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Another dual tank/guage problem

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Starliner

Another dual tank/guage problem

Today I replaced the front tank sender which i confirmed to be ng.
I also checked the new one prior to installing it.
Also today i dropped my rear tank (which had a new, working sending unit), just to replace the filler hose.
All buttoned up, on my way to the gas station and the front showed empty, (as it was), and the rear showed just off empty because of the 2 gallons that were still in it.
Driving from the gas station and both tank show as empty now.
I kept switching back and fourth but nothing showed. I tried key on/off but still no go.
I checked diagrams and I cant figure out how the 5 volts gets to the sending units or where they ground, nor can I tell if the tank selector switch has any interaction with the sending units-to-guage.
Not sure if fuse 15 has any purpose besides switching the tank valve.

Of course tomorrow I will take a volt meter to fuse #15 but any other ideas please shoot them my way.
I realize this is a popular topic but couldnt find the answer.

Sorry, wish I could have met the show deadline.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC

ArdWrknTrk

Re: Another dual tank/guage problem

Administrator

The instrument cluster voltage regulator pulses the D.C. voltage of the truck to create an 'average' 5.5V or so.
The cluster flex circuit routes this through the gauge and out to the tanks.
Depending on your system (ill have to check) the fuel switching valve changes which sender is connected.
Power goes through the sender (rheostat) and then to ground.

So, the sender is limiting power through the gauge from the ground side.

If you have a functioning oil pressure or water temp, then the problem is not power.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

ArdWrknTrk

Re: Another dual tank/guage problem

Administrator

This post was updated on .

Yep.
Here is pg 106 from the EVTM.

Ground 701 is behind the instrument panel, near the right of the radio.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Another dual tank/guage problem

Administrator

In reply to this post by Starliner

Joe - First, get me the entry info today and I'll get it in.

Jim - I get lost, as you know, in what fuel systems where used when. Are you sure Joe's '84 will have that fuel system setup? I would have thought that his '84 w/a 351W would have this setup:

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

ArdWrknTrk

Re: Another dual tank/guage problem

Administrator

Is there no egg on your face smiley???

So perhaps it is the switch in the climate control bezel that is faulty.
Or connector 208.

But it's definitely not the fuse, if the other gauges function.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Another dual tank/guage problem

Administrator

I agree that the fuse powering the gauges themselves is working. So it must be something else that is in common with both tanks, and that does suggest the switch or the connector.

Gary, AKA "Gary fellow": Profile

Starliner

Re: Another dual tank/guage problem

Guys I really appreciate the thoughtful response.
Back to work.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC

Machspeed

Re: Another dual tank/guage problem

Administrator

This post was updated on .

Following this thread closely, as I too have no fuel gauge readings. Several years ago did what you did and replaced both sending units. I had the bed off when I did this and the gauges seemed to work fine. I could move the floats and watch the gauge move. And, they seemed to be where they needed to be based off the amount of fuel in the tanks. However, when I put the bed back on, I noted no readings. Haven't had a working fuel gauge in years. Time to fix! Please keep us advised on your hopeful fix?

John

"Blackie" - 1986 F150 4x4 - Mildly warmed over 351W HO - Original owner

Starliner

Re: Another dual tank/guage problem

Sure will.
Thanks to the guys I now understand that:
If the other guages work I am getting ground,
Also,
Going to the sending unit should be around 5.5v and that, or less going back to the guage.

These guys know their stuff.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC

ArdWrknTrk

Re: Another dual tank/guage problem

Administrator

Note that you will see pulsing voltage on the sender wire.
The ICVR acts like a very fast flasher module.

Also you will see the zigzag line between the 'N' and ICVR in the diagrams above.
That is a resistor used to limit current applied to the instruments.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Starliner

Re: Another dual tank/guage problem

Out of the blue the rear tank started reading again.
Front tank still no show on the guage.
Actually not fully no go, it comes right up to E when I turn the key on.
I guess I'll run the tank empty and start over.
I'm leaning toward a bad plug at the sending unit.
I will update.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC

Gary Lewis

Re: Another dual tank/guage problem

Administrator

Joe - You can test by grounding the wire that goes to the sending unit. The gauge should go to Full and then some.

So if you ground the DB/Y wire at the tank and the gauge pegs you'll know that the wiring to the front sending unit is good. Ditto the Y/LB Hash wire for the rear tank. Don't leave it on forever, but you can ground it for a while and not hurt anything.

Gary, AKA "Gary fellow": Profile

Starliner

Re: Another dual tank/guage problem

Wow, cool trick knowing it wont kill things.
You guys have obviously suffered through this stuff to have suck a knowledge base.
Thanks.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC

Gary Lewis

Re: Another dual tank/guage problem

Administrator

Some of my "knowledge" has been acquired vicariously as I've been "reading the mail" regarding these trucks on forums for over a decade.

There's another test that might actually be easier if you have a test light. You can connect it to ground on one side and to the wire to the sending unit on the other. It should blink if the circuit is good.

Gary, AKA "Gary fellow": Profile

Machspeed

Re: Another dual tank/guage problem

Administrator

In reply to this post by Starliner

Joe, are your tanks out? I'm almost wondering if it would be easier to pull the bed than to drop the tanks should I have to go there.

John

"Blackie" - 1986 F150 4x4 - Mildly warmed over 351W HO - Original owner

Starliner

Re: Another dual tank/guage problem

Sure, blinking because of the pulsing voltage, I will look.
Because there is no rust, i can drop both tanks in 20 minutes.
People love these trucks. I often hear "what year is that" pretty much every day. Now that I have it running right I love driving it.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC

Starliner

Re: Another dual tank/guage problem

Gremlins.
Now both guages are working.
I'm thinking intermittent ground issue, (maybe wiggle the dash plug), but since it ain't broke now I am going to leave it be.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC

Machspeed

Re: Another dual tank/guage problem

Administrator

Well good for you! Bummer for me though, as I was hoping I could find some common issue for my fix, which I think may be ground related.

John

"Blackie" - 1986 F150 4x4 - Mildly warmed over 351W HO - Original owner

FuzzFace2

Re: Another dual tank/guage problem

IIRC the ground wire for the rear of the 82 or 83> trucks runs to the fire wall behind the radio as a bunch go there.

I am pretty sure the 80/81 trucks don't have this ground and things ground to the frame or somewhere else on the body. I know my 81 does not have this "behind the radio" ground but has a bunch on the firewall in the engine bay side.

Also how is the ground from the battery to motor / frame / body?
If the frame or body ground is in question that could be the issue.
Dave ----

Dave G.
81 F100 flare side 300 six / AA OD / NP435 / 2.75 gear
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck -RIP
http://cars.grantskingdom1.com/index.php/1981-Ford-F100

Starliner

Re: Another dual tank/guage problem

Definitely clean all grounds you can on an old truck.
I'm not sure why my guages woke up but I CAN tell you that I do not baby the girl and maybe hitting a good bump helped.

JOE
1984 F250 HD 2wd auto w/air,
351W, 2bbl, Dana 60 3.73, no EEC