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740 No fuel at the rail, both pumps new and working

bmdubya1198

Active member
Joined
Aug 24, 2016
Location
Charlotte, NC
I'm at the point now that I have spark and injector pulse (only with a y-jumper, I guess my working fuel system relay is dead) but my 740 STILL won't start. After pulling the fuel line at the rail, nothing came out. I blew some air through the line from the fuel filter and the line is clear, air came through and sprayed a small amount of fuel out of the hose.

I know for sure both pumps are running, and they are both new. I just went through a lot of work replacing the in-tank pump and cleaning nasty old rancid gas from the tank, and now it's all back together. I put a couple gallons of fresh 93 in and it still isn't getting fuel at the rail. Do I need more gas? I can't think of any other reason this is happening.

This car is driving me absolutely insane.
 
Pretty sure they're correct. I know for sure they are both running.

I have 6 gallons of gas in the car, no reason at all that shouldn't be enough. After pulling the feed line to the rail there is pressure out when I put my finger over it, so I assume the pumps are pumping properly.
I'm ready to burn this piece of crap to the ground, a car has never driven me so insane. It's possessed.
 
Pulled the line off the tank pump and there is no pressure at all, and it's bone dry. There is no gas coming out of the pump/sending unit. How is this even possible!?!?
 
Is it wired backwards? One pump running in the opposite direction isnt going to get fuel to the next pump to feed it to the rail. Just check. I've done it before. Had the same issue.
 
I don't think the main pump is wires backwards. The main line going into the fuel rail is pushing out towards the rail, so the main in-line pump is working properly. I'm PRETTY sure the in-tank pump is wired up properly, but (as much as I don't want to) I can pull the pump out tomorrow and double check. I'll probably have to yank it out anyway just because any other issue here is related to that fuel sender unit.

I put the red wire on positive and the black on negative (pretty sure those are the colors).

Also, what can be done about this hose so I still have a fuel level reading? It seems Volvo doesn't sell it anymore, and the piece of fuel hose I installed in place of it (between the main pump and the hard line) won't allow the canister that sends the fuel level reading to move.
My gas gauge doesn't even move now... it used to show a reading. Maybe those wires (which I soldered back on) are backwards, but I don't really think it matters which terminal those wires go on. But I'm pretty sure it has to do with the "float" unable to move.

Number 7 in this diagram: http://volvopartslisle.com/assembly/473793/Tank-Sender
Picture: https://photos.app.goo.gl/J6l1Ab8Z4prf26gq1
 
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Test light or DVOM the wires going to the pump to be sure they are correct. I'm going to agree, it sounds like the pump is wired backwards.

The fuel hose is available from many aftermarket manufacturers. Just google the Volvo part number.
 
Well, the lack of that accordion part is what I'm worried about. The float isn't able to move with the standard hose because of where the pump is attached to the housing.
 
Volvo updated the accordion hose to straight hose but you have to buy a piece that's longer than you need. If you have to have the accordion hose, I have this one made by MTC for a 740 part #3514360.

SubmersibileFuelHose.jpg
 
Good to know. I couldn’t find it before.

I pulled fuse 11 to see if the main pump could pull in some fuel (in case the tank pump is wired wrong), and I still got nothing. I just pinched the relay and ran it a couple times for about 4-5 seconds each. I’m assuming the wiring is fine, because the main pump should have enough power to get fuel to the rail without assistance from the tank pump.
 
Pulled the line off the tank pump and there is no pressure at all, and it's bone dry. There is no gas coming out of the pump/sending unit. How is this even possible!?!?

if there is a leak in the hose between the intank pump and the outlet connection that leak will act as a short circuit. The pump will run but fuel will not be pushed into the fuel line but it will just be dumped back into the tank. There will be no pressure on the fuel line between tank and filter/pressurepump.
 
if there is a leak in the hose between the intank pump and the outlet connection that leak will act as a short circuit. The pump will run but fuel will not be pushed into the fuel line but it will just be dumped back into the tank. There will be no pressure on the fuel line between tank and filter/pressurepump.
Yep. Needs to pull the pump to check the wiring just in case. I replaced that hose while I was in there. Had to take it back out because I was noob and wired it backwards. :oops:
 
If you remove the line between the main pump and the tank pump and test, and no fuel comes out of the line when the tank pump runs.

The tank pump is running backwards, or the fuel line is not connected to the pump, or there is no fuel getting to the tank pump.
 
I'm ready to burn this piece of crap to the ground, a car has never driven me so insane. It's possessed.
Everyone who has ever owned or worked on a 7 series has said this before.
If you remove the line between the main pump and the tank pump and test, and no fuel comes out of the line when the tank pump runs.

The tank pump is running backwards, or the fuel line is not connected to the pump, or there is no fuel getting to the tank pump.
This sounds like the easiest test to do. Disconnect the line underneath the car, then jump 12v to the tank pump and see what happens.
 
Everyone who has ever owned or worked on a 7 series has said this before.

I'm not surprised!

I pulled the hose from the pump itself and ran it, nothing came out. I was pretty sure that would be the case anyway, otherwise I probably wouldn't have done it that way to avoid the potential mess.
I'll be pulling the pump today and inspecting. Updates to come...
 
Wait a second, reverse polarity and try again. That works how i think it does, correct? Reversing polarity will spin the pump opposite direction?
 
Apparently that's how it works, never really thought about it until this thread. Apparently it's pretty common for cars to have a black positive and red negative... freaking Volvo...
 
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