1993 Grand Caravan - high pressure in gas tank, gas smell

Discussion in 'General Motoring' started by Lee Cremeans, Nov 15, 2003.

  1. Lee Cremeans

    Lee Cremeans Guest

    We have a 1993 Grand Caravan with the 3.3l V6, and recently (the past
    year or so) we've been noticing that it has a strong gas smell after
    driving it for a while (long enough for the the engine to go into

    Last spring, I noticed that one of the hoses to the evaporative
    canister (the hose going from the purge valve output to the engine)
    was disconnected. I reconnected it, and that helped a little, but the
    smell never completely went away. Later in the spring, I took a look
    at the vacuum routing for the engine (comparing against the Chrysler
    diagram), and noticed that everything was messed up. The rubber
    Y-junction in the manifold vacuum going from the tree to the EGR valve
    and the canister purge solenoid was cracked, the EGR valve and EET
    were partially disconnected, and the cruise control vacuum was
    connected to the backpressure port on the EGR valve! I fixed all

    I've noticed since then that the gas tank tend to get a LOT of
    pressure in it -- when you take the cap off, the gas fumes hiss out
    and you can smell them really strong. I ran the engine tonight until
    it got warm, and I noticed no gas smells under the hood, but the tank
    vapor pressure was very high. (I'm pretty sure it's not vacuum,
    because the smell is so strong.)

    Knowing that the canister output and the control vacuum were
    disconnected for so long, I'm wondering if the canister may be soaked.
    I'm also going to double-check the connections at the purge valve,
    just to make sure they're secure, but is there anything else I should
    check? I've already checked for fuel line and injector leaks under the
    hood, and found nothing interesting.

    Thanks in advance for any input you can give me.

    Lee Cremeans, Nov 15, 2003
  2. Lee Cremeans

    Mike Martin Guest

    According to the 93 Chrysler manual, the tank should have positive pressure
    in it when in operation (cap design is for 1.58-1.95 psi release). Is the
    cap an original, or a proper equivalent replacement? Having the wrong cap
    could be allowing pressure vapours to escape.

    Also you could have a leak in the top of the tank, or in the fuel filler
    vent tube or hose that is allowing the positive pressure to escape. there is
    also a pressure relief/rollover valve on the top of the tank that could be
    relieving too soon.

    And of course, you could be correct in that the tank pressure could be too
    high and causing either the filler cap or the tank relief valve to release
    the excess pressure. One possible cause for this is the fuel pump not being
    shut off when pressure gets to correct value. When you turn the key to run
    without starting (driver door open!) you should hear the tank fuel pump whir
    for a couple of seconds, then shut off as the pressure reaches the correct
    value. Or does it continue to run and build excess pressure?

    Just a few thoughts to consider.

    Mike Martin, Nov 16, 2003
  3. Lee Cremeans

    Lee Cremeans Guest

    I'm pretty sure the cap is original, and the pressure only seems to
    escape in earnest when I remove the cap, so it's definitely holding
    pressure. It seems like it's more than the pressure you mention, though,
    since it takes a few seconds to vent.
    Nope, it's hitting pressure and shutting off.

    Lee Cremeans, Nov 16, 2003
  4. You are misreading the manual, *OR* misinterpreting what you read, *OR*
    there is a typo in the manual -- any or all is possible. It is by no means
    the case that the tank "should" have positive pressure when the engine is
    running or at any other time. The fuel tank is designed always to have
    nominally atmospheric pressure inside. It *may* have slight positive or
    slight negative pressure at any time, regardless of whether the engine is
    running. The tank cap is of the so-called "pressure/vacuum" design, with a
    2-way valve that vents excessive pressure and relieves excess vacuum so
    that the tank remains nominally at atmospheric pressure. Vacuum occurs
    for two reasons only: due to the fuel level dropping as fuel is consumed,
    and as a result of downward ambient temperature transitions. Pressure
    occurs for one reason only: as a result of upward ambient temperature
    transitions. There is no other means by which for the tank to be
    None of this is correct.
    This is also not correct. The fuel pump pressurizes the line between the
    tank and the injectors *only*. The fuel pump is not "shut off when the
    pressure gets to the correct value"; the pump may run for a present time
    (zero to 2 seconds, variable depending on time since shutdown) to
    pressurize the line prior to startup. Once the engine is running, the pump
    runs continuously, it is not cycled on and off. The fuel pressure
    regulator, located at the inlet of the fuel rail, prevents overpressure at
    the injectors by shunting some portion of the pumped fuel back to the tank
    via the return line. If you'll think about it for a few seconds, you
    should realize that even in the never-happens condition of one hundred
    percent of the fuel being returned to the tank via the return line, it
    would not be possible for the pump to pressurize the fuel tank.
    No. See above.
    No. See above.

