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Thread: Additional Slide Valve Or Auxilary Air Valve

  1. #1
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    Additional Slide Valve Or Auxilary Air Valve

    My question is at the end of the background info -
    I am very close to having a happy ending to an engine rebuild saga on my 82 320i. It is far too long a story for this space. I have made the final attempt to have the engine run as it should by installing a new (rebuilt) fuel distributor and WUR. Once the engine temp comes off the peg – less than 3 mins after start – everything is sunshine and roses. Before that, the car will stall when I come to the first stop sign. On the normal trip from home, this will mean one or two restarts, then all is well.

    After I spoke with the folks at Fuel Injection Co. in Tracy, CA who supplied the fuel distributor and WUR, they shipped me a second, “adjusted” WUR, and it moved me closer to the goal of no restarts. (Perhaps I am being to picky with a 35 year old car).

    When I asked the mechanic who rebuilt the engine, he said the last piece of the puzzle could be the Aux Air Valve (which makes sense when you consider this is all about air/fuel mixture at cold start.)

    He said, pull the hose off the Aux Air Valve and check the position of the “slide” when the engine is cold. Just pull the hose and look in the pipe. The slide should be open, but he wasn’t clear on how much it should be open. When the engine is hot the slide should be full closed and it is.


    Aux Valve.jpg
    All of this for a simple question – Does anyone know how far the slide should be open when the engine is full cold? If you consider the view down the pipe to be 360 degrees, my slide is open perhaps a bit less than a 45 degrees slice of the 360 degree pie. Thanks for reading this far.

  2. #2
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    When the engine is cold the slide should be about 1/2 open. Congrats on the rebuild of the motor,wur, and Fuel Distributor and getting them in thats a big step forward with these cars.

    As too the stalling, when the car is cold the idle should kick up to 1200-1500 rpms and then as the wur and aav warm up the idle will drop back down to 850 +/- 50 rpms curb idle speed after a few minutes to several minutes, mine did that years ago it was an old O2 sensor-stalled at a light, also check the air hoses and make sure they are good, after awhile they get hard and crack causing an vacuum leak,,these cars are sensitive to vacuum leaks and will shut down when idling if there is a leak.

    Randy
    Last edited by 320iAman; 02-23-2018 at 11:10 AM.

  3. #3
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    Can't thank you enough for the response and the kind words. You raised an important point that I failed to mention. Before the rebuild, the start sequence was as you described -- Engine starts and idle is around 1200 then drops after a few minutes warm up. The engine did not stall.

    Now, there is a steady idle (the shop set it at about 1100) and there is no drop off. I don't understand what is going on with the idle.

    My understanding is that the WUR increases fuel pressure = more fuel when the engine is cold and then decreases fuel pressure as the engine warms up. I assume that the increase/decrease in fuel pressure translates to higher, and then lower, engine idle rpm. This is not happening now.

    As part of the rebuild, all hoses are new and tight. I will check if the O2 sensor is new. The AAV is only open about 1/8.

    My choices seem to be one or more of the following -

    1. Have the shop that rebuilt the engine do the pressure tests and attempt to adjust the WUR if needed. ($150) I don't have the test equipment.

    2. Install a salvaged, warranteed AAV for $50

    3. Have the shop that rebuilt the WUR tweek it again. ($15 shipping and an hour or two removing and installing)

    I am so close to a successful ending of this project, it is hard to just stop here and live with it.
    Last edited by dbaldwin; 02-23-2018 at 03:13 PM.

  4. #4
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    The idle is set to 850 +/- 50 rpms,,that is curb idle speed is 800-900 rpms,,Idle needs to be reduced. Timing is 25 BTDC @ 2200 rpms,,the pressed in steel ball- a BB is seen in the flywheel inspection window with the timing light pointed at it, can also use the hash mark on the crank pulley or nose pulley and pointer on the front of the timing case,,a little more difficult -- I use it as a close measure then use the flywheel inspection window to see the pressed in steel ball, the vacuum advance hose is plugged while setting timing by rotation of the distributor.

    So order of setting timing and idle speed.

    1.) disconnect the vacuum advance hose and plug it-I use a screw driver
    2.) Loosened the distributor bolt and nut--not a lot as it will move to far upward from engagement of the cam worm gear it meshes with.
    3.) Rev the motor to 2200 rpms and check timing,,the pressed in steel ball is in the flywheel inspection window
    4.) Rotate the distributor with motor at 2200 rpms no more no less until the pressed in steel ball shows up.
    5.) Once it shows up let go of the throttle lever and tightened the bolt on the distributor--dont overtightened -7 ft lbs is maximum as its an M6 bolt and nut, 5-6 ft lbs is okay.
    6.) Rehook up the vacuum advance line.
    7.) Adjust the air idle screw till 800-900 rpms,,I like around 900 rpms

    Your done.

    Randy

  5. #5
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    Thanks for the detailed reply. Having paid a small fortune for the engine rebuild, I assume they got the timing right, but I will check it before I fiddle with the other options. Looking at other posts re: the AAV, a good cleaning sounds like the first step with that unit. Thanks again for the guide.

  6. #6
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    Quote Originally Posted by dbaldwin View Post
    Thanks for the detailed reply. Having paid a small fortune for the engine rebuild, I assume they got the timing right, but I will check it before I fiddle with the other options. Looking at other posts re: the AAV, a good cleaning sounds like the first step with that unit. Thanks again for the guide.
    Hi ... if you have a look at this link there is an explanation and drawings showing how it all works.

    http://forums.bimmerforums.com/forum...9&postcount=12

    A good cleaning out and testing the resistance of the internals is a good place to start

    Cheers
    hmm .. Wonder what happens if I do this ...

  7. #7
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    The aav is adjustable and the idle should be 800-900 rpms,,too high and negates the cold start circuit, mine this morning around 32 F went up to 1500 rpms during warm up and the idle is around 900 rpms.

    Randy

  8. #8
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    Thanks for the link - it is very helpful and probably confirms that my AAV is open just about right at cold temps. (45 degrees SF Bay Area)

  9. #9
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    Thanks Randy - I am a bit confused by your comments that high rpm negates the cold start circuit and your cold idle was 1500. If the cold start circuit cuts out with high idle, what component takes your idle to 1500. In fact, that is one of my major questions. What component is responsible for the increase and then decrease in the idle in the cold start sequence? I have read that the WUR is responsible for enriching the fuel by influencing the fuel distributor and that would make the actual start and initial cold running possible, but what component influences the idle or is it just the fuel enrichment?

    I pulled my AAV and cleaned it, tested out at 48 ohms, but couldn't figure out what influence loosening the nut had on anything. From the link GDAus posted, my AAV may be open just right for the cold start. It does close all the way at normal operating temp. The O2 sensor is fine. I will check the timing, idle, fuel mixture today and see if I can get closer to the goal.

  10. #10
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    Briefly ,The cold start system provides more air and fuel for cold start up and then as the car warms up this additional air and fuel is closed off, when air idle screw is set above 800-900 rpms(factory specifications), these excess air leans the fuel down and thus a drop in rpms in cold startups. Too much of either gas or air on cold startups or warm startups, the car wont start, a slight amount effects its idling speed, thus what you experienced when the idle was kicked up, cold start idle kicked down.

    Take your time and familiarize yourself with the car and its systems, its a learning curve, enjoy it.

    Randy
    Last edited by 320iAman; 02-26-2018 at 08:21 PM.

  11. #11
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    Quote Originally Posted by GDAus View Post
    Hi ... if you have a look at this link there is an explanation and drawings showing how it all works.

    http://forums.bimmerforums.com/forum...9&postcount=12

    A good cleaning out and testing the resistance of the internals is a good place to start

    Cheers
    OK - How is this for confusion. After reading the info in the link you posted, I focused on the fact, confirmed by the simple drawing and one of the comments, that the AAV contacts will ring the buzzer on a continuity test. I could not get continuity on my AAV with my trusty multimeter, so now I think I have found the problem. Off I go to the salvage dealer (with my multimeter). After testing 3 salvage units with no continuity, he opened a brand new AAV and no continuity.

    The schematic shows a simple loop wiring that appears to be continuous. The meter works just fine. Any ideas what's going on?

    - - - Updated - - -

  12. #12
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    I use resistance in ohms to test devices with coils or bi metal wire,if the coil is good you'll see resistance show up in ohms, The warm up regulator for instance has around 21 Ohms,if 0 ohms coil has a wire or connector that is broken. Today I'll be testing all the devices as its annual tune up time.

    Randy

  13. #13
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    Quote Originally Posted by dbaldwin View Post
    OK - How is this for confusion. After reading the info in the link you posted, I focused on the fact, confirmed by the simple drawing and one of the comments, that the AAV contacts will ring the buzzer on a continuity test. I could not get continuity on my AAV with my trusty multimeter, so now I think I have found the problem. Off I go to the salvage dealer (with my multimeter). After testing 3 salvage units with no continuity, he opened a brand new AAV and no continuity.

    The schematic shows a simple loop wiring that appears to be continuous. The meter works just fine. Any ideas what's going on?
    - - - Updated - - -
    Well ... Now I am confused ... You said you measured the resistance on you AAV at 48 Ωs. That confirmed the heating element was fine. I certainly didn't put anything in any of my posts about continuity! The heating element is a RESISTANCE wire and that may be too much resistance for the continuity circuit in your multimeter to sound the buzzer .... was the multimeter showing any reading for the voltage drop across the AAV?

    I'm an electrical engineer .... and if I found your original +3 random + a new AAV not showing any readings, I would be checking my multimeter! Did you short together the multimeter probes first to check it was working properly ? I always have a spare set of leads for my meters because they do fail. Also some multimeters will get a bit erratic when their batteries are almost flat.

    Having said all that .. there is the possibility that your AAV has an intermittent fault or an electrical fault in the supply wiring. AAVs will eventually close due to the heat of the engine, so that may explain the "3 minute" effect you have described.

    It would be worth while to check the voltage across the plug terminals going to the AAV with the engine running.

    Cheers

    P.S. moving the little stud with the nut on it from one side to the other should change your idle speed by about 200 RPM ... if it doesn't you may have a vacuum leak(s) you haven't discovered. Even a worn crankshaft oil seal or a deteriorated seal on the oil filler cap can have an effect.
    hmm .. Wonder what happens if I do this ...

  14. #14
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    Can't thank you enough for the suggestions. My multimeter was the first thing I checked - new batteries and the probes are fine. I have used it a lot in a recent audio project with no problems at all. Your comments have been helpful and I will now go through the check list again, including the resistance, line voltage while the engine is running, and vacuum leaks. I read that sometimes the AAV has a vacuum leak where the around where the electrical leads attach.

    Can you confirm that a cold engine start sequence begins with a higher idle, up to 1200, then as the AAV closes, the idle drops to normal idle 800 - 900 rpm. I have read that the additional air that the AAV provides on cold start causes the system to add more fuel, which in turn raises the idle. Makes sense to me, but is that what really happens?

    I adjusted the little nut to max opening position and looking in the tube I could see an increase in the opening to about 1/4. The salvage AAV's and the new AAV that I looked at, all had about the same 1/4 opening. Not close to half way open. Thanks again.
    Last edited by dbaldwin; 03-01-2018 at 08:11 PM.

  15. #15
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    Some tid-bits to help understand the k-jet:

    Fuel 'system pressure': begins at the inlet of the fuel distributor and is controlled by the fuel pressure regulator, this is a constant pressure.

    Fuel 'control pressure': is controlled by the WUR - fuel pressure on top of the fuel distributor's 'fuel meter piston/plunger' will change as the WUR temperature changes between cold and warm. When the WUR is cold, there's less 'control pressure' which will allow for the 'airflow meter plate' to lift easier (as air passes by it) which will enrich the fuel. As the WUR warms-up, the 'control pressure' eventually increases to it's specific 'warm control pressure' to achieve proper fuel/air mixture.

    Air going through the slotted 'idle speed adjust screw' and the 'aux air valve' is 'metered' air - meaning any change/adjustment of these, does Not affect the air/fuel ratio.

    I hope that was explained ok.

    * make sure you don't still have the original cloth braided hoses (3 pieces, attached the metal 'Y" fitting) on the suction side of the external fuel pump. If they are original, they are allowing air to get sucked-in and probably seeping fuel. Replace the fuel filter if it's old too. Cannot set proper fuel/air mix with dirty fuel filter or air bubbles in the system.

    Here's an old but informative video, 'most' of it applies to our k-jet systems...
    Tbd

  16. #16
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    Great explanation and video - Thanks - Still have the same basic question - Which component is responsible for the increase/decrease in the idle speed at cold start and warm up.

    I am on, what I hope to be, the very last lap of this project. The fuel pump, hoses, filter all new. Fuel distributor and WUR are newly rebuilt. All new air hoses. I had a decent clutch and the price tag on the engine rebuilt ate up new clutch money. I should have broke the piggy bank and done the clutch when the engine was out of the car. As I said, once it is slightly warmed up, it runs sweet and clean.

    In the whole scheme of this project, the small glitch in the start/idle sequence is solved by a 2 minute warm up with my foot on the gas pedal.
    Last edited by dbaldwin; 03-02-2018 at 01:05 PM.

  17. #17
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    Quote Originally Posted by dbaldwin View Post
    Great explanation and video - Thanks - Still have the same basic question - Which component is responsible for the increase/decrease in the idle speed at cold start and warm up.
    Assuming everything else is proper, it's the aux air valve (additional air slide valve).

    The aux air valve simulates your foot being on the gas pedal to keep the engine idling when the engine is cold. Here's some examples that can poorly affect cold engine idle speed: If the 'cold control pressure' is too high, the fuel mix will be too lean for the aux air valve to do any good when the engine is cold. Similar will happen if the fuel mix is adjusted too lean - have you adjusted the fuel mix yet (3mm allen tool)?
    Tbd

  18. #18
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    The aux air valve is solely responsible for the rise in idle speed. It works exactly like pressing the gas pedal a little bit, by letting a little more (metered) air through the intake log, bypassing the throttle butterfly.

    Extra fuel (from the WUR cold start mechanism) only makes the mixture richer, which isn't nearly as effective for adjusting engine speed, but does allow the engine to run much better (or at all) when cold.

    The idle speed adjuster screw works exactly the same, by adjusting another (very small) air bypass around the throttle.

    The mixture adjuster screw works differently, by instead making a change in the position of the fuel distributor piston relative to the position of the air flow meter plate. The fuel distributor piston being that which actually controls the "control pressure".

  19. #19
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    Thanks epmedia for the previous comment, I also hadn't understood Randy's statement before, but now I think I get it.

    I wonder if this might explain my car's own cold-running issues..

    It actually starts readily even in freezing weather, and idles around 900 or so for the first minutes, but THEN starts to have trouble idling all the way up until the temp needle gets to about the first mark. Idle rises a little more even until its as high as 1100 when fully warm (temp gauge about halfway, aux fan starting to cycle).

    I was thinking this indicated a bad aux air valve, because pinching the tube when cold didn't seem to do anything. But now I'm wondering if perhaps instead my WUR needs a little adjusting, to make it a bit richer when cold.

    I'm pretty certain the high "hot" idle indicates a slightly rich mixture, which would be caused by having richened the mixture screw a little to compensate for the WUR in finding the best balance between cold and warm running behavior.

  20. #20
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    Quote Originally Posted by cgifool View Post
    ...The fuel distributor piston being that which actually controls the "control pressure".
    I'll rephrase this for us...
    The fuel pressure on top of the piston/plunger is controlled by the WUR.

    The force required to lift the 'airflow meter plate' as air passes by it, is relative to the 'control pressure'.
    Tbd

  21. #21
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    Not to hi-jack this thread; I have a cold idle symptom myself the troubleshooting of which might add to the great info shared so far.


    Background: 1982 model year w/recently rebuilt engine, NOS WUR, new fuel pump and accumulator (filter too), new injectors, and all new fuel and vacuum lines. Timing is set properly per the blue book and has been double-checked.

    Symptom: from cold it starts right up and settles into a nice ~1100 rpm high idle. As the engine begins to warm the idle begins to drop and then starts to stumble to near stalling - quite rough. If you drive the car during this period of stumbling there is a distinct surging effect. This lasts a short period of time until the engine is "warm" and then it idles nicely at ~850 rpm.


    I have not attempted to adjust the mixture screw but that is my next step. Do you think I am on the right track? Adjust the mixture screw when engine is fully warm correct? My theory is that as it is warming up and entering closed loop control the freq. valve is creating the surge due to the base mixture being off. I have a feeling the mixture screw was adjusted over the years to compensate for small vacuum leaks (prior to my ownership).

    I have access to a wide-band O2 that can log data and the plan is to watch the AFR during this series of events. I hope this will lead me to whether I need to go richer or leaner with the mixture.

    Appreciate further thoughts on this.



    MJ

  22. #22
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    Great information - Thanks to all for going deep into the details. I hoped I would get at least one reply pointing me in the right direction. I am very grateful for the time you all took to pass on the wealth of information. The car is at the paint shop. They are touching up a small detail. Once I have it back in my garage next week, I will run through the series of suggestions. I think I finally understand the sequence. Thanks again.

  23. #23
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    Now I understand what the mechanic (who rebuilt the engine) was doing when I asked him to adjust the warm engine idle. He did it by ear, no gauge. He had a screw driver for the idle speed adjuster screw and when I got a better look at what he was doing, I saw he was simultaneously tweaking the mixture. He lowered the warm engine idle from 1100 rpm to 1050 rpm in that fashion, and said drive it for a while.

    At the next cold engine start, I still had the same issue -it will stall at the first stop sign (if I don't press the gas pedal)- If I let it stall, after one or two restarts, it now idles between 1050 - 1100 and stays there between 1000 and 1100 when warm. No big change. With your info, I am getting much closer to the solution. Thanks for you help.

  24. #24
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    Interesting.

    Randy

  25. #25
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    Quote Originally Posted by mjweimer View Post
    Not to hi-jack this thread; I have a cold idle symptom myself the troubleshooting of which might add to the great info shared so far.


    Background: 1982 model year w/recently rebuilt engine, NOS WUR, new fuel pump and accumulator (filter too), new injectors, and all new fuel and vacuum lines. Timing is set properly per the blue book and has been double-checked.

    Symptom: from cold it starts right up and settles into a nice ~1100 rpm high idle. As the engine begins to warm the idle begins to drop and then starts to stumble to near stalling - quite rough. If you drive the car during this period of stumbling there is a distinct surging effect. This lasts a short period of time until the engine is "warm" and then it idles nicely at ~850 rpm.


    I have not attempted to adjust the mixture screw but that is my next step. Do you think I am on the right track? Adjust the mixture screw when engine is fully warm correct? My theory is that as it is warming up and entering closed loop control the freq. valve is creating the surge due to the base mixture being off. I have a feeling the mixture screw was adjusted over the years to compensate for small vacuum leaks (prior to my ownership).

    I have access to a wide-band O2 that can log data and the plan is to watch the AFR during this series of events. I hope this will lead me to whether I need to go richer or leaner with the mixture.

    Appreciate further thoughts on this.



    MJ
    Possibly,,yet adjusting the slow running adjustment adjusts air and fuel at the same time, if fuel needs to be adjusted by itself the WUR adjustment is done.

    Randy

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