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BJ8 Suspiciously good fuel economy. ... nope fuel gauge is pinned

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CDNRDTRK Avatar
CDNRDTRK G G.
CALGARY, AB, Canada   CAN
I finally got a good run in my 1967 Austin-Healey today and noticed that my fuel gauge did not waiver from the F. I thinking that I was getting some great fuel economy then I realized that this is a 1967 Austin-Healey. smiling smiley
To err on the side of caution I put some fuel in being aware not to overfill up the filler neck.

With the ignition turned off the guage sits at empty. As soon as the key is turned to run it pins the needle at F.

I reviewed other posts on the forum regarding similar fuel guage problems and checked my connection at the guage and all seemed in order.

I next pulled out the fuel sender and compared to the schematic as to orientation of the sender. It appears my sender had been installed in the incorrect orientation.

I corrected the orientation of the sender and checked the resistance which didn't appear to vary from more than 46 ohms.

I'm thinking that the sender is defective however is there any other troubleshooting tips before I order new sending unit?

Suggestions?

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petnatcar Avatar
petnatcar Silver Member Peter Carbone
Watertown, NY, USA   USA
Did you rock the sender up and down with the ignition key on while watching the Fuel Gauge?
This may help pinpoint the problem if you get any movement on the gauge.

Be sure to disconnect the power from the coil if you leave the key on for more then 30 seconds.
I burned out a brand new coil once due to this oversight.

Good luck,
Peter

Jack T Avatar
Greensburg, PA, USA   USA
Do you have a separate ground wire to the tank? A pegged needle on Full is what happens without a good ground.

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pkoot Avatar
pkoot Peter K
Alkmaar, NH, Netherlands   NLD
Hi,

I would first check the gauge without the sender. Instead of the sender use 2 resistors of 80 ohm, which you can switch in parallel to 40 ohms. 0 ohm is empty, 80 ohm is full and 40 ohm is half full. This is a way to calibrate the fuel gauge with the 2 screws on the back and moving the coil inside. But be carefull!! The wires inside of the gauge are very thin and can easely break.
On YouTube you can find a lot of information of how to calibrate the gauge or check the sender.

Peter

Phase2 Avatar
Phase2 Derek Snead
Augusta, GA, USA   USA
I've noticed coil gets hot when key is left on but I didn't know I could damage coil in 30 seconds! Derek Phase 2

petnatcar Avatar
petnatcar Silver Member Peter Carbone
Watertown, NY, USA   USA
Derek,

From what I’ve learned the engine needs to be running in order to keep the coil within operating temperatures.

They run hot anyways but will burn out if the engine isn’t running unless you disconnect the power lead.

I had a new coil and was running some electrical tests with the engine off but the switch on and power to the coil.
This resulted in the engine not not starting again for 2 weeks.

After pulling my hair out for a week I broke down and had it towed to a shop
where by the mechanic replaced the new coil with one from the garbage can and of course it started right up, and
I've been running it like this for the past 2 years. Go figure. (see attached pic)

I would like a little more clarification on this as well but I wasn’t going to argue with
the mechanic who got my engine running better then ever in the past 40 years.

He also suggested I make a solid dedicated ground point. (see attached pic)

So whenever I work on the electrics I unplug the coil first.

Good luck,
Peter


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CDNRDTRK Avatar
CDNRDTRK G G.
CALGARY, AB, Canada   CAN
I did some additional troubleshooting and I have a decent ground at the sender. I also isolated the sender lead and the gauge still pins over to Full. The ground at the gauge also appears to be good.
Is it possible that the gauge itself is defective?

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RAC68 Avatar
RAC68 Raymond Carbone
NJ, Jersey Shore, USA   USA
Hi All,

You mentioned having a good ground at the sender. How good? If you have installed a fuel filter between the tank and pump by severing the metal fuel line, you have cut the main ground connection for the tank/sender. Unless you have installed a replacement ground line between the tank/sender mount and local grounding point in the boot, your tank may be receiving its ground through a warn spot between the bottom of the tank and floor/frame and continuity could vary with humidity and movement.

Additionally, you mentioned having a reading of 40 Ohms on the sender. Does the reading vary with the rise and fall of the float. Keep in mind that, over time, the evaporation of fuel will leave an insulating coat of varnish on the sender coil and float contact. I have cleaned these contacts with electronic tuner cleaner to regain good connections and changing readings through the full length of float travel along the coil.

Further, you mentioned having a good ground at the gauge. Since the reading of the gauge is dependent upon a varying ground reading, I would check the continuity of the line between the gauge and sending unit. If you have a faulty line that is grounded, I believe you would getting an Ohms reading that would pin your gauge to full.

As previously mentioned, the gauge reading can be altered by slightly loosening and moving 2 nuts at the back of the gauge securing 2 internal coils. DO NOT REMOVE THE NUTS and if loosened MOVE THEM ALONG THEIR SLOTTED PATH VERY CAREFULLY AND SLOWLY. Again, as previously mentioned, these nuts secure 2 internal coils that alter the needle's position on the full side and empty side by magnetically influencing the needle's counterbalance. However, this adjustment is meant for small differences and I don't believe will change the condition of a pegged gauge.

That's all I can think of for now. All the best luck,
Ray(64BJ8P1)

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