355 Fuel issue | FerrariChat

355 Fuel issue

Discussion in '348/355' started by doschainz, Jun 23, 2024.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. doschainz

    doschainz Rookie

    Jan 29, 2021
    5
    Full Name:
    Dylan
    Can somebody confirm the fuel inlet and return passage on the rail? I’m having issues with fuel after an engine out and I just want to cross that off the list.

    The fuel pump has already been rebuilt by SRI, it will prime when I put power to it from the fuse box but i do not believe it is priming with key on. I’ll be plumbing in schrader valves to check pressure later today. All signs show that immobilizer is disabled.

    any other ideas to check?
    Image Unavailable, Please Login
    Stolen picture from google
     
  2. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    14,285
    Sydney
    Full Name:
    Ian Riddell
    Do you have a Motronic 5.2?

    The fuel pump on the 5.2 car will only prime for a few seconds when using the key. After this time, even if you cycle the key, reset the battery or whatever, the pump will not run until the ECU sees engine cranking rpms.
     
  3. doschainz

    doschainz Rookie

    Jan 29, 2021
    5
    Full Name:
    Dylan
    yes, 98 5.2 F1

    I spoke to you about this issue a month ago, I'm just getting back into it after waiting a month for a new fuse box to come in
     
  4. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    14,285
    Sydney
    Full Name:
    Ian Riddell
    Sorry, I forgot.

    Did you read my edit?
     
  5. doschainz

    doschainz Rookie

    Jan 29, 2021
    5
    Full Name:
    Dylan
    I can distinctly hear the fuel pump prime when I manually apply power, but I'm not sure if I do when I crank. That's the reason why I'm installing the valves to read fuel pressure. I suppose I'll report back when I do
     
    Qavion likes this.
  6. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    14,285
    Sydney
    Full Name:
    Ian Riddell
  7. Rifledriver

    Rifledriver Three Time F1 World Champ

    Apr 29, 2004
    37,099
    Cowboy Capitol of the World
    Full Name:
    Brian Crall
    The location of the feed and return hoses at the fuel block at front center of engine is counter intuitive. The rear hose goes to the front position and the rear hose goes to the front position.
     
  8. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    14,285
    Sydney
    Full Name:
    Ian Riddell
    I just checked on my car (5.2). My front fuel block hoses (i.e. closest to firewall) go to the end of the rail (which is further forward than the lower connection). The rear hoses (closest to bumper) go to the lower connection on the rail. i.e. the same as the parts manual.

    Image Unavailable, Please Login
     
  9. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    504
    Chicago IL
    There should be a shrader valve on top of the fuel filter.

    The pump will only prime for a few seconds and only on the first key turn. From there the engine must be cranking. That said you should see pressure come up at the filter valve.
     
  10. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    14,285
    Sydney
    Full Name:
    Ian Riddell
    Are there any check valves or restrictors in the system (between the fuel filter and the rail). I'm wondering what the pressure difference would be between the fuel filter outlet and the rails. Would the fuel filter outlet pressure be an average of the regulated pressures in theL/R bank rails?
     
  11. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    504
    Chicago IL
    No check valve just the regulators on the return.
     
    Qavion likes this.
  12. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    504
    Chicago IL
    #12 Zamboniman308, Jun 23, 2024
    Last edited: Jun 23, 2024
    There is a procedure in the work shop manual to verify the fuel pressure and proper regulator function.

    The only check valve would be at the fuel pump then it's straight hose to filter then to the splitter block manifold which T's it off to each rail inlet.

    I've never understood the dual regulator arrangement on a single pump 5.2 car. Where there is no isolation between sides. Makes total sense on the early cars with dual pumps. All I can think of is it was easier to leave it as is when they went to single plump rather than reengineer the rail setup. Can't say I've seen this arrangement on any other car. You'd expect one rail to loop into the other with a single regulator and return at the end. Nope they came up with that elaborate T manifold thing and a bunch of hoses that chafe and catch on fire.
     
  13. Zamboniman308

    Zamboniman308 Formula Junior

    Feb 2, 2020
    504
    Chicago IL
    Basically I think so. The pressure regulators are both operating properly and equal all should be the same.

    Going back to the posters issue. Step 1 is to just verify pressure is coming up to spec as expected and to do that all you need is a guage. No extra valve modifications necessary. Having a 90 degree fitting on your guage makes it a hell of a lot easier but isn't necessary. Sometimes you may need to loosen the filter bracket to make some room. Once you get a guage on it you'll know in seconds if you're good. And if your system is holding pressure over time per the WSM. Note I've seen a situation where it can work intermittently sometimes giving proper pressure other times not. I've also seen barely finger tight wire connections on the in tank pump
     
    Qavion likes this.

Share This Page