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

Reply to
Lee Cremeans
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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

Reply to
Mike Martin

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

Reply to
Lee Cremeans

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

Reply to
Daniel J. Stern

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

Reply to
Daniel J. Stern

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

Reply to
Lee Cremeans

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

Reply to
Daniel J. Stern

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

Warren

Reply to
warren

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

Reply to
Lee Cremeans

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