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Thread: Solving RF Interference Issues in Sniper EFI Installations

  1. #1
    Join Date
    Sep 2015
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    Palm Bay, FL
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    162

    Default Solving RF Interference Issues in Sniper EFI Installations

    Perhaps you have encountered problems in your Sniper EFI installation and had someone tell you that you have radio frequency (RF) interference issues. And possibly your thought was, "Thanks a lot, but what does that mean?" Because I have a few of our customers who have faced this challenge, I wrote an article on our EFI System Pro Hangout blog that goes over the symptoms of RF interference, common targets & sources, and then tips for solving it. I thought I'd mention it here in case someone else might find it useful: Solving RF Interference Issues in Sniper Installations

    As with much of what I write, I receive lots of insight & inspiration from this forum and the key contributors (I should at least mention Danny Cabral, S2H & REL3RD). I enjoy the fine-tuning of my understanding that is required to write a complete article. Further, I believe it's helpful for someone who is particularly beleaguered by a given subject to get the information in consolidated form. As always, if anyone sees anything that should be revised, or if you find value in the article, please post something in either location. :-)
    Chris Myer
    800-880-0960 x654
    chris@EFISystemPro.com

    Check our www.EFISystemPro.com website for live stock status on
    all Holley items, including the full line of Holley HyperSpark Distributors!

  2. #2

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    Well all RIGHTY then!! In addition, try to run signal wiring close to a ground plane, I.E. the firewall.
    In stubborn cases, maybe a plastic car, you can buy shield braid and run it around the signal wires. Ground this and ONE END ONLY.
    Don't disregard "wrenches in the works" like an alternator with a bad diode, which causes hash & spikes on the 12V bus.
    It's not just EFI. A guy on another board was suffering interference between an MSD and the voltage regulator. The MSD caused the regulation to go nuts.
    You mentioned rotor phasing. There has been cases where even factory distributors have phasing issues.
    "Back in the day" before Al invented the internet, this showed up as cap carbon tracking. Some of us did not know much about that, then.

  3. #3
    Join Date
    Sep 2015
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    Palm Bay, FL
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    162

    Default Tracking Down RFI/EMI Issues

    I recently collected some data from a customer's installation that graphically shows how dramatically EMI from the alternator can impact your EFI system. Most folks hardly give a passing thought to the alternator when trying to find EMI/RFI issues, but as you will see it can be pretty strong.

    In this first picture, you see a great example of EMI riding on the RPM signal from the coil. Seeing this, you might immediately assume that because of the proximity to the ignition system and the obvious strength of the interference that it was coming from the there. And while that is a good guess, in this case it turns out to be incorrect. The light-green trace shows the throttle being depressed, and the bright red trace is the RPM increasing then decreasing with huge spikes. At the same time you see how this is affecting the ECU. The brown trace shows the ECU providing extra fuel for these fake RPM increases.
    Click image for larger version. 

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    The customer didn't find anything suspicious in his ignition system, so he decided to do something that would quickly tell him the problem, he disconnected the alternator. As you see, that immediately eliminated all hint of EMI:
    Click image for larger version. 

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    If RFI/EMI problems have you frustrated, consider reading my longer post on: Solving RF Interference Issues in Sniper Installations over on our website.
    Chris Myer
    800-880-0960 x654
    chris@EFISystemPro.com

    Check our www.EFISystemPro.com website for live stock status on
    all Holley items, including the full line of Holley HyperSpark Distributors!

  4. #4

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    Thanks Chris. This makes me wonder if Holley did anything to shield the ECU?
    I have seen the Holley Sniper EFI assembly video (LINK), but can't see the ECU or cover.
    I'm curious if some shielding like copper foil many electronics use inside the cover would solve some issues?

    Click image for larger version. 

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  5. #5

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    Yes, Holley absolutely needs to do something about shielding the ECU. With the size of the throttle body being so small, there is no reason why they couldn't make the front ECU housing bigger to accommodate some shielding method. I just went through a week of hell chasing every known path on a RFI issue on a Small Block Ford. The only thing that seems to have resolved it, is wrapping the plug wires on the distributor with ugly heat shielding. Looks stupid, but seems to work. The only way the car would run is with all the timing settings exactly the same. Either 15°, 15°, 15° at idle, cruise & WOT. Or even 20°, 20°, 20°. Or 25°, 25°, 25°. As soon as I changed the cruise & WOT timing settings to around 32° or 34°, the Sniper picked up serious RFI noise just from the timing moving as little as 10°. It's crazy how sensitive this unit is on a Small Block Ford with the distributor right out front. I'm going to say that if you intend to convert a small block or big block Ford, just save yourself the headache and buy the Holley Terminator unit.

