Fuel pump for a 1979 Eldorado?

[mcgreggor]

Hey everyone, just a quick question to those, who know old Caddies pretty well. I've got a 1979 Eldorado, and it won't get gas to run. All the hoses seem to be fine, and I assume the problem is with teh fuel pump. Now, how do I determine that that's really the weak spot? Is there any sort of troubleshooting step-by-step guide or something I should check?...
And also, does it make sense to try to fix the pump? Thanks.

[35-709]

FI or carburetor?  If it is the fuel pump with either it will need replacement, they are not rebuildable.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050890.m570.l1313.TR0.TRC0.H1.X1979+Cadillac+shop+manual.TRS0&_nkw=1979+Cadillac+shop+manual&_sacat=6000

If it were me, I would grab this one quick before someone else gets it --- a wealth of information.

https://www.ebay.com/itm/1979-CADILLAC-Shop-Service-Repair-Manual-Set-Fisher-Body-w-Electrical-diagrams/152793247116?hash=item23932fed8c:g:mw0AAOSwT~ZZuVAo&vxp=mtr   

[TMoore - NTCLC]

Which engine is in your car?  Is the 350 Fuel Injected engine? 

Let us know which one, and we can help troubleshoot.

[TJ Hopland]

79 Eldo standard engine was the 'Seville' multiport EFI.  Option was the diesel, he said gas so I assume its not the diesel.   

Bruce Roe could confirm but I believe these still had the dual pumps, one in the tank and one on the frame.    If it is still the dual pumps then it will also have the common issue of damage to the fuel pump circuit inside the ECU so you could have a pump that was going out and damaged the ECU on its way out so now neither pump runs.   I have not done it but it sounds like an easy repair for someone that knows electronics and then you rig up an external relay to prevent that from happening again. 

If its been converted to a carb at some point in its life look up a 79 Toronado, those never had an EFI option so that would be the correct fuel pump for that engine with a carb.     

[bcroe]

Takes a lot of manuals to cover that car.  In addition to those listed above,
get 1976 Cadillac EFI Diagnosis Service Manual, which is the best source on
70s Cad EFI.  Some on Evil bay now, try 182843998432 and others. 

The 79 Eldo EFI has a pump in the tank, another in the frame.  The fuse for
this model is in the fuse block.  You should hear the pumps run for a second
or 2 when the ign is turned on; should continue if engine is turning; check for
39psi fuel pressure when cranking.  The ECU (under glove box) controls the
pumps, and often is damaged by the pump current.  The Nov-Dec 2010 Self
Starter page 24 describes avoiding that problem or sometimes fixing it; its
also on my PHOTOBUCKET and I have a kit for the fix.  If the ECU has an
internal failure, send it here for a repair. 
Bruce Roe CLC # 14630  79 Eldo owner

[mcgreggor]

Thanks for the replies, folks, and I am sorry that could not reply sooner.
It is fuel injected, neither carb nor diesel.
Good to know that one won't repair it, will then search for the new one prior to disassembloing everything...

[mcgreggor]

And one more point, folks, what does it mean - inline? When talking about the fuel pump?
It means that it goes inside of the fuel tank?

[TJ Hopland]

Stock it had both, one inside the tank which was low pressure then there was one on the frame which was the booster to give high pressure.   The frame one is often called inline. 

Bruce just recently installed a newer design in tank pump to eliminate the frame one.  He can fill in the details like what sort of modifications were needed.

[bcroe]

It is fuel injected, neither carb nor diesel.
Good to know that one won't repair it, will then search for the new one prior
to disassembloing everything...   

Don't buy any parts or take it apart until you do tests.  See if you hear the
pumps run when ign is turned on.  If yes check fuel pressure.  If no check
for pump power, problem might be traced to ECU.  Bruce Roe

[T.Skytte]

Hi all,

Old thread, I know..
I have the opportunity to buy a NOS ACDelco external fuel pump. But it's like twice the price of the most expensive Delphi they have on RockAuto..
I would like to keep things as original as possible, but just worried that a pump that has been sitting on the shelf for perhaps decades might be degraded in some way? Anybody have experience with this? Do you think it would be ok?

I need to replace my external pump as it has developed a fine crack so is dripping a little...

If not the ACDelco, which of the ones on RockAuto would you choose?

https://www.rockauto.com/en/catalog/cadillac,1979,eldorado,5.7l+350cid+v8,1025941,fuel+&+air,fuel+pump,6256

Spectra Premium SP1252
Carter P74015
Airtex E2315
Delphi FD0011

The PSIs they deliver seem to vary quite a bit, worried that they might deliver too high pressure compared to original?

Thanks and Best regards,
TS

[bcroe]

Don't buy any pumps till you check the fuel pressure, there is a port on the
rear of the fuel rail.  If the pumps run, the trouble is more likely a bad ECU
not giving enough gas, most frequent cause is a failing MAP.  Can be repaired. 

Another approach is put some gas down the throttle body and see if it will
start for a few seconds.   Bruce Roe

[T.Skytte]

Thanks but in this case the pump is dripping because it has a thin crack.
The car runs just fine, only issue is the pump is dripping a little. Just might as well replace it as it will probably eventually fail completely.

What do you think about buying a NOS pump? do pumps deteriorate with time sitting on the shelf?

Much appreciated.

Best regards,
TS

[bcroe]

My opinion is a modestly replacement is just as good as an outrageously
priced NOS (if you find one).  That dual pump setup is a troublesome
kluge left over from carb electric pumps.  My 79 Eldo has been converted
to a single in tank mounted high pressure tank.  Actual fuel pressure is
controlled by the pressure regulator, not the pump. 

Another issue in my opinion is the vent and return line.  The fuel supply
line is typically 3/8 inch, fine.  In carb days a 1/4 inch partial return
circulation line was added to help with vapor lock.  Then a line was added
to vent to emissions equipment, apparently made 5/16 inch to avoid
mixing any of them up.  My 79 EFI Eldo followed this plan.  Trouble is
that with EFI and a fuel pressure regulator, almost ALL the pumped fuel
must return thru a far smaller line when idling.  I revised it so the 5/16
inch line returns fuel, and the 1/4 inch line is used for venting.  Bruce Roe

[grunner]

I would like to get more details on installing a non stock hi pressure fuel pump in 79 eldo... previous entrys indicate that bcroe did this.... thanks....grunner .. bill grun

[79 Eldorado]

Hi Bill and welcome to the forum,
Take a look at this other relatively recently updated thread. Bruce answered the same question there. He explains generally what he did but also explains why he doesn't want to try to get into a step-by-step instruction.

I would read through this entire thread as it's only a single page and has good info in it:

http://forums.cadillaclasalleclub.org/index.php?topic=160362.msg465204#msg465204

Hope that helps,
Scott

[bcroe]

I would like to get more details on installing a non stock hi pressure fuel pump in 79 eldo... previous entrys indicate that bcroe did this.... thanks....grunner .. bill grun.

bill grun, I today sent you a long email on the subject, hope you got it.  Bruce Roe