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Thread: Couple Idle and Starting Questions

  1. #1
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    Default Couple Idle and Starting Questions

    Getting my car going again. I currently have it on e85, and for some reason starting it when cold it will not start up the first attempt. let off then hit it again and it will fire up immediately. I'm trying to figure out why the first time with a cold engine it won't fire. Is it adding or subtracting fuel the second time for it to fire off? Is my airflow settings off? Once it is started I can shut it off and it will fire right back up, its only the first time after it has cooled down for several hours.

    Attached is a log (10-23-18newidle8.efi) showing the starting issue. You can see the first time I crank it hits a little bit but never enough to start. The second time fires right off. All I'm doing is letting off the key (not turning it completely off) then cranking again. I have attached my tune if anyone wants to see it.

    Secondly, working on dialing my idle and am very close. The only issue I see is when I rev the engine it hunts for idle. Looking at the logs, once the engine is rev'd for about 5 seconds after it holds the spark timing constant. Once the spark timing is able to start adjusting again the idle stabilizes. Why does it hold timing constant for that 5 seconds? Would {B4506} Spark Airflow Speed Control Delay be the culprit? Attached is screen shot. you can see every time I blip the throttle the spark timing does the same stall at 16 degrees (base spark setting) for 5 seconds.

    One last question. With the current Desired Airflow setting it is running slightly less spark then the Base Spark table. I imagine it is pulling timing to keep the rpm at desired speed. However, when I lower Desired Airflow it wants to stall. Should I leave it as is? Or remove some Desired Airflow while increasing Base Spark? Is 16 degrees at idle too low?
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  2. #2
    Joe (Moderator) joecar's Avatar
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    I'm looking at your files...

    I take it you're running a referenced FPR... did you measure rail pressure (with reference removed)...?

    How are you avoiding the 512 g/s airflow internal limit (are you scaling...?)...?

  3. #3
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    Quote Originally Posted by joecar View Post
    I'm looking at your files...

    I take it you're running a referenced FPR... did you measure rail pressure (with reference removed)...?

    How are you avoiding the 512 g/s airflow internal limit (are you scaling...?)...?
    Yes, this is a turbo car with referenced FPR, and i'm running a custom operating system in SD mode. I had rail pressure set before, but i haven't check it since i got the engine running. Reason being, the V2 doesn't seem to be reading the voltage input anymore. I had another thread about it. I get 2.5v to the V2, but it doesn't display anything. Not sure if in the 2 years the car sat that something went wrong with my v2 or what.

    Is there some place in the tune Im going beyond 512g/s?

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    A little update. Did some testing with the startup issue. I put table B4343 Startup Friction Airflow Correction back to stock. I had originally added a few grams of air flow to it like i did to the idle tables, but I think this was making it too lean when cranking. Then added 2 degrees of timing to B5909 Spark Timing when Cranking to help it light off faster. I'm running e85 and at higher altitude, so figured a little more timing couldn't hurt.

    Tested it out tonight and it fired up on the first crank. Wasn't super quick but a substantial improvement. I'm thinking I need more fuel when cranking a cold engine. What is the best way to do this? Modify commanded fuel when cranking table? Looking at this table I'm not sure if it is displayed in lambda or EQ ratio?

  5. #5
    Joe (Moderator) joecar's Avatar
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    Which table id are you looking at...?

  6. #6
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    Typically... if you have to try to start the car twice before it fires, you need more fuel or maybe a little less air.

    Also.. if you have fuel pressure regulator and it bleeds off fuel when car is off, i would suggest setting B3202 to 2s. After that ... just wait till pump primes and then start.
    "All that is needed for the triumph of evil is that good men do nothing..."

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    It feels like it needs more fuel, and in the past tuning E85 in the cold it always needs more fuel than gasoline to fire up quickly. so what is the best method to add fuel while cranking?

    The table I was thinking is commanded fuel while cranking B3604. I was going to decrease the values by 15%, as it is in lambda I believe. (thus need lower values to richen up).

    The fuel pressure does slowly bleed off pressure, I will try out B3202 at 2 seconds. I think I will also increase the initial fuel prime B3201 by 15% as well to get more fuel before I try starting it.

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    One more question unrelated question looking over my tune, at some point I put B3601 Ratio of Air to Fuel for Stoichiometry to 10 (this is the lowest limit even though e85 stoich is 9.7). I believe before I always had it set to 14.7, as the wide band was working on a gas scale anyway. Once I enable stft at idle, is this going to make it run extremely rich?

    Is AFR really used by the pcm? or does it base everything off lambda and eq ratio? If so why does it want to know AFR anyway?

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    make one change at a time and test...
    "All that is needed for the triumph of evil is that good men do nothing..."

  10. #10
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    AFR is a final multiplier... it needs to be correct or your fueling/airflow model will be off.
    "All that is needed for the triumph of evil is that good men do nothing..."

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