Gas Gauge Senders

[Rob Mayercik]

Hey all -

about a year ago I had to replace the gas tank, fuel pump, and sender assembly on my '92 (both tank and sender had rusted out, the sender was original). Since then, I've noticed that the needle on the fuel gauge drops faster than the gas in the tank - when the needle reads "1/4", I only take on 10 gallons. Certainly it's better to read lower than actual as opposed to higher than actual, but my Engineer's nature can't let it go.

I'm fairly sure the tank is indeed a 20-gallon model, as I got a good look at it prior to install (gave it two coats of flex-seal to protect it from mud/stones/etc.) - there were no big things in the tank taking up volume, and the vent tube had no downward bend in it within the tank - seemed to just go straight in from the side and stop. the only baffling in the entire tank was a small rectangular thing about 1-1.5 inches high, enclosing an area something like a 5x7 or 6x9 photo, near where the pump and sender come through the front (I'm guessing this is slosh protection for when you're running on fumes). Besides, do they even sell the 13.5-gallon model any more?

This leads me to think that the sender's the issue - I don't recall the website I got it from saying it was for a 13.5-gallon tank instead of a 20-gallon tank (think it just said for 91-95XJ with 4.0L). I know it's just a pivot-armed float hanging on something like a potentiometer or variable resistor (honestly, the first thing I thought it looked like was the float ball assembly in a toilet tank).

I know that the tachometers for engines with different cylinder counts aren't directly interchangable, there's some sort of scaling at work there - is the same true of gas gauge senders for different tank capacities?

Or are there likely simpler answers, such as:

- The float arm got bent during install (I didn't do the install myself, I just sourced the parts)?

- Wonky electrical connection between the harness on the new sender and the gauge?

Since it's cold and I'm busy at work (and the Jeep's not a DD) I'm likely not going to get around to poking at it until spring, but I would like to start the information-gathering phase now.

Thanks, all!

 

[wizardPC]

Who made the pump assembly?

 

[Rob Mayercik]

Don't remember, got it from rockauto.com - I'll have to see if it mentions manufacturer name on the order confirmation email.

Think that might be important?

 

[Green Mesa XJ]

Don't remember, got it from rockauto.com - I'll have to see if it mentions manufacturer name on the order confirmation email.

Think that might be important?

Aftermarket will not read the same as oem. At least that was my experience with them.

I did a pump and sender assembly aftermarket and it never read correctly after half a tank. Part of the reason I put the oem back with a new oem supplier pump a few years ago.

In theory there should be away to adjust it to read correctly. My old aftermarket setup was kind of cheap looking I thought I break it fiddling with it so left it alone. But if it's like my old one the entire setup is different, I though at first to swap the floats or gauge sender, they didn't look interchangeable to me. And this was ten years back so a lot may have changed.

 

[Green Mesa XJ]

It should be the sp7072h you have if you got the kit tank and pump. Looks like from reviews it's a crappy sender. A lot of complaints. Sorry.

I'd hit junkyards or eBay to find a oem sender/pump. Maybe some NOS out there still and get a new sender assembly.

 

[Rob Mayercik]

Green Mesa,

I found the order details, and you nailed it - I did get the Spectra Premium SP7072H pump/sender unit. I just read the two reviews on Amazon and see what you mean about the sender.

You'd think something that simple would be hard to mess up, but I keep forgetting that the difference between Genius and Stupid is that Genius has limits. (put another way, there are are people out there that could break an anvil)

Ah, well. The pump is working fine, so for now I am disinclined to mess with it. I might cliimb underneath come spring, pop the electrical connector, and make sure that the connections are clean, but unless it stops reporting in altogether I will probably leave it alone.

Hm, just did a quick google for "gas gauge calibration" and found this link: http://www.mgexp.com/article/fuel-sender-adjust.html. Was an interesting read - perhaps sender just needs calibration? Something I can think about...

 

[Green Mesa XJ]

In theory there should be a way to fix it. You'd think as they manufacture it since they have the specs it'd be easy to check the right readings at the right places. (They list the ohm readings in the descriptions!)

I mentioned how cheap the aftermarket sender and pump I had looked but I need to give credit for them working without incident for 8 maybe 9 years with out failing. Only pulled them because well I was sick of not having accurate gauge l, that and my sister was going to be using it, knowing her I didn't want to risk her taking me literally at "Empty still has almost half a tank".

Oh if you do try to adjust it here something I learned after a few years trying to get my 85 XJs gas gauge working again. I finally learned to plug the sender up without installing it in the tank and test it with the key on.
For that old XJ it was the only way to trouble shoot the wiring trouble I was trying to trace. But if you do try to calibrate it this may be the easiest way to do it. Turn it on just so the gauge comes to life and manually adjust it until you figure it out. If it's even a error that can be compensated for. Honestly I'd probably leave it alone until it either failed or not working accurately started to really bother you.

 

[Royal Nonesuch]

Like many others, I have the same problem with my 1988. I replaced the entire assembly with a newer used Bosch model which didn't help. I did all the ground checks, pulled apart the dash and cleaned the gauge contacts, etc. Nothing changed a damn how it read. Finally I gave up and just obsessively track mileage with the tripmeter. It does bug me, but it's manageable.

If it was a street-only XJ it wouldn't bother me at all, but I will admit it still makes me nervous when I'm out in the desert and it's showing a 1/4 tank or less when I know I have 1/2. Oddly enough, the low fuel warning light still seems to be quite accurate - it pops on with about 4-5gallons left. Therefore, I have trained myself to only look at the gauge when I notice the light go on :wierd: Dunno why the light is spot-on; maybe there's a hidden ground somewhere I'm missing, or maybe the delicate-looking wrapped wire resistor/sender deal is just as janky and dumb as I secretly believe it is!