What causes excessive pressure to build up in the fuel tank?

Tiny
DFP1954
  • MEMBER
  • 1996 DODGE RAM
  • 100,000 MILES
What causes excessive pressure to build up in the fuel tank of my 1996 Ram 1500? When I remove the fuel cap to refuel, there is an excessive amount of air escaping from the tank. I know that some air would be normal, but there is a lot. Nothing like I have heard on any vehicle, at any time. The fuel pump, gas cap, and fuel evaporator cylinder are all new. The gas cap, fuel pump, and gas evaporator cylinder have all been replaced and the problem still exists. Do you have any suggestions?
Saturday, August 27th, 2011 AT 12:13 AM

3 Replies

Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
Looking at the EVAP sytem is a good to check next.. Did you get new solenoids for the system. There are 2 purge solenoids that will get stuck into whatever position they failed in, i.E. Stuck open.
Does gas escape trotu the fuel filler when you open it?

Is the Idle Air Control Valve, IACV, which is sometimes also referred to a the engine Load Sensor, ELS.
This is an electro-mechanical device which idles up the engine when loads such as; power steering, A/C and other accessories or situations call for it.
It can adversely affect the performance of the engine.
It is tough to diagnose problems such as these because electric/mechanical control modules feed from sensors all over the engine and accessories which makes it hard to tell if a sensor is bad, the control unit is bad, an IACV is a control unit that sometimes has integrated sensors, or if the is a problem with the Vehicle Main Computer.
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Saturday, August 27th, 2011 AT 3:27 AM
Tiny
DFP1954
  • MEMBER
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I did replace the "Purge Solenoid" that mounts on the drivers' side, rear of the engine. The one that has the double vacuum line connection and mounts on a metal bracket by sliding on it. I was not aware that there was another purge solenoid involved. The Idle Air Control Valve has also been replaced. All of this "Replacing" has been in an attempt to stop the engine from "Cutting Out" and occasionally dying at slow speeds. I am pretty sure the entire engine cuts outs and then restarts at higher speeds, and I guess it just dies if the "problem" occurs during idle. There is nothing consistent about the problem. It may run perfect for two or three days and then may cut out 3 or 4 times on a 15 mile trip. I have had the truck in to a reputable Dodge dealer twice and they cannot find anything. No "check engine" lights come on when the problem occurs. This all started about a year and a half ago when the engine would not start and it turned out to be the engine control computer. I even replaced it after about six months thinking that it was the cause of the problem. Something that has always bothered me is that there is not an EGR Valve on the truck. I think they found a way not to have one in 1997, but this is a 1996. I am always wondering if the replacment computers that I get from NAPA are truly designed for this engine. I don't know if I'm the only person on Earth to have to deal with this, so far I haven't found anyone to help. I thing I have replaced ever sensor, except the oxygen sensors, on the truck. The coil, ignition wires, dist. Cap, rotor, cam position sensor, crank position sensor, throttle position sensor, and more. You can mill over this for a while and over any direction you may have.
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Saturday, August 27th, 2011 AT 4:06 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,144 POSTS
Despite having replaced the fuel pump, gas cap, and fuel evaporator cylinder, there are a few potential causes to consider:

Ventilation System:

Evaporative Emissions Control System:

Check Valve:

Faulty Pressure Regulator:

Restricted Fuel Return Line:
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Thursday, December 7th, 2017 AT 8:24 PM

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