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1990 deville fuel pump problems/fixes

Old 06-01-2008, 06:06 PM
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Join Date: Jan 2008
Posts: 76
Default 1990 deville fuel pump problems/fixes

I decided to make a thread for my fuel pump woes as well. When I originally replaced the fuel pump it was because I had the fuel tank out to fix a leak. After I fixed the leak I decided to put in a new pump just so I dont have to drop the tank 2 months later with a dead fuel pump. So much for that idea.

Basicly the new pump ran great for a tank of gas. Then when I changed the transmission fluid and filter I fired it up to get the trans. fluid level right and while doing that it just died. no sputtering or running rough just like someone turned the key off. And then it wouldn't start again. The next morning just for kicks, I tried it again and surprisingly heard the fuel pump come on. (I couldn't hear it after it died before) So I cranked it and it fired up. So I get out to finish checking the trans. fluid when it died again (about 30-60 secs. after being started.) And I havent heard the fuel pump since.

So I did some reasearch online and checked the fuel pump fuse (it was good). Then I swapped the horn relay with the fuel pump relay. The horn still honked and not a sound out of the fuel pump (tried starting it with no success) Hooked up a fuel pressure guage and got nothing. So, I know the pump is simply not running.

Oh and I had installed a new fuel filter the same time I changed the trans fluid. So to make sure the line wasn't plugged some how I unhooked the line to the filter and turned the key on and nothing. So I don't think the fuel line is restricted.

After that I gave up for awhile and then went to trying to fix the high level stop light (https://www.cadillacforum.com/m_23148/tm.htm)
When I did that I found a bundle of wires going to the underside of the car that is near the passenger side of the fuel tank:

So curiosity got the best of me so I drilled out the 3 rivets holding the rusty cover plate on. And it was basicly what I'm calling a bulkhead connector/fitting so the wires (including an air line) could safely pass through the floor pan. Once it is through the floor it splits off into a few wire groups going to different things. One of course is for the fuel tank unit. This fitting doesn't seem to unplug so you have 2 more rivets to drill out and then you can pull it up a little bit.

Then with it lose you can reach under the car and unplug the connector to the fuel tank unit and push it up through the hole. The male end of the connecter will barely reach and hang on the hole. So now you have topside access to the fuel tank unit connections:

I wouldn't recommend doing this if you need to test the connectors. It would be easier to do it from underneath. I only did it this way because I had the seat out and had already started drilling rivets. For what its worth you can also get to this fitting thing from inside the trunk. It is behind the carpet wall (carpet glued to cardboard) at the very rear of the trunk.

Here is a close up of and the fitting:

Here is a close up of the hole and you can see the ground:

This is a diagram on the plug wiring:

I can get turned around on plug diagrams sometimes so I made a picture of the plug showing which two are for the fuel pump ground and hot wire. At a different angle I listed the color of the wires on the the plug:

The plug above is the female connector that goes to the front of the car. So to make sure that is good I probed the gray and black wire while the key is turned on. And then it gave me 12v. So I know that the wiring/fuses/relays ect. and good between the battery and that plug. Becuase of how these cars work it will only give you the voltage for about 2 seconds before going dead. thats normal. You can turn the key off and then back on and you will see the voltage come back for 2 more secs.

I have made an extender for my meter to test the wire continuity when doing the brake light. So for the hell of it I ran the wire from the negative connector on the battery and with the other probe toched the ground on the plug to see if it would beep (indicating a circuit) It beeped loud and clear and gave the same resistance reading as if I were holding the two probes together. Which means I have a nice solid ground.

Here is a picture of the wire extender I made so I could run from the front of the car to the rear. And of course touch the probe to the other wire to make sure you dont have problems with your connections which could give a false reading.

So now that it has juice up to the fuel tank units connector it's time to drop the fuel tank and find out whats going on. I will do that tomorrow.

Old 06-02-2008, 01:00 AM
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Join Date: Jan 2008
Posts: 76
Default RE: 1990 deville fuel pump problems/fixes

I went ahead and did a little more work. I wanted to get the gas out so that it is ready pull out tomorrow.

Here is a pic of where the filler hose and vent hose connect to the tank:

here is a close up:

The first time I took the tank down, getting the two hoses pulled off the tank is a real pain in the ***. If your having trouble use your favorite penatrating oil all over where it meets the tank. If you can pry up a little on the hose so you and squirt some inbetween the hose/nipple. And it gets worse. The two hoses are not seperate they are joined at the center for about 8in. So I assume this is some sort of specialty hose? So don't think about cutting it unless you can locate one or willing to pay for a new one.... or they are common and cheap I dunno, I didn't cut mine. I thought about it after 6 hours of trying to get it off. But then tried the penatrating oil and that helped alot.

Also there is a bracket bolted to the frame that stablizes the filler neck. If you unbolt that it gives you just enough wiggle room to get the hoses off. This pic shows the bolt and the round hose/tube looking thing that is the filler neck and vent tube that goes up to the fuel door:

After figuring out those two tricks the first time it still took me probably 2 hours to get the hoses off. Now when I put the tank back in I sprayed the **** out of the two nipples on the tank with silicone spray. That not only helped the hoses go back on, it only took me about 30 min to get the hoses off this time.

Here I got the vent hose off and the filler hose about half way off:

then I stuck a hose down the vent nipple into the tank and pumped out the gas.

From here it should be smooth sailing getting the tank out.

Old 06-02-2008, 10:21 AM
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Join Date: Jul 2006
Posts: 424
Default RE: 1990 deville fuel pump problems/fixes

You have to be thinking, what the hay would this have cost you at the dealership?????? Very nice detailed description of this other wise labourious task.
Old 06-02-2008, 05:24 PM
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Join Date: Jan 2008
Posts: 76
Default RE: 1990 deville fuel pump problems/fixes

lol. Tons of money im sure. I have also put in a new radiator and some kind of emissions control valve thingy. I forgot what it is really called. either way the new valve cost 565 dollars... no wonder the junk yards were sold out. When its not working right the car runs rough and acts goofy and gets bad gas milage. They have two exhaust check valves I also replaced to be darn sure I didn't cook my new valve (I think that is what cooked the old valve as it has soot inside and smelled like exhaust). I will have to take a picture. It is easy to change and it is right on top of the engine.

Back to my fuel pump. I pulled the tank and tested the fuel unit wiring harness and it was good all the way to the two studs on the fuel pump. I tried to jump the pump from the battery and it wouldn't work.

So I have a dead NEW fuel pump. I'm pretty pissed as that was the whole reason to put a new pump on so I wouldn't have to deal with this **** a few months later. I mean one tank of gas and the pump goes belly up? WTF is up with that?

Anyway here is a few pics of the fuel tank unit. I dunno what the white stuff on the fuel pump is either.

Old 07-09-2008, 01:41 AM
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Default RE: 1990 deville fuel pump problems/fixes

Definitely a FAQ thread ...

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