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Thread: surging idle switching from sync to async

  1. #1
    Carb and Points!
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    surging idle switching from sync to async

    Hello fellow Gearheads, I've been visiting this great forum for a couple years now and have always been able to get most of my answers by just reading post........up until now. My project is an 87 Jeep YJ with a Chevy Vortec 350. The project started around two years ago with a TBI350 from a late eighty G2500 van. Then last November the motor lost a cylinder so I decided to go with a rebuilt Vortec 350. I figured from all the hours and hours of reading on this forum that I would be able to make the required changes to the fuel/spark tables etc. and have a good running stock Vortec 350. At first things seemed to go well with the stock injectors 61.2# but I always had a slight miss. So while pondering on the reasons for the miss I convinced myself that the old injectors must need cleaning or be replaced so I threw down the cash for some rebuilt 65's. At first all was going well. I used the TBI calculator to set the new BPW and injector bias then data logged to set the VE table. This is when I started having problems that I haven't been able to solve. The main issue is at idle, it switches between sync and async. This is causing a surging idle that I haven't been able to figure out over the past few months. To make a long story short I decided to set the BPW and Injector bias back to stock 135/0.42 (I know 0.42 isn't stock but close to 0.396) and started over today. Things seemed to be going great with two data logs....idle was good and BLM were getting close to 128 after a few adjustments. Then I decided to take a break and came back two hours later and now the problem with the sync/async switching at idle started again. So now I'm bowing down before the TUNING GODS asking for leniency on my retribution for a failed Tune. Seeking any help or direction to a thread discussing this issue. The vitals are has follows:


    Fuel pressure at 15psi (verified by gauge)
    TunerPro (purchased)
    Moates Hardware
    350 vortec stock L31 bored 0.030
    Edlebrock performer dual plane intake
    TBI/intake adapter is 1/2 thick aluminum (I've verified no vacuum leaks)
    Shorty Headers

    1987 jeep around 3300lbs
    4:56 gears 33 tires
    custom Dana 44 front ARB locker
    custom Ford 8.8 rear ARB locker
    TH350 custom built mated to Early Bronco Dana 20 Transfer Case
    Hydro Boost Brake system disc front/rear
    High steering with Performance unlimited steering system


    Bin:
    Started with ADYR $42
    Spark table is modeled off Dave W Vortec table listed on this forum
    Some changes have been made to the IAC setting to bring down idle a little quicker
    Included are two data logs and Bin File
    Data logs included are: Last data log for setting VE table and idle log showing the switching between Sync/Async.


    One other thing I noticed on this last log was an Error code on the VSS. For some reason this pops up from time to time. I can sometimes disconnect the battery or change the Chip and it goes away. I do utilizes a 2 pulse VSS sensor from JTR. I think I'll check the connection at the position switch to make sure I'm getting a good grounded connection in park position.


    Thanks for any suggestions

  2. #2
    Super Moderator dave w's Avatar
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    Have you looked at these parameters?

    See pic

    dave w

  3. #3
    Carb and Points!
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    Thanks Dave for the reply.
    Yes I did switch those parameters. It would start and idle okay but when I tried to accelerate the motor would cut out and fall flat on its face. Perhaps I did the adjustment wrong?

  4. #4
    Super Moderator dave w's Avatar
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    Quote Originally Posted by mike65 View Post
    Thanks Dave for the reply.
    Yes I did switch those parameters. It would start and idle okay but when I tried to accelerate the motor would cut out and fall flat on its face. Perhaps I did the adjustment wrong?
    Vortec heads like lots and lots of AE. Maybe your going lean would you try to accelerate the motor? Maybe you have access to a Wide Band O2 sensor to see what the AFR's are doing when you accelerate the motor?

    dave w

  5. #5
    Carb and Points!
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    Not sure what happened I replied to your last comment Dave a few hours ago and it appears it didn't post. Anyway!!

    In the early stages of the project I did set the AE tables and the motor responded well under acceleration. I even used a WB O2 to verify. My sync/async switching problems started after I changed the Injectors to 65#er. Initially no problems then when I got to the fine tuning the sync/async switching started. My first step to eliminate was trying the parameters changes you mentioned above. These changes caused the motor not to rev above 1000rpm....couldn't even get out of the driveway.


    Today because of your suggestion I tried to make the changes to the Async setting again. The same thing happened today as before. Would idle but wouldn't rev up....pig rich! I did notice that the units in the Asnyc note didn't match the units in the scalar (Usec vs Msec). Has anyone noticed this before? I'm using $42-1227747-V5.9.3 xdf.


    Mike D

  6. #6
    Super Moderator dave w's Avatar
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    I noticed the Microsecond (Usec) vs. Millisecond (Msec) differences. The conversion is: 1000 Microseconds = 1 Millisecond. Let's cover the basics, then work from there.

    dave w

  7. #7
    Carb and Points!
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    Thanks Dave,
    I'm on business travel for the next few days. Once I get back home I'll try changing the setting and let you know the results.
    Mike D

  8. #8
    Carb and Points!
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    Dave,
    I set the async off parameters with the correct units and now the sync/async switching at idle has stopped!

    The first thing after the chip change that I noticed was after warm up the idle speed was higher at about 1050rpm so I adjust down to 550rpm with IAC at 40 and then took for test drive.

    During the test drive I noticed the following:

    -DFCO is now very noticeable and cuts in/out every 1/2 sec right up until I come to a complete stop. I could feel these before, but now much more predominant.

    -Async kicked in once or twice while cruising at about 40mph???....but only for a very brief moment.

    -After short drives, while left at idle for a couple minutes, it starts going in and out of open/close loop.

    All sensor info looks good and no error codes.

    Any Thoughts?

  9. #9
    Super Moderator dave w's Avatar
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    There are several parameters for Open / Closed loop. I use the Parameter Finder from the Tool Menu to display parameters. See attached screen shots. I think it would be a good plan, to adjust one Open / Closed loop parameter at a time to achieve the desired idle you want. That's Tuning.

    dave w

  10. #10
    Carb and Points!
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    Just wanted to leave an update......been on business travel for the past week and tonight was the first chance I've had to run the jeep. What I noticed tonight was different from before....last time it was idling up and down as it went in and out of open/close loop. Tonight it was idling up and down while in closed loop around 800rpm with 200rpm swing. One thing I noticed on the TunerPro dashboard was that it was showing "Park' all the time which seemed odd. I did some troubleshooting and discovered that the switch was bad and staying grounded all the time. Once I disconnected the wire lead the idle dropped off and the motor died. I repeated reconnect/discount several times and the same thing every time, the motor would drop off in RPM and die. I would've thought the RPM would increase as it when from park to drive. Any thoughts?.. I'll replace the switch this weekend and continue tuning.
    Mike

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