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81 Eldo Fuel Pump Problem

Started by 76eldo, October 25, 2020, 08:16:19 PM

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76eldo

Saturday I spent the afternoon with Joe Caristo dropping the fuel tank on my 81 Eldorado and installed a fuel pump that I had saved from the fuel tank of an 85 Seville that I had saved because the car ran and had a digital dash like the Eldo.

We installed it and the car started right up and the fuel gauge registered 1/4 tank which seemed correct based on how much fuel was in the tank.  Took the car for a short ride and parked it.

This morning I went to move the car and it would not start, and the fuel gauge is registering empty.  Either a wire loosened up on reassembly or there is a blown fuse somewhere.

Is there a fuse for the fuel pump???

Thanks,

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

smokuspollutus

Brian, is the gallons remaining display registering E or " -- "? There is a difference, and " -- " would make more sense as that indicates an open ground for the sending unit and subsequently the fuel pump.

76eldo

I was wrong, this one has the standard display and the fuel guage stays on empty and the fuel pump is not running.  It worked fine on Saturday and stopped working on Sunday.  I am hoping that it may be a fuse, not a wiring issue at the tank.
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

TJ Hopland

What was the original issue that caused you to make the swap?

I have had used fuel pumps have issues with dead spots after sitting.   

Was there some sort of harness connector back there you can check to see if you have power?   Is there a reason you seem to be connecting the gauge and pump?  I don't think they are related electrically since I assume the pump has its own harness ground and the sender uses the tank ground?

I don't have my 81 book handy so not sure where the relay is for the pump.    That would be where I would go first to make sure there is power there then jump it out so you know you are getting constant power to the pump.   At that point you could try the bang on the tank trick.

StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

76eldo

The original problem was that the car would start and idle somewhat but would die as soon as you tried to rev it a little bit. It was not running right at all.
Then I sprayed a bunch of carb cleaner in the throttle body and it would run on that and would continue to run as long as you fed it carb spray and would rev like crazy.

So I decided that fuel flow was the problem. I changed the fuel filter first and there was no change. So I had another fuel pump and sender out of another tank that I had saved. I put 12 volts to the pump and it ran so I decided to install it in the eldo.

It started and ran after we reinstalled the tank. Fired right up and we drove it around the block. I parked it and went to start it the next day and it would crank and cough but would not run. Exactly like it did before we put the pump in.
Also the gas gauge was in E instead of the 1/4 reading it had the day before.

There may be a fuse that blew out but normally of a fuse blows there must be a reason.
If anyone knows which wire on the ECM switches on the fuel pump please let me know.
I need to be able to move this car around.  I’d like to put voltage and a ground to the pump to see if it’s working before I pull the tank again.

Thanks

Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

J. Skelly

#5
Brian,

What happens if you turn the ignition key on, but don't crank the engine?  You should hear the fuel pump activate (pressurize) for a couple of seconds. 
Jim Skelly, CLC #15958
1968 Eldorado
1977 Eldorado Biarritz
1971 Eldorado (RIP)

smokuspollutus

The fuel pump drive circuit is kind of complicated to write...

Pump fuse on TBI almost always runs the rear lights as well. So check there first, if you've got no brake lights or reverse lights you may get lucky...but for me of course its never just a fuse though...

The pump relay is in the relay center under the drivers side black hush panel. You should hear it click as TJ mentions (and ideally the pump run ;) ) for a second or two after turning the ignition on.

If the relay is clicking but the pump not running (and fuse verified good), take the big connector at the tank off. Probe each pin with a helper cycling the ignition on (after cycling off, have her wait a few seconds before turning it back on) Eventually one of those pins should light for about 2 seconds and then turn off. That's the fuel pump drive pin. If it lights: bad pump. If it doesn't light, an open in the wire between the pump relay and the big connector.

If the relay is not clicking at all, you have a control problem which will be more work to sort out than it sounds like you're interested in, and at that point I would jumper the 30 and 87 holes on the relay and get the car where you need to go. Do not try to trigger the relay to energize by messing with the ECM.


TJ Hopland

Don't know where my 81 book is and I know I don't have the 81 electrical manual so best I can do is the 80 which I would think is going to be mostly the same assuming we are talking about the DEFI engine. 

