Access to the fuel tank sending unit on '77

[merrill77]

I know I could access it on my 87 GW...but the TSM pictures seem to indicate this would not be the case on my '77. Is that correct - I need to drop the tank?

After un-kinking the vent line, I am starting to think that I *am* filling the tank completely and that the gauge and/or sending unit are reporting lower fuel than what is actually in the tank. It only goes a little past 3/4 when the evidence says it is full (gas coming back out the filler).

I've been a little worried about letting the tank get too low - as I've heard that the tank/pickup design allows an FSJ to run "out of gas" with 4-5 gallons still in the tank. Between these two, I'm only putting 8 gallons in the tank at a time. I just got a AAA membership, so maybe I should just drive around until the gauge hits "E" and see what happens?

[mx71]

You need to drop the tank.

[merrill77]

Thanks.

Any my apologies for the duplicate posts - I received SQL errors several times when posting this...looks like the posts went through before reaching the error

[letank]

I've been a little worried about letting the tank get too low - as I've heard that the tank/pickup design allows an FSJ to run "out of gas" with 4-5 gallons still in the tank. Between these two, I'm only putting 8 gallons in the tank at a time. I just got a AAA membership, so maybe I should just drive around until the gauge hits "E" and see what happens?

It depends if you still have the sock at the tip of the pick up tube, or if the PO modified it. I removed my sock at least 150Kmiles ago, and put a simple hose to make up for the loss of depth. You do not want to go all the way down to the floor of the tank. Then add a filter before you Epump. Where is your electric pump now?

THe last time I ran out of gas, I filled up with 21 gallons...

Otherwise the next step to make your gauges more accurate with the CVR mod

http://www.fsjnetwork.com/forum/viewtop ... 4&start=20

[merrill77]

I've been a little worried about letting the tank get too low - as I've heard that the tank/pickup design allows an FSJ to run "out of gas" with 4-5 gallons still in the tank. Between these two, I'm only putting 8 gallons in the tank at a time. I just got a AAA membership, so maybe I should just drive around until the gauge hits "E" and see what happens?

It depends if you still have the sock at the tip of the pick up tube, or if the PO modified it. I removed my sock at least 150Kmiles ago, and put a simple hose to make up for the loss of depth. You do not want to go all the way down to the floor of the tank. Then add a filter before you Epump. Where is your electric pump now?

What is this sock of which you speak? I don't see it on the TSM diagram.

I'm not actually positive where the fuel pump is. I thought it was just ahead of the tank, but the red & black wires go right past what must be, after looking at the pic again, the fuel filter.

THe last time I ran out of gas, I filled up with 21 gallons...

That is encouraging

Otherwise the next step to make your gauges more accurate with the CVR mod

http://www.fsjnetwork.com/forum/viewtop ... 4&start=20

So you think incorrect voltage at the cluster may be to blame for the inaccuracy of the fuel gauge? Hmmm...

[letank]

What is this sock of which you speak? I don't see it on the TSM diagram.

I need to look at the parts manual, in fact bj's carries the sock or fuel filter at the intake in the gas tank

I'm not actually positive where the fuel pump is. I thought it was just ahead of the tank, but the red & black wires go right past what must be, after looking at the pic again, the fuel filter.

It is probably above the rear differential or find the source of the buzzing sound

Otherwise the next step to make your gauges more accurate with the CVR mod

http://www.fsjnetwork.com/forum/viewtop ... 4&start=20

So you think incorrect voltage at the cluster may be to blame for the inaccuracy of the fuel gauge? Hmmm...

Our gauges are notorious for being tempermental due to the basic design of the CVR based on a heated resistor built into the temperature gauge. Usually at some point -every 100Kmiles from my experience- the resistor or CVR fries slowly and you gauges are either too high or too low for gas, oil and temp. changing the coolant temp gauge would fix, but now looking at the units sold, it is a bit below the OEM specs, the best way and this prooved well for my was to build your own CVR as pictured and referenced in the above post. There is a good article that I found in an old blog in 94 where the whole CVR basis is discussed, i posted it on the mothership, these guys even considered better to do a CVR for ea gauge, I did one CVR for all 3. it is fairly accurate, going up hill, the temp will slowly creep up, and after a long downhill the coolant will go down, as low as the cold indicator in below 50F, the trans temp will follow a lot slower than the coolant, my trans temp gauge is aftermarket and is independent of the cluster CVR.

the long story about the CVR, see post #4
http://www.ifsja.org/forums/vb/showthread.php?t=185312

Edit thank you Flint for adding the sock ref

and I forgot to say that the sender should be tested for accuracy with a resistance load as per specs on the TSM, another llink to add

You need to check your gauge and sensor for accuracy, if you put a known resistance between the engine ground and the temperature, oil pressure or gas gauge wire(s) outside the cab with 15,25, and 78 ohm resistors (from radioshack)... you should have Hot , middle, then cold., or high mid low for pressure or gas

The other way around it to see the resistance value of your temp sensor between ground and the temp sensor you will read a high resistance when cold.... > 80 ohms and so forth.

For those reading, remember that for the 86 and latter the resistance scheme was changed, no CVR and the resistance values were different

I did a little gizmo with a breadboard




and put all those resistors, it is convenient to test gas as well as oil pressure and gas tank sender as the values are the same or similar.

[fulsizjeep]

What is this sock of which you speak? I don't see it on the TSM diagram.

So you think incorrect voltage at the cluster may be to blame for the inaccuracy of the fuel gauge? Hmmm...

http://www.bjsoffroad.com/Fuel-Pickup-T ... p_822.html
The sock (filter) fits on the end of the pick up tube.

Voltage:
There may be a voltage problem at the instrument cluster if the power to the AMP gauge is loose or corroded. I have personally found that the fuel gauge is a little more accurate when I put a ground wire from the stock metal tank to the frame. If the tank has been swapped out for a poly tank (MTS or 80 and up stock tank), you need a ground from the sender to the frame. We put an MTS tank in my wife's 77 many years ago because the internal baffle detached in the original tank. I attached the ground wire to the sender lock ring where it is screwed into the tank.

[merrill77]

It is probably above the rear differential or find the source of the buzzing sound

It is near the back of the tank, on the inboard side. I found the original fuel lines still in place, I think - I see that they run on the other side of the tank. Maybe I should re-route the fuel line over there, farther away from the exhaust.

I just patched up the exhaust - the crimp-joint was just barely holding the muffler to the pipe - it may have been leaking a lot of hot exhaust from there. It finally broke loose a few days ago and got REALLY loud. I combined some of the fiberglass patch tape with a 2" wide exhaust clamp. Will see how it holds.

I'm going to come back to your advice on checking the gauge and the cluster after I sort out a few more pressing problems. I've done about 100 miles since the last fill-up. With city miles, that probably means 13-14 gallons. Once the needle got down around 1/4, it kinda stopped going lower. I'll see how that plays out.

Thanks to all for the advice! I'd be lost without you guys