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Thread: Ignition timing erratic

  1. #11
    Registered Member Troy's Avatar
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    Hello Lazlo,

    I don't claim to know anything about these new fangled electronic fuel injections and ignitions, but on all of my modern cars to check or set the timing there's usually a plug that has to be jumpered to adjust it. Is that something that might be going on with yours?

  2. #12
    Registered Member chevynut's Avatar
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    Quote Originally Posted by Troy View Post
    Hello Lazlo,

    I don't claim to know anything about these new fangled electronic fuel injections and ignitions, but on all of my modern cars to check or set the timing there's usually a plug that has to be jumpered to adjust it. Is that something that might be going on with yours?
    No Troy, that plug is there so you can set the base timing on a factory setup. On mine I just sync the ECM timing to the engine timing and I'm done. The only thing the base timing if for on the C950 is cranking advance. I guess I can set that anywhere I want to. And I got the erratic timing fixed. There were some bogus numbers in the spark map for some reason. I could even hear popping out of the exhaust now and then and I think that was due to the 63.75 degrees that was in one cell. Still don't understand how that got there and I hope my ECU isn't flaky.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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  3. #13
    Registered Member Fladiver64's Avatar
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    Lazlo,

    I have been tuning my LT1 with a mega squirt ecu and have had some of the same issues that you have run into. Couple of things I have learned is all the work you are trying to fine turn at idle without a running/driving car is just a guess at best. As you have noted the computer interpolates data between cells so what may be the "best" idle in park , is not the best in Drive or may cause a stumble right off idle, so all of this will get returned many times over in getting the car driving well.

    I am not familiar with the Holley commander system but I did find it easier to disable some of the closed loop systems while I was getting the base maps correct. For example I would run the IAC at a fixed position vs engine temp and then tune the timing and idle fuel maps for smoothest idle and best vacuum, then re adjust the iac. Once you get a good idle with the fixed iac position, then let it control the idle. Otherwise you end up in a loop of one thing tying to correct another and it is very difficult to find the sweet spot.

    You also have to find what your combination likes, for example one of the options that is very common on newer EFi engines is for the computer to vary the timing to maintain idle speed, my engine combination did not like this method at all and ran very rough as it took too much timing variation for the differences between Park, Drive and AC on or off. I ended up with a combination of IAC and timing advance/retard vs a target Idle rpm working the best for my combination.

  4. #14
    Registered Member chevynut's Avatar
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    Thanks for the feedback Michael. I don't have "park" and "drive" so I don't have to worry about that and I don't think it will change with a running car. I don't know if I have the capability to disable the IAC without disconnecting it but I can check. I do know that my throttle plates aren't open far enough to let the engine idle by itself, without the IAC opening. That's one of the adjustments I had to make. Also, there is an A/C input so the ECU knows when the compressor is engaged and it bumps the idle up. Did you have a wide range where your engine didn't seem to respond to changes in idle timing? I know I can disable my O2 sensor and run open loop so maybe I'll try that.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
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    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  5. #15
    Registered Member chevynut's Avatar
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    I give up! I started the engine a couple of times and the PC gave me a "runtime error" and made me re-boot it to get it to work. The RPM cells had 12,000+ RPM in them when I tried to read the ECU. However, after I re-booted the data was correct so it's the damned PC. I ordered a new disc drive for an XP Professional PC I have that I already ordered a new battery and charger for, so I'll get it set up. Really tired of this PC screwing me up.

    And that's not all. The last time I re-booted it I tried to start the engine and the starter wouldn't engage. It spins but won't engage the flywheel. So I said screw it and pulled the headers and put them in a box to ship to Jet Hot. Now I have to pull the starter and see WTH is wrong with it. It worked flawlessly up til today.

    Is it still Friday the 13th??
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  6. #16
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    Looking at idle speed doesn't seem like a good metric because the IAC tries to compensate for the choppy idle as it bounces around due to the cam.
    Maybe look at the IAC counts instead of speed. You just want to smooth things the best you can with timing and fuel. And set the target idle speed up a little too if needed.

  7. #17
    Registered Member Fladiver64's Avatar
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    I forgot about that third pedal hanging down. Normally in the idle section there is a way to run open loop, that way the IAC is set to a fixed number based on engine temp. Once warmed up you are right the throttle blades need to be set such the IAC is almost closed, is low idle counts. Other wise you may not have enough room left for additional air at cold start, and things like ac coming on.

    Im not sure what you are using for a USB adapter but I do know some devices are very picky about the chipsets uses in the adapters. I am currently using a Bluetooth adapter from here https://www.efianalytics.com/registe...egory=Hardware. Works as good as the wired one and nice to not have the cable.

