Sniper FI Fuel Pressure troubleshooting

Discussion in 'High Tech Retrofits' started by 8pack, Oct 3, 2019.

  1. 8pack

    8pack Veteran Member Lifetime Gold Member

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    SET UP:

    Holley Sniper
    RobbMc Surge tank
    Edelbrock high volume 10PSI Fuel pump
    Sniper CD box
    Sniper Coil
    Sniper Hall effect distributor
    In cabin Electric Fuel Pressure gauge

    I was having intermittent lean spikes with my Sniper and I thought I traced it to my mechanical fuel pump not producing enough volume/pressure to the the Surge tank. I swapped out my stock mechanical pump for the high volume Edelbrock pump. I am pretty convinced that was at least part of the issue.

    Fuel pressure has been a steady 63psi at idle and drops down to 58/9 under throttle. That seems pretty normal. I was still seeing some periodic lean spikes on my sniper control panel but the car was running well.

    Last night I suddenly lost all fuel pressure and the car shut down. I was luckily across the street from autozone. I went and got a test light to see if there was power at the pump, by the time I got back and turned the key on I was showing pressure again.

    That led me to believe the relay was bad and overheated so I swapped in a new one. 12V 30Amp. I checked all the grounds and those are also solid. Is that the right size? The old relay had no indication of size on it.

    The real question is here....when I went to start the car again the pressure was at 63 before I turned the key. When it started it dropped down to 20-40 swinging back and forth and then after about 10-15 seconds went back to a solid 63. I drove it home with no further issue.

    I am pretty confident the surge tank is not overheating and the fuel is not boiling. I have it wrapped in that thick exhaust insulation with the aluminum reflective layer. I reached in and the tank was barely warm.

    If everything just started up normally without that initial drop in fuel pressure I would be 100% confident it was the relay. However, that initial pressure drop has me confused. If the relay went bad would the throttle body have continued to pull fuel for a period and created an air pocket in the line that had to purge itself when the car restarted and that is why it was still show proper pressure with the key on and car not running? Or is there a potential issue with the fuel pump that is acting like a relay problem? I am going to test the old relay, but given the fuel pressure came back up again after the car cooled it seems like it is a heat related issue which won't show up in a standard test of the relay.

    I don't feel like I can drive it far now as I don't know for sure whether the issue is the relay, pump or something else.

    As always, thanks for your time and sage advice!
     
  2. BigBlock73

    BigBlock73 Veteran Member Lifetime Gold Member

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    I have the RobbMc tank.
    I haven't experienced any issues.
    Do you have the return line connect?
     
  3. 8pack

    8pack Veteran Member Lifetime Gold Member

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    I am using the stock return line. Robb said it should be fine although there is a small chance it might be too small with the higher volume mechanical pump. The fuel pressure has been totally steady since I installed the new fuel pump
     
  4. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    Are you using what you would consider a reliable fuel psi gauge and where is the sensor mounted? I thought Holley Sniper had that readout on the screen, but I didn't see it. As for the return line, RobbMc says a 1/4" is good unless you're doing extended periods at WOT. That kind of goes against conventional wisdom that input and return need to be the same, but remember that old 60's hemi's ran on 5/16 fuel lines. All in all, I'm guessing you just saw a burp in the system. Take it for a couple short hops and see what happens. I like to short hop up to Hooters. :D
     
    73 Z likes this.
  5. Aussie78Z28

    Aussie78Z28 Member

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    Make sure your battery is solid. I had a few weird things happening and it turned out to be a battery on its way out (possibly could also explain the weird gauge readout). Probably isn't that, but it's an easy check :)
     
  6. 73 Z

    73 Z Veteran Member Gold Member

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    Noted! time to put a spare relay in the glove box. Good luck!
    I'm still fighting a no start, start then foul plugs, just because I went from progressive linkage back to 1-1. might be a bad fuel regulator
     
  7. 8pack

    8pack Veteran Member Lifetime Gold Member

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    I am using a Speedhut gauge. They private kable their gauges for Holley. The pressure sensor is mounted about 8 inches before the intake connection on the Sniper.

    Although there appears to be an option for fuel pressure readout on the Sniper screen, there is not. The sniper does not report fuel pressure. The software is used for other Holley FI products as well which may have the ability to read fuel pressure.

    If anyone has suggestions on a heat tolerant relay I would take that as well.
     
  8. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    When I went with dual electric fans, I bought a 5 pack of relays from Amazon, of course they're made in China, but they're the higher quality ones.

    I know this isn't what you really want to do after going with the RobbMc system, but when I installed my Eddy ProFlo 4, I went with this Holley setup.
    https://www.holley.com/products/fue...uel_pumps/muscle_car_efi_modules/parts/12-304
    It's a simple drop in, is internally regulated, has it's own fuel return, and has worked well for me. I already had battery in trunk, so relay wiring was no issue.
    Good luck in getting this figured out.
     
  9. 8pack

    8pack Veteran Member Lifetime Gold Member

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    Excellent suggestion. I had tried to find that set up awhile ago and it looked like they didn't have it for our cars yet. I am sure I missed it.

    I will try the new relay route and if I still have problems then will consider the in tank set up.

    Did you use the stock lines and it says no return required but doesn't the sniper require some kind of return?

    thanks!
     
  10. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    I used stock lines, EFI rated rubber and clamps where stock rubber was. I did some research on the Sniper before I went with Eddy, IIRC Holley says that pump is good to go with the Sniper because it has a built in return system. Should be some info on Holley forums. Also good idea to check electrical as suggested, and you are using a dedicated positive and negative cable directly to be battery for this system? Nothing else at all on those wires?
     

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