1970s 1978 Seville: In Tank Fuel Pump Died

[Gary Christensen CLC # 21112]

I finally got the dash back together after a bunch of under-dash wire fixing -- driven initially by a loss of power to my in-tank fuel pump -- and happily had a running car again, for about 2 miles.  Another *!@# tow...

My in-tank fuel pump (which is how the car has worked for years after a switch to a carburetor) seems to have died.  I ran a wire directly from the battery to the pump connector to validate that my wiring wasn't to blame and the pump didn't come on.  Previously, my running a wire along the side of the car from the battery was how I was moving the car around while I sorted out the electrical problem that had sapped power from the pump.  That the direct line now no longer lights up the pump makes me assume that the pump has now completely died.

I'm pretty discouraged, to say the least!

Rather than dropping the tank and removing/replacing the pump, I'm considering simply adding a new electrical pump outside of the tank.  The idea would be to pull fuel through the old (and not operational) in-tank fuel pump.

Does that sound like a simpler solution than dropping the tank?  I don't have a lift which makes under-car work hard and I'm frankly intimidated by the idea of dropping the tank.

Thoughts?

Gary

[smokuspollutus]

If the car isn't that rusty I would drop the tank. Actually I would regardless.  It's not that difficult to do and a lift is definitely not necessary. In-tank pumps are quieter and longer lived than external.

If the tank is full (they always are when the fuel pump dies), a cheap siphon is your friend. Possibly powering the fuel pump while whacking the tank with a rubber mallet might shock the pump past the dead spot and run long enough to drain the tank with the supply hose disconnected.

[TJ Hopland]

I too would drop the tank.  Pretty much every pump design but the engine mounted mechanical pumps suck at sucking so if you have to use one you want to do everything possible to give it the best chance of working.  Drawing through another pump even if its designed to do that with minimal drag is still going to cause some drag.  What if what killed it is some debris jammed in it?

If you are running a carb why not install a mechanical pump?  Or did they do something like not install the cam or tap the holes on these things?

If you are staying with electric I think I would pick up a pump for one of the TBI engines and fit it to the existing sending unit.  Seems like some of our resident EFI guys was working on fitting a single high pressure pump for the EFI?  Maybe they can share what issues they ran into so you could figure out if the TBI pump would still have those issues.  TBI's only ran at 13psi so maybe a smaller pump than ones that could do 30+?  Probably very similar to whats in there now since it was just being used as a lift pump. 

[Gary Christensen CLC # 21112]

Thanks guys for the advice.  I guess I'll bite the bullet and drop the tank.  I need to find a replacement in-tank pump for my Seville.

There's only 2 gallons of gas in the tank.  I had previously siphoned most of the gas out of it when I thought I would have to drop the tank originally -- before I realized that my original problem was electrical.  I had put a couple of gallons back in so that I could get it started and let it idle a while after I fixed it.  I was on my way to the gas station when it died...

[TJ Hopland]

Hopefully Bruce or who ever it was will be along soon to talk about or point you to the thread where they were replacing the in tank pump with something more modern.  I'm almost positive they were doing to to keep the EFI going and it wasn't a perfect solution but like I said maybe a lower pressure pump would be a closer fit. 

If in tank isn't practical then hopefully there were pics of the sending unit so you can get an idea what will be needed to bypass the pump if that is decided to be the best route.  Also probably Bruce will know if the fuel pump cam is still in these engines.  I can't remember is the olds just a bolt on the front of the cam unit like the big cads?  If a mech can be bolted on doing that and bypassing the pump in the tank is likely the best route.  Eliminates other issues like how you are controlling the pump.

I have been screwing around with 'aftermarket' EFI for close to 30 years now and I would say about 73.29457% of the issues many people have are related to inline electric pumps.  With a carb you get a slight buffer because of the float bowl but if you loose prime you are still in trouble just a few seconds later than you would be with EFI.   

[bcroe]

Pull the tank, it is regular maintenance here.  Here
is my 79 in tank pump in 2017, the special submersible
rubber hose sheared.  Yours by now is a lot older. 

Yes the Olds still has the pump cam on the cam shaft,
you can remove the plate and insert a mechanical pump. 

Bruce Roe

[Gary Christensen CLC # 21112]

Thanks Bruce.  The whole unit was replaced at CPR when I bought the car, 4 or so years ago.  The old one was a total mess!!  Because it was new and I haven't put that many miles on the car, I'm surprised that the pump died but oh well.

On every Cadillac I own, the problem is almost always the fuel pump!  I always carry a spare in the trunk.  Of course replacing them is easier on the older cars.

Thanks for the help!

[TJ Hopland]

That really looks like what they were using later.  Just a quick look and it seems like there is pretty much one pump GM used on most everything through the 80's. 

Since you are running a carb seems like going to the mechanical pump would be the way to go.  This place looks like they have a sock filter and the pick up hose you could use to eliminate the pump on your original sending unit.  I don't know the place its just the first thing that came up that didn't look like junk.
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