L98-C4-HI

ok I got another weird one for the forum! Just R&R'd the tank float + pump assembly for new and the gauge appeared to be working - at first. But as I drove it today the level started increasing from half all the way back up to full as I ended the day??? At key off and back to start position it went back to half. My guess is should be 1/4 as I was running it hard for a while.

It was difficult putting the new one in. Is there a special pocket in the tank supposed to finesse the new one in to? Or is there something wrong with my dash / gauge?

aklim

There is a baffle in the tank but I can't understand what it could be. IF you got it wrong, the float might be stuck in the baffle and not move but I have doubts it could move the float upwards. Maybe it is your sender that is bad which means assembly removal.

billschroeder5842

True. I had this very similiar situation with my 89. I took the sending unit apart and very carefully cleaned both the contact and the wires and now my gauge is remarkably accurate.

Gently use 400 grit sand paper on the contact arm point. Clean the wires on the sweep using WD40 and Q-Tips cleaning with the wires and not "scrubbing" against. You will be surprised at how much dirt you clean from your wires.

Also CAREFULLY bend your contact arm 1/32 to 1/16 of an inch to either side so when it makes contact with your freshly cleaned wires it has a fresh "lane" to travel as the thin wires wear over time.

bosshog8

I don't specifically know about this year but this happened with me on a different year after a replacement of sender and gauge. It needed some going through the ground and cleaning everything to sort it. The ground was weak and so the signal traveled back somehow in the opposite direction.

johno504

I put 2 new Delphi fuel pump assy. in my 96 this summer. project started out as simple PM issue, no problems with pump or sender that was in the car ( threw it away like a dumb *** ) BOTH new sending units were bad .RA replaced one pump only and none of the $300 labor. had the pump pulled a third time to check wires etc. fuel guage still not close to being right. after spending $800 I gave up. woe is me.

aklim

Took 3 hours to install 2 pumps? I could have had a couple of cigars while doing it.

Seriously, where did you get those assemblies?

L98-C4-HI

no updates today as I did rear shocks on my truck and gardening chores :p
but the vette is an '88 and I got the new assembly from Rock Auto like johno504. and evidently this was a must do for a new pump anyways as the old one was weak and probably ready to fail soon.

bosshog8 which grounds did you clean? maybe I plugged the darn connector in backwards but aren't they keyed so one way only, hmm.

another thought I had was does the tank need to be near empty for the install so the float goes in a specific channel or something. I'll pull it out again and shine a flashlight to see in there. very weird. - just read a bunch of other threads about channels and socks now really want to see in there. new float/pump assembly came with a large sock vs. what came out (small and dirty lol)

glad to see I'm not crazy and not seeing things!
just checked and it's still reading one bar below half so no change overnight at least.

12/27 still no update yet but I will say the new assembly is a GM part says the box from RockAuto. Not going to take it apart but will pull and test before trying to get a replacement.
At least this new Iphone X works perfectly right out of box. ahem.
:p

pcolt94

Don’t try to sand anything or bend anything till you know what the exact problem is (It's new). Has to be plugged in correctly or the pump would not run and it is keyed.

First find out if the gauge is performing correctly. Pull the pump unit out of the tank. Connect an ohm meter and read the fuel sender unit resistance at full and empty by moving the float. At full position it should read about 100 - 120 ohms. At empty it should read about 0 - 20 ohms. If it reads proper then you can move the wiper around and make sure there is no dead spots or radical changes in resistance when changing.

If all is good, connect the car connector to the unit and pull the fuel pump fuse. Then key on and move the arm and check the fuel gauge for proper indications.

Depending on the test results will give you a direction.

johno504

both Delphi units came from Rock Auto . mechanic threw box away on second unit. no box ,NO return. entire PM job turned into a cluster frick.

aklim

So buy a new one and 2 months later apply for warranty. Worst case you have a new pump you can ebay

johno504

no way, i'm done @ $840.00 to pm pump that was not broken to begin with.

aklim

IDK your location but I'd put it in the profile so if say we were nearby we might be able to swing by after work. If you were near me and I was on the way home and the facility is warm, I'd be happy to take a peek and see what gives. The job is so easy, I could have charged you 2 steak dinners and still have change left over. Someone gave me a pump assembly to do some testing a few years ago. I'd have let you have it for testing and pass it on. Also because I'd be curious as to what you find. At this point, it will cost you a gasket and a few bits to check what is going on.

PatternDayTrader

I wonder if its possible to get the fuel sender signal and its ground reversed.

PatternDayTrader

Like if someone cut the connector off and spliced in a new one backwards.

billschroeder5842

IDK, but as we are all "amateur electricians"I'm not sure you can ground "backwards."

My thought is that the lack of ground becomes... ungrounded?

PatternDayTrader

Well if I remember correctly there is a four wire connector as part of the sender/pump assembly. Grey and Black were for the pump. Purple and black were for the sender. If you had to replace the connector body because say its all melted, then you could connect the pump properly maybe the fuel sender backwards. I don't know though since I would never make such an epic blunder, but a company that remans these units or someone that might not know better probably could.

aklim

OP said it read more and more full. How does it read the level? Isn't it resistance based? IOW more resistance means this, less resistance means the opposite. OR is it a one way sort of thing?

PatternDayTrader

Its not all that different from a throttle position sensor. It is would sort of explain things if voltage from the gauge in the dash was connected to the sending unit backwards. What was the low resistance point would then be the high resistance point because you would be applying voltage from the opposite side of the resistor.

whalepirot

Resistance has NO polarity.

OP said it read higher, then LOWR. RTFP!

Inspect it carefully; treat those fragile wire windings very gently, and NO... it doesn't fit into any "channel" and requires no empty tank.

I reworked mine and it has never operated better.

PatternDayTrader

Yeah probably just a messed up sending unit.