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Thread: Cold Start Tuning a 2006 with a 6.7 Swap

  1. #1
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    Cold Start Tuning a 2006 with a 6.7 Swap

    Hi Folks,

    I've been working away on my 6.7 swap into a 2006 Ram and could use some advise around cold starts. The truck is running a complete 2008 6.7, hold for the MAP sensor, off the original 2006 ECM. My tune is based largely off the 2007 6.7 parameters. I have it running pretty happily thanks largely to the great info and advise on this forum.

    The last area I'm chasing is cold start; the 'make a little change and test' method is tricky here since you only get one a day! I've been able to improve starts from above freezing from 'embarrassing smoky mess' to 'could be stock', but there's still room for improvement now that the temperatures are dipping down to -16C (around 3F for those south of the 49th). In the log attached you can see the roughness on initial startup; this is accompanied by some white smoke. It smooths out and cleans up as the ECT is getting close to 0C.

    2006 6.7 Swap v5.11.hpt
    2021-01-25 - 6.7 Swap v5.11 - Cold Start.hpl

    Suggestions?

    Thanks,
    Chris

  2. #2
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    I made some progress on this thanks to the lovely cold snap we've received. I took some inspiration from how the 2003 runs when it's cold and increased my pilot volumes and pilot advance at cold temps (dropping rail pressure to bring the duration in line). It's now quite happy (even at -25) after the first grid heater cycle ends; just need to sort out that high load period after it first fires.

    Chris

  3. #3
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    It looks like the 6.7s use alot more fpr duty cycle during cold startup than you are using in the tune posted. Its in the Fuel pressure section under Regulator DC/Current. Not sure if you had noticed this yet or not.

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    Yeah that's a timely comment; I was planning to experiment in that area next. It's currently cold enough here (yay?) that the truck doesn't fire immediately, so my cranking fuel pressure is climbing higher than I'd like it to be.

    What I'm not clear on is the relationship between Regulator DC & pressure. Looking at the Base DC table; higher MM3s (which typically come with higher pressure) have a higher duty cycle. This suggests that higher pressure requires more duty cycle. Yet with my current cold start duty cycle of 0% I have pressures climbing higher than I'd like. This is the opposite of what I would expect from above.

    Anyone have a good explanation for the Regulator DC to pressure relationship?

    Thanks,
    Chris

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    The MPROP duty cycle is related to current flow to the MPROP, the less the current the more flow of fuel into the CP3 is allowed, higher the fuel demand, the higher the flow into of fuel into the CP3 is needed. The pressure tables are based off rpm and total fuel quantity, so where desired rpm is set and the ECM?s calculated need of total fuel to maintain that rpm lands, is used to determine where in the rail pressure to pull desired rail pressure value. The base duty cycle table and PID controls are used to help meter the fuel inlet flow to maintain desired pressure targets. Manipulating the base duty cycle table or PID values can lead to out of control pressure regulation.

  6. #6
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    I don't see your duty cycle in the log that you posted. Do you have the right channel selected? I use Fuel Control Actuator DC Actual and it works the way you understand it. Higher % DC = Lower Fuel Control Actuator Current resulting in higher rail pressure like Jim described. That is why when you unplug the FPR rail pressure spikes.

    I am also curious why you changed base duty cycle table? Are you using 6.7 injectors in your setup?
    Last edited by squeaksleaks; 02-11-2021 at 08:07 PM.

  7. #7
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    Curious; I typically am logging the duty cycle, but it's not on that one. Must've been an older channel & layout file.

    Yes aside from a couple sensors I'm running a complete 6.7; injectors, pump, etc. so matching the base duty cycle to the hardware. This was also one of the tables changed in the '6.7 Injectors in a 5.9' spreadsheet Jim previously shared; those were the settings I'd started with initially.

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    That spreadsheet is roughly where I had left off from when I was messing around with 6.7 injectors in a 5.9 engine with 5.9 ECM. Not what I would use for a 6.7 engine with a 5.9 ECM.

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    It was still useful though; tells me that the duty cycle and PID settings aren't solely ties to the PCMs algorithms, so they'd likely need some fiddling to work with my hardware.

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    Update for those following along at home: Adding more pilot quantity and advance helped out quite a bit and let me dial back some of the main advance it needed when it was cold. I also lowered the rail pressure, particularly in the ECT override table and cranking table using the 2003 duration as a guideline. As the stock 6.7 runs multiple injection events; I imagine that would have a similar effect as lowering pressure to increase duration.

