Solving RF Interference Issues in Sniper EFI Installations

[thecowwatcher]

I could, but they're the same wires. This is all new. I just put on coil, box and distributor, removed the HEI distributor and install HyperSpark system and new wires with same MSD wires; only difference is the color.

So MSD Street Fire Spark Plug Wire Sets 5552 and what part number for the spark plugs? Is there a good ground from the engine to the frame?

[thecowwatcher]

Understanding RFI/EMI is key to troubleshooting it. Plenty of articles and videos out there explaining the basics.

I do want to point out one thing almost all of us have in common with these Sniper installs. Most of us are putting EFI on vehicles that were not originally equipped with it! So of course our chassis ground is just enough for the gauges and lights to work.

I can not stress enough how important grounding is. Just going from the battery to the frame is not enough. I have grounds from my frame to the core support, to the bed of my truck, to the cab, alternator, and one to the engine. EVERYTHING ties in to the frame and my EFI, HyperSpark and fuel pumps all ground directly to the battery. If a ground is present then remove it and clean it well, apply a corrosion inhibitor and make sure it's tight.

[tdford5]

I could, but they're the same wires. This is all new. I just put on coil, box and distributor, removed the HEI distributor and install HyperSpark system and new wires with same MSD wires; only difference is the color.

[gregs69rs]

Can you put the old wires back on to test?

[tdford5]

I replaced wires as I installed new I HyperSpark system (box, coil & distributor). I know it's not the fix, but just wanted to make sure what the issue was. So MSD Street Fire Spark Plug Wire Sets 5552 is what I put on. So now is it coming from the wires or distributor? I attached a couple photos. Please don't mind the mess I wanted to make sure everything was going to work before looming all the wires. I'll take any help on how to stop this and make it work. Thanks.

[cmyer]

Applying aluminum foil is not a fix or even a band-aid, though it can give some clues on the source of the problem. In your case, the problem is clearly coming from the area of the distributor. Have you replaced your spark plug wires with a wire with proven capability to prevent RFI (not just "claimed" to prevent RFI)? If you've done that, have you replaced your cap and rotor? And if you've done that, have you replaced your distributor? Is there is a coil under your that aluminum foil have you replaced it?

[tdford5]

Same issues here I tried this out of desperation and it worked removed aluminum foil and truck stop running. So now to block this and look nice, any ideas/pictures?

[Firebob]

Was there ever any resolve to the RFI talked about in this thread? I'm experiencing almost the exact same situation. I did even try running a separate battery for the power feed for the EFI. The only thing that has seemed to make a difference is dropping off the alternator belt, as Danny mentioned in post #6. Doing that has allowed the engine to start & run.

[cmyer]

Thanks for the great suggestions. In addition, Jason at Holley Tech Support suggest that he move his alternator hot wire from the battery, back to the starter positive just to put some distance between it and the Sniper EFI power (sort of like what Brian suggested.) He already has the alternator power wire shielded, but I suggested also shielding the yellow wire to the coil (-). Jason also mentioned (as did Brian) trying a filter, so I suggested putting a capacitor in parallel with the Sniper EFI power/ground. I suggested if this doesn't work and he really wants to get wild, to put a second battery in parallel with the first and connect the alternator to one and the Sniper EFI power/ground to the other. Kind of outside the box thinking, but we just need something to change the pattern so we can get a clue where we're looking.

As I mentioned, the car & customer are in Thailand, but fortunately the customer is an English speaker or else this would be impossible. Thanks again for the suggestions, I'll post what we find.

[BrianSanDiego]

Great idea bingo. It sure sounds like a ground loop issue.

[bingo2]

You might also try a dedicated ground for the alternator. Typically, as you know, the case is grounded through the block by the mounting hardware. However, if the block isn't grounded properly or the alternator mounting hardware doesn't provide a good ground path, there can be issues.

[BrianSanDiego]

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.

[cmyer]

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?

[cmyer]

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.

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!

[HOTRODHARLEY66]

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.