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

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
closed-loop).

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
these.

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

 

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

 

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

 

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
pressurized.

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.

DS

 

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
malfunctioning.

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
valve.

DS

 

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

 

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!

DS

 

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

Warren

 

[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