Sniper on battery...joy. Sniper on alternator...sadness!

[EK1965]

Hi all, I seem to have an RFI, ground or voltage related issue. I have a BP347 with sniper. Runs great from the battery but when alternator is hooked up it stalls immediately. Have tried everything that I can think of including 4 different alternators, shielding the alternator from the sniper, checking grounds, adding grounds, splitting the looms and isolating wires, basically using the car as an engine stand and eliminating all non engine functions from the loop, hooking it up cold, hot and during a run cycle. I can get the engine to run with the alternator connected but only if I jump on it from start, it runs albeit badly above 2,500 rpm with the odd backfire but as I approach 2,100 rpm the afr goes up, iac opens and it shuts down. The car is in body now so can't try anything new but if there is any hope for a solution ill try when it returns, otherwise will replace with a carb. Any insight appreciated, Earl

[Norm B]

Where is your alternator mounted? Is it high or low? Where does the wiring harness from the alternator run? What air cleaner do you have?
I know, lots of questions.��
My alternator is mounted low on the passenger side and don’t have any issues with interference from it. I had to shield the distributor to cure the same symptoms you’re having. My COBRA oval air cleaner channeled RF directly from the distributor to the ECM on the Sniper
According to the Holley Tech Support guy I talked to, our fibreglass hoods don’t help.

Norm

[sread]

Can you give a detailed description of how you have the sniper wired? Are the main power leads connected directly to the battery? (they should be) How is the alternator wired? Can you make a datalog of what is happening when the problem occurs?

[EK1965]

The alternator is high passenger side, cobra oval air cleaner and BP now puts an aluminum shield on the front of the carb. I tried making an aluminum foil dam around the entire carb in an attempt to shield from RF and removed the air cleaner. I wonder if the alternator throws a field if it is spinning but not wired and charging. I have tried almost every permutation of wiring direct to battery in an attempt to isolate any wire based RF issues. Tried wiring the alternator direct to battery in hopes that the only difference between a battery only run and a battery plus alternator run is higher voltage in the system and RF interference from the active alternator. My assumption was that the battery should act as a buffer and any wire based interference should be the same on battery or alternator. Unfortunately the cable did not arrive before I sent the car to California so will need to wait until July to download and revisit.
wiring is the same as papa posted may 3,2021, with the pos and neg direct to battery.
https://thefactoryfiveforum.com/showthread.php?39567-Holley-Sniper-EFI-Wiring-Spot-Check
Everything I heard and read suggested that voltage up to 16v should not affect the sniper but keep coming back to high voltage being the issue.

In order to test if its RF from the alternator without voltage gain in the system can I hook up a second battery positive from the alternator and negative to the frame
Thanks

[Rsnake]

I am going to jump in here on this sniper issue. My son installed one on his 65 mustang with a 347 and couldn't get it to run worth a crap.
We tried everything including sending it back to Holley and they said it was fine. He was just about to throw it in the trash and after reading about the RFI interference I set a piece of aluminum between the distributor and the sniper. All problems solved!! It should not be like this and Holley should fix this issue. Enough of my rant.

[RBachman]

Make sure you have direct connection to the battery and route wires away from the alternator.

[first time builder]

I installed Sniper on a 69 Camaro with steel hood 14" air cleaner 427 BB . No shielding at all and have no problems.

[Papa]

Did you de-pin and terminate any unused connections in the Sniper harness? Ensure your coil wires are not near the rest of the wiring. Double check your alternator wiring and ground connection. Is the engine properly grounded to the chassis?

[Alan_C]

Is the Sniper harness shielded with metallic braid? If not, you can put a metallic braid around the cable with a wire to ground at one end and one end only. This is the type of shielding we did on spacecraft cables when at Boeing. This may not be easy to do, but the reduction in RF noise induced on the cable conductors would be considerable. Maybe a last resort, but also a possible remedy.

