Holley Sniper Air Fuel Ratio Issues & Start Up Issues Symptoms & Fix 

I’m so glad I found this video. I installed a Sniper system on my 69 Camaro 396 and it ran like crap. After watching your video I did the same thing and installed the O2 sensor 10” from the header flange. I moved the sensor to 6” from where the header pipes come together and she started up and ran good. Thank you Thank you Thank you.

Appreciate the time you took to make a video to help others out!!

thanks for taking the time to help all of us out here having Holley Sniper problems.....great job 👌

I uninstalled my Holley Sniper eFI and Hyperspark system and went back to simple , trouble free carburetor. I fell for the hype!

I am putting a sniper on a 454 in a very well used dually. The SMOG exhaust parts had rotted away leavening many open holes in the exhaust. I plugged the exhaust leaks until I can put on headers, etc. The stock distributor was a computer controlled one, but the computer was removed when I bought the truck. I opted for the hyper spark too. Everything you mention is right on point! Exhaust leaks are detrimental to the sniper running correctly

I adjusted my iac valve worked great thank you. I was having trouble when stopping and going without stalling out

Thank-you for the video. Had a similar issue. Moved the O2 to the other bank. O2 started working perfectly. Went from 6 inch on the PS exhaust. To 12 inch on the DS. Idk, if it was a connection issue or flipping the wiring. But fixed now.

GREAT VIDEO SIR !!

Thanks for the video, solved my problem after months of the same issue 👍

Great information

Did the same thing, redid the exit pipe routing, put the 02 sencer 2 ft away, and forgotten the 6 to 8" instructions, 2 years earlier. It was belching, backfiring, ect... Put another bung for 02 sencer 8" away. Good. Lost 6 weeks over that.

Awesome mate cheers

Perfect. Thanks! Have the same problem with the afr reading 35.6 and couldn’t figure out how to reduce the over fueling. Engine runs great but rich. Positioned the o2 sensor 6” from header flange not collector.

Great video!!

I only say this to help. I spend 7 days a week making my living supporting Holley EFI, Snipers more than others. Misinformation is the biggest thorn in the side of the Sniper. You can't really put the sensor too far down the exhaust within reason. You could put the sensor 4 ft away from the collector and as long as you had no leaks and no reversion from the tip of the exhaust it would read exactly the same as 4ft closer. The oxygen sensor does what the name implies, it reads oxygen content of the exhaust. If the pipe was sealed there is no way the oxygen content of the exhaust could change from the collector to 4ft down the pipe. You either had an exhaust leak letting clean oxygen in or the sensor was too close to the end of the pipe. You need at least 18" of exhaust pipe after the sensor to prevent reversion of clean oxygen.

Have a sniper kit for my 350 sbc in my 82 C10. Had a hell of a time getting the AFR to quiet down. Messed with it for 2 days. Completely removed the sniper kit and reinstalled it. Turned out I had a tiny crack in the header. One of those simple stupid things. Got it fixed then the head gasket decides to take a vacation the next weekend lol. Pulled the engine out and just rebuilt the the old tired girl. About to put everything back together this month. Fingers crossed, I'm ready to have my old truck back.

My chevy big block truck runs great and the O2 sensor is in the stock location from chevy which is at least 12-14 inches from the manifold. And the injector harness issue is very common but easy to fix with a zip tie. Good luck

Thanks for the info! I’ll probably go back to spider injection, this plug and play is killing me. I have the atomic efi, and I have been digging for info since I installed it. No info for a work van, and the msd techs get snappier every time I try to explain to them. About 2 grand shot up a wild hogs ass!

Thanks

Bad Kitty is getting there!

Great video

Thank you for all the info I’m going to go through mine step by step and see if I can figure mine out . I have a feeling mine is the location of my O2 sensor. Or more less the angle of if because mine is mounted at the top of my exhaust and not on the side of the pipe at a 10 degree angle like they said in there instructions. I have a rock crawler and I’m mostly at 1200 to 1500 rpm idling through the wood and it will do fine but all of a sudden it will hit 22 to 35 on the air/fuel mixture and die . Then has to sit for awhile before cracking and most of the time I have to cycle switch before it will crank

I had EVERY one of these problems with my Holley Sniper Unit. I had to send it in for injector repair. They fixed it under warranty but I lost 8 weeks of my driving season. However, since then I have replaced the O2 sensor every year. Not very happy with this unit.