    Daniel J. Stern, Nov 16, 2003
  5. On 15 Nov 2003, Lee Cremeans wrote
    This indicates there's still something wrong with the evaporative emission
    control system, which consists of the fuel tank, fuel cap, evap canister,
    rollover valve and all interconnecting lines.
    Usually is, in cases like this! I call these "IPO" problems -- Idiot
    Previous Owner who thought he was "improving" things.
    Ye gods...

    Evap canister and associated valves and lines are your primary suspect.
    Fuel cap is also strongly suspect -- the type of idjit who foozles the
    vacuum hoses as you describe them having been foozled is also the type to
    glue shut the valve port in the cap.

    See my other post in this thread for a *correct* general description of
    how the system operates. It seems likely that fuel returned to the tank
    via the return line, having been heated by its trip through the engine
    bay, is increasing the temperature (therefore pressure) of the fuel tank,
    which is probably not properly interconnected with the evap canister and
    associated valves, and/or the canister and/or valves may be

    Since 1971 in North America -- 1970 in California -- fuel systems have
    been required NOT to "relieve themselves" to the atmosphere in the manner
    Mr. Martin incorrectly asserts yours should be doing via the rollover

    Daniel J. Stern, Nov 16, 2003
  6. Lee Cremeans

    Lee Cremeans Guest

    I'm thinking it was an idjit tech, in this case...the van was in a crash
    back in 1998, and around this time, the VECI label disappeared. (I
    should call Chrysler and see if I can get a replacement for it...)
    Sometime between then and when I caught the mess that was made, the
    cruise control mysteriously stopped working, as well as the EGR (the van
    wouldn't pass emissions here in Northern Virginia because of high NOx,
    and we were mystified as to the cause for a long time). Funny how you
    can fix so many problems with just a few hose connectors, a diagram and
    some common sense...
    Yup, this is pretty much the conclusion I've come to as well...the cap
    really is the Chrysler original, as far as I know, and could probably
    stand to be replaced. I'll have a better look at the evap canister when
    it's light out, since I remember not being able to get the best of fits
    on the canister output hose when I reconnected it (it was a quickie job
    in a rest area parking lot on the way home from Busch Gardens
    Williamsburg, so I didn't have too much time to work).

    Lee Cremeans, Nov 16, 2003
  7. Festive.

    Interesting thing about VECI labels: You can buy them for $3 or so right
    over the parts dep't counter, no calls to Chrysler or VIN required. Just
    specify you have a '93 Grand Caravan with the 3.3, say whether it's a
    California, Canada or Federal car, they'll look up the part number, and
    either order it for you or say "It's been discontinued", in which case
    have them run a Locate on it and they'll probably find one for you.

    This gets "interesting" when you realize that the other Federally-required
    label, the Vehicle Safety Certification Label (VSCL) located on the
    driver's door or doorframe, absolutely CANNOT be had as a replacement
    part. No way, nohow. If it gets painted over, lost or destroyed, all you
    can do is beg the automaker for a letter identifying the vehicle by VIN
    and stating it conforms with all applicable Federal Motor Vehicle Safety,
    bumper and antitheft standards in effect on the date of manufacture, and
    specifying the date of manufacture. If the mfr will not supply such a
    letter for any reason, you're S.O.L. if the VSCL ever needs to be checked
    -- you move to Canada, for instance, or even to a state that requires
    such a check of incoming vehicles, or you take the van out of the country
    and then want to bring it back in.

    Now, it gets even more interesting when you realize that the Federal
    penalties for false declaration of *emissions* compliance are up to 5
    years imprisonment and up to $275,000 plus assorted other fines -- this is
    the crime that could be committed, remember, by paying $3 at your local
    dealer for a genuine factory VECI label that does not in any way indicate
    it's a replacement and, like the original, does not show a VIN.

    The Federal penalties for false declaration of *safety* compliance are up
    to 2 years imprisonment and up to $15,000 -- this is the crime that would
    be considerably harder to commit due to the unavailability of replacement
    VSCLs and each VSCL identifying its vehicle's VIN.

    Go figure!

    Daniel J. Stern, Nov 16, 2003
  8. Lee Cremeans

    warren Guest

    anyone know what the final fix was on the gas tank problem.

    warren, Nov 19, 2003
  9. Lee Cremeans

    Lee Cremeans Guest

    [posted and mailed]
    Nothing at the moment; I'm suspecting it needs a gas cap, but I haven't
    had the cash to test my theory yet. I'll post more info to the group
    when I have it...

    Lee Cremeans, Nov 23, 2003
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