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Return Fuel Stumble
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<blockquote data-quote="SecondhandSnake" data-source="post: 16419873" data-attributes="member: 116684"><p>Might have to burn it down- clearing the filter doesn't seem to have fixed the problem. I've ruled out fuel temperature as a cause. Temperatures didn't even exceed 70 deg F.</p><p></p><p>I'm also fairly confident the issue here is around the regulator rather than the pump. Even after fuel pressure decayed to 34psi, I could adjust the regulator and I was able to bump it up to 50+ psi on a whim. If the regulator was truly chasing the set point and was unable to deliver it (i.e. delivering 34psi on a set point of 39psi), then the regulator would have been fully shut returning no fuel at that point and adjusting it would have made no difference. But I can bump it up all I want and the pump will deliver it. For whatever reason it's not maintaining the correct base pressure. I can't even chalk it up to a vacuum leak, because if anything that should cause the base pressure to be too high.</p><p></p><p>On the finer points of testing it, my first attempt it dropped 5psi within 10 minutes of slow driving. Even worse than before. So I tried bumping up the regulator set point back to where it should be while idling stationary. That was easy. I let it sit and idle for 10 minutes and it varied less than 0.5psi. But as soon as I took it out on the road it was dropping again. Something is just...odd.</p><p></p><p>Regulators should be pretty simple devices. You have a valve/seat, vacuum chamber, spring and diaphragm. Something is not behaving the way it should. I can probably rule out diaphragm since it's not leaking fuel everywhere. Which means either the spring is varying, it's getting too much vacuum (if that's even possible?) or something is wedging in the seat. Maybe another spider. Who knows.</p></blockquote><p></p>
[QUOTE="SecondhandSnake, post: 16419873, member: 116684"] Might have to burn it down- clearing the filter doesn't seem to have fixed the problem. I've ruled out fuel temperature as a cause. Temperatures didn't even exceed 70 deg F. I'm also fairly confident the issue here is around the regulator rather than the pump. Even after fuel pressure decayed to 34psi, I could adjust the regulator and I was able to bump it up to 50+ psi on a whim. If the regulator was truly chasing the set point and was unable to deliver it (i.e. delivering 34psi on a set point of 39psi), then the regulator would have been fully shut returning no fuel at that point and adjusting it would have made no difference. But I can bump it up all I want and the pump will deliver it. For whatever reason it's not maintaining the correct base pressure. I can't even chalk it up to a vacuum leak, because if anything that should cause the base pressure to be too high. On the finer points of testing it, my first attempt it dropped 5psi within 10 minutes of slow driving. Even worse than before. So I tried bumping up the regulator set point back to where it should be while idling stationary. That was easy. I let it sit and idle for 10 minutes and it varied less than 0.5psi. But as soon as I took it out on the road it was dropping again. Something is just...odd. Regulators should be pretty simple devices. You have a valve/seat, vacuum chamber, spring and diaphragm. Something is not behaving the way it should. I can probably rule out diaphragm since it's not leaking fuel everywhere. Which means either the spring is varying, it's getting too much vacuum (if that's even possible?) or something is wedging in the seat. Maybe another spider. Who knows. [/QUOTE]
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