Im using a returnless system, even holley sells a returnless system kit BUT IM only at 55 psi BUT its running Okay BUT Im sure it would do a lot better at 60-60 (even 58 is okay) psi so thanks for the tip.

thanks... my O2 was on passenger side at 2 inches from flange.... driverside is at 5 inches..

I guess I got lucky. I put a sniper on a 5.3 LS in my old 84 blazer. Just a hunting, fishing, gravel road rider. Sometimes back and forth to work. 3 years now. Now problems. Mounted the fuel pump in the frame rail and it's a noisy bastard. But other than that no complaints.

went ahead and sub'd. you have a lot of good info in the video, but also a lot of info that's not 100% correct. 1. you should have 58-60psi fuel pressure. you don't have to have this.. realistically, anything between about 50-70 would run fine. the lower the fuel pressure, the more the injectors must compensate. and raising fuel pressure higher is how you deal with lack of injector size for a higher fuel/HP requirement. higher pressure = more fuel when injectors cycle. i do recommend a fuel gauge, however i don't recommend it on the sniper directly. i always suggest running an external reg with gauge on that. if you have a super sniper, put the pressure sensor on the sniper directly and datalog or use digital fuel pressure gauge. 2. the o2 placement isn't THAT critical. keep it towards the top of the pipe so moisture can't collect. your first location isn't what caused your lean condition at all. if i had to guess, it was a leak at that collector flange pulling in fresh air. tuners clip on their own dyno O2 sensor at the end of your tailpipe to pull a reading. my o2 sensor is waaaaaaay past that collector as I'm a single turbo 302 in my mustang. i have 2 collectors, crossover pipe, y to the up-pipe, turbo, then its about 20" from the downpipe flange.. runs just fine. further away it is, the safer it is from too much heat killing it, but the more delayed the reading is. the closer it is, the faster the reading, but less accurate if the pipes haven't merged well yet and the more heat it'll get to it. 3. the fact the 2 injectors up front weren't working makes me question if you had the quadrajet selected when you ran the wizard. injector connectors are a problem with the sniper. heat shrink and ziptie will correct the issue. you should have stopped trying to crank it when you saw 2 injectors not working unless you didn't know all 4 were supposed to work. 4. you don't have to wait until the fuel prime/prime shot to crank if you have your efi tuned for it. all depends how you have your cranking fuel and iac park set. 5. an intank pump is the way to go with EFI. but if you do run an external, make sure its even or below the tank. you just have to make sure fuel can be gravity fed to the pump. easy way to check, loosen the fitting at the pump inlet.. if the tank wants to drain, you're fine. - there was probably some other stuff in there i'd comment on but don't recall. i'll definetely keep watching your content though. videos like these is what helps everyone learn and betters this community.

Holley doesn’t have to do the injector connectors. Just open it up and zip tie or shrink tube them tight. I have minor issues with this thing, and can’t wait to get rid of it.

Great info and I appreciate your videos, I pretty much have gone through all the steps you have already described my engine does run good but it runs eye burning rich. That’s why I got rid of my Holley 650/and went with the MSD Atomic 2. I had my AFR setting at 13.5 based on the original factory settings. I moved it to 14.1 just to lean it out a bit am I going in the right direction, is there any harm in that? I have read that 14.7 is ideal AFR I don’t want to go to lean. I also have a situation after a warm start the engine knocks like crazy and refuses to start. I’m not sure if it’s a detonation or the fuel prime issue I backed off my fuel prime from 1.50 to 1.35. Do you have any comments on that?

My holley sniper efi nothing but headaches would recommend it

Thanks for the video. Any issues with starting after the car is warmed up?

All electric fuel pumps pull to some extent. When they call it a pusher that means they want it as close to the gas tank as possible and not in the engine bay. The electric fuel pump will work fine with your fuel sending unit as long as it's below the gas tank. Sounds like you were unable to get the fuel pump there because your gas tank is already really low under the car. I was success with the setup because my gas tank is behind my seat, 73 Dodge Power Wagon, which made getting the pump below the gas tank very easy. A little bit of pulling from the electric pump and after that it's a siphon effect doing the job.

