle plates are closed at idle and deceleration.

Another consideration is that the IAC valve is never fully closed, and provides a supply of combustion air at all times. When the engine is started, there is a reduced air flow to the engine until the IAC valve bi-metallic strip is heated and the valve opens fully. Heating of the IAC valve by engine coolant can be thought of as relatively proportional to the opening of the IAC valve. I mention this because the IAC valve bi-metallic strip only has power when the fuel pump is operating. The valve heats up gradually, as does the engine coolant.

Good to revisit this and other threads for any number of reasons, design issues being at the top of the list. Since we'll never know exactly why the Honda design engineers did something, our musings can/may provide an insight into why the design is what it is.
 
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Rednaxs60

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Was discussing this issue with my brother, and in doing so, reflected on how the FI system is designed and operating.

The 1982/83 and 1985/86 Honda motorcycle FI models were the forerunners to the Honda FI system - probably done in conjunction with the automotive side of the house. These FI systems had no O2 sensors that are an integral component to modern day FI systems for idle control. The 1985/86 FI systems had a crank sensor for engine timing and two cam sensors for injector timing control. The ECU also had a circuit that tested for system integrity, and would produce error codes as required - forerunner to the OBD tools used today - brilliant design. The IAC system on these motorcycles is a passive system whereas the newer systems primarily use an active IAC system with a stepper motor.

I am looking into and researching the requirements for a replacement aftermarket ECU. Most require an O2 sensor. Most aftermarket ECU products can utilize a crank sensor, but can only use one cam sensor for injector timing. A passive IAC system can be used but the active system with a stepper motor seems to be more preferred.

The fact that Honda had an FI system that worked well without using an O2 sensor, using two cam sensors, and had an integral OBD system is quite remarkable.

The 1985/86 LTD and SE-i FI models also integrated the travel computer and digital dash into the FI system. There are input signals that come from the ECU needed for the trip and fuel readouts, and inputs from the travel computer to the dash - everything is tied together. This is a consideration when looking into a replacement ECU for these motorcycles.

I have probably posted this info before, but a refresh is always good.

Cheers
 

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Hi Ernest!

Well, one of the things that DOES reveal the engineer's reasons, is to alter or disable something, then become witness to the result... :doh:

(can you tell I've done that before? :swoon: )

One thing I've been kicking around (since my '84 Aspy has an endless desire to drop the #1 cylinder at idle) is acquiring an injected example like yours. I realize that the EFI componentry is getting somewhat... er... 'classic', so critical parts might be getting close to rare...

Or another possibility, is to build two small throttle bodies, one for each side, mebbie use a single injector between the two, and a MegaSquirt to run the fuel (and control the ignition)... but at the moment, I have more than enough projects to keep me alive for 250 years...
 

mcgovern61

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Even my boat (cooled with river water coming in at 78F on an 85F day) forms frost on the OUTSIDE of the intake... which is integrated into the exhaust manifold... so it's very, very real.

My 1956 KL engine with an updraft single barrel Zenith carb has a water heated intake manifold. Here is a great picture of a KL engine (same as mine) on a set of blocks showing the setup. The hot water comes out of the top of the exhaust manifold end cap at the front of the engine and enters the manifold just above the carb. The water exits the manifold and then out through the exhaust elbow and overboard:

image.php
 
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Rednaxs60

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Have looked into the fuel pump requirements for the early '80s FI models. Honda maintained a base specification between all these FI models in that the fuel system static pressure (key on engine not started) is 34 to 38 PSI and at idle 28 to 34 PSI. The fuel pump is designed to operate at 4.5 to 6.0 Kg/cm2 (64 to 85 PSI) after which the excess fuel flow will flow just within the fuel pump housing when fuel flow is blocked or restricted. The fuel pump flow is to be a minimum of 1.5 litre/min (0.4 USG/min or 0.33 IGPM).

These are the base specs for the 1982 CX500T, 1983 CX650T, and the '85/'86 LTD/SE-i models. With these specs it is reasonable to surmise that these motorcycles all had the same fuel pump and fuel pressure regulator requirement.

The one difference is that the turbo engines operate with a vacuum and pressure in the intake air chamber. When boost is not used the fuel pressure in the system is maintained at the above design specifications, and all four models work the same. When boost is applied to the engine, the positive pressure in the intake air chamber acts on the fuel pressure regulator diaphragm, causing the pressure in the fuel manifold to increase until the fuel pump flow overcomes the pressure on the diaphragm. This continues until max boost is achieved, approximately 20 pounds. This indicates that the fuel pressure in the fuel manifold must be at least 48 to 54 PSI to feed fuel to the engine at max boost, and the fuel pump fuel flow must be sufficient to provide this fuel flow plus fuel flow to overcome the boost pressure on the fuel pressure regulator. This pressure is below the maximum design pressure of the fuel pump.

When a replacement fuel pump is needed, the challenge is to find a fuel pump that meets the above specifications, and that is used external of the fuel tank. The same goes for the fuel pressure regulator.
 

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