Fuel gauge inaccurate - ZR-1 Net Registry Forums

Chuck Banks · 10-09-2023

I installed new ACD FLS 1102 fuel pumps and sending unit in my 92. I bought the pumps about 10 years ago from Rock Auto and GM part number is 19180770. The part was still in the box and says made in China. The pumps work great and my 102,500 mile ZR that I?ve owned for 30 years is still performing well.
The fuel gauge starts to drop after driving 25 miles, and hits the reserve with 2 bars showing after 175 miles. I thought I might have bent the float arm when installing the pumps so pulled them but don?t see any problem. Unfortunately I discarded the original pumps so don?t have them to compare with. The ohms read 1.1 with the float at the bottom of travel and 89 ohms at the top. Has anyone else had a problem like this after installing new AC Delco fuel pumps? Any suggestions?
Thanks,

Chuck Banks

Jagdpanzer · 10-09-2023

From 1965 through 1997 GM produce cars used 0-90 ohm fuel tank senders (0 ohm empty, 90 ohm full). Your empty/full ohm values are what they should be. Unfortunately, due to the shape of the C4 gas tank the sender output doesn't track accurately throughout the range of actual fuel level. I'm not familiar enough with the dash side of the C4 fuel gauge circuitry if there may be a way to adjust the visual gauge indication.
Perhaps someone more familiar can chime in.

Sent from my iPhone using ZR-1 Net Registry

geezer · 10-10-2023

What I'm seeing in your pics is a single pump unit. Zr-1 is duel pump so does the unit sit in the tank at the designed level? Zr-1 pump is approx. 14 inch from base plate to bottom pump bottom(emply) & 3inches from base plate to full float position. Does your unit fall in these dimensions?

Chuck Banks · 10-11-2023

This is a dual pump OEM pump and sender unit. I determined that the float was about 1 1/2 inches above the bottom of the tank when installed. The arm and float are removable so that I could bend the arm so as to lower the float. In and out of the tank twice, and I'm now much closer to accurate readings. Reserve warning comes on with about five gallons remaining in the tank, but I can live with that. I think the original sending unit waited until about three gallons remaining before hitting reserve, but as you all know, pulling and reinstalling this pump is a real PIA.

Young1 · 10-11-2023

You are on track. Possibly the arm got tweaked/bent. Why is it easy to get the pumps out and a pain to get back in? Mystery.

10-09-2023	#2
Jagdpanzer Join Date: Apr 2007 Location: Northern VA Posts: 2,658	Re: Fuel gauge inaccurate From 1965 through 1997 GM produce cars used 0-90 ohm fuel tank senders (0 ohm empty, 90 ohm full). Your empty/full ohm values are what they should be. Unfortunately, due to the shape of the C4 gas tank the sender output doesn't track accurately throughout the range of actual fuel level. I'm not familiar enough with the dash side of the C4 fuel gauge circuitry if there may be a way to adjust the visual gauge indication. Perhaps someone more familiar can chime in. Sent from my iPhone using ZR-1 Net Registry __________________ Phil Wasinger 1994 Torch Red ZR-1 WAZOO Member George Braml Intake

10-10-2023	#3
geezer Join Date: Aug 2010 Location: ottawa canada Posts: 156	Re: Fuel gauge inaccurate What I'm seeing in your pics is a single pump unit. Zr-1 is duel pump so does the unit sit in the tank at the designed level? Zr-1 pump is approx. 14 inch from base plate to bottom pump bottom(emply) & 3inches from base plate to full float position. Does your unit fall in these dimensions?

10-11-2023	#4
Chuck Banks Join Date: Nov 2018 Location: Prescott Valley, AZ Posts: 11	Re: Fuel gauge inaccurate This is a dual pump OEM pump and sender unit. I determined that the float was about 1 1/2 inches above the bottom of the tank when installed. The arm and float are removable so that I could bend the arm so as to lower the float. In and out of the tank twice, and I'm now much closer to accurate readings. Reserve warning comes on with about five gallons remaining in the tank, but I can live with that. I think the original sending unit waited until about three gallons remaining before hitting reserve, but as you all know, pulling and reinstalling this pump is a real PIA.

10-11-2023	#5
Young1 Join Date: Sep 2016 Location: Ocala, FL Posts: 895	Re: Fuel gauge inaccurate You are on track. Possibly the arm got tweaked/bent. Why is it easy to get the pumps out and a pain to get back in? Mystery. __________________ Steve Young 1991 ZR-1 Quasar Blue Metallic/Black #729 Second Owner 1991 ZR-1 Dark Red Metallic/Black #2040 SOLD 1990 ZR-1 Dark Red Metallic/Saddle #1670 SOLD Double your happiness.....complain half as much.