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Car is new to me. Starts easily; no stalling or rough running; cruises smoothly, sufficient power. Have driven several 15-mile trips, no problem. On two longer trips, after ~20 miles, it began to hesitate and bog after some deceleration eg. coming down hills, slowing for a corner. I replaced the in-tank pump (was bad) and the connector hose (was fine).
Thought that fixed it but today after ~25 miles the problems began and seemed noticeably worse. Reached a point where it wouldn't go above 25 MPH on the flat. I drove like that for 4-5 miles and gradually got some power back: it would go 55 but slow down on hills. Had a steep and long hill to go up about 5 miles ahead. Assumed it would die out on the hill but it drove up at a steady 35 MPH - the speed limit.
Stopped and filled up with gas: took -7.5 gallons. Drove 12* miles home, no problems: no stalling, hesitating, ... drove up a long grade at 55 and could accelerate; after downhills and curves there was no hesitating as before. When the problem was at its worst, there was none of the backfiring or bucking I associate with fuel starvation. It just wouldn't go any faster.
Back at home: in-tank and main fuses had good contact - were not hot. Main fuel pump a little noisy but not warm. Fuel filter had some resistence when air was forced through it. I replaced the main pump and filter. The main (a good used one) is quieter but that could be from less resistance through the new fuel filter. The car mostly sat for ~ 4 years and there was fine sediment in the tank.
We'll see what happens when I drive it. The self-improvement on the road is puzzling. With clogged fuel filters I've seen before, you lose power when you exceed the flow capacity. When you stop at a sign/light, it replenishes and you can go ahead with full power. I stopped to let this one idle and still had no power when I restarted. And no bucking/ jerking when I start up.
It's possible that the sediment clogged the new sock in the tank; or that the hose between the in-tank pump and sender tube is bad and I didn't see it.
Perhaps electrical? The power stage wouldn't clear up while in use. Same with MAS. CPS is new.
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240 drivers / parts cars - JH, Ohio
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