I'm having an issue with my '95 L36. When I start the car, the gas tank makes a loud "ping" sound as vacuum increases in it and the tank contracts. After I turn the car off, it will again make a loud sound as the vacuum decreases and the tank expands. I swapped gas caps with my '96 Bonneville, and even tried a new cap, but it didn't change anything. The check engine light is off, so it isn't throwing any codes.

I searched the forums here, but didn't have any luck finding a discussion about this problem. I had the fuel pump replaced around 47k miles (the car has 73k now.) Can anyone suggest where I start looking?

Thanks,

Sam

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'96 L36 Bonneville SE, 95k miles (leather) 17" SLE rims
'95 L36 Olds 88 (leather) (x2) (both sold)
'91 Olds 442 w-41 (1 of 204): '79 Olds Holiday 88 coupe. Factory buckets, console
1958 Impala Coupe 348 75k miles
1958 Impala convertible 283, 51k miles

There have been two other people on this forum with the same problem. Myself and another guy that posted here 1X about this issue never to return.

I still have not come up with a solution other than disconnecting and bypassing the evap system completely.

Sounds like the evap purge solenoid is stuck open.

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Link:

viewtopic.php?f=19&t=22060&p=228954&hilit=gas+tank#p228954

Plus somewhere in the archive is my original posts on the topic engine pulling vacuum on gas tank.

Guys,

Thanks for the responses. Reb, I read the previous thread -- thanks for posting the link. I can't tell from your post, did you try replacing the purge solenoid?

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'96 L36 Bonneville SE, 95k miles (leather) 17" SLE rims
'95 L36 Olds 88 (leather) (x2) (both sold)
'91 Olds 442 w-41 (1 of 204): '79 Olds Holiday 88 coupe. Factory buckets, console
1958 Impala Coupe 348 75k miles
1958 Impala convertible 283, 51k miles

I replaced both the purge and evap vent valve solenoids. Plus checked to the best of my ability that the charcoal canister and vent line from gas tank was not clogged. Changed all accessible vacuum lines.

A new mechanic that I started using (for problems I can't fix myself) said he was familiar with the problem (gas tank flexing in from engine vacuum)and has seen other makes/models of cars with this issue. First mechanic I have spoken to that has heard of this problem. He said one of the vacuum lines must have a blockage somewhere (spider web?), perhaps by the gas tank. My gas tank and sending unit were changed not long before this problem arose.

I even went to a GM Pontiac dealer back when this problem started a few years ago and they could not fix it!!

If I can get through the summer without any more repairs/expenses on this vehicle (I just spent $350.00 on maintenance/repairs) I am going to have this mechanic hopefully fix the problem once and for all.

But if you or anyone else do find the fix, please post to this thread.

check your actually vent valve on top the tank or on the fuel pump

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The gas tank vent valve is integrated within the gas cap. IIRC from my research, these vehicles don't have an additional vent valve on the actual gas tank.