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1973 DeVille, 1975 Hearse
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Discussion Starter #1
I just bought a '79 Eldorado that's been sitting for quite some time (probably close to twenty years; the "next oil change" sticker is dated 1998 or 8,000ish miles and the odometer is still under 7,000). The gas tank's been cleaned out, so that's taken care of. However, the fuel pump near the rear driver's wheel is making a load buzzing noise. I suspect the fuel filter is probably gummed up, so I'd like to replace that before I go replacing the pump to see if that takes some stress off it and makes it quiet down. That being said, I can't find the stupid thing. The car is fuel-injected.

I saw something that might be hiding a little fuel filter, but I can't get it to come apart. And it looks to be attached to some delicate parts that I'd hate to break. So I figured before I tried anymore, I'd see if I was even headed in the right direction. The thing I'm referring to is this:



I've seen a couple people say the fuel filter is near the rear driver's wheel, but I think they may be mistaking the pump there for a filter, because I was unable to locate a filter housing in that area. One video on YouTube even went as far as to call the big metal canister that I'm sure is a pump the fuel filter. RockAuto and Autozone both show the car taking what appears to be a regular little filter that you would normally find right by the carburetor, so I don't think the car has any funky big canister filters or anything like that.

If someone has one of these cars and is able to snap a photo of the fuel filter location, that would be extremely helpful.


As a side question, I think I'm going to pick up a manual for this car since it's been sitting so long and will probably need a little things done as I start to drive it, is this the manual I want? While searching I found a couple different types, and I want to be sure this is the proper GM service manual for mechanical/electrical components before I buy one.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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20,227 Posts
looking at the description of the fuel filter elements -
it is NOT a thumb-size filter -

the filter element is 3.4" tall - and a little over 2" diameter -

---------------------

this car probably has 2 fuel pumps -
a low-pressure/high volume pump in the gas tank -
and a high pressure external pump - usually mounted in the frame rail -

I suspect the fuel filter would also be mounted in the frame rail -
after the high pressure pump -
 

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1973 DeVille, 1975 Hearse
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36 Posts
Discussion Starter #3 (Edited)
Ah, of course the particular one I was looking at on RockAuto didn't list the dimensions. Guess I probably should have clicked on a couple other ones there.

That was my understanding about the fuel pumps, too.

I'll crawl under the car again tomorrow, take another look for a big canister, and report back my findings. What baffles me at the moment is that in this video, the spot the guy points his camera when he identifies the fuel filter is the spot where my external fuel pump is. I suppose it's conceivable that someone rearranged things in my fuel system, because I can tell the fuel system had to be cleaned out and parts replaced once long ago from sitting for years on a different occasion.



Found it. I'm surprised I missed it before, because it's literally right next to the external fuel pump. Here's a picture of the location:



It looks like it's supposed to unscrew like an oil filter, but I had no luck with that. I'm mid-way through taking the old one off, but took a break for dinner. I've got to say that this is by far the stupid fuel filter change I've ever had to do on a car.



It was supposed to unscrew like an oil filter. After I got it off, I was able to get enough leverage to get it apart. Some goopy brown oily gunk came out, so I'm glad I switched it. However, my fuel pump is still buzzing away. Interestingly, my fuel filter is not like the one in the YouTube video above. I thought it was stated somewhere that the video was of a '79 Eldorado, but maybe not.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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Did you verify the in tank fuel pump works? You have 2 fuel pumps on this car. Frame rail and one attached to the gas tank sender with a filter screen attached commonly called a "sock" Same arrangement on the smaller Seville. Same pumps but smaller spray pattern injectors on the 350 in. Seville.
 

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1973 DeVille, 1975 Hearse
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Discussion Starter #5
Yes, the one in the tank was replaced with a new one when the tank was cleaned out a couple weeks ago.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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I say again, have you verified the in tank pump works? If it doesn't turn on, the rail pump will be loud.
 

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1973 DeVille, 1975 Hearse
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Discussion Starter #7
I've not personally verified that it works. It was installed by the person I bought the car from, whom I've know for years and has been a mechanic for over forty years. So I'd assume he installed it correctly and tested it. I can check it again myself, though. What would be the process for that? Disconnect the fuel line at the tank, crank the car, and see if gas sprays out?