The circuit is a little different than I was expecting so good thing I looked it up.    Power comes from fusible link 'A' with also feeds the 'body fuse 20a' that looks like among other things runs the auto door locks.   First thing it hits is the 'fuel pump relay' which as noted is under LH side instrument panel at accessory relay panel.   

Where it gets different than I expected is that relay feeds more than the fuel pump.  It feeds 3 fuses in a mini fuse block that doesn't appear to have a location given.  Its apparently got 4 fuses in it.  One is the 'crank fuse 3a' that gets fed from the key and then signals the ecu.  2nd and 3rd fuses that get fed from the fuel pump relay are also 3 amps and feed each injector.   Red for one and White for the other,  ground gets modulated by the computer over blue(for the red) and Green(for the white).    4th fuse is for the fuel pump 10a and is a blue wire to the ecu.

That blue wire from the fuel pump fuse taps off with one to the ECU then the other through 2 connectors before changing to purple then 2 more connectors before back to blue apparently near the pump at which point there is a tap off that goes to the ELC height sensor.   At this point I'm not going to look at that page but I can if we need to.   Ground for the fuel pump isn't specified with a number which is sort of odd since most of the rest seem to be identified. 

The fuel pump relay is being told to engage from a green white stripe wire from the computer.  Pin 10 but I would have to dig deeper to figure out which connector its in, looks like there are 3 on the ECU.   

So I would say look for the 'mini fuse block' and see if you got power at the 2 injector fuses and fuel pump fuse.   If no then go look for the relay.   If yes including the fuel pump fuse then you have at least 4 connectors on the way back to the pump.    I don't see any mention of the fuel level stuff being involved at all. 

Just for fun I just looked at the ELC diagram.   Not sure why but that fuel pump power wire just goes into the module, one of only 5 wires.  Pin 2 grounds the vent solenoid, hot comes from LTR fuse.  Pin 3 sends a ground to the compressor relay which is up front and its power comes from GA/Trans fuse.   Pin 4 is grounds.  Pin 5 is that fuel pump one.   Pin 6 is power from the body fuse.  I didn't read every word of the text but didn't see any mention of what that fuel pump signal does for things.  System needs the key on to power the GA/TRANS fuse to do anything so not sure why it cares if the fuel pump is running or not.    I only mention all this because if you have a blowing fuse it could be related. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

76eldo

Wow TJ and Smoke. that’s a huge help.
I’ll dig into this tomorrow. It was raining all day today.

Thanks and I’ll report back.
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

81 BENY Biarritz

Here is relay convenience center layout for the 81 Seville/Eldo.   It comes from the 1981 Cadillac Electrical Troubleshooting Manual and shows the fuel pump relay and fuel pump fuse.  It is located facing down toward the floor on the left side of the steering column.   If you need the drawing that shows the fuel pump circuit let me know and I can attach it.   Can't seem to find one drawing that shows all the pinouts in the connector above the fuel tank at the filler inlet but can also send the two that show the sender and the ELC connections through it if you need it.   Hope it is helpful.  Dave

81 BENY Biarritz

Brian, here are the other drawings from the 81 manuals that you might want.  If you want to try to run the pump by jumping the connector (C347) at the tank fuel filler it appears to me that you would put +12V on Pin C (light blue wire which is used for both the ELC and fuel pump supply) and -12V directly to the car frame.  It looks like the fuel pump itself is grounded through the tank mounts to the car frame.  As for the fuel sender, the black wire 150/151 on Pin D is used for the ground on the fuel sender and the pink wire 30 on Pin A is connected to the power supply coming from the gas gauge.
Make sure you try this with the connector completely disconnected and that you are connecting only on the tank side as otherwise you will create a back feed to the ECM if you connect on the wrong side.  I would only do this with a helper to watch what is happening under the hood at the throttle body just for safety's sake.   Good luck and be please be careful.   Dave

76eldo

Beny,

Thanks for the additional info.

Unless the pump is bad, I should be able to identify the problem.  Will be looking at fuses hopefully later today.

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

TJ Hopland

Interesting they did make some changes to the circuit between 80 and 81.  Still looks to be doing the same thing just a different feed and relay for the injectors but the injector relay gets run by the fuel pump circuit.   I also notice there is a test connector in the 81.     Does the 81 manual say why or what the fuel pump signal does for the ELC?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason