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Thread: Engine Shudder

  1. #1

    Default Engine Shudder

    Had an engine on the dyno the other day with a Sniper on it and the engine would shudder as soon as we applied throttle. The shudder was very, very serious. The dyno operator had to quickly pull back on the throttle and we could not give the engine any throttle or else it would start to shudder again. We have used this Sniper before and we had run the same program before so we didn't think it was a Sniper problem. We spent most of a day trying to figure out what the problem was and finally decided to switch back to a carb. The engine ran great with a carb, made 715 HP. Put the Sniper back on and had the shudder problem. I finally decided to build a new tune using the Wizard and that solved the issue. Engine hammered out 710 HP with the Sniper which isn't too bad. Duty cycle was around 98% at WOT so the Sniper was really at the limit.

    As I said earlier, this was a known good Sniper and a known good tune. Only change that I know of is that I upgraded my laptop to Build 4 PC software. I have no idea if that caused the problem but it is the only thing that I changed that I can think of. To cap things off, we later ran another engine with a different Sniper and it also had the shudder problem. Since I'd seen this movie before I built a new tune with the Wizard and the problem went away.

    I can't say I know what the issue is, but if you see a severe engine shudder problem try building a new tune with the Wizard. I have no idea what is going on during the shudder but it is something major. I have data logs from the shudder and they look normal to me. The engine appears to be happy on the data log but it won't run. Weird stuff.

  2. Default

    I observed some strange behavior with my tune after changing to v1.2 Build 4.
    Original tune in Sniper was created with V1.2 build 3 and was working as expected. PC upgraded to build 4 without changing my tune. Synced tune to the PC and observed Sniper no longer Learning, yet it was enabled and had met the Learn criteria. Thoroughly tried various things to resolve.
    The only thing that worked was running the Wizard (I had backups anyway).
    I synced the new Wizard file to the PC and used the comparison function to literally copy my previous Config File over the top of the new Wizard file.
    Returned the updated Wizard file and now it works and Learns as expected.
    At the moment I'm putting it down to changing build versions. Next time a firmware/build is released, I'll recheck to see if similar behavior is observed.
    1970 XW Fairmont (presented as a GT Falcon Replica), 351 Cleveland with Aussie 302 2V closed chamber heads. Edelbrock F351 2V dual plane intake manifold. Camtech CT21544 (234/238@050", 570/579lift, 2600-6200rpm quoted range, 110lobes) 1.73:1 roller rockers. AOD Transmission. Ford 9" 3.5 Diff ratio. Pacemaker #PH4050 2v Tri-Y extractors to 2.5" Hi Flow V-Tex merge pipe with dual 2.5" exhaust through Hooker Aero Chamber Mufflers. Holley Sniper EFI 4150 Super Sniper 650 with HyperSpark Ignition.

  3. #3


    I had a Sniper that wouldn't Learn also after I upgraded to Build 4. I didn't think about that until I read your post. Perhaps Build 4 has some bugs in it? Actually my Sniper would Learn, but then it'd forget what it had Learned. I could sit and watch the Learn Table populate while the engine was running, but when I'd shut down the engine the Learn Table would go back to zeros. So it was Learning, but the Learning wasn't being written to memory. I'd never seen that before and I don't understand how it was happening. I should of shot a video of it, since I'm sure people don't believe that it happened.

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