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Thread: Engine spasms when Manifold Pressure reaches atmospheric.

  1. #11

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    That Base Fuel Table looks very funky. A lean condition could cause a misfire under load. So could bad timing. Sounds like spark plugs and ignition components could be eliminated as variables. I'd save your current config and reset the Sniper with the Wizard and see if this changes anything. If it doesn't, I would then triple check the timing and systematically verify the functions are correct. Don't assume anything. Verify it.

  2. #12

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    I think it's also a bit of a reach to look at different operational theories between fuel delivery of a carb over throttle body injection. Carb won't work at zero manifold pressure without sustained velocity. This is why a carb can be too large. TBI isn't dependent on air velocity, it will squirt fuel and adjust flow based on demand. Larger plenum could cause fuel to fall out of suspension, but if velocity is high it wouldn't matter too much if it's heated or not.

    You would be seeing two distinct issues. If you were over carbed or too large a plenum, throttle response would be poor and hesitation would exist if the throttle was stabbed off idle. But you should be able to ease into the gas to keep velocity up and engine should respond. I'm not entirely buying the fuel emulsion theory.

  3. #13

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    Quote Originally Posted by Gen2Van View Post
    That Base Fuel Table looks very funky. A lean condition could cause a misfire under load. So could bad timing. Sounds like spark plugs and ignition components could be eliminated as variables. I'd save your current config and reset the Sniper with the Wizard and see if this changes anything. If it doesn't, I would then triple check the timing and systematically verify the functions are correct. Don't assume anything. Verify it.
    Yeah, funky is a good word for it. Would a lean misfire show as rich on the WBO2? Still, I don't think that's the case, since if I ease into the acceleration, and the MAP slowly climbs, I can watch the mixture enrich nicely. Then, around 90-ish on the MAP, it'll start jumping around between 11 and 12, and the engine will spasm. So the AFR seems on. If it leaned out and then went rich, that'd make sense.

    I usually save my current config every few days, so I have a good, long history of configs. I've also reset to base using the Wizard a few times now. Once when I was experimenting, and another when I got the replacement Sniper from Holley, and it relearns in the same fashion. I'm quite certain that if I did it again, I'd be looking at the save VE table again within a day or two of driving.

    I've mapped out the timing on the ignition before, using a vacuum pump for vacuum advance, then disconnecting it and raising the RPM and tracking the mechanical advance, but it's been a year or two. I could always do it again. Who knows if something has happened between now and then.

    Quote Originally Posted by Gen2Van View Post
    I think it is also a bit of a reach to look at different operational theories between fuel delivery of a carb over throttle body injection. Carb won't work at zero manifold pressure without sustained velocity. This is why a carb can be too large. TBI isn't dependent on air velocity, it will squirt fuel and adjust flow based on demand. Larger plenum could cause fuel to fall out of suspension, but if velocity is high it wouldn't matter too much if it's heated or not.

    You would be seeing two distinct issues. If you were over carbed or too large a plenum, throttle response would be poor and hesitation would exist if the throttle was stabbed off idle. But you should be able to ease into the gas to keep velocity up and engine should respond. I'm not entirely buying the fuel emulsion theory.
    That was my thinking as well. I was having a hard time buying it. From my reading, a TBI atomizes better than a carb, and emulsion is done in the emulsion tubes to help keep a proper AFR, not to better mix the fuel.

    And yeah, most, if not all, of the issues with heating the intake for a carburetor are for idle, low throttle, off the line response. I don't know why that would switch to high velocity with a TBI. I was certainly willing to entertain the idea, because I've been chasing this for months and am out of ideas, but it still didn't seem likely.

    I also remember the hesitation/lack of throttle response when I had a 600 cfm carb on this engine for a while. Easing into the throttle helped a lot. With this 2BBL Sniper setup on my engine, it's very responsive off idle, and pulls HARD all the way up to 5000 RPM, as long as I don't push the throttle too much to get full cylinder pressure.
    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.

  4. #14
    Join Date
    Dec 2009
    Location
    Connecticut
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    Quote Originally Posted by Gen2Van View Post
    I'm not entirely buying the fuel emulsion theory.
    Of course not. Every aftermarket intake manifold I've used didn't have an exhaust crossover passage, and the engine ran great. And I ran TBI for many years before converting to MPFI.
    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.

  5. #15

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    Quote Originally Posted by 85 Phoenix View Post
    Would a lean misfire show as rich on the WBO2? Still, I don't think that's the case, since if I ease into the acceleration, and the MAP slowly climbs, I can watch the mixture enrich nicely. Then, around 90-ish on the MAP, it'll start jumping around between 11 and 12, and the engine will spasm. So the AFR seems on. If it leaned out and then went rich, that'd make sense.
    A misfire will show lean as a result of unburnt O2. When the AFR reaches 11/12, it might need more timing at that MAP kPa. Overlay a datalog on top of the Config File and find the area where it starts to "spasm". Look at the timing in the respective cells on the timing map and add a degree or two and re-test.
    Last edited by travisch; 04-25-2019 at 11:09 AM.