    The piece I'm currently chasing is fuel pressure. I switched the small pressure error PIDs and base DC back to the 2006 which keeps the actual pressure following the target more closely, particularly in stead state conditions, but the pressure still flares at startup and somewhat at the voltage & load change of the grid heater cycling. Anyone have tips where I should be looking? My current thinking is the Large Over Error PIDs, and I expect those will impact how large of an adjustment the PCM will make (aka. how quickly it will respond) for a large over pressure condition.

    2006 6.7 Swap v6.1.hpt
    2021-02-24 2006 6.7 Swap v6.1 - Cold Start.hpl

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    Cranking and crank exit fuel command tables and rail pressure tables is where you want to change things for cranking and crank exit. When I was messing around with 6.7 injectors in a 5.9 engine on a 5.9 ecm, I needed to lower that spike when the engine first catches as well and that?s where I fixed it, but I also adjusted some slew rates that HP Tuners doesn?t have mapped for bringing things down quicker as well. The spike during grid heater cycling is quite normal, that?s a huge load rapidly coming in and out every time it cycles, the lower the engine rpm the more pronounced it?s just going to be. You can?t change the load it throws on the engine, it?s either on or off. If the actual pressure spike is greatly larger than the desired, the PID control needs some finessing.

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    Thanks Jim. To be more clear; it's my actuals that are spiking at startup and (less so) when the grid heater is cycling.
    Pressure Flare.PNG

    For the grid heater I was planning to try the Regulator DC Battery Voltage compensation next as it seems like it's over compensating for the change in voltage.

    For the startup flare, I did try setting the Cold Start DC to a reasonable % for that RPM & MM3s. Perhaps it too high and skewing the desired DC up during the high RPM change rate of startup.

    What are the crank exit tables? I didn't see anything like that defined in HP Tuners.

  13. #13
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    HP Tuners doesn?t have everything defined. But it?s in there in the ECM.

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    Seems like the startup DC was a good hunch; I set everything above 0 RPM to 0% and pressure flare over desired on initial startup is nearly gone. That said; it is a bit warmer out (barely below freezing) so not entirely conclusive, but certainly promising!

    My experiment on the pressure deviation from desired at the start and end of the grid heater cycle was less successful. I reduced the Regulator DC Battery Voltage compensation a bit for low voltage; I'm not sure the behaviour is better, but it is different. Where I previously has an over pressure and then under pressure following the grid heater cycling on; now I only have an over pressure (and the opposite when the heater cycles off).

    2006 6.7 Swap v6.2.hpt
    2021-02-25 2006 6.7 Swap v6.2 - Cold Start.hpl

    I suspected that was going to be the answer regarding the crank exit tables. Any tips where to start to figure out other table definitions? eg. Is there Cummins technical documentation floating around the interwebs that roughly applies to the Dodge PCMs?

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    Working on tuning a 6.7L with BD 120hp injectors, BD 12mm stroker CP3 and BD Super B Special turbo, being ran off of a 2005 ECM.

    Here?s a link to how it cold starts on stock 2005 tuning.

    https://youtu.be/Jx30mROOAW4

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    Here?s a link to how it?s starting now on a semi-cold start, coolant temp was 45*F.

    https://youtu.be/5DIICpHTXIs

    Doesn?t stumble anymore but needs some work on timing and fueling, overfueling a fair bit at the cold temperatures currently. Runs smooth once warmed up.

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    Coolant temps at 40*F, near smoke free and smooth start up.

    https://youtu.be/IYbVTye8PmU

  18. #18
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    Looking good! Any new learnings to share? I have mine starting a running pretty well. Chasing some little bits on the luke warm restart (20-40 C coolant temps).

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    Finesse timing and rail pressure, I cut back duration in the area used during cranking as well but I also modified a bunch of stuff not shown in any of the tuning platforms, this truck also has 120hp injectors. It runs and pulls hard. Needs some transmission tuning though too.

  20. #20
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    What sort of unmapped parameters were you adjusting? (Always nice to know what I don't know!) Adjusting the rail pressure in cranking & cold start to bring the duration closer inline with the 5.9 injectors probably got me the biggest leap forward in cold start performance. Next up; set up temporary SOTF tuning so I can do some easier A-B testing to optimize fuel economy.