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Thread: Engine spasms when Manifold Pressure reaches atmospheric.

  1. #31
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    Quote Originally Posted by 85 Phoenix View Post
    Still, that might explain some of the abnormalities, but it wouldn't explain the ultra rich condition that causes the engine to buck and spasm under full acceleration. Even though the AFR table is set to 12.5, it can dip down as low as 9:1 - 10:1.
    I may have missed it, but I didn't see a WOT pull in your datalog. I did see it going lean on a moderate load.

  2. #32

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    Here's a good datalog of it. This is on the interstate headed home yesterday. About 70 MPH. You can see where the Target AFR dips to around 12.5:1 to accommodate for acceleration, but the actual AFR just keeps dropping beyond that. It goes down to around 10:1-11:1 and becomes erratic. Sniper.zip
    1985 Ford Bronco. 300 (305) ci inline 6. 9.1:1 compression, P&P head with enlarged valves, high flow exhaust. 32" BFG A/T tires. 5 speed ZF5 manual transmission with 3.55 rear end. Holley 550-850 2300 Sniper EFI.

  3. #33
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    In your Target A/F Ratio table, you're at 14.5 AFR at 71 kPa, then at 76 kPa your Target AFR is 12.5. That's a big jump in Target A/F Ratio in a small kPa range. So as the Target AFR drops quickly and the actual does not respond this quickly the CL starts to add fuel. Then the actual AFR drops because the Closed Loop has overshot itself and the actual AFR drops below your Target AFR. Then the Closed Loop starts to pull fuel back out, and it gets to your Target AFR. I'd try smoothing the Target A/F Ratio table as it transitions from your cruise AFR to your heavy load AFR. And always save a Config File at the end of a run so we can see what the Learn Table is doing.
    Last edited by 81 TransAm; 05-02-2019 at 12:17 PM.

  4. #34

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    That's good information, and hopefully that's all it is! As said, I've been fighting this issue for 8 months, and the Holley techs even sent the issue over to the engineering department, with no answers. "Overshooting" seems to almost always be the case.

    I'm not sure if you saw my previous AFR table, but this one was smoothed out considerably from that one. But yeah, right where that trouble issue is, is still another big jump, from 14.5 to 12.5. I haven't seen any good examples of AFR tables. The only one I've seen is the default one that Holley provides, which is pretty harshly stepped. Do you, or anyone else, have some examples of good AFR tables?
    1985 Ford Bronco. 300 (305) ci inline 6. 9.1:1 compression, P&P head with enlarged valves, high flow exhaust. 32" BFG A/T tires. 5 speed ZF5 manual transmission with 3.55 rear end. Holley 550-850 2300 Sniper EFI.

  5. #35
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    https://forums.holley.com/showthread...8640#post88640 (Target A/F Ratio Table & Base Timing Table Reference)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  6. #36

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    Thanks for the link. I'm reading it over. Good info! I have a question about your Target A/F Ratio table image. I notice that in that image, the MAP kPa values along the Y axis are different than mine, and seems to allow for some finer tuning at the higher MAP readings. Mine just jumps from 80 to 100. Is this a setting? Or something that was changed in newer versions of the EFI software? I'd definitely like to have have more 'steps' for fine tuning, if possible.
    1985 Ford Bronco. 300 (305) ci inline 6. 9.1:1 compression, P&P head with enlarged valves, high flow exhaust. 32" BFG A/T tires. 5 speed ZF5 manual transmission with 3.55 rear end. Holley 550-850 2300 Sniper EFI.

  7. #37
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    Quote Originally Posted by 85 Phoenix View Post
    Is this a setting?
    http://forums.holley.com/showthread....4365#post44365 (MAP kPa & RPM Axis Configuration/Tuning Information)

    Or something that was changed in newer versions of the EFI software?
    No, the Base Fuel & Timing Table axes (RPM & MAP kPa scales) have always been editable.
    See "X & Y Axis Resolution", page 7 & 8: http://documents.holley.com/techlibrary_199r11259.pdf (Holley Sniper EFI Help Manual - EFI Software, Tuning & Datalogging)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  8. #38

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    Very cool. I didn't know you could do that until now. I must've missed it when reading over the PDF initially. Since that upper MAP area has usually been my problem area, it's been frustrating not being able to get a larger spread of variables I can edit. This well help a bit. Thanks! I spent some time greatly smoothing out the AFR table, so I'll give it a few drives and see how it does. Hopefully this can put the issue to rest.
    1985 Ford Bronco. 300 (305) ci inline 6. 9.1:1 compression, P&P head with enlarged valves, high flow exhaust. 32" BFG A/T tires. 5 speed ZF5 manual transmission with 3.55 rear end. Holley 550-850 2300 Sniper EFI.

  9. #39

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    Okay, so following up on this. Smoothing the fuel table made a nicely noticeable difference in overall driveability. However, it didn't address the issue at hand at all. The engine still spasms when I get on it all the way. This was horrendously noticeable when I was driving to Moab & back, as I was going over a 7500 foot elevation pass (where atmospheric was only around 80 MAP). The AFR just went crazy when I was putting the pedal to the floor to get climbing/passing power. This one is a little more difficult to truly look at, since I'm pretty sure that whatever Learn values the ECU acquired for the higher elevation were unlearned when I dropped back down. Still, the datalog is worth looking at. Around town here (2500 feet), it's not nearly as drastic, but it's still taking place. The datalog I included (local) is at 75 MPH or so (which is why the RPM don't quickly climb), and just pushing the gas pedal to the floor. Spasm.zip
    1985 Ford Bronco. 300 (305) ci inline 6. 9.1:1 compression, P&P head with enlarged valves, high flow exhaust. 32" BFG A/T tires. 5 speed ZF5 manual transmission with 3.55 rear end. Holley 550-850 2300 Sniper EFI.

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