  6. #16
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    Dec 2009
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    Connecticut
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    Originally Posted by Danny Cabral
    Quick Datalogger Information:
    Always provide data, not just symptoms. Is the AFR & ignition timing optimized? Overlay the datalog onto your Global File.
    Ensure the Target A/F Ratio table is properly programmed for your engine. Ensure the ECU is "Learning" (Learn Table LINK).
    Scroll through the datalog to the problem area. Then look exactly where this happens on the Base Fuel & Timing Tables. Scrutinize:
    RPM, MAP, MAT, TPS, CTS, IAC, Target AFR, AFR Left, CL Comp, Ignition Timing, Duty Cycle, Fuel Flow, Fuel Pressure & Battery.

    Using the Holley EFI software (LINK), look at where the live cursor moves to during this occurrence, and
    manually tune that area of the Base Fuel Table (enrich or lean) & Base Timing Table (optimize ignition timing).


    I find the most helpful datalog function, is overlaying the datalog on your Global File.
    I'm in the habit of using the datalog Overlay feature every time I review a datalog.
    Click on "Datalog" (on the top Toolbar), "Activate Overlay", then "Open Data Log".
    You can literally "playback" a recorded event, and watch it as it happened on any screen.
    Minimize (shrink) the datalog window, and move it to the bottom of any Global File screen.
    Then click & scroll anywhere on the datalog, and watch it playback on your Global File (EFI software).
    http://documents.holley.com/techlibr...9r10543rev.pdf (Holley EFI Datalogger Instructions)
    https://forums.holley.com/showthread...s-amp-Datalogs (Datalog & System Log Information - Read "NOTES")
    https://www.youtube.com/watch?v=iqHO...C6FEA0BB99AF17 (How To Record & Email A Datalog)
    https://www.youtube.com/watch?v=q7OZUXLRS1Q (How To Record A System Log & Diagnose A No-Start Condition)
    https://forums.holley.com/showthread...7531#post77531 (Closed Loop Datalog Tuning - Posts #2, #4 & #6)
    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.

  7. #17

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    Quote Originally Posted by travisch View Post
    A misfire will show lean as a result of unburnt O2. When the AFR reaches 11/12, it might need more timing at that MAP kPa. Overlay a datalog on top of the Config File and find the area where it starts to "spasm". Look at the timing in the respective cells on the timing map and add a degree or two and re-test.
    I figured a misfire would show as lean, so it's not that (it's always rich.) It's just different than "rich" bogs I've had with a carb, which just makes the engine feel soggy. This is a shudder/spasm that can be felt in the vehicle. As for the timing, my distributor was custom tuned by DUI with specs from my engine. Changing the timing on it is not an easy task, since it isn't controlled by the Sniper. I'd like it if it was, but that'd require yet another ignition. Unless, someone knows how to control the timing of an HEI distributor with the Sniper.

    Quote Originally Posted by Danny Cabral View Post
    Originally Posted by Danny Cabral
    Quick Datalogger Information:
    Always provide data, not just symptoms. Is the AFR & ignition timing optimized? Overlay the datalog onto your Global File.
    Ensure the Target A/F Ratio table is properly programmed for your engine. Ensure the ECU is "Learning" (Learn Table LINK).
    Scroll through the datalog to the problem area. Then look exactly where this happens on the Base Fuel & Timing Tables. Scrutinize:
    RPM, MAP, MAT, TPS, CTS, IAC, Target AFR, AFR Left, CL Comp, Ignition Timing, Duty Cycle, Fuel Flow, Fuel Pressure & Battery.
    Thanks, I've made many, many datalogs. I'll be sure to grab a few I can find that illustrate this and post them up.
    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.

  8. #18

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    I had a SBC engine that had a low performance cam and poor flowing heads. It hit a brick wall at 4500 rpm. It just didn't want to spool up any higher. I then got into superchargers and used that engine to learn on. The supercharger made it worse after 4500 RPM. Needless to say a higher performance cam and better heads with heavier valve springs solved the RPM limitation. I also had a few straight 6s, the Ford 4.9L and Jeep 4.0L, they were all turds after 5000 RPM. Typically they likes to stay below 4500. Especially the Ford 4.9L.

    If it's running great up to a specific RPM, and especially if manifold pressure equals zero at that RPM, you may simply be at the capacity for that engine to pump air.
    Another thought. Do you have a rev limiter? If so, bypass it and see what that does. Some HEI modules have built in rev limiter.
    Also being HEI, it's easy to adjust the timing curve. Make sure you use manifold vacuum for vacuum advance. Verify your mechanical advance is all in by 3000 RPM. You can also limit the advance for mechanical and vacuum to allow more initial timing.
    Last edited by Gen2Van; 04-26-2019 at 12:03 AM.

  9. #19
    Join Date
    Nov 2014
    Location
    Ont. Canada
    Posts
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    To add to Gen2Van's comments, I had a ZZ3 crate engine that would not rev above 5200 in first gear. It ended up being valve float. Who would have thought, on a new engine.

  10. #20

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    Ah, didn't realize that you were NOT using the Sniper to control timing. I'd just advance the distributor a couple degrees then and go test to see if it eliminated the problem.

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