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Thread: Sanity check, please...

  1. #21
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by Rich Z View Post
    I think perhaps I have just been looking at Power Enrichment as something different that is not correct. I've been looking it as being the programmable equivalent of the accelerator pump on a carburetor. Back in those days, the manual accelerator pump would give an extra squirt of fuel directly into the carburetor upon spirited gas pedal pressure. I presumed that this function must be incorporated somewhere into the PCM tuning software, and PE just sounded like the logical equivalent.

    Have I been barking up the wrong tree?

    I believe I had PE disabled when I was doing what I thought was calibrating the MAF. Of course, I just now stumbled on that B0120 setting that I somehow overlooked, so I'm not even sure WHAT I was really doing....
    Carburetor accelerator pump provided momentary extra shot of fuel to avoid transient lean when throttle butterfly was rapidly opened...

    PE is different than this as you can see by its enabler tables.

    Never disable PE during tuning, it provides enrichment when you're engine is at load... of course you mesh this together with B3647 as said above.

  2. #22
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by Rich Z View Post
    Somewhere along the line I must have done that because I do have a MAP that shows kPa columns from 15 to 285. When I look at the log file included in this thread, I have to make the map display all cells with at least one hit to see much above 100kPa. Apparently even rolling into those high revs still doesn't give a lot of sampling for each cell. But from what I can see, the highest value there is only 1.09. I was thinking that that isn't TOO bad, now is it?
    You mean the average BEN in the map was 1.09 in one of the high load VE cells, and the surrounding cells were closer to 1.00... that's not too bad...

    have a closer look at what surrounds the 1.09 cell and judge whether it is correct (remember, VE phyiscally does not have sudden jumps)...

    [ do the surrounding cells need to come up a little, or should the 1.09 cell be pushed down a little...? ]

  3. #23
    Lifetime Member Rich Z's Avatar
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    Quote Originally Posted by joecar View Post
    You have an interesting point about failing the MAF at 12000 Hz... it will fail immediately (DTC triggers, and now VE table is the sole source of cylinder airmass)... but it won't re-enable when the frequency falls below 12000 Hz... for the MAF to re-enable, the MAF DTC must be cleared by the PCM, this involves some amount of drive-cycle (it doesn't just clear instantly).
    Ah, so, that one statement makes using the MAF a completely moot point for me. I didn't realize that once it is failed, it STAYS failed. I had hoped it was more dynamic than that and I could possibly run MAF when possible, then VE only when needed. So scrap any more attempted calibration of the MAF. So now I have to look more closely at what Bret has suggested I do.

    Darn, just spent a lot of unnecessary time on playing with that MAF. I would be miles ahead if I just knew what questions I need to ask when they needed asking. But learned a couple of new things along the way, so I guess it wasn't a complete waste.

    BTW, B0120 was set to 7000 in my tune, so what exactly does that mean in this MAF/VE scheme of things? I'm presuming I just have to fail the MAF and be done with it and stick with the VE tables only.

    Oh yeah, got to look at PE a bit differently as well. So there really isn't an accelerator pump equivalent in the PCM programming? I was using it because my logs were showing a brief lean spike at gas pedal application so I was trying to get rid of that using the PE options. Ah well, back to the drawing board. Now to find the last tune I did working solely (I think) with the VE tables

    Thanks for your help.

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

  4. #24
    Lifetime Member Rich Z's Avatar
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    Quote Originally Posted by joecar View Post
    You mean the average BEN in the map was 1.09 in one of the high load VE cells, and the surrounding cells were closer to 1.00... that's not too bad...

    have a closer look at what surrounds the 1.09 cell and judge whether it is correct (remember, VE phyiscally does not have sudden jumps)...

    [ do the surrounding cells need to come up a little, or should the 1.09 cell be pushed down a little...? ]
    Moot point now. I had MAF enabled for that log, so that was wasted effort. When I get some logs looking at the VE table calibrations, I'll post them up for review. But maybe Bret can give me some pointers on his suggested method for fueling with SD first. Looks like more rain on the way, so I probably won't be taking the car out the next couple of days anyway. Even with my fumbling tuning efforts, the car is a handful at WOT, so I'm certainly not going to run it on wet roads.

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

  5. #25
    Joe (Moderator) joecar's Avatar
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    B0120 = Dynamic Air Threshold (in RPM)

    When MAF is active (and not failed):
    when RPM is below B0120: MAF is used for steady state conditions, VE is used for transient conditions;
    when RPM is above B0120: MAF is used exclusively.

