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#534296 - January 29th 2012 5:43 am Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Ram4ever Offline



Registered: March 26th 2007 8:05 pm
Posts: 3671
Loc: Dundee, Michigan
Your amp gauge reading is unrelated to the erroneous readings of the other gauges; it's not powered by the voltage limiter.

You said the fuel gauge appears to be working with the new voltage limiter... what does it actually read that indicates this? I'm suspicious of the readings being inaccurate, as the other gauges haven't changed, and both are acting up. I'm 102% with Boot on using your original regulator, at least until you obtain realistic readings from your fuel gauge.

When the oil and temperature gauges peg, that usually indicates faulty grounding of the instrument cluster, just like Reed said. The "E" terminal on the round multi-pin instrument cluster connector should go to a white/black wire terminating in a terminal which connects somewhere on the dash/chassis metal frame to provide the instrument cluster ground. You said you traced a ground, but have you actually tried checking with an ohm meter between the (-) connection where the voltage limiter plugs in, to the chassis to see if there really is continuity? You could always run a temporary wire directly from the voltage limiter to the battery to be sure.

Typically what actually fails on these fuel gauge systems that throws everyone for a loop while they replace all the other parts right up to the bitter end, is the ground wire that runs between the sending unit on the fuel tank and the frame. It can fail (frequently due to corrosion) internally within it's plastic insulation, or it can have a bad connection on either end, either at the terminals or the contact surfaces. The simplest thing to do is replace it outright, and clean up both the surfaces it connects to. I'd put some dielectric grease on the cleaned up connections to help keep Oxygen and moisture out.

I have to wonder if the tab off the back of the NAPA regulator is actually the flange of a three-terminal solid state regulator like Reed referred you to? They do have a small screw-hole for mounting to a heatsink. If the NAPA limiter is in fact a solid state regulator, (not so easy to tell without measuring it) that tab may need to be grounded since a ground reference is needed for the solid state device to regulate, and that ground reference can't readily be derived from only the input and output terminals.

BTW, if you make up your own solid state regulator, please try to locate a "low dropout" version of a three-terminal voltage regulator; something like an LM2940. They are much less common, but are what was really designed for use in automotive applications. They will regulate over a much wider range of voltage before losing regulation. This is especially important if you may run your battery down. As further benefits, they are typically far more resistant to voltage reversals and nasty voltage spikes than a generic LM7805 regulator, and will disconnect themselves and the load as a protection mechanism in case of a drastic overvoltage condition.
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#534314 - January 29th 2012 8:29 am Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Lee7673 Offline
pooh-bah

Registered: July 26th 2009 3:08 pm
Posts: 4620
Loc: Maryland
Let me see if I can answer.

"You said the fuel gauge appears to be working with the new voltage limiter... what does it actually read that indicates this?"
With the new limiter the fuel gauge rises to about 3/8 of a tank which is close as I have about 8.5 gallons of gas in it and its a 22 gallon tank (being that I just installed the tank I have kept track of the amount of gas I put in). With the old limiter the fuel gauge doesn't move at all (it is just below "E".)

"The "E" terminal on the round multi-pin instrument cluster connector should go to a white/black wire terminating in a terminal which connects somewhere on the dash/chassis metal frame to provide the instrument cluster ground. You said you traced a ground, but have you actually tried checking with an ohm meter between the (-) connection where the voltage limiter plugs in, to the chassis to see if there really is continuity? You could always run a temporary wire directly from the voltage limiter to the battery to be sure."
I found the ground wire (white with black tracer) and traced it to a spot on the dash next to the steering column. I took it of and cleaned it real good and sanded down the dash as well to get a good ground. ( I didn't check it with an ohm meter - I will try that today). I did take a ground wire off of the back tab of the voltage limiter (that's the ground tab - its just an extension of the front grounding tab) and ran it to a bolt on the motor but that didn't change anything.

'Typically what actually fails on these fuel gauge systems that throws everyone for a loop while they replace all the other parts right up to the bitter end, is the ground wire that runs between the sending unit on the fuel tank and the frame."
I did check this. I decided to use the old wire vs the new one that came with the sending unis as it had a better connection and fit on the sending unit better. I did check it with a meter and I cleaned it (and the frame) real good to make sure I had a good ground.

"I have to wonder if the tab off the back of the NAPA regulator is actually the flange of a three-terminal solid state regulator like Reed referred you to? They do have a small screw-hole for mounting to a heatsink. If the NAPA limiter is in fact a solid state regulator, (not so easy to tell without measuring it) that tab may need to be grounded since a ground reference is needed for the solid state device to regulate, and that ground reference can't readily be derived from only the input and output terminals."
It is definitely a ground. It is just an extension of the same tab on the front that is the grounding tab (it is all one piece). I held a ground wire to it to the frame but it wasn't screwed or fitted on for a real good connection - was going to try to ground it today with a fitting) I don't know how to tell if it is a "solid state device".

"BTW, if you make up your own solid state regulator"...
That is WAY beyond my knowledge smile

I am going to try to get a better ground on ther limiter today and see what happens or try to run another hot wire from the limiter to the fuel gauge and see what happens......it's driving me crazy!!!











Edited by Lee7673 (January 29th 2012 8:32 am)
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#534547 - January 30th 2012 8:20 am Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
DrBob Offline
pooh-bah

Registered: October 29th 2009 1:21 pm
Posts: 3001
Loc: Stephentown NY
Hope this isn't your problem but I had a wire come off inside the tank before.
_________________________
I don't mind Coming to work,
but that 8hr wait to go home is a bitch.
No matter how little I do,
I always feel I could do less.
"The only thing wrong with a perfect drive to work is that you
end up at work."
NOVA VANS
1990 Dodge B150

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#534710 - January 30th 2012 9:05 pm Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Lee7673 Offline
pooh-bah

Registered: July 26th 2009 3:08 pm
Posts: 4620
Loc: Maryland
I can get all of the gauges working if I run both voltage limiters!!! I am beginning to think that there is something wrong with the old voltage limiter and the new one. As I mentioned before with the old one in, all of the gauges work except the fuel gauge. With the new one in, the only gauge that works is the fuel gauge!!!! If I put the old voltage limiter in and take the hot feed off of the fuel gauge and then hook up the new voltage regulator and run it just to the fuel gauge all of the gauges work.

Is there an issue with hooking it up this way (using two voltage limiters)? If I do this I understand that the hot feed to the 2nd limiter will have to be one that works off of the key.

I am thinking about buying another voltage limiter (because I do think the 1st one is defective) but it is getting expensive since they won't take any electrical parts back.

What do you think????

PS THANKS for all of the help so far!!!!
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#534752 - January 30th 2012 10:47 pm Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Reed Offline
carpal tunnel

Registered: August 27th 2001 12:00 pm
Posts: 8446
Loc: Fircrest, WA
Uh, if I were you I would pick up a spare instrument cluster and try swapping the whole mess out. You are getting some funky results that sound like a combination of bad wiring and bad components.
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#534786 - January 31st 2012 12:43 am Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Boot Offline

Captain Overkill



Registered: November 16th 2003 12:00 pm
Posts: 3116
Loc: Myrtle Beach, SC
If it works, and you can secure the second limiter, I'd say run it. But, if it were me, I'd run an inline fuse (10a max) on the J8-18BK/W line that runs into the "H" terminal on the circuit board plug in. This wire feeds the power to the gauges only, but comes in live from the key switch.

If you follow the diagram back from that plug in, you'll see that that particular wire runs off the key switch terminal 11, which also feeds a bunch of other things as well, on the J10-16R line. So I'd say better safe than sorry.
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#535207 - February 01st 2012 12:21 am Re: HELP PLEASE with fuel gauge/sending unit [Re: Boot]
vandude360 Offline
enthusiast

Registered: February 05th 2009 6:02 pm
Posts: 243
Loc: puyallup, washington
Here is an easy method (listed in the '77 Factory Service Manual) of testing your voltage limiter:

Connect one lead of a voltmeter to the temperature sending unit and the other lead to a good ground.

leave the sending unit lead wire (pink w/black tracer line) attached to the sending unit.

Turn the inition switch to the "ON" position.

A fluctuating voltmeter indicates the voltage limiter is operating.
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#535883 - February 02nd 2012 10:45 pm Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Lee7673 Offline
pooh-bah

Registered: July 26th 2009 3:08 pm
Posts: 4620
Loc: Maryland
AGHHHHH......after replacing (and checking) everything else, I believe the new sending unit I just installed is defective and is the culprit. Looks like I will dropping the tank again this weekend!!!!
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#536066 - February 03rd 2012 1:17 pm Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Boot Offline

Captain Overkill



Registered: November 16th 2003 12:00 pm
Posts: 3116
Loc: Myrtle Beach, SC
bummer man. Sorry to hear that, but glad you're persistant!
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#536664 - February 05th 2012 9:36 pm Re: HELP PLEASE with fuel gauge/sending unit [Re: Lee7673]
Lee7673 Offline
pooh-bah

Registered: July 26th 2009 3:08 pm
Posts: 4620
Loc: Maryland
OK....here is the update and it is driving me nuts!!!! Hopefully someone will have some input or an idea. I ran every test and scenario that I could think of and it all kept leading me back to a bad sending unit (even though the sending unit and tank were brand new). So....I got another sending unit and dropped the tank (again) to replace it. When I pulled out the new sending unit it worked (I hooked it up to the gauge) but wouldn't work in the tank. I installed the new sending unit (I did check to make sure it was working before I installed it) and my fuel gauge only comes up to "E" (I have 15 gallons of fuel in it). I have tried to isolate everything to find the issue. I ran a new hot lead direct from the battery to a limiter, a new ground wire direct from the battery to the sending unit (trying to eliminate a bad wire), a new wire from the sending unit to the gauge and it still will only go up to "E". So....it appears that both of the new sending units work but NOT when installed in the tank). Why??? Also...one other thing...if I wire the gauge up without the voltage limiter the gauge reads correctly. I did this the first time when I had 3/8 of a tank and it would read empty when hooked up through the circuit board but would read 3/8 when hooked up to 12 volts (which is what it should have read with the amount of gas I had). I tried it again today and now it reads empty when hooked up correctly but will read about 5/8 of a tank when hooked up to 12 volts (which would be correct with the amount of fuel I have in it now). Why would the gauge read correctly when hooked up direct? I know it is supposed to run at 5 volts coming out of the limiter. My friend and I have probably spent 12 hours (or more) trying to figure this out....including dropping the tank twice, replacing the sending unit twice, changing out voltage limiters, and even trying 3 different gauges and I always get the same results. What am I missing? I REALLY need some help.....its driving me NUTS!!!!
Thanks....
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