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Testing '87 Park Avenue fuel pump-sending unit


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I'm dealing with a much newer Buick than most of you are talking about but if you can help I'd sure appreciate it. I let gas sit too long in my '87 Park Avenue and the fuel pump plugged up. I have a parts car with a beautiful gas tank and very nice-looking fuel pump-sending unit. I'll put the parts car's tank in my running Park Avenue. Before doing so, however, I hooked up the nice-looking FP-sending unit to my car's wiring harness to test it. Well, according to my factory Buick manual the FP is supposed to operate for 2 seconds when I turn on the ignition. It doesn't - or at least I can't hear it from the driver's seat. And I'm not so sure about the sending unit. When I place the float in its lowest position, my dash gas gauge reads 1/4 full. When I move the float as high as it will go, the gas gauge needle buries itself far to the right of the "F" mark. Do I have a FP and bad sending unit? Does having gasoline in contact with the FP, the sending unit - or both - produce different results? Am I completely goofy in conducting the tests I am?

One other question regarding the fuel pump: The manual says that by sliding the FP upward on the fuel line to which it's attached you will free the bottom of the FP from its mount and thereby be able to tilt it outward, bottom first, to remove it. True enough. But I can't move the FP high enough for the mesh filter on the bottom of it to clear the metal ring that anchors the bottom of the FP. I want to install a new filter. Any secrets here? Thanks & cheers, Curt

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Hi Curt, that mesh filter needs to come off before removing the pump from the sending unit. I believe it can just be pried off as new ones are just pushed on.

I don't know about your tests. I do know on slightly newer cars ( 89's - 93's) there is a tag attached to the wiring harness outside the tank. That tag should have a 3 letter code on it. I would verify that the parts car tag matches your original tag before installing that pump.

Also I know I would opt to install a new pump when doing this job. Even though most often the problem appears to be chaffed wires on the intake pump, I feel like the tank replacement is one job I would rather do once. The cost of a new pump is relatively cheap compared to another 3-4 hours under the car balancing a loose tank with a lot of gas in it.

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Thanks for your thoughts, John! You are so right: I don't want to waste any more time beneath the car fooling with the gas tank. I am going to pay the $30 or $40 for a new fuel pump and be glad to spend it. I'll follow your advice about removing/installing the mesh filter. Right now, however, it's the sending unit that's holding up the show. A good new one from Rock Auto is about $100 + shipping. If I can confirm that the one off my parts car works as good as it looks, I'd like to install it and use the $100+ I've thereby saved to buy some other needed Buick parts! I appreciate your help! Cheers, Curt

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Hey Curt, I think you're making the right choice. I reviewed my original response to you and have a correction and a suggestion.

The correction is I did not intend to say "intake pump" at this sentence. "Even though most often the problem appears to be chaffed wires on the intake pump, I feel like the tank replacement is one job I would rather do once. " I don't know why I typed the words "intake pump" as no such thing exists. What I did mean is the wires that go from the mount surface of the sending unit to the pump itself ( this would be inside the tank) will fail. I got this from the instructions on some of the sending units I installed the last few years. I understand that you can still buy just these wires off the "Help" board at most full scale auto parts houses.

And the suggestion I have is this: I watched my friend with the GM school education and 20+ years GM dealership experience take a sending unit and using an ohm meter, check for continuity of the gas guage sending unit. I do not know what ohm reading he was looking for but he told me that he has opened sending units, sanded with very fine grade sandpaper, lightly, just to remove any possible glazing on the spring where the points ride, and salvage the unit.

Since the pump is separate from the sending unit and just rides within the cage built onto the sending unit, you may be able to salvage one or both of your sending units by replacing the wire harness and pump.

However, do not overlook the condition of your external metal fuel lines on the part of the sending unit outside the tank. If there appears any substantial rust, I would just go for the new sending unit. Once again the tank has to come out to deal with that issue.

Good luck.

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Hi, John. I do have all the manuals for 1987. Perhaps if I dig a little deeper I can discover what an ohm-meter test of the sending unit should reveal. Your remarks got me thinking, however. The contacts that the top of the float arm rides on are open - actually exposed directly to the gasoline! I ran the tank in my Park Avenue parts car (the one I'm preparing to put in my running Park Avenue) dry on white gas (Coleman lantern fuel, which evaporates without leaving varnish or any other residue behind) perhaps 10 years ago. Since then, the contacts have been exposed to air in the tank. I presume the contacts are copper but instead of being shiny they look grayish. It wouldn't hurt anything for me to carefully brighten then up, as your mechanic friend has been known to do, and then repeat my test of the sending unit. On your good suggestion, I will also inspect the fuel pump-sending unit wiring harness very carefully.

It's funny - a friend of mine, Stu, who is very familiar with these cars, says "check the ground." I was expecting to find a ground wire coming directly off the top of the FP-sending unit and grounding to the chassis nearby. Such a ground would naturally be very rusty on a 25-year-old Nebraska car. But the factory schematic shows the FP-sending unit ground runs all the way through the wiring back to the battery ground. I have to get back to Stu about what he means. In reality, I suspect the ground for the FP and sending unit actually runs from the locking ring that holds the the assembly in the top of the tank, through the tank to the chassis through the strap fasteners. I've cleaned up some very corroded tank straps; maybe that will be enough to solve a grounding problem, if I even have one.

As to the external metal fuel lines, they're in surprisingly good condition. I am replacing the flex fuel lines - one for the gas feed, one for the return - not only because the metal end fittings are very rusty but because the rubber is 25 years old. I don't want to have to repeat the tank removal & replacement a few years from now because one of the rubber sections is leaking! Thanks again for your suggestions. Cheers, Curt

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Hi, John. Although I have some older non-digital pictures, I don't have any recent overall shots of the car, unfortunately. It's a medium-blue metallic 4-door with a light gray leather interior. Pretty nice shape yet. My mom bought it new in early 1987 and, boy, is it loaded with gadgets, from a Sky-Top moonroof and an automatic day-night mirror that responds to headlights behind you to a "Twilight Sentinal" with a photoelectric cell that automatically turns the headlights on or off. I got it from my mom in 1995 and have put, oh, about 70,000 miles on it. The grand total is 156,000 miles now. A couple of years ago the struts went bad and some other problems developed. I was building a house at the time and just too busy to deal with things so it's been parked inside since then. I'm replacing struts, front and rear ball joints, tie-rod ends in the front and suspension stabilizer link ends in the back, installing a new transmission filter and changing fluid and so forth - just trying to get it back up to snuff for several more years of carefree driving. By the way, the sending unit tested OD for continuity but I wasn't getting a variable resistance reading across the float rheostat so, today, I ordered a new sending unit (to keep the new fuel pump company)! I think I'll have the gas tank better than new by this weekend. Thanks & cheers, Curt

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Redwind 89 ( my son) is currently driving an 89 Park Ave white with blue interior. Not that many miles but starting to run up against these same problems.

Anyway I think you'll be better off with new stuff inside there. sorta takes the worries off..

Good luck, and post pics soon. I love those cars!

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