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
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    Default

    I realize this shouldn't be you responsibility, but I'm sure I could fabricate a nice looking
    shield that attaches to the ECU bolts with spacers. I'd first try the easier shielding tape.
    Personally, I think something else is wrong: https://forums.holley.com/showthread...5559#post95559 (His original Sniper EFI forum thread.)
    Just for reference: https://forums.holley.com/showthread...8868#post88868 (Sniper EFI Datalogger Interference/Noise Malfunction)
    Sometimes it's in the alternator: https://forums.holley.com/showthread...050#post106050 (Related Forum Thread)
    Sometimes it's in the distributor: https://forums.holley.com/showthread...9634#post89634 (Related Forum Thread)

    FYI: It's not safe to run an alternator with the wiring disconnected; remove the alternator belt (safe alternator test).
    http://www.pvv.org/~syljua/merc/TooSeptST07.pdf (Alternator AC Ripple Voltage Test)
    http://assets.fluke.com/appnotes/aut...e/beatbook.pdf (Fluke Multimeter Testing - Page 3 & 4)
    https://forums.holley.com/showthread...0251#post50251 (Related Forum Thread)
    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

  7. #7

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    I tried DEI gold shielding tape. It did nothing. I also fabricated a shield. It also did nothing. The only thing that worked was shielding on the plug wire ends on the distributor.

  8. #8
    Join Date
    Sep 2015
    Location
    Palm Bay, FL
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    Default

    Not to belabor this, but I received another customer's datalog today and it is another great example of interference. Here's what should grab your eye: Any time the throttle position is fixed, a change in RPM should roughly be mirrored by the manifold pressure. In the example below, you see that the throttle position is zero throughout. At the same time, the RPM is jumping around erratically between something around 1500 RPM & 600 RPM, yet the manifold pressure is generally following the top of the RPM trace (at or about 1500 RPM) and is ignoring the trips down to 600 RPM. This should tell you that, in reality, the engine is idling roughly along the top of the RPM trace and those bottoms are RFI/EMI ghosts.

    Click image for larger version. 

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    It would be a bit easier to determine this in person, because you would look at the trace and immediate recognize that the engine wasn't surging like the RPM trace implies. The spikes on the duty cycle, however, are not make-believe. The ECU sees the changes in RPM and is actually making these huge swings in fueling to try and keep pace with what it thinks the engine is doing. Next step: Find & fix that RFI problem!
    Chris Myer
    800-880-0960 x654
    chris@EFISystemPro.com

    Check our www.EFISystemPro.com website for live stock status on
    all Holley items, including the full line of Holley HyperSpark Distributors!

  9. #9
    Join Date
    Sep 2015
    Location
    Palm Bay, FL
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    Default

    OK, now I'm hoping someone might have some insights on one that has me stumped. You might have read post #3 and thought (as I did), okay, replace your alternator and you're all set. And the customer has. Three times. Twice with brand new 1-wire alternators and once with a Toyota alternator with external regulator. Each time, the same results: Noise on the RPM signal that is creating havoc. Each time, if you remove the alternator belt (or if you simply disconnect the alternator wire) the problem disappears. Reconnect, problem is back. So clearly it is related to the alternator.

    Here is what we've tried and confirmed:
    -Power/Ground for Sniper EFI System sourced directly at battery.
    -Ignition wired correctly. No MSD CDI box, Summit Ready-To-Run distributor, yellow wire to coil (-).
    -Standard 12 volt negative ground charging system. (Hey, the guys in Thailand so you check these things!)
    -Voltage Drop @1500 RPM under load checked between Alternator output and Battery + Post (.38 volts, within spec).
    -Voltage Drop @1500 RPM under load checked between Alternator ground and Battery − Post (.02 volts, within spec).
    -All external electric circuits not required to run engine disconnected, problem persists.

    I've called Holley Tech Support and Jason said he wasn't aware of anyone else with a problem like this. Any ideas?
    Chris Myer
    800-880-0960 x654
    chris@EFISystemPro.com

    Check our www.EFISystemPro.com website for live stock status on
    all Holley items, including the full line of Holley HyperSpark Distributors!

  10. #10

    Default

    I don't know too much, but...could it be that the distributor is putting out a bogus tach signal? Can he hook up an auxiliary tach (or already has one)? Might be his tach isn't playing nice with the alternator for some reason. If everything checks out and there's still noise on the power line, maybe try a +12V power filter on the feed to the Sniper EFI? The type you'd use on car audio equipment. I'd try to isolate wiring & components by possibly hooking up a second battery to run the Sniper EFI from, and jumping alternator power over to that, bypassing any of the existing wiring & grounding. Just ideas. Good luck.

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