Page 4 of 4 FirstFirst ... 234
Results 31 to 40 of 40

Thread: Pop back though intake problem!

  1. #31
    Join Date
    May 2014
    Location
    Bostwick, GA
    Posts
    364

    Default

    If it's a mechanical issue please someone explain to me how the vacuum is a solid 14 inHg. All I can find on the internet and forums address backfiring out the tailpipes not so much info on carb backfires.
    It's going dead lean. And could well be as a result of the Fuel Pressure dropping. Lean backfire is usually through the intake, and a exhaust is usually due to being fat.

  2. #32

    Default

    The regulator may have been damaged when you had it plumbed backwards. The Sniper does not know how much pressure is present, it depends on you to tell it what the pressure is and also that you know that it's supplied with constant pressure. When pressure drops the Sniper will attempt to compensate (when it is in Closed Loop) by adding more fuel. If you floor it while driving there is a period when it will kick out of Closed Loop and you will indeed, as mentioned just above, go dead lean. No tuning will correct this.

    You have two options. One is to get a replacement regulator for the Sniper. This may take care of it. The other is to eliminate the internal regulator by either taking its guts out and putting an external regulator on the outlet side, or installing an external regulator at the inlet side. High pressure fuel in, regulated pressure to the Sniper, and a return from the regulator.

    If, however, your pump is bad, the regulator won't fix it. I'd start with the regulator and watch the pressure carefully. If it drops like it currently does when you just blip the throttle then there's some problem with your pump. I just swapped to a Terminator with the Stealth throttle body and external regulator. I set the pressure and and it never wavers. Given your unit's history, I'd lean towards an external regulator.

  3. #33

    Default

    OK, due to many people suggesting the valvetrain is the problem, I took the intake off again and put an indicator on each cam lobe and checked the total lift of the cam lobe, all were within .005" of each other and within the Crane Cam spec. I then checked the pushrods for straight, all good. I pulled the lifters out one at a time and checked them for collapsed by putting in a vice and squeezing them slightly (between pieces of wood). I then checked the lifters for flat using highspot paint and precision parallel. All lifters checked good. I inspected each rocker arm for damage or bent, all checked good. I then called a good friend which has 30+ years as a mechanic and he inspected the cam and confirmed it was good. The compression is good and even between cylinder and I have good smooth vacuum on the gauge. So I can say without a doubt the valvetrain is good.
    I also replaced the fuel pressure regulator as suggested above, and it made no difference in the fluctuation in the pressure from 60 psi → 40 psi momentary during WOT throttle snap. It does immediately recover to 60 psi after throttle snap.

  4. #34

    Default

    I recently moved my Sniper to my Mustang and installed a Terminator X on the Truck. I took a long datalog yesterday, and I'm able to datalog fuel pressure. It never deviated from 59 psi for the whole datalog. The Sniper (and the Terminator X) does not monitor fuel pressure and compensate for changes. It relies on a steady fuel pressure for calculations of fuel delivery based on conditions of RPM, MAP, etc. A momentary drop in fuel pressure will immediately cause a lean condition and likely a pop back through the intake. I don't know why you see a pressure drop, but you can't tune around it and if it happens when you crack the throttle on the driveway, imagine what's happening under load. I suspect a supply issue rather than the regulator, but all I can suggest is that until you sort out your pressure and keep it rock solid you'll have running problems. What you think it "can't be" may be what the problem is. If it can't be the pump, it may be the pump. Same goes for filters, fuel lines, return lines, pump pickup, etc. It's easy to blame the Sniper since that's where it's popping through, but it was never designed for variable pressure.

  5. #35
    Join Date
    May 2014
    Location
    Bostwick, GA
    Posts
    364

    Default

    ^^^^ This.
    Injector Inspector
    USAF 1960-1964
    Drag racing since 1955

  6. #36

    Default

    I disagree that the Sniper can't function at 40 psi. I'd have to see some documentation from Holley engineering to support that statement. I've had cars that ran fine on 38 psi. If the Sniper does need 60 psi at all times, then Holley should supply the necessary fuel pump with every kit not just the Master Kit.
    As for the pop back, I eliminated it by simply increasing the timing to be all in (34°) by 2200 RPM give or take, and the pop backs have disappeared.

  7. #37
    Join Date
    Feb 2020
    Location
    Wheeling, WV
    Posts
    1,210

    Default

    @mnorrod, if the question is whether or not it will function at 40 psi or even a momentary 40 psi, then the answer is, yes, it will function. Now, do you want it to function correctly? If you do, find a way to keep the fuel psi where it should be for the application. A N/A engine with a Sniper on it without power adders, functions the best at a constant fuel psi and for the most part, you can just about pick the fuel psi you want. The EFI software has a variable for it. In general, the fuel psi. recommended is more dictated by the style of injector than most other variables.

    You very well may have found your problem or maybe even put a Band-Aid on it, that doesn't mean your momentary fuel psi drop is an accepted practice for a Sniper ECU.

    It's not good practice to compare a entry level, stand-alone system to any OEM equipped EFI engine. If you do, you'll be chasing your tail as far as the diagnostics go.

  8. #38

    Default

    @a b c: The question was never about the fuel pressure, it was about backfire at low RPM. That's what someone else was trying to say was the solution to my problem. I was saying that it was the tune, but no one would give specific directions, just "you need to eliminate all issues first." So I kept reading different forums on this problem and came to the conclusion to increase timing to "Try" and get rid of the backfire that way. I had no idea if it'd work, but nothing else suggested here did. So my suggestion to anyone reading this trying to figure out a backfire under similar condition, try increasing the speed at which your timing comes in, and maybe this will work for you. I'm going to say this topic is finished.

  9. #39
    Join Date
    Apr 2021
    Location
    phoenix, AZ
    Posts
    9

    Default

    I had a hard time with backfiring out Sniper and exhaust. Spent about two months tryning to figure it out. Finally got it running and put a few miles on it. Datalog and Config File everything looked fine. Then it sat overnight and wouldn't start again. After much back & forth about grounds, EMI/RFI, and exchanging of Sniper unit and HyperSpark distributor, I removed the Sniper/HyperSpark to go back to my carburetor and HEI setup. Car started right up, idled, and runs like a champ again. Thought the Sniper would've been an improvement, but it wasn't for me and my ride. Just my two pennies.

  10. #40

    Default

    I've heard of people having issues with Hyperspark distributors, but I've never seen a problem with them. I recommend a Hyperspark for everyone. It would be nice to know what was wrong with yours.

Page 4 of 4 FirstFirst ... 234

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
About us
Holley has been the undisputed leader in fuel systems for over 100 years. Holley carburetors have powered every NASCAR® Sprint® Cup team and nearly every NHRA® Pro–Stock champion for four decades. Now, Holley EFI is dominating the performance world as well as our products for GM's LS engine. Holley's products also include performance fuel pumps, intake manifolds & engine dress–up products for street performance, race and marine applications. As a single solution, or partnered with products from other Holley companies - Hooker Headers, Flowtech Headers, NOS Nitrous, Weiand, Earl's Performance Plumbing, or Diablosport - Holley products can give you the edge you need over the competition.
Join us