News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

** 1981 eldorado 6.0 fuel problems! Any information will help!

Started by Jonathan Johnson, March 26, 2023, 03:13:00 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Jonathan Johnson

I was told to post in technical forum so I hope I'm doing this right. But I have a 1981 Cadillac Eldorado 6.0 I have zero fuel pressure and I have no power at the pump I have good ground though, also one thing I noticed were many of the relays and fuses were replaced and also there were two spare ecms in the trunk and the ECM in the car is just hanging down also when I go to turn the car off the ECM just keeps running and will kill the battery I can hear it buzzing, it starts but will not run it'll just crank and crank I can get it to run with starting fluid I'm hoping I can pick somebody's brain and they can help me out thanks everyone for reading my message have a great day
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

TJ Hopland

Hopefully the Mods can clean up the multiple posts to make this a little less confusing to all.  Here is my reply from one of the other places you asked the same questions:

What pump are you talking about? The fuel pump?  If so that explains the lack of fuel pressure. Where and how were you checking for power?

What do you mean by replaced relays and fuses?  They are cleaner and different than others?  Or did they modify things and use completely different model relays and or fuses?

Do you have a factory service manual?  Even without this problem its a good thing to have but this issue I don't think can be solved without one.  There are several on ebay right now ranging from $5-$40. They have a pretty plain silver cover and say Cadillac 1981 Service Information.

What other systems have you checked?  Do you know how much gas was/is in the tank?  How does it smell?  Can you safely get a sample to see condition its in?  If its really nasty it may be a good thing the pump hasn't run yet.  There were places that had ethanol 20 years ago so if the car happened to be from one of those places things could be pretty nasty.

Later I will try and look at my 81 manual and see what the fuel pump circuit looks like so we can help you keep troubleshooting while you are waiting for your own copy of the manual to show up.  You do want to make sure the fuel isn't too nasty before we get the pump going.

Even if we get it going you may have to drop the tank anyway because at this age even if the pump is good the rubber line inside the tank that connect it to the sender will fail sooner than later if its not already failed. If there are any signs that the fuel is bad it may be worth just dropping the tank to clean it out and replace the line and test the pump while you are in there.   
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

TJ Hopland

My 81 manual seems to have gone missing but I do have the 80 which I assume is gonna be pretty close.  If things don't seem to match that may be why and we will have to wait till someone can lay their hands on a 81 manual.

Fuel pump power path is a fusible link from starter that taps off to a 20 amp 'body fuse' that among other things feeds the ECM after that tap it continues to the 'fuel pump relay'.

When the ECU activates the fuel pump relay that powers up a 'mini fuse block'.  I don't see a location listed for the mini fuse block but its got 4 fuses, 3 amp 'crank' that is between the key and ECU, this is not powered by the fuel pump relay.  The relay powers 2 3 amp fuses that run to each injector.  The 4th fuse is a 10 amp that leads to the fuel pump. 

If you can find that mini fuse block it should be easy to probe those fuses to see if you are getting any power to those circuits.  If you do then its not likely a computer issue.  I do see 4 connectors between that mini block and the fuel pump and note that the ELC height sensor also gets powered from the same wire at the back of the car so if someone has been messing with that it may be related.

If you can't find the mini fuse block you could check for power at the injectors.  The fuse side is red for one and white for the other,  blue and green are the grounds that the computer modulates.  Fuel pump relay is in the accessory relay panel under the dash. 

At this point I would not start jumping out things out and sending power places till you have a better idea what has been going on with this thing.

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

TJ Hopland

Further notes....

That fusible link power wire body fuse to the ECU isn't the main power to the ECU so don't assume the ECU has power based on that.  Main power has its own fuse.  ECU appears to be monitoring all sorts of power inputs.

ECU only runs the fuel pump for 1 second with key on unless it senses the start signal which is that other fuse in the mini block.  Fuel economy indicator operating is the step in the sequence before the ECM 'turns on the fuel pump relay for continuous operation'
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

Jonathan Johnson

Thanks for all the info just to answer a few of your questionst I have dropped the tank got the old gas out of it with new gas, I also replaced that rubber neck at the fuel pump and I also replaced the fuel pump itself. It's funny you mention the 81 manual. I ordered a Chilton repair manual and a 81 Grey cadillac manual both yesterday. Off of ebay. BTW I'm checking with a test light. I know that's not the best method but I'm getting ground at the 2 ground wires at the pump but no power. And when I push the valve by the tbi there is no gas what so ever complete dry! L
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

Maybe I should explain better, there is a metal fuel line going to the tbi, and there is a valve you can put a fuel pressure gage on. When I push that valve there is zero gas, completely dry. Sorry for the confusion.  I wanna get this thing going so bad
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

One other thing Tj , the darn ecm won't turn off. I have to unplug the battery or it will be dead.
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

TJ Hopland

If you can cancel or return the Chiltons I would.  About the only use it has is maybe the pictures of spark plugs and if you have a really wobbly table that needs a thick shim.  Its not even thick enough to use as a wheel chock. Covers way too many models and years to be of any real use.  The factory manual is by far the best. When do you expect the official Cadillac manual to arrive?

