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Thread: Sniper EFI idle/strong fuel smell.

  1. #1


    Hi all. Recently installed the Sniper EFI. Just wondering if there are any tips to why at idle, I get a very strong smell of overfueling (usual culprits checked i.e. tank/lines/cap, etc.) I'll say this though, it's a very very new install and hasn't had much time to Learn. Is the idle fueling something that will be corrected by the Learn mode? I'm off now to get it up to temperature and put some miles on it, so will check the idle again later. (Ford 351W with 393 heads for info.)

    UPDATE: OK, so an update. After driving the car today unfortunately it's gone from bad to worse.
    As a bit of background the EFI was recently fitted and actually drove beautifully when first installed. Responsive, strong power delivery, smooth acceleration.

    One issue was the car kept throwing the alternator belt. So it's been in to have that issue resolved.
    Whilst I had this downtime I uploaded the most recent software to the unit, to fix an issue I had with the custom dash setup.
    I then reset and reconfigured the EFI as before - correct engine size, cylinders, cam and EFI controlling the timing via the MSD.

    Now today whilst driving out of garage I had spluttering and backfiring.
    Unfortunately, I think this was due to the car coming back from the alternator being fixed with very low fuel.
    I parked up and went to fill a Jerry can to refuel & continue.

    Since this the spluttering and backfiring has not stopped.
    In fact, it seems to be getting progressively worse, as is the smell of richness/overfueling.

    The parameters on the Digital Dash all seem to be 'normal' as such - but will take a friend along so he can monitor as I drive to see if he can spot any trends.
    I figured I may have collected some debris from tank when the fuel ran low, but to be fair it's a new install and tank was removed and cleaned out, so unlikely to have any sediment.

    Are there any thoughts on here of my next course of action, or anyone who has suffered similar issues that knows of a solution? Thanks.

  2. #2


    Have you checked your fuel pressure, maybe it's high and causing the Sniper EFI to put too much fuel in. Mine was initially and smelled like gas as well. The little screen on the regulator was plugged with some liquid varnish like substance. Cleaned it off and now have other fuel issues, but it's not high anymore.

  3. #3
    Join Date
    Dec 2009


    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

  4. #4


    UPDATE #2: When the car is cold, it seems to be 'OK'. Well, not perfect but better.
    After a couple of minutes driving the backfiring started again, along with a strong smell of fuel.
    It got progressively worse until I was forced to pull over and turn off the engine.

    I had a friend with me this time but nothing looked to be out of the norm on the instruments.

    I decided to start from scratch again and upload the standard, preprogrammed ECU with just a few minor changes (RPM limit etc.).

    Weirdly the car drove far better than ever before. But then, after about a minute or so, the backfiring started again and it was almost undriveable.

    I limped the car back at very low RPM and I guess that's it, I won't drive again until I can figure out what the issue is.

    Guys, thanks for the fuel flow info. I'll check this. Other thoughts. WBO2 sensor, would it cause these problems? Ignition timing?

  5. #5


    I believe the WBO2 sensor would be giving you bad readings on the handheld if it was messing up. Another quick question, are there any exhaust leaks? It might also cause issues and it's simple to check. Did you do the install with the ECU not controlling the timing at first? How did it run then? If you're using the Sniper to run your timing you might have interference coming from something else. There's a few threads on here that cover that subject and some tuning adjustments that might help. I'm sure Danny can put a link on here that will take you right to it. If you haven't tried running the car without timing control, I would start there so you can eliminate that from the scenario.

  6. #6


    It was only ever setup with the Sniper EFI controlling the timing, and initially had no issue whatsoever. It ran far better than it ever had on the old carb setup. You may be right though, worth trying without. I guess I'll start with fuel and work my way back from there.

  7. #7


    I would defiantly switch it to not being timing control and try it out. If you had some wires moving around while driving they may now be creating issues. Holley recommends not doing the timing control at first for this reason, it makes it harder to troubleshoot it. I'm planning on putting about 1500-2000 miles on mine and letting the system Learn the fuel side of it before I try to switch to timing control. This will give me time to save up for the dual sync distributor as well, since it seems the MSD one makes it difficult to have the timing control setup. Interference with the timing control could be causing you to have unburnt fuel due to bad timing, which may explain the sputtering & strong fuel smell. Have you put a timing light on it since it has been sputtering, just to see what the system is doing? Give it a little throttle while checking it, just to see what the timing control is doing to the timing. If it's jumping around and not following the settings you put in the system, then you probably have some interference going on.

  8. #8


    Personally, before doing anything, pull a spark plug and see if it's loaded with fuel. This would cause a misfire/backfire. It won’t fix the overfueling, but will make diagnosis easier. You could have a WBO2 sensor that’s failing, which drives the AFR lean and causes the EFI system to dump more fuel. You stated it was overfueling.
    Last edited by Dubob; 02-01-2018 at 11:08 PM. Reason: More info.

  9. #9


    So had some time to have a look this morning.
    First, checked fuel pressure. It's around 64 psi I think, so that's pretty much normal.
    Second, the timing control was returned to the standard setup so the Sniper was isolated from that.
    So the car will start. Run (very very rich) and rev up with pretty much a normal throttle response.
    The issue comes after a minute or two of running, when the engine is turned off, it refuses to start or even fire up at all.
    To get it to start, we have to upload the original map to the ECU (previously saved this in the Files/Global section).
    When that's uploaded and ignition is cycled, it'll immediately start right back up again, then the problem repeats.
    So essentially we've checked fuel pressure, and isolated the MSD/timing, and I'm still having the same issues.
    Next I'll try replacing the WBO2 sensor I think. I'll also email Holley Tech today and see if they have any ideas.

  10. #10


    Mine was a similar issue and the timing was setup incorrectly, using the Holley dual sync distributor. Follow this video it will help. Be ready, this will take awhile to get correct.

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