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  1. #1
    Ken62465's Avatar
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    CMD surging issues

    Anyone suffer surging from CMD's Auto tune in vacuum range? For some reason Auto tune insists on a 30% fuel change over 1 cell at 4k and 5k rpms. This large fluctuation causes the ski to surge. I've cleared the cells and Auto tuned from scratch...comes right back after 3rd accepted trim and sending map. Once under boost the CMD is perfect. I tested zeroing out the rpm range in my target afr table, so the CMD would not Auto tune. I then manually tuned that rpm and got the surge gone with far less fuel variation between cells, but why does Auto tune struggle? I had a thought that what I'm going to do is manually tune right to 6k, or when boost kicks in. Then as air temp fluctuates I'll use my LCD to add/subtract fuel to 6k and manually correct it. I'll let Auto tune handle all boost. I prefer Auto tune do it's job but some days the surge comes in even at 3k, but always at 4k and 5k it can't tune, but why 4.5k is fine I don't know. Carrying a laptop around is starting to get to me so this corrective idea should work fine.


  2. #2
    Got Boost? psycho rxp's Avatar
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    Quote Originally Posted by Ken62465 View Post
    Anyone suffer surging from CMD's Auto tune in vacuum range? For some reason Auto tune insists on a 30% fuel change over 1 cell at 4k and 5k rpms. This large fluctuation causes the ski to surge. I've cleared the cells and Auto tuned from scratch...comes right back after 3rd accepted trim and sending map. Once under boost the CMD is perfect. I tested zeroing out the rpm range in my target afr table, so the CMD would not Auto tune. I then manually tuned that rpm and got the surge gone with far less fuel variation between cells, but why does Auto tune struggle? I had a thought that what I'm going to do is manually tune right to 6k, or when boost kicks in. Then as air temp fluctuates I'll use my LCD to add/subtract fuel to 6k and manually correct it. I'll let Auto tune handle all boost. I prefer Auto tune do it's job but some days the surge comes in even at 3k, but always at 4k and 5k it can't tune, but why 4.5k is fine I don't know. Carrying a laptop around is starting to get to me so this corrective idea should work fine.
    After u get the tune close in most areas, u have to drop the max enrichment & enleanment settings from 30% down to like 5%. 30 is way to high. That way it can only go out of range a max of 5%, which would be hardly noticeable. Then manually tune the trouble cells closer to each other, so there's not such a big difference between those cells.
    If you get a sensor on its way out, it can screw up your whole tune 30% in all areas.

    Remember your AFR's need to be between 10.0- 16.0 for it to even autotune.
    If it sees 10.0 or less, it struggles to try to lean out that cell, till it gets too far out of range either way, thus causing the surging.

  3. #3
    Ken62465's Avatar
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    I was never out of the 10-16 range. I have a reflashed ecu mapped for 80's. Prior to installing the CMD my idle afr was 11.2-11.5, then would spike to 15 at 5k then gradually drop to 11.5 @ wot. This was not a good tune to me so hence my opting for the cmd.

    I had already lowered the max enrichment/enleanment settings but what would happen is if I accepted the trims it would add/subtract yet another fueling and eventually things start surging again. I never meant my setting is at 30%. I meant that Auto tune eventually keeps upping things with each accepted trim to where I'll see a 30% fuel change from one cell to the next and that seems to be when the surging takes place. Even if one set that max enrichment/enleanment to 30 why would Auto tune ever fuel it to a point of surging and not hitting your target afr? Doesn't sound real efficient to me to do so. To me if Auto tune is doing an efficient job it should never tune things out so bad it causes surging as I watch afr's fluctuate from 12 to 14 at 4k no matter how many times you accept trims...doesn't do that under boost. Some rpm ranges, due to air temp changes, would need a little extra beyond my max setting so I was forced to accept trims knowing it was the only way to get the added fueling. Temps a bit whacky here in NE right now. One day 78 next day 90.

    The 02 sensor is bran new so I have to doubt that's the issue, especially given that under boost it's spot on and not once been an issue.

  4. #4
    Ken, Are you running an LCD-200? Can you post you CMD file here?

    This sort of thing happens on occation and is normally easy to fix.

    Andy

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  6. #5
    Ken62465's Avatar
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    Yes Andy I have the LCD. I did a couple logs last week and upon review all I saw was exactly what I already knew from watching the afr's freak out at those 2 rpm spots I mentioned, due to the drastic fueling change from cell to cell. Sadly I think I deleted them. I'll be out again this coming week and make a new log. Unfortunately I had zeroed out the 4k & 5k cells so Auto tune wouldn't muck with it again and start surging on me. I manually tuned those ranges so I'll have to undo that work and let Auto tune surge the pig then log it.

    What's the easy fix?

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    Ken62465's Avatar
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    ohh and for the record. I ride mostly glass. I've seen posts of this surging issue with Auto tune occurring due to ridding the chop but that's not the case for me.

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    Got Boost? psycho rxp's Avatar
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    If everything else is spot on except those 2 spots, Turn off autotune, and manually tune the bad areas closer to each others values. Then save the map. Autotune is no longer needed at that point.

    If it keeps auto tuning that area way off, its a bad tune in the ECU itself, but the CMD can smooth it out as long as u are using it.

  9. #8
    I have seen this come up on my ski. It has to do with the response time of the o2 and the feedback getting into oscillation. You may have a motor that gust happens to do this and some point in the power band. I do not run full time autotune above about 7800 rpm for this reason.

    If you have a log, it is fairly easy to spot in MegalogviewerHD.

    I think I posted this on the CMD thread. I will snoop around and see if I can find the post.

    Andy

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