4 vents on gas tank.

[rradar71]

Can I chime in here and ask a dumb question. I have noticed that with the warmer weather, I sometimes hear a loud popping noise that sounds like it is coming from the left rear, maybe the vapor separator. It will sometimes make the noise while driving or just sitting in the garage. If I let the pressure out of the tank and leave the cap loose it won't make the noise. I replaced the tank and hoses, but I have the original vapor separator. It appeared to be in good shape. I was thinking about getting a different cap, or is there anything else I can check. Thanks, Ron.

[72RoadRunnerGTX]

The 71’ FSM description for that vapor separator includes the term expansion tank. The separator’s internal pressures will be that of the fuel tank. Popping noises would be unusual however, could be a venting problem. Make sure the line to the valve cover breather is open. Then I would pull the shields off the separator; make sure there are no foreign objects between the separator and the shield or wheel well. Slight expansion/contraction separator movement could be transferring to the shield; it could be making the noise.

[rradar71]

OK, thanks I'll try that instead. The first time I heard the noise, I was in the house. It sounded like something fell on the car.

[72RoadRunnerGTX]

Tonight I happen to be cleaning up one of these 71’ style vapor separator shields that I have left over from a donor car. After removing the undercoating and some light blasting, I was startled at the level of noise it makes when flexed. It’s a large flat un-reinforced piece of thin sheet metal slightly concave, likely from thousands of small road stone impacts. Very load popping “paint can” type sound when flexed slightly. I’d be looking closely at your shield as the possible source of the noise.

[rradar71]

Thanks. I think your exactly correct. I haven't had time lately to remove it, but I took the heel of my hand and lightly hit the shield and I duplicated the sound I had been hearing. Ron.

[dangina]

where can one buy a vented gas cap to fit our car? what size do we need?