Page 1 of 2 12 LastLast
Results 1 to 10 of 17

Thread: Fuel Pressure

  1. #1
    Join Date
    Jan 2004
    Location
    Houston TX
    Posts
    292

    Default Fuel Pressure

    loosing residual fuel pressure over night in 94 530 so have to crank a while before it starts. Sooo either check valve in Pump, pressure regualator or leaking injectors......best way to determine which one.
    Don't currently have a fuel pressure guage...might though buy one.

    Callen 94 530i 91 535i 89 735il

  2. #2
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,730

    Default

    you have an electric fuel pump, should pump up almost instantly. You probably have another problem like vacuum leak or need to change the plugs.
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  3. #3
    Join Date
    Dec 2003
    Posts
    835

    Default

    There is a retrofit in line check valve to be placed between the pump(tank) & filter. The check valve in the pump assembly wears & allows the line to bleed down overnight.

    I don't have the part number handy, but Pat@BMA knows the item. It is cheap enough to try first.
    erased due to slander

  4. #4
    Join Date
    Jan 2004
    Posts
    4,148

    Default Here's that part number for the check valve kit.

    Quote Originally Posted by Martin in Bellevue
    There is a retrofit in line check valve to be placed between the pump(tank) & filter. The check valve in the pump assembly wears & allows the line to bleed down overnight.

    I don't have the part number handy, but Pat@BMA knows the item. It is cheap enough to try first.

  5. #5
    Join Date
    Feb 2004
    Location
    Minnesota
    Posts
    499

    Default

    Does anyone know how long of a "crank" starts to become a concern? Are we talking more than a couple seconds, ten seconds? or what? Both of my BMW's take a couple seconds or so to fire up, cold.

  6. #6
    Join Date
    Jan 2004
    Posts
    4,148

    Default The check valve problem is primarily a hot start problem and if you

    had it you'd know it... its more than a couple of seconds, more like between 7 and 10 seconds...





    Quote Originally Posted by JonE
    Does anyone know how long of a "crank" starts to become a concern? Are we talking more than a couple seconds, ten seconds? or what? Both of my BMW's take a couple seconds or so to fire up, cold.

  7. #7
    Join Date
    Jan 2004
    Posts
    4,148

    Default To elaborate a little more, on older carburated cars vapor lock used to

    occur because fuel would boil in the fuel line between the gas tank and the engine because of the low pressure of the fuel and the heat absorbed by the line from the exhaust and other sources. One of the reasons that the fuel pump was placed in the gas tank on most injected cars is that this way the entire fuel line from the tank to the engine is under pressure , typically 35 to 45 pounds. By raising the pressure in the lines it raised the boiling point of the gasoline quite a bit, helping to prevent vapor lock from occuring in the fuel line. The check valves job is to ensure that the fuel lines always have fuel under pressure right up to the injectors. If you have a bad check valve then the pressure will drain back to the fuel tank and the fuel in the lines will mostly likely boil at some point close to the engine causing a vapor lock condition, which requires more cranking of the engine to get fuel to the injectors to overcome this. So the fuel pump was actually moved to the tank for a good reason.






    QUOTE=Bill R.]had it you'd know it... its more than a couple of seconds, more like between 7 and 10 seconds...[/QUOTE]

  8. #8
    Join Date
    Feb 2004
    Location
    Minnesota
    Posts
    499

    Default

    So Callen, is this a cold start problem only? Either way, it sounds as though checking that fuel pressure might be worthwhile, and, like Jeff said plugs and vacuum leaks.

  9. #9
    Join Date
    Jan 2004
    Posts
    4,148

    Default Don't get me wrong Jon, it still affects cold start, its just much

    more noticable on hot start, but leaking injectors or a bad fuel pressure regulator will definitely affect cold start too.. Knowing Callen, i'm fairly certain that the plugs have been changed and typically a vacum leak wouldn't affect cold start much. The temp sensors and the engine computer determine how much fuel to inject on the initial cranking when cold, if it had a vacum leak it might run poorly immediately after starting but when starting I don't think its taken into acount on a cold start.







    Quote Originally Posted by JonE
    So Callen, is this a cold start problem only? Either way, it sounds as though checking that fuel pressure might be worthwhile, and, like Jeff said plugs and vacuum leaks.

  10. #10
    Join Date
    Jan 2004
    Posts
    4,148

    Default All that said I would still try the check valve kit first , since its cheap and easy

    Quote Originally Posted by Bill R.
    more noticable on hot start, but leaking injectors or a bad fuel pressure regulator will definitely affect cold start too.. Knowing Callen, i'm fairly certain that the plugs have been changed and typically a vacum leak wouldn't affect cold start much. The temp sensors and the engine computer determine how much fuel to inject on the initial cranking when cold, if it had a vacum leak it might run poorly immediately after starting but when starting I don't think its taken into acount on a cold start.

Page 1 of 2 12 LastLast

Similar Threads

  1. Fuel pressure q's...
    By paanta in forum 5 Series BMW
    Replies: 12
    Last Post: 03-11-2009, 12:11 AM
  2. Replies: 8
    Last Post: 10-08-2007, 08:16 PM
  3. HELP! can't get fuel pressure regulator out of fuel rail....
    By ryan roopnarine in forum 5 Series BMW
    Replies: 2
    Last Post: 01-21-2007, 09:26 PM
  4. Replies: 4
    Last Post: 01-13-2007, 01:47 AM
  5. no fuel pressure
    By Dr. evil in forum 5 Series BMW
    Replies: 9
    Last Post: 09-07-2006, 10:32 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •