Fuel gage pegs low after replacing bilge pump

[mainexile]

Basics: 1978 Grady White Pacer 174 w/ Mercruiser 470. My bilge pump died and I replaced it with a new Shoreline Marine 800 GPH. I connected the wires from the pump to the same connections as the old one, and it worked as advertised. However, after installing and connecting it, my fuel gage now pegs on the low side. The old pump received its ground from the same wire as the fuel sender, so the first thing I did was to wire the sender's ground to a dedicated ground (battery). Still pegs low with the key on. Any ideas? Thanks in advance.

 

[alldodge]

Fuel gauge reads full when resistance is low and empty when resistance is high. What might have happened and the main fuel sender wire became disconnected. Take the wire on the sender with the key ON and ground it, the gauge should peg full. If it does measure the resistance from the sender post to ground with the wire off

 

[mainexile]

Fuel gauge reads full when resistance is low and empty when resistance is high. What might have happened and the main fuel sender wire became disconnected. Take the wire on the sender with the key ON and ground it, the gauge should peg full. If it does measure the resistance from the sender post to ground with the wire off

I assume (I know, bad word) that you're talking about the positive (pink) wire when you say "main fuel wire"? I pulled up the inspection cover in the deck above the tank sender to check the positive and ground connections, and they were fine. The only sender wire disturbed during the bilge pump swap out was the ground, but I put it back exactly where it had been before the pump installation. Tomorrow, I'll run the test you described and see what happens.

 

[mainexile]

I assume (I know, bad word) that you're talking about the positive (pink) wire when you say "main fuel wire"? I pulled up the inspection cover in the deck above the tank sender to check the positive and ground connections, and they were fine. The only sender wire disturbed during the bilge pump swap out was the ground, but I put it back exactly where it had been before the pump installation. Tomorrow, I'll run the test you described and see what happens.

OK. I did as you suggested and grounded the main (pink) wire on the sender with the key on. Gage pegged on the empty side. Then I removed the gage cluster and grounded the sender wire on the gage. Gage pegged full. Then I reconnected the pink wire to the sender and checked voltage on the gage - 10.6 VDC, but the gage still reads pegged empty. Any other thoughts?

 

[alldodge]

Sound like your ground on the take is not grounded, its floating. Either that or power is being feed back to the gauge on the pink wire. Disconnect the pink wire at the gauge and measure voltage at the pink wire and ground. If no voltage check pink wire to ground for ohms

 

[mainexile]

Sound like your ground on the take is not grounded, its floating. Either that or power is being feed back to the gauge on the pink wire. Disconnect the pink wire at the gauge and measure voltage at the pink wire and ground. If no voltage check pink wire to ground for ohms

No voltage on pink to ground with wire disconnected. Resistance on disconnected pink to ground (on sender) 51.5 ohms.

 

[alldodge]

I'm guessing you have a connector which is corroded or loose somewhere.

Meter to ground = Full good
Pink wire to ground = empty bad
Sender shows 51.5 ohms, gauge should show full or real close to it

So either the pink wire has a break or bad lug on it, or when your moving things around the power going to the gauge is connecting and disconnecting, same could be with the ground

Try this: disconnect the temperature gauge wire (Tan) from the gauge and also have the fuel gauge disconnected. Connect the temp wire to the fuel gauge. it should show empty, now at the temp gauge sender remove the wire and jump to ground, it should peg full.

 

[mainexile]

I'm guessing you have a connector which is corroded or loose
Meter to ground = Full good
Pink wire to ground = empty bad
Sender shows 51.5 ohms, gauge should show full or real close to it


So either the pink wire has a break or bad lug on it, or when your moving things around the power going to the gauge is connecting and disconnecting, same could be with the ground

Try this: disconnect the temperature gauge wire (Tan) from the gauge and also have the fuel gauge disconnected. Connect the temp wire to the fuel gauge. it should show empty, now at the temp gauge sender remove the wire and jump to ground, it should peg full.

Temp wire to fuel gage with key on = pegged empty. Temp wire to ground = no needle movement on gage

 

[alldodge]

Your gauge has to be bad.
It should swing from 240 ohms empty to 40 ohms full

 

[mainexile]

Thank you for taking the time to help me out with this. I'll order a new gage when I get home. Then we'll see this weekend. I'll let you know. Thanks again.