[seagull81]

I used one of these 1993-1995 Ford Mustang Cobra 5.0 Rubber Engine Distributor Cover Boot Cobra Logo fro Ebay and it seems to have help my Sniper.
https://www.ebay.com/itm/183889418303?hash=item2ad0a9d83f:g:MzsAAOSwQExj2pB J&amdata=enc%3AAQAHAAAA8CGcYrzTD4PuZpLjNa3VLwJO9byeg lKXLliLYGnRlA%2FSUuWOb0IFjClP7Mbqa9VYLZtEACGYYg443 wM3DzWptZhg6yI63MRv%2Bq%2BJbI6EjHWhMaZtvPtTd2Rt6F8 COkZuNCibegpdhVJTB4aumGqT3c4xNj1SqyjYHZbybe4gzzblH vwzM9Rf%2F0sr9ATDsBAKx3yBeEyPVCuXLVlkMEzkGfj1REq%2 Fh0F9A1ZX4t6h8696h675s%2FX6X0g0LicZ2c8r3eQJ2TIvE7V QrWp%2B%2FQJOLeqg7mpNvW5k1%2B%2F1fjj%2ByRHUaPGaAPy VSgZ3m%2BOfZor7eA%3D%3D%7Ctkp%3ABFBMruTz9ehh

[EK1965]

Thanks for the thoughts, the strange thing is that it works perfectly with the alternator wire removed, so battery only. That should indicated that its not distributor, coil or plug wires.
The new BP 347 includes an aluminum shield that extends from the front of the carb and goes up to shield the ecu from the distributor. I also made tin foil dams around the coil & distributor, the entire sniper and between the alternator and sniper. Will try braided shielding on a few wires.
I ran the car with 12v+ and ground direct to battery for the sniper, alternator direct to battery, added ground from heads, checked all frame grounds by continuity but not voltage. Its hard to check when the engine won't hold idle with the alternator attached. I also ran the engine as a closed system, separate from the fuse panel to remove any non engine ground related issues.
Yes, removed the unused pins from he harness that is not fixed to the sniper, the coil wires do run next to some other wires so will check that when I get the car back from da bat. again I wonder why its not an issue when its just battery.
I am convinced that is is a sniper hardware issue but is also seems that this type of issue is relatively common with the base sniper. So I am considering either going upstream with efi or old school where I know any rfi will be a non issue. Ill try better isolating wires one more time than move on. Again, thanks for the ideas

[RBachman]

You may be right, but they're probably going to ask if you ran the Sniper negative direct to the battery as well. This will help eliminate anything between the battery and your Sniper. My general wait time with Holley was always around 15-25 minuets. The wait was worth it as I've always received great assistance.

[EK1965]

I have had a good experience with the help line as well. I ran out of time to press harder for them to test/repair so if I change then will send in for them to assess.

[FF33rod]

You may be right, but they're probably going to ask if you ran the Sniper negative direct to the battery as well. This will help eliminate anything between the battery and your Sniper. My general wait time with Holley was always around 15-25 minuets. The wait was worth it as I've always received great assistance.

Just doubling down on checking the main power to the Sniper. It needs to be a separate wire that goes directly to the battery. Right now it sounds like it's likely connected to a distribution point for +12 like the starter.

Steve

[EK1965]

Just doubling down on checking the main power to the Sniper. It needs to be a separate wire that goes directly to the battery. Right now it sounds like it's likely connected to a distribution point for +12 like the starter.

Steve
12v direct to battery, also tested with 12V + and negative direct to the battery with wires run outside the car to avoid any unintended rf interference.

[JJK]

This may help

https://www.efisystempro.com/efi-pro-hangout/holley-sniper-efi-instruction/solving-sniper-rfi-problems

[EK1965]

This may help

https://www.efisystempro.com/efi-pro-hangout/holley-sniper-efi-instruction/solving-sniper-rfi-problems

That's awesome, thank you!

[EK1965]

Hi JJK, reached out to the author and he suggested "it sounds like your pink key on 12v wire is in some way connected to a circuit that the alternator is feeding"...will give that a try when I get my hands on the car. Thanks again for the post! Earl

[Alan_C]

Do you or can you get access to an oscilloscope. It would be very interesting to look at your positive 12V lead when in both configurations. It would seem that the alternator is generating noise on the 12V power feed. If you find the alternator to be the source of the noise, then either you suppress it via shielding and filtering or replace the alternator.
Have you discussed your issue with a tech at Holley? They may have ideas and suggestions.

[JJK]

once you get the car back and the RFI sorted out, post your solution. I am curious as to where the problem is.

[RBachman]

once you get the car back and the RFI sorted out, post your solution. I am curious as to where the problem is.

Same here.

[EK1965]

Will do.