Does anyone know why the C4S has a taller fuel pump cover?

Hello! I have tried to search in the forum, but I didn't find any conclusive information about this topic As many of you probably know, the fuel pump cover in the C4S US version, has a taller cover, than the rest of the versions, as you can see here The RoW C4S, has the lower cover, and also, none of the others 996s using the AWD chasis (US or ROW) have the taller cover (Carrera 4, Turbo, GT2 or GT3). This is a RoW version In the book from Adrian Streather, he mentions something about the 4S US using the fuel pump of the GT3 because the fuel evaporation recovery system (?) but is not clear either. Also the GT3, as I mentioned, uses the lower cover. Does anyone know the technical reason "under" (pun intended ) that?

Cars exported to NA did have a different fuel vapour recovery & warning system fitted than ROW cars. I recall reading something about a pump and sensors used to pressurize the tank & lines to test for leakage. It is more complex than the ROW system. It's possible the taller cover houses these extra components?

Also the location of the fuel pump in the gt3 is not under that cover. The gt3 uses a c2 tank and the fuel pump is under the battery. Therefore if the fuel system is different it wouldnt matter to that cover.

Not sure of cover height, but the tank system is very different in order to clear over the awd. c4 uses 1 split tank with another pump pick up in the other side of tank lower sump, for 2 tank pickups, 1 in each sump. That makes the pump pick up system and gauge system more complicated than a c2. I don't have a c4 or ever have worked on one, just read the manual.

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I think is related with that, but still wonder why the Turbo does not have the same. I guess different fuel supply system too, like in the GT3 That I did know, but that design is the same in the RoW cars, so wouldn't justify the different cover

Is that your car with the high cover? I have been trying to find a part# for that for a long time... it is not in any of the parts catalogs. The parts catalog shows that the Turbo and C4S use the same tank lid, the short one from the Turbo. I cannot find any reference to the taller lid - and I want one. Could you find the part# on that lid so I can get one?

997 part 99750447100 all 996's use the same lid far as know/have ever seen

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Whoo, that's the taller one Rob?

yup tall one, has a slant to it but overall much taller

Awesome I have been looking for one to use for my AN line upgrade.

good idea for clean install

Well, I think that I have found part of the mystery https://www.ebay.com/itm/Porsche-911...3247682?_ul=CO This control unit 996.620.115.00 it seems to be located under that cover, and only in the 4S. The other part of the mistery, is to know what is that unit and why is located there I have tried to search that part number with no luck. Not in the ETA, nor in online shops. All what google brings are ebay sales. In many of them, it is listed as cruise control unit, in others as wipers control unit. I'm not sure about any of those, as, as I mentioned, it is not listed in the ETA, and besides, the 996.620 parts group is related with the fuel supply system. Is anyone able to tell what that control unit is for?

Wild guess,, A pwm pump controller for cars with a non-return fuel system?

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Very good " wild guess" !! It is correct, a VDO PWM fuel pump controller...AKA --996-618-150-01

General comment,, If you haven't seen how a PWM works, it allows the ECU to control the pressure/volume of the pump dynamically to prevent over working the pump, On non-return fuel systems your "dead heading" the pump against the regulator. Your pressure after the regulator is controlled but the pre-regulatpr pressure can be at pump max, not really a good thing. This causes cavitation in the pump, heating of the fuel, and a ton of heat in the pump which is in the tank heating up your fuel as well.

Thank you all! So I understand that all 996.2 have that control unit, but just in the C4S is located there, in that cover, right? By the way, what PWM does stand for? Thanks again

pulse width modulation...because the 6.2 Carreras have return-less fuel system, the PWM module 'pulses' the fuel pump to control fuel pressure vs running steady-state

Thank you! I still wonder why only the US C4S has that module placed there...

It's the NON return fuel system, if you have a return from the fuel rails to the tank, you don't need PWM I am guessing because all the manuals show a return, but my 2003 C4 does not have a return line. And it has the PWM, same as a lot of other cars(Like some with a supply line only. )

So determined better (less expensive? less complex?) to have this PWM pump controller and cover than have return lines from the fuel rails. Interesting trade offs!

Its because the non return system qualifies for a better Low emission cert.. PWM pump runs cooler since its not at 100% rotation at lower pressure. It also helps prevent the fuel in the tank from heating up since your not returning heated fuel from the engine bay. C4's also have a saddle tank and the fuel from one side is siphoned on demand by the flow through the system to the side with the electric pump. (At least that how I think it works, its ridiculous amount of tubing in the C4 tank. Volvo's have the same setup.

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Is your 2003 C4 US Spec?

Yep Sold to owner 1 in Virginia in Dec 2002. It's on all c4's I think from 2003 ish onward. I asked a mech at my local indy about it. I don't know for sure if there is a PWM stashed elsewhere even on other models.. It could be anywhere and look completely different especially if were Valeo or some other supplier to Porsche.