I just replaced my fuel pump in the 93, the fuel gauge now isnt working right.. Key on engine off it reads correct, but once i start the car the gas gauge starts going up rapidly.

What can cause this? is the new fuel pump drawing to much current and since it shares a ground with the sending unit, they are fighting?

its a AEM 320 E85 fuel pump.

Thanks

 

Are the intank connections all good and solid?

the sender is pretty simple. Variable resistance and there isn't much that can go wrong.
In your case there is something loose or crossed in the tank wiring.

Rule of thumb(s)

when a problem appears immediately after having some work done, return to the place where the work was performed to find the "new" problem....

looks like you gotta pull the pump and take a look.

When you DO, operate the float manually and see what happens. I do not advise taking the sender apart until its a sure thing that its bad. Its too fragile to mess with just 'cause...
If its starting to read across the bars, not being as accurate as it once was, that's good reason to take it apart and clean the sweep and contacts. You can also spray it out with good electrical cleaner if you do not want to take it apart yet. I use a mild caustic solution or mild acid to dissolve the residue from the blended fuels that leave a film on the senders contacts that cause it to read weird...Just douche it out, maybe a Q-tip if you can get it in there, rinse with some gasoline and finally lube and protect with machine oil or ATF until its submerged in fuel again. I always 'oil' it even if its going back in right now just to be sure.

The tank is prone to grow rust inside because of the blended fuels that actually carry and hold water, and you do NOT want it to have a place to take hold in the senders contacts. That's why I spray it with lite oil or ATF before dropping it in the tank again.

 

i did pull it out already again, the wiring is correct and everything is working except for the described issue above.

it does read manually, thats why i reassembled it.. and when I put it all back together its reading the correct amount of gas thats in the tank.. about $10 worth.

Theres no rust or anything inside the tank either. its only not reading correctly when the car is running or in other words when the fuel pump is running.

 

Jay, This is just an observation your saying everything works until you put it in the tank and the pump runs.
So did you have a way to run the pump before it was in the tank or was that just a float level test ?

 

before i reinstalled it the second time, i just tested the float level. didn't want to run the fuel pump dry.

 

Check the voltages on the sender connector. You should see 5 volts from the dashboard to operate the fuel level sender. Check it with the engine running to see if it changed.

I think you might get your symptoms if the ground is not connected properly. Measure the voltage on the ground connection. It should be very close to zero. If it is not zero then your ground connection is bad.

 

Jay, it's sounds like the ground side of the float is being raised.
Do a recheck of the wiring to ensure it correct and grounds are clean and tight as already suggested.
How is the condition of the wiring coming to the fuel filler side ??
The ground needs to be 100% all the way from the battery.

 

If anyone else has this problem with a aftermarket fuel pump, I fix it by making a custom wiring harness with a thicker gauge ground wire that is separate for the fuel pump and the sending unit.

 

You need to work on the unit real time powered up.
Remove the unit again and lay it across the rear with some towels. Pull the fuse for the fuel pump. Then you can power it up and make the measurements and see what going on. See if any grounds are above ground and if B+ is steady. Move the float around and check the gauge.