Fuel gauges read too low

[Real1shep]

Started the thread about covering up the below the dash wiring and whatnot on a Dodge chassis 1978 Brave with the 440-3. I finally explained to my customers that my strong suit is not fabricating panels to cover up wires and whatever. I got a reprieve from that task.

So moving on to everything else in this old gal W% ....I dropped both the aux and the main tank. Took out both sending units and put them on the bench. One was fine, the other was not. The bad one I took apart, examined the track and cleaned all the corrosion off. Both sending units then worked perfectly with a nice steady Ohm scale reading up & down as the float lever moved.

Put everything back in including a new switchover valve. Both tanks switch now from the dash just fine. My problem is that the gauge reads low for both tanks. I.e., when the back tank is switched over, it reads a little over a 1/4 tank when we actually have 1/2 tank in there. On the aux tank it reads a smidgen over 1/2 , we really have about 3/4 of a tank in there.

I assume it's the gauge...it's not an individual gauge alone, as it's in a combo cluster.  Any way to check the accuracy of the gauge itself or change its readings?

Also, the Brave was made in those nebulous yrs where RV's, boats and off-road equipment got a free pass to keep running on regular gas.....even though unleaded had been out for everyone since 1975. I know there's some Mopar heads who would know probably by serial #, but I need to know if the 440-3 of that yr production had the hardened valves and seats?

Kevin

[Elandan2]

440-3 engines had induction hardened seats and exhaust valve rotators. On ours, the exhaust valves in cylinders 3 and 5, and 4 and 6, finally started to succumb to the added heat of having them located next to each other. I had the heads reworked with stellite seats pressed in. That ended the problem of using unleaded fuel.   

[Rickf1985]

Rick answered your question on the engine so I will try to address the gas gauge. It could be the gauge but usually if the gauge is bad it simply does not work. I don't know if the Dodge used a dashboard voltage regulator or a pulse type setup for the gauges. If you can get a meter on the output side of the gauge see if you are getting a steady voltage and what is the voltage. In any case if it is a voltage issue it should be affecting all of the gauges. Gas, oil pressure and water temp. It could also be something as simple as a bad ground. From all you have done at the tanks I will assume you checked the grounds back there so look for the ground point for the gauges/dashboard. This usually requires a wiring diagram which I am pretty sure you don't have so I can't help you there, But what I always did in these situations is just pick a wiring loom and follow it from end to end and any grounds take them off, clean and replace. Do this for all of the looms. It is the only way to be sure the wiring grounds are all good and this could fix things you did not even know where on the list.

[Real1shep]

Thanks, I'm gonna pass on the info to the owners to use a lead substitute when traveling with this engine. It may be expensive, but in the long term I think it will pay off.

I made sure both tanks were well grounded and cleaned all the contact points back to shiny metal painstakingly. The fact that both tanks act the same with respect to the gauge, I'm inclined to believe it's a problem in the dash wiring/ground. It's very possible this gas gauge issue had been a problem before for yrs and I'm flogging a dead horse.

No, I don't have a wiring diagram.

Kevin

[Oz]

I know this was a common issue with 1973 through 1975.  After that, I'm not really sure.

Since you are a Full Member, go to the member area -> manuals, diagrams and tech info.

In the right column, you will find an excellent article on troubleshooting and fixing these troublesome fuel gauges!  It's at least worth a read.

You can contact Winnebago and they will send you a wiring diagram.