Fuel level meter

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amelecsol2000

Fuel level meter

Post by amelecsol2000 » Mon Sep 19, 2005 4:34 am

I am trying to build a fuel level meter for my sons truck, as the fuel guage does not work.
The variable resister in the tank ranges from approx 75 ohms full - to 165 ohms empty.
I have tried to use a sound level indicater circuit with led's. But to no avail.
Does anyone have any ideas?
Thank you

terri
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Re: Fuel level meter

Post by terri » Mon Sep 19, 2005 5:44 am

Make and model year, please?<p>Other diagnostics you have done? (Fusing, mechanical interference with the float from rust or dents, continuity checks, etc.?)<p>Recommendation: Don't eff with the fuel tank: don't add stuff, especially electronics, in the tank. Boeing airliners have gone down because of some supposedly safe wiring in the fuel tanks.<p>
Have you checked for Technical Service Bulletins (TSBs) on the net or with the dealer? Here are some links for your convenience:<p>
www.alldata.tsb.com<p>
www.infotraxx.com<p>
www.tsbdata.com<p>
Yeah, yeah, I know, you want to gadgeteer it and show off your expertise. The best "expertise" here is to do it the right way: Either repair or remove and replace according to the manufacturer's specs. Now that would be showing real expertise!<p>[ September 19, 2005: Message edited by: terri ]</p>
terri wd0edw

Dean Huster
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Re: Fuel level meter

Post by Dean Huster » Mon Sep 19, 2005 6:01 am

You'll have to work the tank's rheostat into a voltage divider circuit where you can get a range of voltage that you can convert using an op amp to what the "sound level meter" needs. Don't forget that the sound level meter is probably expecting an AC signal and may not work in this application without a lot of modification.<p>Although a project like this provides the opportunity to have a fuel level gauge that's deadly accurate (my, what a concept!!), you may find that a replacment gauge (check out your favorite junkyard) is a lot cheaper and less work (well, there IS the dashboard, though ...) than designing and building a circuit that will end up looking like ... well .... added-on and alien.<p>A lot of junk yards will sell the gauge, but YOU have to pull it. But that's an advantage: you can wreck THEIR car trying to figure out how to pull the dash before you try it on YOUR car!<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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jollyrgr
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Re: Fuel level meter

Post by jollyrgr » Mon Sep 19, 2005 7:26 am

Your best bet is to FIX THE TRUCK CORRECTLY! In other words figure out what failed within the original setup and replace those parts. As others have remarked, what is the year, make, and model? I've repaired fuel levels before. Sometimes it is simple as a poor ground between the tank and frame; others it is as simple as a blown fuse. The wiring in cars is strange. In many older cars (Cadillacs from 1978 to 1982 or there abouts) had a strange problem where if the fuse for the radio memory backup blew, opening the car door while the engine was running and the radio on caused the radio to turn off and the fuel gauge to drop to zero. On a 1984 Cadillac the fuse for the cigarette lighters blew and the gauge went to zero. I can't recall which car it was I had that there was a ground strap between the tank and the frame. Simply loosening and retightening the ground strap brought the guage back to normal operation.<p>The risk of having your home grown circuit fail is too great. Sparks/heat in a partially filled gas tank because you overheat the variable resistor is not worth the risk. Asking a "how do I design my own..." with a fuel system is not a good place for a novice to start. If you were asking about a water tank or something 'safe' then this would a have been a decent question for a forum such as this.<p>Comment to Dean: I wish this were true around my area. There was a number of these "pull it yourself" by me years ago but slowly they disappeared. Some, because of liability, stopped letting people into the yard. Others went under because the employees were absolutely jerks. You'd pull a part and they'd do everything but strip search you making sure you didn't pull something else. (These places lost loyal customers such as myself.) You're lucky if they still let you pull parts in your area. The places that pull parts for you charge as much if not more than buying remanufactured or even new.<p>[ September 19, 2005: Message edited by: Jolly Roger ]</p>
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Dave Dixon
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Re: Fuel level meter

Post by Dave Dixon » Mon Sep 19, 2005 10:58 am

I agree with the others. Try to fix it instead of a DYI something from scratch. It could be too dangerous.
I had a '67 Karman Ghia that I had re-wired once. The only time my fuel gauge worked was when I turned on the windshield wipers!
Best of luck,
Dave

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Re: Fuel level meter

Post by Robert Reed » Mon Sep 19, 2005 4:02 pm

Mark If you already have a connector for this External to the fuel tank, you should be safe. Problems will occur if you actually have to rewire into this internal to the tank. With less than perfect connections, a fault here could cause some minor arcing to occur (not good). Also design should include some current limiting protection to the "sending unit" so as to never cause overheating of that rheostat. As to the subject of just replacing the fuel gauge, I have an interesting but sad story on that subject. 3 years ago the fuel measuring system on my Blazer went out (and naturally it occurred 3 days before leaving for vacation). With that short of time span, I was forced to take it to a dealer for immediate repairs.It turned out I had a bad "sending unit. GM with all their infinate wisdom(?), decided they would put no floor access plate in to get to this part, so dealer has to remove tank to service. bottom line--$240 just for a simple "sending unit". I told the dealer I coundn't have been lucky enough to just have had a bad gas gauge instead. He then looked up replacement cost for this--Part only was $600 as it was integral to the instrument cluster and the whole ball of wax has to be replaced as one unit. The point of all this, if done properly, it may be worth your while to replace your gas gauge with a home brew item. I guess the age of vehicle and replacement cost will weigh heavily on your desision.

