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RPM drop with 1/4 full fuel tank

Old 7/14/18, 09:30 AM
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RPM drop with 1/4 full fuel tank

1 minute ago
Hello, Just put in a new gas tank into my 1997 SN95 mustang. Used all existing components except for new filler tube grommet. Filled the tank - no leaks = win, problem solved right?
Not. When the fuel gage got to just under 1/4 a tank, the RPM would drop to idle while driving on the highway. it would coast and then re-engage to full rpm and the drive train would engage... a few more miles, same thing, RPM would drop to idle speed and I had no acceleration... then re-engage to normal. Acted almost like it was out of gas, but the engine never completely shut off, just RPM lowered to idle setting.
Filled the tank and no problems, ran normal.... This only happened when the fuel level was just a smidge below 1/4 of a tank.
Could this be a tank baffle issue, a faulty fuel pump, or something else. I'm not looking forward to dropping the tank again as it was a pain getting it back in when I replaced it. The tank is new, but the components were reused (new fuel filter though & new filler neck grommet).
Thank You So Much as this has the Mrs. worried and scared to drive it now....
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Old 7/14/18, 10:47 AM
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Any chance the fuel pickup isn't reaching down far enough?
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Old 7/14/18, 10:59 AM
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Could be... The new tank appeared to be identical as the one I removed. However, even after the rpm's return to normal and the car acts normal, it would drive for about 15-20 miles before it would happen again, and last for about 3-5 seconds before returning to normal operation... and I was able to drive it for several more miles before it would suddenly act up again... If the pickup wasn't reaching down far enough, wouldn't it just stop as it wouldn't be able to obtain any more fuel?
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Old 7/14/18, 03:30 PM
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This is an odd one for sure. Is the tank venting system not working properly? Of course I'd think that would cause a problem at all times, not just at a 1/4 tank or below. Is the tank the same internally?
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Old 7/14/18, 07:37 PM
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It appeared to be the same dimensionally in every aspect... It only happens when the fuel level hit just under 1/4 of a tank. I've been racking my brain... I'm wondering if the inlet to the baffle inside the tank is perhaps a bit askew or too small, perhaps a burr or something.... I agree that if the venting was irregular, then it would be happening consistently... Thanks for the reply....
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