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Thread: Sniper EFI - Truck is now running, first test drive, getting spark knock?

  1. #1

    Default Sniper EFI - Truck is now running, first test drive, getting spark knock?

    Hey guys! I finally got the Sniper EFI in my 1986 C10 up & running. Full build is here in case any of you would like to check it out: http://67-72chevytrucks.com/vboard/s...d.php?t=706825
    Anyway, I've installed a Sniper EFI kit on to this truck and at first start, it fired up and ran great, idled well, seemed to run good. I do have timing control enabled and I have followed the setup instructions for the MSD distributor in the manual to a T.

    My setup is:
    1996-2000 GM Performance 5.7L Vortec crate engine (all stock)
    Weiand Street Warrior Vortec carburetor conversion manifold
    Long tube headers with 3" dual exhaust with x-pipe
    MSD 85551 distributor with timing locked out (no vacuum advance) & adjustable rotor
    MSD 8.5 MM plug wires
    All spark plugs are brand new OEM
    Using the Holley timing control module
    My initial timing is 15° and total timing is 32°, verified on the balancer. My cruise timing was 36°, but I backed it down to 32° as well for now.
    The truck has a 700R4 transmission with stock converter, and stock other than a full TransGo shift kit. 3.73 gears. I have retained all lockup components on the transmission.
    Even though the engine is fairly new, I have installed a balancer cover with fixed timing marks to eliminate any chance of the balancer having slipped.

    The engine starts quickly, even when cold, and idles just fine. I can rev the engine in park and it revs up and comes right back down with no hesitations or stumbles. When I initially drove the truck, it felt fine, but I stayed below 1/4 throttle just to take things easy. My problem is coming when I try to get on the throttle, the engine starts to rattle like it has spark knock very badly. It will bog the engine down and limit power, and sometimes will engage into OD. I can prevent this my easing into the throttle very moderately, and it will get up to highway speeds without an issue. However, even at speed if I get into the throttle, it will rattle again. I did notice that when it does this, I can manually shift from OD to D, and the engine will instantly rev up and the knocking sound will be eliminated, and then I can get on the throttle heavily with no issues. However, if I let the engine settle back down and then try to get on the throttle from that point, the rattle returns. It does appear to be load related and I've had times in the short distance that I've been able to drive it that it seems like Overdrive engages too soon at times. Either way, I think something with my timing setup is off. Everything else as far as I can tell is reading okay, the ECU is seeing 175°F at warm up, so it's in Learn mode. AFR seems to be good for it having no run time on it, and all the other sensor readings seem normal. The only odd thing I can find was under the "Closed Loop/Learning" section, it was disabled. I enabled this, but that area is showing 0°F as a coolant temp and will not find a reading, even though the ECU itself does. One other thing, I've seem to notice that my cruise TPS reading is about 15%+, but when I "get on the throttle", 20-25% or more is about when the spark knock issue occurs.

    I'm not very familiar with the handheld yet (I WISH Holley had Sniper laptop EFI software available!!!), but I can try and get any readings or settings requested. Please help as I'd rather keep all 8 pistons on the inside!

  2. #2
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    Quote Originally Posted by Nick_R_23 View Post
    I do have timing control enabled and I have followed the setup instructions for the MSD distributor in the manual to a T.
    My initial timing is 15° and total timing is 32°, verified on the balancer. My cruise timing was 36°, but I backed it down to 32° as well for now.
    Did you actually check the ignition timing synchronization at higher RPM (Inductive Delay)?
    The Sniper EFI software is available (LINK), it's the CAN/USB Dongle that isn't yet.
    However, your engine Config File can still be transferred using the SD card.
    https://forums.holley.com/showthread...6350#post86350 (Sniper EFI Config File/SD Card Information)
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #3

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    Also, check rotor phasing. Maybe the spark is "arcing", I.E. firing the wrong plug or two at the same time.