Knowing you have the tank clean and its got a new pump and internal lines is good information.  It also makes total sense that if you are not hearing the fuel pump run that you don't have any fuel pressure.

Based on what the 80 manual says the fuel pump relay should click on for one second when you turn the key on.  You may not be able to hear the relay or even the pump because there will be other relays clicking at the same time and 1 seconds isn't very long.  Later years maybe even 81 they made that time longer like maybe 5 seconds.  

If you have not found the relay or mini fuse block maybe hook your test light between an engine ground (not the blue or green) and either the red or white injector wires.  Set the light up so you can see it when you turn the key on and see if the light comes on for a second.  The injector connectors have a release tab you squeeze kinda in the center then the connector pulls straight up off the injector. 

If you are getting this initial pulse then try cranking and see if the light stays lit as you crank.  Let us know the results of this test.  No light gives us a completely different direction to go than if you are getting the light but still no pump. 


On the ECM staying on thing how do you know its the ECM?  Are you unplugging its connector(s) or removing its fuse then the battery doesn't die?   That may be a clue, not sure to what yet but I also want to know what makes you think its the ECM itself.  
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

Jonathan Johnson

Ok so I know it's the ecm because it was already unbolted and just laying on the passenger carpet, and when I lift it up and put it to my ear you can hear it buzzing, and that sucks to hear about the chilton...I only payed 17 bucks so not horrible, but my service cadillac manual should be here the 1st of this coming month. And when I turn the key on I put my ear by the relays, I don't hear anything unfortunately,  and I'm in my early thirties so my hearing is still pretty decent.
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

The only thing that really confuses me,  is why the heck is there so many ecms in the car 2 spare ones in the back and the one in the car is just laying unbolted on the carpet lol.
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

35-709

Sounds like someone went to the junk yard and collected several hoping to find one that works in that car.  Just changing out parts in the hopes of getting lucky really doesn't work well with the more complicated and sophisticated F.I. systems (and now ancient) you have in your car.  A methodical, knowledgeable, approach is needed with the right reference materials.  And I agree, Chiltons is not it.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Jonathan Johnson

1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

TJ Hopland

One of the problems is at this point is we don't know if any of the ECU are the right one for the car or are any good.  Even if they were all 'good' we don't know if they should work in this specific car. 

Were you told anything about if it 'ran when parked' or if it was parked because of an issue?  Did they give you any clues what the issue was?    Any clues to if all the ECU's got put in there 20 years ago?   Like is there any papers or packing that may have dates on em?   

Are you fairly sure you have found the fuel pump relay?   What was the deal where you said some had been replaced?  Replaced with stock ones or did they modify things to install a different style of relay?   Are there wires and things that don't look factory?
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

Jonathan Johnson

So yeah there are some old relays, by the looks and some newer Bosch Shiney black relays where the fuel pump and something else I can't remember at the moment are. But he didn't tell me much super super nice guy he said he bought the car like that. He said he drove it for a year or 2 then parked it in his garage and it sat since 2003. He told me it needed a fuel pump, but I think there's more going on then I was told. He was 80 year old farmer outside of Rochester mn, either maybe he forgot or just isn't being totally upfront
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

So tj, I seen on ebay they have a remnafactured ecu for around 200 bucks. It says it will fit in my eldorado but my thing is how do I know if it will pair how it supposed to with my car if you know what I mean.
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

Oh I forgot to tell you, I'm disconnecting the battery once I finish tinkering with it. That's How I stop the ecu from killing my battery.
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

TJ Hopland

I would not buy another ECU just yet, you may have 3 good ones now for all we know. 

So the guy you bought it from didn't say anything about the spare ECU's?   He bought it 22 years ago and drove it 2 years till it quit which he thought was due to a fuel pump issue?   Just making sure we know what you know.

Take your test light under the hood and disconnect the fat pink wire from the distributor cap, hook one end of your test light to that wire and the other end to a good ground.   See if the light goes on and off with the key.  There is a tap off that wire to the ECU which I assume is the one that tells the ECU to power on so if that stays on something is going on with the key circuit keeping it on.

I don't have any sort of diagram of the ECU's internals.  All I got is a big blue rectangle showing pin numbers and wire colors and what those go to so for the most part can only guess what's going on inside.  Ecu also gets a crank signal from the key.  Oddly my diagram does not show the starter solenoid itself so I don't know if that taps off this signal wire or of the ECU actually triggers the starter solenoid.

I don't know what would be on one of these ECUs' that would make any noise.  The diagram doesn't look like there would be any relays internally.  Everything you would expect to have a relay appears to have an external one.   Its kinda curious but not for sure something I would be worried about yet.   
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

Jonathan Johnson

I'm going to go outside now and do what you told me to do, Thanks again Tj!
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

Hey tj so on my distributor there are 3 separate connectors and one of the connectors is a single wire and it's orange, but the other connectors have multiple wires,  so I'm assuming the orange single wire connector going to the disturbtor? Also I seen something really weird here's a picture, it's the 4 prong connector going to the disturbtor looks all messed up
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

I'm trying to figure out how to send you a picture sorry
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls