what does this adjustment screw do? (Balancing vacuum on plenums) | FerrariChat

what does this adjustment screw do? (Balancing vacuum on plenums)

Discussion in 'Boxers/TR/M' started by Veedub00, Aug 19, 2021.

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  1. Veedub00

    Veedub00 F1 Rookie
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    I am having a hard time getting vacuum down in the left bank and vacuum up in the right bank.

    I've checked for vacuum leaks, but that left side is always very high vacuum. How do I lower it?

    I have both air bypass screws in all the way, throttle sensor pinned to get open loop mode, do I adjust adjustment screw 5? What does that do really? Opens up the throttle butterfly valve inside the throttle body?
    I have the connecting rod 4 detached. Do I have to have that attached to make a difference?

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  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Aug 19, 2021
    Last edited: Aug 19, 2021
    Are you saying that by using screws 1 you are unable to achieve the conditions in step a10 on page D102? Screws 5 aren't mucked with until step a12 (after presetting them in step a6).

    Turning screw 1 inward should raise the engine RPM and reduce the vacuum on that bank. Likewise, backing screw 1 out should decrease the engine RPM and increase the vacuum on that bank.
     
  3. Veedub00

    Veedub00 F1 Rookie
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    yeah. I can't lower the vacuum in the left side hardly at all by using screw 1.
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    I don't believe you ;) -- if you turn it in a bunch (and confirm that the throttle plate moves a lot) and back out the other screw 1 to keep the same engine RPM does not the left side vacuum go down?

    I.e., are you sure the left side screw 1 is actually touching the throttle plate mechanism and moving it? Does the engine RPM go up when you turn the left side screw in?
     
  5. Veedub00

    Veedub00 F1 Rookie
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    well I pulled the plenums to see what was going on. The left throttle butterfly was alot more closed than the right throttle butterfly. I think I am going to set them equal, hope to find the correct starting point.
     
  6. carguy

    carguy F1 Rookie

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    Please correct me if I'm wrong....but it seems like the throttle plate "stop adjustments" are only supposed to prevent the throttle plates from impacting / wearing-into the aluminum housing during the throttle plante closing, they are not intended to adjust air-bypass. All bypass air is controlled with the large bypass screws.
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    That is technically a true statement because "bypass air" is defined as the air that flows thru the air bypass screw path. However, the throttle plates are supposed to be slightly open at idle (to provide enough airflow for a 700 RPM idle speed when the air bypass screws are fully closed), then the air bypass crews are opened to provide the additional bypass airflow to raise the warm idle speed to 1000 RPM.
     
  8. carguy

    carguy F1 Rookie

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    Thank You Steve for clarifying that. How is the throttle plates "slightly open" condition achieved? Is it purely by intake vacuum? (meaning when the engine is shut down the plate is closed) Or is it by the throttle plate stop-screw holding the plate open slightly?
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    By that, but it also provides the benefit that you noted -- the throttle plate shouldn't touch/rest on the inside bore. It's not a lot -- like maybe ~1/16th of a turn of screw 1 after it makes contact. If the throttle plate is resting on the inside bore (and its arm is not touching screw 1), but you still get the 700 RPM with the air bypass closed = most likely the throttle plate is not well-centered in the inside bore and should be repositioned on its shaft, or something's wacky in the throttle shaft/bearings, etc..
     
  10. Veedub00

    Veedub00 F1 Rookie
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    thanks for the discussion. I have been trying to balance the vacuums and get a good A/F ratio using a multimeter on the O2 sensors,
    This is so frustrating. Getting, the idle speed and A/F ratio and vacuums to agree on both sides is very frustrating. I feel like I am just chasing my tail. Like I make an adjustment, and then the A/F ratio drops out of whack. I feel like I am almost there time and time again.

    The best one I got so far, then the engine felt unbalanced. The car was not idling smooth as I thought it should be.
     
  11. leslie_choo

    leslie_choo Formula Junior

    Aug 5, 2012
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    Steve may I ask for 90s testarossa after we get the intake balanced and idling at with 700 rpm ( throttle stop screw) + 300 rpm (bypass screw) . Do I need to set the potentiometer at an certain angle ( or voltage ) ?

    I believe once the intake is balanced idling at 1000 rpm , will the ECU collect all the data from sensors and auto adjust the fuel /air ratio ? Or we have to manually adjust this at the air/fuel ratio screw ?

    Thanks
     
  12. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #12 Steve Magnusson, Oct 11, 2021
    Last edited: Oct 11, 2021
    If by "potentiometer", you mean the Mixture regulator potentiometer, Item 14, on page D68 of the TR WSM (also discussed in this thread: https://www.ferrarichat.com/forum/threads/ke-jetronic-air-flow-meter-potentiometers.644465/#post-148001786) = no. Its position is adjusted (by the factory) based on where the airflow metering plate is located in the funnel when a certain amount of air is flowing thru the funnel. Its position should not need to be readjusted unless the airflow metering unit components are changed. That other thread gives instructions on how to test it if you think it is misadjusted or faulty.

