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Thread ID: 126539	2012-09-03 10:03:00	Probably a weird question - fuel lights	pcuser42 (130)	PC World Chat

Post ID	Timestamp	Content	User
1298680	2012-09-05 17:15:00	OK.. Here's a video I watched a while back from Airtex/Eric the Car Guy. (www.youtube.com) It seems a pump would overheat because they are so compact with little air space and many working parts. Think they would make them larger or more accommodating to the initial high pressures required. Then the filter - mine was grey as when I replaced the pump. This may add even more work/pressure to the pump, of which filters cannot be easily replaced like a oil/air filter. Though the Walbro's I think have higher pressure - at a much higher cost. Yup - that's a typical 'capsule-type' pump. But did you notice the height of the reservoir in which the fuel pump is installed? This assembly stands upright, not lying down - and it is approximately 1/2 the height of the actual fuel tank itself. The unit you see is a typical GM-version that goes into almost every GM vehicle since about 1995 or so. Some have replaceable pumps and some are capsular installed EG: the pump itself can be changed out, while in others the whole assembly is required to be replaced when the pump goes bad. In any case - as noted in that video, the pre-primer impeller MUST be submerged in fuel for it to work and it cannot by design draw a vacuum by itself. Being able to draw a vacuum or raise fuel in this case from a lower level requires a positive displacement pump which an impeller is not. Inside the roller/vane assembly is where the actual pressure to operate the injectors is generated. It's height alone is indicative of the level of fuel necessary to keep that canister full and the pump submerged to keep it cool and lubricated. One blatant mistake in that video is in stating that the purpose of the check valve is to keep overnight pressures up, is just wrong. It's not the pressure that's necessary to keep overnight since there are return circuits in the FI rail that are designed to return the fuel without restriction when the vacuum from engine operation is off or non-existing, but it keeps the lines charged with fuel which (by the law of fluids) is instantly pressurize-able when the pump is recharging the system at start up. The pressure ultimately has too many circuits (leaky injector(s), pressure relief/return circuit in the fuel rail itself, etc) that allow it to seep out when the system is dormant (overnight when the key's off f'rinstance) for that to be a necessary consideration. And again around 00:08:00 or so, the canister assembly shows the two electrical connections on top of what we call 'the bung'. The engineer calls the black one a 'vapor sensor'. That's wrong. It is a barometric-piezzo sensor that reads the vacuum that is achieved in the tank and relays that as an electrical analog signal to the ECM to tell it that the system is holding a negative atmospheric pressure, ensuring that there are no fumes getting out of the tank that are not being at least directed to the vapor recovery system (charcoal canister or purged directly into the engine or crankcase for consumption eventually in the combustion chambers) - thus ultimately alleviating photochemical smog and the escape of noxious fumes. But the sensing of vapors is NOT it's function - but just that of airtight integrity. Run the engine with the fuel cap off and the CEL will come on advising you that you've done so - and that is the primary function of that black electrical connector. At 00:09:02 he talks about maintaining the fluid level inside that 'cup' which is necessary to keep the pump happy, cool and lubricated. Note that that cup is at about 50% or the height of the pump chamber itself, therefor if the fuel level is not up to at least that level (approx 1/4 tank) the pump is out of the cooling/lubricating medium - the fuel itself. Remember that this whole assembly stands upright in the tank. Other than those glaring malapropisms, it's an interesting video.	SurferJoe46 (51)
1298681	2012-09-05 21:55:00	All this because I just wanted to know where my low fuel light was? :stare:	pcuser42 (130)
1298682	2012-09-05 22:08:00	All this because I just wanted to know where my low fuel light was? :stare: Absolutely.	Agent_24 (57)
1298683	2012-09-05 22:11:00	All this because I just wanted to know where my low fuel light was? :stare: See what you started? :p	WalOne (4202)
1298684	2012-09-05 22:47:00	Well at least it's a better response than what came from the Campaign for Better Transport forum :p	pcuser42 (130)
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