 

[alldodge]

Ya know you might want to try one more thing just to make double sure. Reason I bring it up because you said you have 10.6V on the gauge.

Turn the ignition ON and ground the temp sender, the temp gauge should peg hot

 

[mainexile]

Ya know you might want to try one more thing just to make double sure. Reason I bring it up because you said you have 10.6V on the gauge.

Turn the ignition ON and ground the temp sender, the temp gauge should peg hot

Sorry, I didn't see this response until I got home. If the temp gage pegs hot, does that rule out everything except the fuel gage itself? If I go back to the boat tomorrow, I'll try your suggestion. If not, then I'll wait for the new fuel gage and hook it up to see if it (the new one) works OK. If it does, all is good. If it doesn't, I'll always have a spare for when the old gage does finally fail. LOL Of course, if the new gage doesn't work, I guess I'll have to start replacing wires and verifying grounds. Thanks again for your help. Steve Bulger (mainexile)

 

[alldodge]

I'm 99 percent sure it's the gauge, it was just the 10.6V issue. Even with 10.6 V it should still start to move toward full.

If the temp gauge pegs hot it is the fuel gauge. The temp gauge uses the same resistance swing as the fuel, just a different design

 

[mainexile]

I'm 99 percent sure it's the gauge, it was just the 10.6V issue. Even with 10.6 V it should still start to move toward full.

If the temp gauge pegs hot it is the fuel gauge. The temp gauge uses the same resistance swing as the fuel, just a different design

I know it's been a while, but today I finally went to the boat to install the new fuel gage. Hooked up all wires appropriately, but when I turned the key to on = no needle deflection either way. Sender terminal on the gage reads 7.8VDC. Going back tomorrow to pull the sender and manually move the float arm while checking resistance. If resistance varies between 30-240 ohms, then I'll turn on the key and see if needle deflects. Have to add that when I pulled out the gage cluster to check after new gage installation, there were a couple of times that all the gages pegged and then went to zero. Couldn't see any obvious loose connections, and when I remounted gage cluster, all gages (except fuel) worked as expected. One of the PO's rewired the entire instrument cluster with ALL BLUE wires, which makes tracing a real PITA.

 

[alldodge]

Read through the thread again and I was making an assumption you had 12V on the purple wire feeding the gauge. The gauge has to have voltage on it with getting 10.6V or 7.8V on the sender. Only way it wouldn't work is if the gauge had no ground.

Being all blue wires would make it a chore

 

[gm280]

You can always search those "blue" wires and label them accordingly to where the go or come from and make your own schematic diagram for future needs. Yes it would be a lot of initial work, but could save you a lot of time down the road. Just a suggestion. :noidea:

 

[mainexile]

Read through the thread again and I was making an assumption you had 12V on the purple wire feeding the gauge. The gauge has to have voltage on it with getting 10.6V or 7.8V on the sender. Only way it wouldn't work is if the gauge had no ground.

Being all blue wires would make it a chore

I did have 12V on the battery side, and the ground checks good. I may have to post tomorrow when I get to the boat to see if you're online. Tanks for everything so far.

 

[mainexile]

You can always search those "blue" wires and label them accordingly to where the go or come from and make your own schematic diagram for future needs. Yes it would be a lot of initial work, but could save you a lot of time down the road. Just a suggestion. :noidea:

I had planned to do just that two years ago after I pulled the boat for the winter, but a bad case of osmotic blistering resulted in 1.5 years in a shop having the hull refinished, flotation foam replaced and deck redone. I want to spend as much time as possible this summer actually boating instead of working on it. Fall will be the schematic/wiring diagram time.

 

[mainexile]

UPDATE: I ordered and received a new fuel tank sending unit and went to the boat. After a lot of tracing wires (and much swearing), I found that the ground wire from the sending unit was corroded, so I replaced it. Still no reading. I then pulled the old sending unit and checked resistance getting squirrels readings. The I replaced the sending unit and everything read fine. I'm guessing that the pegging I had on other gages yesterday was due to bad ground and bad sender. All is well now. Thanks to All Dodge for tolerating my less than stellar diagnostic abilities.

 

[alldodge]

It's all good so long as it works out. May you have no more electrical problems and a happy boat season