I’m having issues with my afr and I’m assuming it’s because of the placement of my o2 sensor. I have a miss understanding of where it should be placed and I watched so many videos of where it should be. Right now I have it on the collector. But you’re saying it should be past the collector ?? So 10” away from the end of the headers ?

My car has the Holley super sniper and it cranks but won't start, checked all the usual stuff and can't find a the problem, could it be a bad O2 sensor?

I’m having so many issues with Holley I have no more hair hair to pull out. I’m at my wits end I don’t know what to do. I’m basically doing the same thing looking at every forum which isn’t the best thing but I’m desperate. Holly is very slow on the responding back to any questions.

Im having no start issues must be timing. Ive checked and re checked everything is corrrect. Tdc compression stroke 15degrees. Of timing pointing to number one cylinder distributor phasing matches 15 degrees. O clearance rockers timing chain dot to dot. Fuel pressure 59 60 lbs. direct ground direct switched power. Good body ground. I have a new sniper EFI cd box coil and distributor.. They won’t start it tries to. It’s not backfiring out. The carburetor is trying to, but not all cylinders are firing and I also noticed that only a couple cylinders on each side are warm three cylinders on the left side only two cylinders on the right side. This is a brand new 383.

All those videos, with efi ,nothing bur problems, does any of them work ?

blow true carburation way to go

what mufflers do you have on the car?

I installed a spider today, it’s not injecting any gas, my pump produces 43psi I’m installing a pump tomorrow with 94psi would that affect the spider carburator? Should I install a fuel pressure regulator?

My issues is is runni g to rich mine runs at 9.3 to 10.5 a/f i try going lower o. Pressure dont it dont likeme

At about the 11 minute mark into you video, I dont understand when you said the car ran like crap with the original holley sniper on it, you had the o2 sensor already fixed, then you put on the replacement holley sniper and it still ran like crap and you said that you noticed that only 2 barrels was receiving fuel from the new replacement. You then put your original sniper back on and it ran perfect. You are basically saying that you did nothing to the original sniper that was not running well, when you put it back on it ran perfect... What am I missing??? Did you send your original unit to holley to fix the fuel distribution problem??? Did the original sniper all of a sudden just start working when you reinstalled it??? I am very confused what you did to solve the fuel issue... Please can you explain better that part of your problem...

Thanks, but I'll stick to my 4150 Holley, It takes 1 hours to clean and tune not 4 weekends. no injector tickling noise no AIC whistling No 02 sensor or electronics to go bad without warning and did I mention my fuel pump only cost $40 dlls and 30 minutes to replace.

Too many issues with sniper. I'm thinking, class action lawsuit. That self learn feature is balloony. To think I spent an extra 2 grand and get nothing but headaches when I could have stuck with carb, had a good running vehicle, and be 2 grand ahead makes me doubt my own intelligence..

you must have a professional tune on ALL HOLLEY EFI SYSTEMS PERIOD, THERE IS NO SELF TUNNING ECU OR SELF LEARNING

Holley's quality control is garbage. The Sniper stuff, their Chinese intake manifolds etc. just not worth it.

most problems with aftermarket fuel systems are fuel, grounds, and charging.

I have done 6 Snipers Systems, 3 cars are mine and 3 cars for Family and friends……I will tell you this…..90% of all problems are self induced. These things are pretty much bullet proof. I have had to go fix a couple of friends who put them on and in typical Ignorant fashion they installed things incorrectly. I will have to say I have never had on produce anymore than 60 lbs of Fuel pressure……I would venture the guess your Furl pressure gauge isn’t accurate…….I am not a Summit Chinese brand fan so I have no experience with them. I always mount my O2 sensor at the 10” away from the end of the merge collector…..Always and I mount it strait up -10 degrees and alway passenger side. What cracks me up is the BS claims about Holleys Customer Service…….I have felt with these guys for 30 yrs on MANY different situations mainly opinions on what to use, What not to use an the occasional issue like a Distributor issue I had on a 572 Big Block Ford I put in a 66 Mustang Fastback tube chassis car……Distributor Gear was off by .025……I didn’t feel I should have to re-drill shaft and set gear……They took care of it and quickly. Great people to work with