Schutte

My gas gauge goes crazy just sitting at idle. Idles rough it has a small miss. Every time I let it sit and idle it goes where the gauge should be then to empty then back and back to empty. Then fine for a little bit then all over again.

CCKen

You could have issues with a loose fuel pump connector or a corroded connector.


Try uncoupling the fuel pump connector (just in front of the fuel tank) and examine the connector pins and in cavities for corrosion.


The erratic fuel quantity indication could be attributed to corrosion and the rough running could also be caused by the fuel pump not working properly due to corrosion in the connector.


You can also test your fuel pressure at the fuel injector rail test port. You can rent/refund a fuel pressure gauge at your local parts store to do this.


You should see a steady 49.2 +/- .5 psi at idle. The pressure may be oscillating due to the damper on the rail but don't worry bout that unless it's an extreme oscillation.

Schutte

Ok I'll try that and see if that works. Thanks for the help

Schutte

Checked the connection and it was all good. Don't know where to go from here.

rdr8887

Have you checked the fuel pressure? You need to see what's hapenning at the fuel rail. Rent a pressure gauge. Screw it onto the Schrader valve on the fuel rail. Start the jeep. Watch what the pressures do and report back.

Schutte

I'll get one tomorrow and see what it does.

CCKen

Although I covered checking the fuel pressure in my previous post, this won't account for erratic fuel quantity indication.


The fuel quantity indication comes from the sending unit attached to the fuel pump module assembly. A fixed voltage (12 volts) is sent to the sending unit, the variable resistor connected to the sending unit float changes the voltage based on the float position, which is sent to the PCM, and via the CCD Bus, to the instrument cluster.


If the connector was 'all good', the fuel pump module (fuel quantity sending unit) could be defective. And if the fuel pressure is erratic, change the fuel pump module assembly.


Use a Bosch or Carter pump module - No Other Brand....unless you want to change it again down the road.

cruiser54

What year?

Here's where both the gauge and pump ground together.

CCKen

He has a '98.


The gauge does not ground there, its a CCD Bus gimmick.

Schutte

Well a guy checked my jeep today and he said I needed a new pump and sending unit. The pressure was not steady and when I turned it off and it didn't hold at all. He said it should fix the gauge too. Thanks for all the help.