  4. #4
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    Yes, I would also ensure the distributor's "rotor phasing" is correct:
    http://documents.msdperformance.com/8644_tb.pdf (MSD Rotor Phasing Document)
    MSD has a good video on why it's important:
    http://www.youtube.com/watch?v=aWMlNwGW0tM (MSD Tech - Rotor Phasing Video)

    For naturally aspirated engines, the rotor is usually phased halfway between minimum & maximum amount of timing advance used.
    For forced induction engines, the rotor is usually phased at maximum boost retard, because that's when cylinder pressure is the greatest.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  5. #5

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    Quote Originally Posted by Danny Cabral View Post
    Did you actually check the ignition timing synchronization at higher RPM (Inductive Delay)?
    The Sniper EFI software is available (LINK), it's the CAN/USB Dongle that isn't yet.
    However, your engine Config File can still be transferred using the SD card.
    https://forums.holley.com/showthread...6350#post86350 (Sniper EFI Config File/SD Card Information)
    Quote Originally Posted by Dr_Grip View Post
    Also, check rotor phasing. Maybe the spark is "arcing", I.E. firing the wrong plug or two at the same time.
    I checked the timing at about 2500 RPM when the handheld showed it was "all-in". And yes, rotor phasing was checked when I set the timing.

  6. #6

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    If you don't use the software to build a timing table, it will spark knock like crazy.The timing table that the base system builds when using the handheld will not work at all on a stock small block, and is really bad in a Vortec head application. Here's a link to my Sniper thread on the truck forum: http://67-72chevytrucks.com/vboard/s...ghlight=sniper. I've done a lot of work on my timing table. The truck runs really well. Jimmy

  7. #7
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    I agree with Gadget. Except for the Sniper EFI software, the Target Air/Fuel Ratio Tables & Base Timing Tables in the base calibrations (Terminator, HP & Dominator) are better than the typical centrifugal/vacuum advance curves. Using the Sniper EFI software (LINK), Target Air/Fuel Ratio Table (Fuel ICF) & Base Timing Table (Spark ICF), select "2D Table" Type (not "Simple"). The Target Air/Fuel Ratio Table & Base Timing Table can then be properly tuned for any engine.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  8. #8

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    Another thing to try is go back to the STOCK non-phaseable rotor. I've read reports of it working properly when people had issues with the adjustable rotor. Or just go Holley Dual Sync distributor and be done with it!

  9. #9

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    The spark knock on this truck is the timing table for the most part and the enrichment adjustments are compounding the problem. The stock cam Sniper program puts all the timing in by 1700 that you have listed, for the cruise number at all the MAP pressures except for full throttle. The Vortec head with the chamber design and the plug location can in no way deal with that much timing. Then the dual plane intake on the Vortec engine compounds the problem with the cylinders on the long runners not getting the same amount of fuel. This is an issue I have dealt with both carbed & EFI. In the area of 65 to 85 kPa in the timing map, from about 1600 to 2000 RPM, there's as much as 15° to much timing with the map generated by the handheld. The with the Blanking in the enrichment tables being 15 in most cases, there's not much extra fuel being added. Dropping these to 7 or so will improve it, but still have to get the timing under control. We did a lot of testing on my truck with the dual plane, knowing it was an issue when we started just to see what it would take to make it happy, and get it to run like it did with the carb and the electronic curve. I did get it running well, but there ware the same compromises with timing & jetting that the previous setup had. Then on went the Super Victor with the short heat isolated runners, and we were able to put more timing in the engine in a lot of places and can run 39° at cruise in settings between 45 & 70 MPH. We have also been able to pull some fuel out and clean up the idle & cruise areas. I had the advantage of a race engine builder that has done 100s of the Vortec head crate engines for circle track to work with on the tune, and with having run the engine on a carb & electronic curve for 20,000 miles a good understanding of what the engine would tolerate. My combo is the L31 crate engine mild cam, 700R4 & 3:73 gear, so very close to what you are running. Jimmy

  10. #10
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    Again, Gadget is right. It's why I keep writing post #7. And I'm glad he mentioned the "AE vs TPS RoC Blanking" value in Acceleration Enrichment/Fuel ICF. "15" is the outdated value and is too high. Try 7 or 8. Ensure there's no TPS/MAP RoC signal activity at idle, due to noise/kPa fluctuation.
    https://forums.holley.com/showthread...8640#post88640 (Target A/F Ratio Table & Base Timing Table)
    EDIT: A Sniper AE vs TPS RoC Blanking of "15" is appropriate for most applications.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

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