Stupid Gas gauge

[rockfangd]

Hi All.

Car is my 97 Deville D'Elegance

Picking brains before I contemplate dropping tank again. (not feeling that...)

I replaced the fuel pump unit about 3 years ago because of the fuel gauge not reading right under half. New unit completely resolved the issue until this year. 

Currently 

Full tank reads full

18-12 gallons. At idle for any length of time F-E-F-E-F-E, while driving reads normal

11-ditto (empty...) never see it. At idle F-E-F-E-F-E, While driving it is all over high and low. If I accelerate hard it goes to E for a few seconds. 

Imagine driving daily like this. It makes me want to drive it off a cliff. Every time it says E it yells at you, range is like a roller coaster, someday E might mean I am stranded. I fill it every 250 miles (every 5 days or so). I was half tempted to just cut the wire for now. I cannot remember if these still worked by Full ground is Empty and no ground is Full. If it is not then I do not know.

These were notoriously an issue amongst most every model GM made from the 90s-2ks. I really do not want to buy another fuel pump unit, the current one only has about 15k miles on it. And I did do the TSB for the pigtail when I did the pump.

Thanks all

[Dean.Babbitt]

Are you sure the gauge itself is OK?

[Bruce Nunnally]

This sounds like a bad connection versus a bad sensor, but I suppose the sensor could be the bad connection 

[rockfangd]

19 hours ago, Dean.Babbitt said:

Are you sure the gauge itself is OK?

honestly no clue. It is the digital cluster that shows the fuel reading in numbers. 

 

12 hours ago, Bruce Nunnally said:

This sounds like a bad connection versus a bad sensor, but I suppose the sensor could be the bad connection 

I was thinking the same. I pulled the plug behind the tank that goes from the body to the fuel tank. Was like new. Fuel pump and sender appear to share the same ground input so I assume the ground should be fine. I really do not feel like pulling the tank to check there, but I have a feeling I am going to have to. the term critter does come to mind...

[rockfangd]

So I looked a little farther into it. 

Signal is output from the PZM and returns to the PZM. Then via canbus is communicated to the PCM  and IPC.

So it does not look like it works by ground like the old easier ones. So likely it is the sending unit. Gotta love aftermarket.

I am going to pull codes, if any, inspect what I can at the PZM without pulling the back seat, and go from there.

I pulled codes, all history. B1571H, B1552H, B2477H, B0533H.

I also monitored the fuel level from the PZM. Tank should have about 17 gallons (by miles)

Gauge on startup shows 17 gallons. As I let it run the level starts to range from 16.8-17.5

I then put it in Drive and it goes to 20.4-16.5. It goes like a roller coaster between those 2.

I put it back in Park and it kind of levels off but still occasionally goes to 20.4 

[rockfangd]

Ok. I made things worse. The gauge thing has been driving me nuts. I went on a hunch and pulled the black cover off the under hood electrical center. I went right for the 2 row plug (the common issue one) I found corrosion on the pins toward the center. Not nearly as bad as I would have figured. So I did the pull test on each wire at the pin, all stayed put. Cleaned corrosion and all pins. 

Found more corrosion at fuel pump relay and AC relay. Cleaned those and replaced relays. Checked around the rest of the fuses and relays.

Whatever I did now I lost ABS/ Traction control. No Data.😭. I also noted on the way home that sometimes when the gas gauge fluctuated that the ABS light would flicker off and then back on...

I would like a diagram specifically for that plug. I know the cruise control is in that plug, but there is probably 20 wires in that plug.

Any insight? Now I have to deal with 2nd gear start and a crazy dash. I am ready to drive it straight to the junk yard.

[Bruce Nunnally]

Oh no sorry to hear.  The ABS thing happens if it gets unplugged but didn't sound like you were near it.  Possibly when you cleaned the corrosion out of the fuse box / relay center some extra bits got into something else?  Maybe pressurized air to blow out / wash the electrical center?

[rockfangd]

Thank You Bruce. I did that when  I cleaned them.

Tonight  I had a little more patience so I went back to that wide plug. I started the car, then performed a wiggle test, voila Abs, continued wiggle test, car stalled. duplicated, same thing. I then ziptied the plug tight together and both bundles of wire together. I lost Abs again.

So I said the hell with it. I cut and spliced probably 10 wires off of the plug. I found that 2 purples on same pin both black inside, 1 small pink black inside, 1 12g red must have gotten hot on both sides (insulation melted to wires. I basically spliced any wire that looked like power, ign, ground, and data (purple). All that are left in the plug look to be SWRC, and cruise control, possibly another thing or 2.

I also pulled the trunk access behind the back seat and played with the PZM plugs (can't see them as it is behind the back seat). Somewhere I messed up... I thought I was good to go as ABS and Traction lights are off, car runs fine, I backed car out and noticed I have no headlights😭. No high beams, no low beams, no fogs. I re-inspected all of my repaired wires, all look perfect. No blown fuses.

I don't know if the issue could be at the PZM ( I should never have touched it) or if it could be something under the hood, no matter what I did they never came on though. I gave up. I rigged the headlights so I could drive it home. Gas gauge read F all the way home, I left the car running while I disconnected the headlights. When  I got back in the car it was reading E-F-E-F-E (tank is nearly full)

I am going to attempt to pull the back seat and inspect the PZM, I really don't want to junk it with a full tank. This car just does not like me anymore

[Bruce Nunnally]

That sounds frustrating, but it does sound like progress even if these new symptoms / faults arrived with it

[rockfangd]

Well I went to troubleshoot the lights issue today and for whatever reason they all work again. No luck with the gas gauge though.

So I guess at least I prevented another issue with the plug under the hood.

I am going to try to find a way to trick the gauge to think it is full all the time. I am not putting anything else into it, just want to make it through the winter.

Just within the last year this car went from great to crap. I have to figure out what is going to replace it. I'm all ears. 

[Bruce Nunnally]

Glad the lights sorted out; hopefully the gas gauge will find its way too

[rockfangd]

Well I have some good news.

I went on a hunch and ordered a fuel pump/sending unit. (MY replacement unit still has warranty)

I drove the car until gas was as low in the tank as I was comfortable with, I pulled the tank tonight.

The problem was the sending unit. I have been pulling my hair out since this issue started, well over a year ago. lower the tank got the crazier the gauge got. I went crazy driving it the last 2 days.

The design is absolutely terrible, I regret replacing the unit with an aftermarket unit. The saving was not worth it. One of the 2 (Feelers) was broken and in the bottom of the tank. I am glad I did not take apart the back seat, or harness. I had a gut feeling.

It was very peaceful driving home tonight. Had 2 gallons upon assembly, added 10 gallons. IS accurate.

Old unit was 5 years old, and had about 12k miles on it. If it happens again  I am bypassing it.

Note To anyone who cares. DO NOT BUY AFTERMARKET. The oem ones are not the best solution, but they are the only one that appear to last.

I also left the car running when I got home while I checked my mail. Normally If I left the car running for more than about 30 seconds it would pop the check engine light saying lean both banks. Hopeful the pump may have resolved this issue too 

Pic shows what it is supposed to look like. Note the 2 brass colored feelers. They are cheesy, and the black arm is sloppy (Brand new)

[rockfangd]

So it appears the fuel pump replacement resolved 2 issues, fuel gauge and lean condition on both banks.

Today was the test, let it idle in line at the bank and engine light did not come on. It has been coming on if I let it idle too long

[sonjaab]

wow!

[rockfangd]

Lower fingers gone

[sonjaab]

What brand of pump is that?