Idle Speed Motor ***SPLIT from Liner Seals***

[DMCVegas]

So like I said earlier The IAC is still there and working better than ever.
But I respectfully disagree with your first Paragraph. The sense plate Air Metering unit does not account for or even measure air, as it sends no signal to anything. It does allow a constant/Known amount of air to enter the engine for what ever position it is in. So knowing that opened half way it would allow for example would allow 300 cfm, it can be used to allow a correct amount of fuel in. It is a simple air actuated valve that allows a predetermined amount of fuel to flow to the injectors at a given position. The mixture screw is the stop it rest against and simply pushes it down to add more fuel. A/F is controlled by fuel pressure in open loop and Lambda is closed loop. CO setting does mostly nothing off idle. In closed loop CO is Lambda corrected.
IMHO. I could be wrong so I would not put a ton of stock in this post!

Ron summed this up quickly with this reply:

I wouldn't say the plate allows air in depending on its position. The amount of air determines the position of the plate, which is pressed in the opposite direction by the WUR/CPR. As you say, the position will determine the amount of fuel sent to the injectors by the FD. Then the Lambda system adjusts according to what it sees after it is burned, if it is in closed loop.

I think that right now we have a confusion between metering apparatuses. Specifically the Metering Plate, the Throttle Plates, and the IAC. Whatever the later two request as active meters, the former adjusts to as a passive one. Anyways...

K-Jetronic is a modular system. Keep that in mind.

The way in which it functions is that the fuel distributor is split into two haves by way of a diaphragm. The inlets to the injectors butt up against that diaphragm. The farther that diaphragm pulls away from the inlets, the wider the gap becomes into the individual injector ports becomes, and thus allows more fuel and a higher line pressure on those injectors to become. The higher the pressure, the further the spring loaded valves within the individual injectors open.

KjetD.jpg

As the throttle plates open up further, the CFM of air going into the engine increases, yes. As that airflow increases, it presses against the metering plate, which in turn starts to move the plunger inside of the fuel distributor.

Fuel Distributor.jpg

This in turn lowers the fuel pressures in the lower chambers of the fuel distributor, then allows more fuel to flow into the injectors inside of the upper chambers. It does this by bleeding out the pressures in the lower chamber to widen the gap in the upper chambers, and by both feeding that purged fuel into the upper chambers, and dumping excess into the return line to the tank.

What you're doing when you adjust the CO mixture screw is setting the AFR (preferably @ 900± RPMs as per the manual) is setting the baseline. The rest of the entire fuel map has already been dialed in by BOSCH by the port sizes and spring loads in the rest of the components. The rest of the system is purely, 100% mechanical. The Warm Up Regulator has the ability to bypass the Primary Pressure Regulator to reduce lower chamber pressures to enrich the fuel mixtures by dumping fuel back into the return line. It's internal diaphragm valve is activated either by a bi-metalic arm due to cold engine block temperatures, or by sudden huge vacuum spikes in the intake manifold due to sudden RPM accelerations.

Again, all purely mechanical.

LAMBDA is a modular add-on for K-Jetronic. What it does is it fine-tunes the emissions of the engine by monitoring the Oxygen content of the exhaust gasses. It accomplishes this by way of the Frequency Valve. Literally just a giant electronic fuel injector acting as a valve, and does the exact same thing as the warm up regulator: it dumps fuel out of the lower chambers by bypassing the Primary Pressure Regulator. If the mixture is deemed too lean, in increases flow rate to spray more fuel. If the mixture is too rich, it slows the flow rate to increase pressure in the lower chambers of the fuel distributor, in order to reduce how much fuel the injectors spray. LAMBDA has preset values for Open Loop, cold engine, warm engine, and WOT thanks to that little microswitch on the throttle spool. LAMBDA is an electronic version of the WUR, but only for fine-tuning

Now then, having said all of this... All air which is fed to the engine is 100% metered by the initial fuel metering plate. Directly below the metering plate is the inlet for the Idle Speed Circuit. A complete diagram demonstrating this is on page D:01:13 of your Workshop Manual.

[DMCVegas]

Yes. That's the way I've understood it for years. FWIW, I was asking because "taking the ISM out of the system" left me wondering if he was replacing it with a pipe or blocking it off or ???... Seemed a pipe the size of the ISM inlet/outlet would let way to much pass, and if blocked off, the amount of air the brass screw allows to pass would be compensated for by the Idle Speed System when reinstalled....
[I think you will agree? Suppose with your engine's condition, ISM, Oil, ambient temp, fuel, etc, etc., set up per the manual, it idled at 750 RPM. (That's within spec.) If you block the ISM and open the brass screw to 750 RPM, the plate will not change, because the air was metered. The WUR/CPR will not change, so pressure/fuel will not change...Except the O2 sensor will see it go leaner, because more air than the butterflies were originally allowing is getting through. The frequency valve will add fuel causing the RPMs to rise. And the Idle Speed System will bring it back down to 750.
There may be more to it, but bottom line to me is, if you have 750 RPM and the CO is correct with the manual setup and the only real change made is the brass screw is opened, it has to be the ISM compensating for it. In other words, it works!

I've never saw (or noticed) a pic with the extra lines like those in the pic. COOL!
I've read where on some Volvos that, if the balancing screws are shut, the 3rd brass screw does nothing (ie it feeds them only), but I haven't tried it on one.

No, nothing at all changes. In fact, this is what you're supposed to do when properly setting the AFR by way of the CO mixture screw. But more on that in a second. All air is completely metered, and there would be absolutely no deviation in idle speed in such an instance. The only way that we would see the RPMs change on their own is by way of a vacuum leak. That's when the mixture is lean because of the unmetered air coming in due to the leak. LAMBDA enriches the mixture, and the additional fuel then causes a surge in RPMs. Idle Speed Circuit fights the speed increase by choking air off. Now the mixture is too rich. LAMBDA kills enrichment, RPMs plummet. Now the Idle Speed Circuit has to increase air flow to raise RPMs. This causes a lean condition because of the unmetered air, so the mixture is lean because of the unmetered air coming in due to the leak. LAMBDA enriches the mixture, and the additional fuel then causes a surge in RPMs. Idle Speed Circuit fights the speed increase by choking air off. Now the mixture is too rich. LAMBDA kills enrichment, RPMs plummet. Now the Idle Speed Circuit has to increase air flow to raise RPMs. This causes a lean condition because of the unmetered air... Thus we have the surging engine idle condition. You get the picture. In a sealed system, both the butterflies, and the IAC/ISM (whatever we're calling it now) receive their air supply from the mixture chamber, aft of the metering plate.

Now, let's open up that can of worms!

Using dwell to set the CO mixture is *technically* the incorrect way to do things. At least the way that people are currently doing it.

What you want to do is actually set a complete baseline for the engine.

1. Cooling fans jumped by bypassing the Otterstat in order to achieve & maintain the perfect combustion chamber temperatures with no fluctuation.
2. Disconnect the O₂ sensor to force LAMBDA into Open-Loop.
3. Disconnect the IAC and use idle screws to set idle speed tp 900±.

There are too many variables with people's O₂ sensors, engine temps, and sooted spark plugs since lower RPMs save fuel, but run the engine dirty. You will not get a proper reading, and you don't center LAMBDA and give it enough ceiling to fully lean the engine out. See D:04:01

I bent mine when I first got it. That allowed me to let the butterflies shut then turn the screw just enough to know it was not actually touching (carbs, TBs, whatever, I usually do it that way.) It looks like its broke off flush now. Like you, I have the switch setting heavy. Works for me...

======

+1 on good stuff....keep it going!
..I'm wondering what would happen if we separated WOT and Thermal Throttle Enrichment Switch circuits. Then had the WOT ground the connection for the O2 lead, which would push CO to 87° (27°-37° increase).
Maybe make it do some good holding the pedal to the floor when cold too, lol. (I'll have to think about that part ;-)

Yep. I used to have a nasty problem with the engine rubberbanding when it dipped too low in it's Idle RPMs when coming down from high idle. Occasionally it would even stall out. I spliced in that one bad wire, and switched to the Volvo IAC, and that certainly helped. But once I adjusted the micro switch to activate the idle speed circuit early, the RPMs would just float down.

Never really saw a difference when disconnecting the WOT micro switch on the throttle spool. But again, it's for fine tuning, or at least to keep LAMBDA from fighting the WUR.

I can tell you that if you straightpipe the IAC, the idle speed goes to around 2,400± RPMs...

[DMCVegas]

Good post. More reasons why you should have an automatic way to maintain a stable idle speed include the fact that there is no damper on the throttle so on the 5-speed, if you let off the throttle quickly, the engine could stall as the butterfly plates snap shut. The idle also must be increased for a cold engine so it doesn't stall. While it may be tempting to remove a complicated sub system, it isn't that hard to get it to work.

Thank you. That does mean allot to me.

We've still never met, yet for about 20 years you've been one of my mentors. Particularly about ensuring what I already have works, and learning how to fix it instead of blaming it. After all, if I can't get what I already have working with the instructions to do so, how can I expect to get something that wasn't meant to run actually working any better without troubleshooting skills and understanding of the systems?

[Ron]

No, nothing at all changes....

I agree WRT end result. But, there is a minor change in the ISM position, to make up for the (measured) air the brass screw smuggles into the engine.

100% with you on the rest of the post.

[DMCVegas]

I agree WRT end result. But, there is a minor change in the ISM position, to make up for the (measured) air the brass screw smuggles into the engine.

100% with you on the rest of the post.

You're absolutely correct. If the bypass screws have been opened to increase airflow, the ISM will adjust accordingly by reducing it's airflow to get back to the preset idle speed.

So opening the screws has absolutely no impact on idle speed. But Opening those screws would indeed create a buffer against a rubberband effect on idle speed when the RPMs rapidly decelerate. There seems to be a delay in the activation of the Idle Speed Circuit from when the microswitch is tripped. This creates a delay where the RPMs drop way too low, and the engine can begin the lug, or in some cases such as mine, stall completely. Cracking those screws can allow for a permanent flow of air independent of the ISM, and to a degree stop the rest speed from dropping too low. The problem of course is the potential for the cylinder banks running different AFR mixtures from there on out since you don't have that balancing tube. Not that big of a deal when you're running the engine for tuning purposes. Particularly when you're already analyzing each individual cylinder bank to eliminate this issue during tuning (which we can in fact do without an infrared analyzer for less than $150). Otherwise other than long-term damage, we can end up with another situation where LAMBDA starts chasing the dragon and fights the engine for a pseudo vacuum leak. Albeit one we've created internally with those screws.

Or...we can just readjust that microswitch bracket, and possibly switch to a Volvo 760 GLE that works faster and eliminate the risk of imbalance.

[Giamanut]

I wouldn't say the plate allows air in depending on its position. The amount of air determines the position of the plate, which is pressed in the opposite direction by the WUR/CPR. As you say, the position will determine the amount of fuel sent to the injectors by the FD. Then the Lambda system adjusts according to what it sees after it is burned, if it is in closed loop.

Correct what tried to articulate is that you can know how much air can pass through it is a given position so now you can calculate the amount of fuel needed at that position and develop a way to introduce that fuel The FD and of course now you can determine the best Pressure to send to the FD but you need to compensate for atmospheric conditions so you can't use constant pressure you need to control it, enter the control pressure regulator. Then to fine tune you may need to add a little fuel to get the right air fuel mix FV comes into play there.

Now I know I am gonna get flamed for this but I think would be possible to eliminate the cold start valve by Hi-Jacking the FV just a random thought!
Anyway

[Giamanut]

Totally off the wall question but we have a vacuum line that runs from the epavp can to the cold start tube then another to the Oil filler from there. Why not a straight line to the intake? it just a vac port isn't it? Wait never mind I think if you plugged those port the Cold star valve would not work well. I guess the let air in to carry the fuel charge down the tube.

[Ron]

Correct what tried to articulate is that you can know how much air can pass through it is a given position so now you can calculate the amount of fuel needed at that position and develop a way to introduce that fuel The FD and of course now you can determine the best Pressure to send to the FD but you need to compensate for atmospheric conditions so you can't use constant pressure you need to control it, enter the control pressure regulator. Then to fine tune you may need to add a little fuel to get the right air fuel mix FV comes into play there.

Now I know I am gonna get flamed for this but I think would be possible to eliminate the cold start valve by Hi-Jacking the FV just a random thought!
Anyway

Is it me, or this is paraphrasing post 30 then the last part of post 23, minus a lot of punctuation?



J/K

[Ron]

Totally off the wall question but we have a vacuum line that runs from the epavp can to the cold start tube then another to the Oil filler from there. Why not a straight line to the intake? it just a vac port isn't it? Wait never mind I think if you plugged those port the Cold star valve would not work well. I guess the let air in to carry the fuel charge down the tube.

There's not a lot of flow from that side- If you look closely at the ports they connect to, you'll see that the one to the oil fill tube has a tiny metering hole. It's for the crankcase which is sealed. The one coming from the canister is shut off until you break throttle.

[Bitsyncmaster]

Before I found my bad deceleration springs, I tried to plug that hose from the oil filler to get the idle RPM down. What it did was drop the idle 50 to 75 RPM. But running like that, I got some oil pulled up into the air filter so I put it back to stock. Yes that port has a small orifice and the other one in my card is a large hole. So make sure your oil filler hose goes to the port with the orifice.