[DopeStar 156]

My 76 DeVille has a fuel leak in the back by the tank that has gotten so bad the car has lost a lot of the fuel pressure. The leak takes a few seconds to start and only happens when the car is running. I also have reason to believe it's coming from the top of the fuel tank because if the car is parked on an incline it leaks from a different place, runoff. I was planning to jack the car up and crawl under there to look for anything suspicious, any reccomendations? I figure it has to be a line, but there's three that go to the tank according to my FSM.

-Fuel Delivery
-Evaporative Control
-Vapor Return

Which one of these could be the leak?

 

[DopeStar 156]

Think I found the culprit. Looks to me like it's the rubber hose but I can't get my head in there any closer to get a better look. How should I go about fixing this?

 

[Highway Star]

If you have enough room, you might be able to replace them with the tank in place. That's kind of a tight spot though. It's been a while since I pulled a tank out of one of those. Seems like there's a couple 9/16ths nuts that hold the straps on (and they're usually rusty as heck, soak with penetrating oil), then the tank drops down for removal. Much easier to work on with the tank out. Hopefully you can get do it without going to all that trouble. Make sure the car is supported extremely well, that's a lot of car to come tumbling down on you!

 

[DopeStar 156]

I actually took care of it tank in place and all. It was a very, very disintegrated rubber hose. Ran out and got some fuel injector hose and the leak is gone, however my shitty idle is still happening. From there I went ahead and changed the fuel filter and still the idle is very low. Judging by sound and feel I'd say in Park I gotta be getting something like 300 RPMs, it's bad. I'm out of ideas, what's next? Fuel pump?

 

[Highway Star]

If it's the original pump, it's probably time to replace it. Especially since you seem to be having a fuel related problem. At least it's not inside the tank!

 

[DopeStar 156]

If it's the original pump, it's probably time to replace it. Especially since you seem to be having a fuel related problem. At least it's not inside the tank!

Yeah I'm thankful for that. The FSM says to go at it from under the car. I guess it's just disconnecting a few lines and unbolting it from the engine. You think I killed it from running the car with a fuel leak?

 

[CaddyshackCadillac]

do these have fuel pressure regulators?

 

[Highway Star]

Yeah I'm thankful for that. The FSM says to go at it from under the car. I guess it's just disconnecting a few lines and unbolting it from the engine. You think I killed it from running the car with a fuel leak?

I don't think a leak would have caused a problem with the FP. Mostly age and use if it is indeed the FP causing your problems. It's a vital link in the chain from the tank to the carb. I replaced all the rubber fuel line sections on my '79. None were leaking, I just felt like they needed replacing after 30 years.

 

[greencadillacmatt]

I don't think they do. They are not fuel-injected, so the mechanical fuel pump just pulls more out of the tank as needed. Since there is no pressure (since the pump is sucking in the fuel, not pushing it) there should be no reason to regulate it. I am keeping the electric fuel pump on my '84 buildup, so I have to run a regulator to knock the pressure back down.

 

[DopeStar 156]

I figured with the line leaking as bad as it was (I'm talkin' I had a tap goin' on here) I figured it was sucking a lotta air and I figured it ruined the diaphram. The car runs just really low and it drives pretty good, seems to have some of its balls back with the new filter but it's that idle that's killing it. In drive on the brake the RPMs are at near stall it's so bad. Fuel pump's the only thing I can think of that's left....

 

[77CDV]

Is your idle screw on the carb set correctly? Because if the fuel pump diaphragm was disintegrating, the car wouldn't run properly at any speed. And the mechanical fuel pump is really a pretty simple beast, literally like one of those old kitchen water pumps back in the olden days.

 

[fleetwood76]

do these have fuel pressure regulators?

Hello.

In a way they have, but it is integrated in the fuel pump.

There is a bypass passage in the pump unit that continally returns part of the fuel to the fuel tank.
That bypass also returns fuel vapors that may form in the lines or pump under high operating temperatures.

The fuel pump is a sealed unit and is seviced only as a an assembly.

I have changed the pump om my car but there was no doubt that it was to blame in my case, because it went in two pieces and of coarse the car stalled immedeatly.

On the pump is it three hose(pipe) connections, one from tank, one to carb and one back to tank.

jolle

 

[DopeStar 156]

Is your idle screw on the carb set correctly? Because if the fuel pump diaphragm was disintegrating, the car wouldn't run properly at any speed. And the mechanical fuel pump is really a pretty simple beast, literally like one of those old kitchen water pumps back in the olden days.

Yeah everything on the carb is set correctly. This was an all of a sudden thing, just didn't run right one time I started it. I don't have any further fuel leaks and the fuel filter I just changed, so my next guess would be the fuel pump. It looks original with a considerable amount of rust on the thing. I'm starting to suspect a vacuum leak somewhere might be doing this as well. Is that a possibility?

 

[77CDV]

A vacuum leak will definitely cause idling problems. I have to look at the FSM to get the particulars, but I know a vacuum leak will screw up the idle speed, even if the carb is dialed in correctly.

 

[DopeStar 156]

It really sounds, more or less like a line popped off somewhere. It was really all of a sudden. Car was fine then I rolled up to a stop sign and it just didn't drive right.

 

[77CDV]

The FSM lists possible culprits as: faulty air cleaner snorkel damper door sensor or motor; split, kinked, or misconnected vacuum hoses; damaged or disconnected hot air tube to hot air stove; air leaks at carb mounting and intake manifold; bad ignition wires; sticking carb, choke or throttle linkage; misadjusted fast idle cam; flooding carb; faulty vacuum break assembly; misadjusted timing, idle, or choke; leaking EGR, PCV, or EFE valve.

Happy hunting! Finding vacuum leaks on these cars is a bitch.

 

[DopeStar 156]

The FSM lists possible culprits as: faulty air cleaner snorkel damper door sensor or motor; split, kinked, or misconnected vacuum hoses; damaged or disconnected hot air tube to hot air stove; air leaks at carb mounting and intake manifold; bad ignition wires; sticking carb, choke or throttle linkage; misadjusted fast idle cam; flooding carb; faulty vacuum break assembly; misadjusted timing, idle, or choke; leaking EGR, PCV, or EFE valve.

Happy hunting! Finding vacuum leaks on these cars is a bitch.

:crying: