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Thread: Cam Surge-still there.

  1. #1
    Fuel Injected! Terminal_Crazy's Avatar
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    Cam Surge-still there.

    Hello! me again.
    I'm still fighting this cam surge.
    I've tried just about everything I've read about.
    I've just scoured the gearhead site & the web on suggestions.
    Read up threads by Dave_W, Scott PFautsch, Steveo, Bobdec and Greg Banish.

    I've jacked timing up and down without much effect.
    I've just driven back from the anual MOT test with the timing retarded by 15 degrees, idling at 20.

    Ideally...
    The car idles at 39 degrees very nicely, map around 38-41.
    It will pull away by just easing the clutch out & no throttle, dead smooth and no bogs.
    As the car gets upto rolling speed 6-9mph the car starts having a fit, mild to wild.
    Any throttle and load say 5% and more and the car seems quite happy.
    If i hold the throttle until the revs settle (lower map around 30) it will still surge.
    Any time I slow down, drop to 2nd (10-1400rpm) and turn a corner it's there until you hit the gas a small amount.

    Idling with timing at 34 the car is sluggish and soggy when pulling away. Map around low-mid 40's.

    I've tried timing upto 45+ in these higher rpm lower map areas.
    I've lowered it down to 35 at 2800 rpm.
    I've just pulled 15 degrees off the table with EEHack and IT'S STILL THERE.
    It was idling at 20 degrees.

    Fueling has noticably been effected.
    Where BLM's were 125 to 129 they are spread 120/116 upto 139/139 and splits upto 5
    BLM 16 is reading 133 131 & O2averages are sat at 494/484mV


    Is this a symptom of the cam?
    It's not huge 223/231 .610/.594 112 LSA.
    383 LT1 11.5:1 AFR 210 heads 2.08/1.60 Edelbrock LT4 manifold
    Currently running CLSD.

    Any ideas
    TC
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  2. #2
    Super Moderator dave w's Avatar
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    Back in my carburetor tuning days, I tried to get the best idle by:
    Keeping a decent idle RPM ( 700 - 900) by:
    Adjusting the base timing (without vacuum advance connected to the distributor) and idle mixture screws for the "best" possible vacuum. Best possible vacuum is defined as, 20 Kpa is better than 40 Kpa.

    Fast forward to EFI idle tuning:
    Adjust base timing ( with ESC disconnected) to factory spec. (note this is a baseline adjustment - actual timing might vary a few degrees)
    Adjust IAC for 10 to 40 steps (normal operating temperatures, ESC CONNECTED)
    Adjust idle spark table for best possible vacuum.
    Adjust idle BLM's to 128 + / - 3 or 125 to 131.
    Adjust idle table to an idle somewhere in the 700 to 900 range.

    dave w

  3. #3

  4. #4
    Fuel Injected!
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    This may have no relevance to your setup as mine is obd1 BB chev, bit of cam, head work etc, When ever it got close to idle in closed it would surge a bit. In open it didn't happen. I have run open exclusively for almost three years and it runs so much better. It allows ve to be what the motor likes rather than what the epa likes. It goes without saying the ve table has to be CORRECT. I have mat correction of 15% and that makes I so I have no changes summer to winter. It might be worth a test.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  5. #5
    Fuel Injected! spfautsch's Avatar
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    I would have to second myburb - consider going to OL. You don't even have to flash to test, just use the OL selector in eehack and set the AFR to something like 13.8:1 and drive a bit.

    I'm still a week out from getting mine running but I had all the same type of surge and the only thing that seemed to help was tweaking individual cylinder trims. But that only lessened the severity. The only thing I haven't tried is OL. I think what you're seeing is reversion causing O2 corruption which in turn causes the integrator to oscillate at these airflows.

  6. #6
    Super Moderator dave w's Avatar
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    I use a Wide Band O2 sensor (WBO2) to tune with. See attached screen shot showing an idle surge. Blue is good, not blue = not good = idle surge.

    dave w
    Attached Images Attached Images

  7. #7
    Fuel Injected!
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    That cam is not big enough overlap wise to need to run OL. I have had sucess tuning a 232/240 on a 108 LSA in closed loop. What I would look at is the transition from idle to main spark advance. Big changes in timing between the two can cause the surge you are seeing. If you are rolling along at Zero throttle somewhere between 2 and 10 mph almost every GM tune I have looked at goes from close throttle spark to the main spark table.

  8. #8
    Fuel Injected!
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    Check your O2 settings. Your tune may be trying to correct the fuelling to quickly for your engine. Try lowering these if you have them. - PROPORTIONAL GAINS IF STABLE IDLE PRESENT/PROPORTIONAL GAINS IF UNSTABLE IDLE PRESENT

  9. #9
    Fuel Injected! Terminal_Crazy's Avatar
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    Hello again

    Well I had the motor idling at 20 degrees.
    It ran much louder & had a much deeper tone. It sounded lopey which it was.
    AFR's on the guage seemed to bounce much less erraticaly than before but everything was HOT

    So
    Settled on 24 degrees as a base idle. Not as loud and definately not as hot.
    The off idle surge didn't seem quite as severe but it was much more noticable during driving.

    Fueling has richened up by lowering the timing but AFR's on the guage seemed generally more stable even though it doesn't match up with BLM or O2 readings

    I have not adjusted the VE tables yet to match these new timings which might make a difference ??


    I did several Cylinder drop tests with EEHack and the motor shows stronger towards the back. I'll post a separate thread on that.

    All in all a bit disappointing.
    Attached Files Attached Files
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

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