I should also mention that the clamp for the hose before (as in behind) the external pump was broken (now replaced), and gas would leak out of that line pretty steadily after the car was shut off. Would that be a good indicator of pressure in the line, and thus a working tank pump?
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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I would disconnect the rail pump electrically, then place my ear over the fuel filler pipe while someone turns the key to "run" not start. You should hear the pump buzz for a few seconds. Never let raw gas come out of a tank!! The fuel dripping from the hose is not valid. A fuel injected engine has a supply hose and a return fuel hose. You probably replaced the return hose?
 

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1973 DeVille, 1975 Hearse
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Discussion Starter #9
Is there a fuse for the rail pump specifically I can pull? The connection on it looks pretty old and brittle, and I can't see tampering with it ending well.
 

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Eldorado
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There is a 20A fuse in the block marked "EFI". Bottom row of
3, center. It supplies both the ECU and the fuel pumps. Those
cars tend to burn out the ECU pins supplying the pumps, but you
can avoid that by installing a relay per my PHOTOBUCKET first
album, or get my kit.

If the car is original you need to replace all the EFI rubber (running
40 psi) from the injector O rings back to the tank hoses.

If you really want to know what can go wrong with a 79 Eldo, email
or phone me who has owned & repaired mine for 20 years; I also
repair the ECUs.

http://s93.photobucket.com/albums/L71/bcroe/

click on an Album
click on a picture to enlarge + description

BRUCE ROE CLC # 14630 [email protected] Phone 815 234-8039

For maintaining 70s EFI cars I recommend having the
blue & white book: CADILLAC ELECTRONIC FUEL
INJECTION DIAGNOSIS Manual 1099984 / S-1453.
Its usually available on EBay, i have some extra copies.
Get a paper book, not a CD.

In order to properly service that car, should have at least
the 1979 CADILLAC SERVICE MANUAL, Cat No. S-1640.
Another, 1979 ELDORADO ELECTRICAL TROUBLESHOOTING
MANUAL. If you can't get that, very similar is 1978 SEVILLE
ELECTRICAL TROUBLESHOOTING MANUAL, Cat No. S-1556.
 

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Eldorado
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Did you verify the in tank fuel pump works? You have 2 fuel pumps on this car. Frame rail and one attached to the gas tank sender with a filter screen attached commonly called a "sock" Same arrangement on the smaller Seville. Same pumps but smaller spray pattern injectors on the 350 in. Seville.
Actually the 79 Eldo uses virtually the identical engine as the 79 Seville; the only
differences are for the front wheel vs rear wheel drive and bodies. Bruce Roe
 

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1973 DeVille, 1975 Hearse
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Discussion Starter #12
Very interesting stuff, Bruce. Nice color choice on your Eldorado. I have an LTD that's painted a similar cream yellow, and get a lot of compliments on the color.

As I get into working on the car, if I have any questions I'll shoot you an e-mail. I just nabbed a service manual off of Amazon.

In all likelihood, I'll convert this car to be carbureted. I've never cared for fuel injection. I also have a 1980 Riviera with the 350 Oldsmobile engine that's carbureted, and I've been very pleased with its reliability over the years.
 

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Eldorado
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Very interesting stuff, Bruce. Nice color choice on your Eldorado. I have an LTD that's painted a similar cream yellow, and get a lot of compliments on the color.
As I get into working on the car, if I have any questions I'll shoot you an e-mail. I just nabbed a service manual off of Amazon.
In all likelihood, I'll convert this car to be carbureted. I've never cared for fuel injection. I also have a 1980 Riviera with the 350 Oldsmobile engine that's carbureted, and I've been very pleased with its reliability over the years.
I was the second owner, but I would have chosen that color and those wheel covers
instead of fakey wire wheel covers. In my opinion the car runs a bit better with EFI,
but it can be troublesome at this age. I think the 79 Eldo 5.7L was lower compression
than the 79 Toro/Riv, which required the best premium when I owned them. A carb
will work; its easier though to fix the EFI. Certainly make sure the original timing
chain set has been changed out before it strands you. For more performance put
on a better exhaust with a monolithic cat; replace the 2.2:1 final drive with a 2.41 or
2.73, and a 403 Olds is a bolt in with a carb or retune the EFI. good luck, Bruce Roe
 
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