    I did have timing issues when I first started, bit my engine has gm better idea of putting the distributor under the water pump, the great optispark. My problem turned out to be an in accurate timing mark on the balancer . this cause the computer to be off by about 15 degrees from the engine.

    I am running 20 degrees at idle speed and map, then I have a close loop correction set for a target idle speed of 800 rpm, if rpm drops then I add 2 degrees of timing for each 50 rpm and drop 3 degrees for each 50 rpm over. This is much faster control than the IAC can manage, if the drops are larger or longer then the IAC makes corrections.

    Of course after getting this all set then running the car I had to make big changes to the fuel maps, which then started the process over, as many of the correction in tuning are made off the base maps.

    All said it is still better than tearing carbs apart for jet changes.

    One other mistake I make was too much accel enrichment to start with. I fouled a couple sets of plugs quickly before I got things close. The computer can add way more fuel than an accel pump. So pull plugs often in the beginning to see where things are at.

  8. #18
    Registered Member chevynut's Avatar
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    Quote Originally Posted by Fladiver64 View Post

    Im not sure what you are using for a USB adapter but I do know some devices are very picky about the chipsets uses in the adapters. I am currently using a Bluetooth adapter from here https://www.efianalytics.com/registe...egory=Hardware. Works as good as the wired one and nice to not have the cable.
    The Holley ECU doesn't have bluetooth capability and the connection to it is just 3 wires. The other end of the Holley-supplied cable has the serial RS-232 connector.


    And it's dangerous too. In Commiefornia!



    I prefer a direct wired connection from a serial port to the ECU especially since it's readily accessible. The problem is the PC I'm using doesn't have a serial port, so I got the USB to serial adapter for it from Best Buy and I suspect it's giving me problems. I've read they can be very finicky. The other PC I'm trying to set up has a serial port. I can't run anything past Windows XP for this software so I have to resurrect an old PC I have.

    I am running 20 degrees at idle speed and map, then I have a close loop correction set for a target idle speed of 800 rpm, if rpm drops then I add 2 degrees of timing for each 50 rpm and drop 3 degrees for each 50 rpm over.
    This ECU does have "idle spark control" but I don't have it enabled. Right now the IAC alone controls the idle. I suspect that my idle is a little less stable than yours.

    All said it is still better than tearing carbs apart for jet changes.
    A carb and a distributor with weights and springs in it are always a compromise. There's only so much that you can do with them. Once you understand what's going on, EFI is pretty simple.

    One other mistake I make was too much accel enrichment to start with. I fouled a couple sets of plugs quickly before I got things close. The computer can add way more fuel than an accel pump. So pull plugs often in the beginning to see where things are at.
    At one point something happened to my program and it was pouring fuel into the engine. I was smoking black smoke out of the exhaust and I thought I blew an injector. Again, the program somehow got corrupted. I should probably pull the plugs and see if they're clean. I'll be glad when I have a PC I can trust to work right.....if that's the problem.

    Do you have wideband O2? I do and it really helps to see what's going on. My startup idle mixture is running pretty rich so I may have to adjust that. Once it goes closed-loop it seems pretty good. Obviously I haven't been able to do much tuning with the chassis sitting on jackstands.
    Last edited by chevynut; 04-17-2018 at 03:21 PM.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #19
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    I think you did the right thing for now sending the headers off. The real risk for your headers is too little timing at engine speeds around 1500-2000 rpm. This is where you cruise, and this is also where you run the engine to break in a flat tappet cam, which is no concern to you. No EFI engine should be that far off if you start with a decent timing map.

    When you get the headers back and a better PC that you can count on (hopefully it's just the PC), then you can tune the idle for both fuel and timing in open loop mode. Just guessing, you should have a setting in the map for closed loop vs. temperature, maybe even closed loop vs. rpm. Just set one or both high temporarily for your idle tuning, then you can set them back to what they were once you're finished with the tuning.

    You don't want your O2 corrections to be large, try to get them below 4-5% by tuning the map in open loop. The newer stuff does this automatically (updates the map) but your C950 won't. More work but you'll also have more knowledge about what your engine needs as you go through this.

  10. #20
    Registered Member Fladiver64's Avatar
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    Yes I have a wideband installed and it is a great tool, not sure if I would get things tuned very well without one. I kept my system in open loop mode when I started so that I could get the fuel maps close, then allowed close loop with a limit on how much it could adjust.

    I have been using a refurbished Panasonic toughbook for about 3 years now, and has proven to be quite reliable if not the most powerful. Has a serial port native so no adapter, a sunlight viewable screen, which is great in the car and decent battery life. They are available with win XP as well. http://toughruggedlaptops.com/refurb...d-laptops.html

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