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Re: Fuel level meter

Post by josmith » Mon Sep 19, 2005 5:10 pm

How about strain guages on the support straps to measure the weight of the fuel.

amelecsol2000

Re: Fuel level meter

Post by amelecsol2000 » Mon Sep 19, 2005 7:30 pm

A lot of very logical advise. I was using the trucks original sending unit and it's own wiring harness. That is where I got the resistance reading from. I do know better than to wire inside the tank.
I will take the advise ( that is why I came here )and look to the dash gage etc.
Thank you everyone<p> Mark L.

amelecsol2000

Re: Fuel level meter

Post by amelecsol2000 » Mon Sep 19, 2005 7:41 pm

One more thing , it is a 1988 Ford F250.<p> Thanks again.

terri
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Re: Fuel level meter

Post by terri » Tue Sep 20, 2005 9:55 am

"I do know better than to wire inside the tank."<p>OK, but don't put too much power into the sending unit. Arc. Boom. I repeat and reiterate:<p>Don't eff with the fuel tank.<p>You will feel pretty bad if your son is killed in a fiery arc-and-boom because of your tinkering.<p>("Gauge" is spelled alphabetically, that is, "au" rather than "ua." I mispelled this word just about 50% of the time for years until I caught on to that fact.)<p>[ September 20, 2005: Message edited by: terri ]</p>
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Dean Huster
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Re: Fuel level meter

Post by Dean Huster » Tue Sep 20, 2005 5:42 pm

"One more thing , it is a 1988 Ford F250."<p>I have a 1979 F-250 in the back yard (this is the Ozarks, you know). I'll sell it to you cheeeeep -- you haul it. Good rebuilt and stiff C-6. And the gas gauge works -- for both tanks.<p>"Comment to Dean: I wish this were true around my area."<p>Here in SE Missouri, they're too danged lazy to pull their own. They'd rather sit around drinking beer, talk about fishin' and deer huntin' while watching the Outdoor channel.<p>Dean
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Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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jollyrgr
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Re: Fuel level meter

Post by jollyrgr » Wed Sep 21, 2005 10:29 am

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Dean Huster:

Here in SE Missouri, they're too danged lazy to pull their own. They'd rather sit around drinking beer, talk about fishin' and deer huntin' while watching the Outdoor channel.<p>Dean
<hr></blockquote><p>
Just curious, how far are you from I55? (Not asking for directions or anything.) Reason being is I came up 55 when we returned from New Orleans on our way to St. Louis (and points North East and beyond). Stayed the night in Cape Girardeau. I could have driven right past you.
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Edd
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Re: Fuel level meter

Post by Edd » Fri Sep 23, 2005 3:33 pm

Sir Mark:<p>1988 Fordecito 250 Pick-um-up:<p>Looking at the All data’s site on that unit seems to reveal only a 12VDC to the top of the fuel meter and then a flow to the tanks resistive sender to ground.
12VDC-- fuel gauge------tanks float resistor/sender----- Ground
WITH and that’s a definite WITH …….the exception of the flow of the power thru a tank changeover switch in the case that your unit is equipped with a second tank in which case the empty tank would show up as such……any chance that an errant rug rat has been inside the vehickle (go fer’ it Chris) and flipped that booger. I also see that the same gas gauge power wiring loop in the loom is feeding the tacky meter….is that working OK ? (or perchance that was an extra cost option). The last thing to check is if the ground end of the tanks sending sensor (var resistor) is getting a good ground. Make these checks and get me some feedback. That All Data schematic is not good enough to give me resolution of the wiring codes even at 64X…I will check our automotive technology group to see if they have a paper wiring diagram also.<p>GOT IT FOR YOU:
Basic 12VDC power thru wire 640 (RED/YELLOW trace) to connector 208A goes to instrument cluster term #13 then inside the cluster it passes thru the fuel metering gauge and passes out on term #12 to another connector 208A to wire 29 (YELLOW/WHITE trace) which then routes all the waaaaaay down to the sender /var resistor of the tank and that sender is looking for a food solid ground on its wire # 57 (BLACK). Thats the routing....now can you fix that basic ohmmeter for us ....OK then ...make the son dig down into the trenches !
73's de Edd
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:)<p>[ September 23, 2005: Message edited by: Edd Whatley ]</p>

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Re: Fuel level meter

Post by dwdw » Sat Sep 24, 2005 12:03 am

If the gas tank sending unit is OK and the dash unit is bad. Its a pain and costly changing it
I added a gas guage to my tracter a few years ago.
I bought the kit from JC whitney. I think it was only about $20 or $25. It been working fine. They also had guages for different resistance values.
I hope this helped
dwdw

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jollyrgr
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Re: Fuel level meter

Post by jollyrgr » Tue Sep 27, 2005 11:18 pm

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Edd Whatley:
Sir Mark:<p>1988 Fordecito 250 Pick-um-up:<p>Looking at the All data’s site on that unit seems to reveal only a 12VDC to the top of the fuel meter and then a flow to the tanks resistive sender to ground.
12VDC-- fuel gauge------tanks float resistor/sender----- Ground
<hr></blockquote><p>Edd, I think now that it might have been my 1972 Ford Country Squire station wagon that had the ground problem with the fuel guage. (See earlier post.) This car had LOTS of ground problems because it rusted away in the back end. For the tail lights to work I had to run a ground wire from the very back of the car up to under the back seat to find a suitable ground point. If the car/truck is rusting away, this could POSSIBLY be the issue.
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