  6. #26
    Lifetime Member Rich Z's Avatar
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    Quote Originally Posted by BLK02WS6 View Post
    -You are commanding way too rich too soon - using the commanded fuel vs RPM table (B3647) to command boost fueling is not the way to go - that will cause the car to be too rich when rolling into the throttle, and it will bog. May not see it going straight to the mat, but rolling in you will. The way I do it is to command naturally aspirated fueling in the 100 kpa column of B3647 - then, use the PE based on RPM table (B3618) to command boost fueling - do this by setting B3613 to around 110 kpa (may need to vary this a little to get the right transition). Make sense?
    OK, so I'm looking at my B3647 table. I'm not sure I know what you mean. What SHOULD I have that table set to? 1.00 in all cells? 0.99 or 1.01 in all cells? Is this table able to be calibrated using BEN map feedback? What relationship does this have to calibrating the VE table in that same kPa range? Aren't they both basically doing the same thing? Adjusting fuel based on air flow values dictated by that table? So you only adjust one and not the other? VE (B0101) is saying that there SHOULD be this much air volume (based on an efficiency quotient as a percentage of 100 percent) in each cylinder at a given rpm at a given vacuum level. B3647 is saying that it wants the AFR to be what is specified in each cell at a given rpm and a given vacuum level. When you collect feedback via data logging to see how far off you are from the results the wideband is reporting, which table needs to be adjusted?

    And I have to confess that I'm confused about your statement about commanding boost fueling in this table. I thought "boost" is defined as positive pressure (above ambient atmospheric pressure) and I thought that this would be ABOVE 100 kPa, which is the upper limit of that table.

    Sorry, but I'm obviously missing something basic here. Hell, here I was thinking I was actually getting a handle on this till late last night......

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

  7. #27
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    Quote Originally Posted by joecar View Post
    GM has produced many EFI vehicles without MAF's
    Only performance V8 vehicles that GM used Speed Density for was the 1990-95 LT5 ZR-1 Corvette. 1990-91 L98 350 and 1992-93 LT1 Corvette, 1991-92 TPI 305/350, 1993 LT1 Camaro/Firebird. All the turbo V6's TTA,GN, GNX were all MAF, as were all 1985-1989 TPI 305/350 Camaro/Firebird/Vette and 1994-2002 and 2010+ Camaro, and 1994-2013 Vettes all use MAF's. I'm not counting TBI which is indeed Speed Density, but not a performance system IMO. Why is GM holding fast with the MAF system? Here is a pic of the GEN 5 SBC MAF for the 5.3 L83 and 6.2 L86 MAF. They have eight (8) wires. peace Hog
    1997 rcsb stock L31 longblock, Marine Intake with 28# EV6 injectors, L35 2700 stall TC,Hooker LT's 2.007 60ft

  8. #28
    Lifetime Member Rich Z's Avatar
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    I'm sure there have been zillions of discussions about the pros and cons of MAF vs speed density tuning. I've been reading what I can, and each camp appears to be as firmly entrenched in their beliefs as the other.

    I guess what it all boils down to is if there is any difference in accuracy of the data the PCM needs to correctly determine how much fuel is needed for optimum combustion for each instantaneous NEED of the engine. Has anyone created a map to log MAF frequency data in a RPM x kPa matrix? I'd be curious to see if every cell has a completely unique value in it. If so, then they both may just be different ways of solving the same problem of how much air is available for combustion when the fuel injector needs to be fired. But then again, perhaps all of the tables are just too granular for any realistic analysis in that manner.

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

  9. #29
    Lifetime Member BLK02WS6's Avatar
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    Sorry, I've been tied up with a truck that is giving me a hard time. I'll try to go back through and clear up as much as I can tonight. I'll also make the changes that I'm talking about to your tune attached earlier - then you can do a compare and see the changes I made...

    And as far as why GM uses the MAF - I personally believe it is because they don't want to take the time to map out the VE table the way it would need to be in order to get the same driveability and throttle response. It is much easier to use a blend of MAF and VE like they do. I say use the MAF if you can, but there are many applications where you just can't or it doesn't make sense - and yours is one of them...
    GM EFI Tuner
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  10. #30
    Lifetime Member Rich Z's Avatar
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    Quote Originally Posted by BLK02WS6 View Post
    Sorry, I've been tied up with a truck that is giving me a hard time. I'll try to go back through and clear up as much as I can tonight. I'll also make the changes that I'm talking about to your tune attached earlier - then you can do a compare and see the changes I made...

    And as far as why GM uses the MAF - I personally believe it is because they don't want to take the time to map out the VE table the way it would need to be in order to get the same driveability and throttle response. It is much easier to use a blend of MAF and VE like they do. I say use the MAF if you can, but there are many applications where you just can't or it doesn't make sense - and yours is one of them...
    Thanks. I do appreciate your guidance with this. I had in mind trying to do something that apparently can't be done with my tune.

    CorvetteFlorida.com

    2002 Corvette Z06
    427 RHS block built by LME
    STS rear mounted twin turbos
    It nearly died on the operating table, but I'm bringing her back.

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