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

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

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Jonathan Johnson

Hey Dave could you help point me to the direction of the correct ecm off off ebay? Even though that may not be the issue I'd still like to buy a reman, due to the fact I'll then feel better about taking it on long drives and then I'll have  peace of mind knowing a have a good one in there. I got such a deal I planned on putting money in her.  Thanks
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

81 BENY Biarritz

Hi Jonathan, I don't think that I can recommend any replacement ECM unless it is a remanufactured GM/Delco one as I have never had to replace mine and I don't know what the differences are between the two versions (if any).  I have collected a couple of spares from some parts cars for future use on mine (just like your car's precious owner had) although I have never tested them...yet.  You have the correct Part # for your car based on the VIN that you sent so maybe do a search using that # to see what you come up with.

Just had a look at my build sheet to compare VINS out of curiosity and our cars are about 1200 builds apart with mine being later down the line.  That is fairly close based on 20,000 built that year (I think).  Mine was built on Mar 27 if that is of any interest to you.  Have you looked for your build sheet by any chance?  If it is still there you might find it taped to the back of one of the carpeted cardboard trunk liners along the rear fenders in the trunk.  I found one for both of my 81's there.

Back to your fuel pump problem.  I was looking at the electrical drawing that I had sent you already and noticed what looks like a test point on the "light blue" wire #120 that is located between the fuel pump relay and the fuel pump. It indicates that it is "taped to the harness" near the LH bulkhead connector in the engine bay.  I went to have a look on mine and the only thing I could find in that area was what looks like a green wire with green wire connector.  Given there didn't seem to be anything else that might be it in the area I put a volt meter on it and lo and behold it read 11.XX volts for about one second each time I turned on the ignition switch to the RUN position and then immediately went to zero.  Please have a look at the picture to see where it is.  You can test for voltage there in the same way as I did or if you isolate the ECM and the injector connections I would guess that you could put 12 volts on it and "hotwire" the fuel pump.  Please only do this if you understand all the connections as I wouldn't want you to damage your ECM or injector circuit with a back feed.  Also as confirmed by testing on my car the fuel pump only runs for ONLY a second or less and I couldn't hear the fuel pump relay click at all when I was specifically listening for it.

Also found a really good troubleshooting section in the manual which I will scan to you in a bit.   Dave

81 BENY Biarritz

Looks like you can't attach anything to a "Quick Reply" so here is the picture.  Dave

20230328_184307[1].jpg

Jonathan Johnson

Thanks Dave soon as I get home I will do that and also look for the build sheet!
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

79 Eldorado

To me it sounds like you guys are getting close. I'm still interested in the following from what I read:
-Are the 3 fuses mentioned all still good?
-When the key is turned on does the signal terminal on the relay read 12V for 2 seconds? If the logic is the same as the older system the voltage should return when you start to crank.
-If the relay signal terminal is getting 12V is the relay closing (assuming it's normally open)?

A couple of questions:
-If the relay is normally open is there a hot at one of the terminals waiting for the relay to close? I would guess yes; so is it hot?
-Have you cleaned all of the connections and checked the grounds? I guess Cadillac moved to a single fuel pump; not two like the 1979 system.

Scott

81 BENY Biarritz

Here is the troubleshooting page for fuel pump not running from the silver manual.  Sorry for the blurred edges on the first page but the manual is difficult to get to sit properly on the scanner bed.  You should be able to figure it with the help of the flow chart.  Good luck with it...

scan0059.pdf

Jonathan Johnson

Hey Dave I'm not the best with electrical things but I mediocre I see you have an ohms reader going into that greenish wire where do you have the ground going to, I see you have the red going to the wire but where's the black supposed to go let me know thanks Dave
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

By the way I should be home in about 20 to 30 minutes and I'm going to test that wire that you told me to check and then I'm going to look into the other stuff as well thanks everyone for all the advice I hope we're getting close I feel like we are too
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

81 BENY Biarritz

Jonathan, I had the red lead on my multimeter inserted into the green connector as shown in the picture and the multimeter was on D/C Volt range.  I laid the multimeter on the windshield so I could see it from inside the car and held the black wire on the chrome part of the transmission shift lever (an easy ground) so that I could turn the key and watch what the multimeter showed.  You have to watch very carefully as the voltage signal only lasts one second after you turn the key and then goes off.  I didn't try to start the car just turned the key from OFF to RUN.  If you want to repeat the test wait for at least 10 seconds between trying it again as the ECM seems to not send the signal if you try it right away.  Dave

Jonathan Johnson

Got it thank you for explaining that in detail,  I really appreciate it.  I'll let you know shortly what the reading was.
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

79 Eldorado

Dave,
A test light might be more ideal for the test where you only have voltage for a second because you would see the light more obviously flicker than the screen of a multi-meter. As well sometimes a circuit will test fine for 12V but if the terminals aren't the cleanest any load will show an issue where the meter will not.

Edit: One other thing. Instead of trying an old-school scanner try the app "Office Lens". A colleague introduced me to it years ago and it works incredibly well for scanning.

Scott

Jonathan Johnson

Ok so Dave, I put my meter in there like you did, turned it to on position and I got like 11.2 for a split second then went away. Then I waited a few mins. Then got my test light. Stuck it jn that wire. Turned it to on position and it light up for a split second so I'm assuming we're all good there. What should I try next? We're getting closer :)
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

Oh Dave, I'm an idiot yesterday I forgot to tell you, I took out the fuel pump relay, touched it to number 2 cavity and it did light up for a second..sorry I ment to mention that to you!
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

Jonathan Johnson

Also can you send me better pics so I can keep reading the steps 5 thru 11 on that repair manual it's blurry and I can't continue reading. Thanks Dave!
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

81 BENY Biarritz

Jonathan, try the same test while cranking the engine to see if you get voltage at that connector constantly.  If yes then you probably have a bad ground or connection at the fuel pump or broken wire or bad connection in the wiring to the rear of the car. 
You can disconnect the connector for the fuel pump/level sender/auto level control that is located near the fuel filler pipe behind the rear bumper and check Terminal "C" (circuit 120) as shown at the bottom of the attached scan to see if it has 12V momentarily (or constantly while cranking if the test for constant voltage proves out).  If you do then you have ground or wiring connection issue to or at the fuel pump.  Don't drop the tank just yet as there would be several grounds to check first.  Dave

scan0060.pdf 

Jonathan Johnson

So i did do the crank test and it does light up every time. Also I have the tank out of the cat at the moment.
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

81 BENY Biarritz

Hi Jonathan, does the test light stay on continuously while the engine is cranking?   Did you try it at the connector at the rear bumper.  I looked at mine this morning and see a light blue wire at the rear connector so it is making me wonder if the test point in the engine bay is the correct one or not. Seems strange that it isn't light blue also.  Dave

Jonathan Johnson

Sorry maybe I confused you , I meant the wire that you sent me a picture of with the ohms reader connected to it. I tested it at that wire and also the #2 cavity on relay board. I will Check as soon as I get home if it stays on as I crank. Thanks Dave I'll also check the wires to the rear. I know going to My pump there's a red wire and 2 separate grounds if I'm not mistaking. But I know the connector your talking about by the rear bumper that the wires for the pump connect to. That harness
1981 eldorado 6.0
2007 dts
4.9 liter v8 anything
Deville
Seville
Sts
Sls

81 BENY Biarritz

Hi Jonathan, at that connector the light blue wire is the 12V feed to the pump, the red(pink) wire is the supply/return wire for the fuel sender(gauge) and the black wire is the shared ground for both the fuel pump and fuel sender.  This is a picture of what it looks like inside the tank. Original one on left and new Spectra FG15B on right both have fuel pump removed.  Mine has the digital dash and the new one works just fine even though it says it is for non-digital dash cars only.  Difference is in the arm configuration which makes the new one slightly less accurate than the original (which is much better than no display at all).  Dave

Fuel sender - old digital display and new Spectra non digital.jpg 

TJ Hopland

Not related to this current path of troubleshooting but its curious how on the original unit looks like there is a 'condenser' in the pump circuit?  Is it in series with one of the pump wires or is it tapped off like we are used to seeing for noise suppression?   I wonder if that came with the digital dash option or was just part of the DEFI system or was just good old radio suppression or maybe its just something (not even a capacitor?) that they thought they needed in the motor circuit for the pump motor?

 
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