    The injection ECUs only provide the Lambda function and some other minor functions (like adding enrichment during starting). Once you have it warm idling at 1000 RPM, O2 sensors unplugged, and both intake plenums at the same vacuum level, you have to manually adjust the mixture screws yourself. If the warm idle speed changes a lot, then you have to go back and readjust the airflows to get the 1000 RPM, readjust the mixture, etc....
     
  13. carguy

    carguy F1 Rookie

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    Hope you Gents don't mind me chiming in, I've been out of the TR game for 10 years now. STEVE - you were always a fountain of information, and your input saved me many times over the years - Thank You.

    My memory is a bit foggy - but perhaps my experiences will result in further discussions in this most excellent thread. As I recall from my last TR, the previous owner tried to do some "tuning" and everything was messed up - totally FUBAR. The first thing I did was to center-up the air-flow metering plates in their bores, one side was really off and would "drag". I then turned in both air-bypass screws completely, then backed them out the same amount of turns. I adjusted the throttle plate stop screws until both places were just barely off the surface at throttle-closed. I made sure the throttle micro-switch "clicked" at the instant that the throttle-opened. Installed a new thermo-time switch. I confirmed that power was present in the triangular black box and the fuse was good. I then made up some rubber plugs that fit into access holes for the fuel-adjustment screws, these were to plug up the holes between fuel adjustments - otherwise big vacuum leak!. I also had 2 vacuum gauges, one for each intake plenum. I disconnected the O2 sensors. I started the car, and adjusted the air-bypass screws to get the highest vacuum reading, and balance both banks (at something like 800 rpms). Using the Gas Analyzer, I adjusted the fuel mixtures to get something like 150 Hc's (no cat convertors) on both banks. I think I used the air-bypass screws to get the warm idle at 1,000 rpm. I was never quite able to get the vacuum to specs, just a bit shy...but close. The motor ran perfectly smooth, with no surging cold or warm, once things were balanced.

    I'm sure I've missed something....or made an error here and there....but this is what I recall. I tried using wide-band 02 sensors with an LED readout to set the mixtures but it was not consistent. I finally bought a used 4-Gas Analyzer...which was worth every penny!
     
  14. Veedub00

    Veedub00 F1 Rookie
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    Yeah. The 4 gas analyzer is the missing part for me.
     
  15. turbo-joe

    turbo-joe F1 Veteran

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    that is more than perfect and shows the good engine condition
     
  16. carguy

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    I did the timing belts, with Hill Engineering's tensioner bearings. I used a degree wheel and set / verified cam timing, new spark plugs, new plug-extenders, made new plug wires, etc. I also used Stabilant-22 on ALL electrical connections, but this may or may not have helped. The TR really ran great once everything was done. All thanks to the great people on this forum.
     
  17. mikael82

    mikael82 Formula Junior

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    #17 mikael82, Oct 13, 2021
    Last edited: Oct 13, 2021
    Do you have manometer?
    [​IMG]

    What you do is:

    1. Get some one to help you.
    2. install manometer with T-union to fuel regulator (remember air balance should work during adjustment just as it works in use)
    3. close by-pass screws.
    4. screw out idle adjustment screws (car won't idle, you need friend to keep it runing)
    5. Get friend to help you so one hangs revs up over 1500rpm or something, so any slack is removed from pedal wire and you adjust both sides balanced from linkage (4) while engine is reving.
    6. Tighten linkage nuts. (and re-adjust balance as tightening will affect it)
    6. catch idle with throttle stop screws to 800rpm. open both sides and mechanism should rest on both sides evenly (when you open up one screw, affect should be similar to other)
    7. rise idle up to 1000rpm from idle bypass (I keep idle down to 900 side)
    8. rev up few times and see how idle comes down, if it does not; start again, you where not accurate enaugh.
    9. next morning with cold engine start up and see everything works like it should, rev up little bit and engine rpm should come down instantly; if it does not, start adjusting again.
    10. Same with idle faiding when engine warms up; not accurate enaugh and start adjusting again.

    - Remeber to look engine temperatures you can stop enytime and continue after issue is gone.
    - DO NOT remove linkage rods, if you do so, you have to adjust averything again.
    - This instructions are not what factory tell you to do, because factory can work with car that got new parts in it, this way all wear and slack is counted out from adjustment.

    - Adjustment is more accurate then any gauge you ever use, manometer is only tool for this job.

    - think it like balancing ball on board; if it leans up one side it will fall there ie. too much bypass or too rough cut to idle screw causes idle to stick on high rpm. if you got it too heavy on low rpm side and catching up with idle screw and bypass causes engine to stall. Idea is to adjust it to work with as low air as you can and is on very edge on rewing up, then you end up car that drops down quickly from RPM and reacts really fast to accelation. You work with in limit of engine temperature, because that affects most to idle and how if acts.

    - There is two ways to do this, fast and quick, and correctly. If you cut any corner, use wrong tools, not follow instructions, you will end up car that does not work properly and only way to know you done it correctly is to try out one car that works correct.
     
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  18. leslie_choo

    leslie_choo Formula Junior

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    Thank you Steve and Mikael ,

    Mikael , btw I follow your throttle balance setting for our Diablo step by step . I took my car out today , WOW !! it’s day and night !!! And the car is powerful and 0 checklights ! Thank you again !

    Btw I will follow the steps here to balance set up for Testarossa . The next question that I have is what’s next for Testarossa assuming if the balance / idling is done ?

    For my carburetor 308 , I use calortune to get air/fuel mixture right for each cylinder ( 8 of them in total) . For Diablo , after setting the right Potentiometer angle/voltage the air/fuel mixture is all set by ECU leveraging the sensors info. What about Testarossa ?

    Should I use the colortune on 1 cylinder ( adjust the air/fuel mixture screw) to get the right mixture ( and assume the 6 cylinders are consistent since the fuel is distributed equally . Or What do you all do to get the air/fuel mixture right ? Any tool that you use ? Wide band O2 sensor ?

    Fyi - I use Color-tune on my carburetor car and it will show orange when A/F is rich , white when A/F is lean , blue is the correct A/F . But this is a very traditional method , not sure this is accurate enough for an injector car .
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  19. turbo-joe

    turbo-joe F1 Veteran

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    problem with the colortune is you only can adjust in idle or also with higher rpm, but no load on the engine. during driving you cannot see the colortune or put a webcam near, a monitor inside and go driving. when you adjust then disconnect the original O2-sensor ( if you have those ). after adjusting connect the O2 sensors and you will see that the colotrune shows now different.
    best would be a wide band sensor for every cylinder to see if all are doing the same.
    the colortune I used always for my kawasaki 3 cylinder 2 stroke bikes and did very good experiences
     
  20. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Yes, you could use the Colortune on a single cylinder in each bank and probably be in the right ballpark (the fuel delivery from the fuel distributor is usually very equal to each cylinder, but it can vary by up to 10%). If you have a TR model with narrow-band O2 sensors on it, you can also use the signal coming from those (even though they should be unplugged) when adjusting the mixture screw to get an average value from all cylinders. Warm idle is set a little bit rich using the mixture screw (like ~0.7V DC on an unplugged narrow band O2 sensor). I'm not that familiar with the Colortune for what the colors mean (i.e., is blue stochiometric or a little rich, or what the resolution is for each color). For the issue that romano mentioned (if you do have narrow band O2 sensors), each cylinder's air-fuel ratio would be continuously varying slightly when the O2 sensors are plugged in and the system is running closed-loop so that could explain why the Colortune color could look different for the open-loop adjustment versus closed-loop operation (it will run closer to an average stochiometric in closed-loop, but each cylinder will be different based on the individual fuel delivery from the fuel distributor).
     
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  21. turbo-joe

    turbo-joe F1 Veteran

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    blue is not equal always with blue steve. there are so many nuances of blue that it needs some experience. but when blue the stochiomtric is nearly fine, when red too rich, when orange still to rich, yellow and white or nearly white too lean
    have a look here:

     
  22. mikael82

    mikael82 Formula Junior

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    Great to hear! I think most Diablo's have balance not done correctly because mechanics who knew how to adjust are gone and those in modern day overlook manometer as a tool, same goes with Testarossa's.
    Also, both Ferrari and Lamborghini guide for adjusting balance is my opinion done for new parts. But I think factory adjusted these differently from what is written on manuals, pictures from factory and tools point to this.

    Testarossa is a bit different from Diablo, since mechanical fuel injection can not be altered. Jetronic adjustment is basicly set in Bosch factory and adjustment largely done by keeping system clean and o-rings in order. Most important part of Jetronic is fuel pressure, either done (wrongly named) Warm Up Regulator or electronic version depending version car is. If pressure is in order and it works with engine temperature, injectors work, you do not have air leaks - car should work great with balance adjustment done correctly.

    One thing I like to point out is; rarely there is anything wrong ignition and many times issues are wrongly seek from spark side.
     
  23. ago car nut

    ago car nut F1 Veteran
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    Innovate Motorsports wide band A/F ratio meter records and monitors ratio 12 times a second. One of the better ways to monitor overall fuel mixture.
     
  24. Gialllo uno

    Gialllo uno Formula Junior

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    I have and had a FAST (Fuel, Air, Spark, Technology) system that had the ability to monitor on a digital meter 2 O2 sensors at the same time. I bought it for an old 70 Z28 Camaro with O2 bungs in each header collector. It made dialing in a carburetor much easier, left bank cylinders and right bank cylinders A/F ratio instantly. You could see the A/F at idle, warm and also when you got on the gas to see if there was a lean condition and what the overall A/F was during full throttle condition for example. For ease of use in the Testarossa I bought 2 tailpipe adapters and each has its own O2 bung. I have been doing otrher things with the car recently but need to see what my results would be. This is a picture of the unit. This thread has got me pumped to get to work!!!!! Image Unavailable, Please Login
     
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  25. ago car nut

    ago car nut F1 Veteran
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    Does the above record and down load to computer?
     

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