I'm looking for any imformation on the values,part#s for the low fuel thermister on the fuelsender. I've not had any luck with electronic supply outlets without some kind of # Thanks Ragtop:zap:
ragtop
Great question (hope this posts keeps it alive until someone answers).
I spent last weekend replacing the thermistor on my sender with one from a rebuilt unit (the "rebuilt" one had a screw used to replace the low fuel lead terminal, only problem was the screw went through the unit - only a problem if you add fuel to the tank, I guess).
Anyway, the replacement thermistor did not have any part number. I checked to verify it functioned [was not an open circuit, and resistance changed with temperature (decreasing resistance with increasing temperature)], but can not rely on the resistance values.
After the day's work to install, the light still does not work (aside from the self-test on startup).
No doubt someone here has the answer.
Otherwise, I'll have to crawl back under and determine the threshold resistance to get the light to come on, and then start a science project to determine the temperature of a device when immersed in fuel vs. fuel evaporating from the part surface vs. ambient air, to determine the required performance.
That's a lot of effort for an idiot light.
I spent last weekend replacing the thermistor on my sender with one from a rebuilt unit (the "rebuilt" one had a screw used to replace the low fuel lead terminal, only problem was the screw went through the unit - only a problem if you add fuel to the tank, I guess).
Anyway, the replacement thermistor did not have any part number. I checked to verify it functioned [was not an open circuit, and resistance changed with temperature (decreasing resistance with increasing temperature)], but can not rely on the resistance values.
After the day's work to install, the light still does not work (aside from the self-test on startup).
No doubt someone here has the answer.
Otherwise, I'll have to crawl back under and determine the threshold resistance to get the light to come on, and then start a science project to determine the temperature of a device when immersed in fuel vs. fuel evaporating from the part surface vs. ambient air, to determine the required performance.
That's a lot of effort for an idiot light.
Sounds like a science project. I need a whole new unit for my XR-7. Whish someone would start reproducing them with high quality parts. Every XR-7 and Eliminator could probably use one or keep one as a spare.
Havn't tackled my problem yet. Waiting for warmer days.
Havn't tackled my problem yet. Waiting for warmer days.
No personal experience, but Mustangs Unlimited sells a thermistor...
http://www.mustangsunlimited.com/itemdy00.asp?T1=F008+01
Has anyone tried it?
http://www.mustangsunlimited.com/itemdy00.asp?T1=F008+01
Has anyone tried it?
I bought the thermistor and now the light never goes out!
This should be a cheap part, not $35.
Lets figure this one out.
Thanks, Bill B
This should be a cheap part, not $35.
Lets figure this one out.
Thanks, Bill B
the operation of the Tmister is in the shop manuals. I don't recall it was temp related. My recollection was a floating tin ball in there that makes the connection when fuel drops down in tank. MAybe I'm wrong about it cause it was years ago I looked into it however that is what I recall. Someone take a look in the shop manuals and let us know?
If guys are finding the lite still does not work right we need to determine if its the part or the install thats at fault.
If guys are finding the lite still does not work right we need to determine if its the part or the install thats at fault.
I would like to add some imformation as I understand it. A thermister is a temperture sensitive resister. The one used for the Cougars is a negitive temperture coefficient which means the resistance drops as temperture rises. These small parts are very cheap to purchase at electroic stores, a couple bucks. Was offered one of these cheap parts (thermister only) for $30 by someone who read my sad story, claiming it took a lot of research by him to identify this part. Not a bad mark up. GOUGE. As for the light not coming on at start up, must be other problem in your system. There is a low fuel relay somewhere under the dash with a 45 ohm ballast resister in parallel with the relay coil. Thanks for the intrest. And if I do get a number you will see it on this site. Ragtopragtop said:
I would like to add some imformation as I understand it. A thermister is a temperture sensitive resister. The one used for the Cougars is a negitive temperture coefficient which means the resistance drops as temperture rises. These small parts are very cheap to purchase at electroic stores, a couple bucks. Was offered one of these cheap parts (thermister only) for $30 by someone who read my sad story, claiming it took a lot of research by him to identify this part. Not a bad mark up. GOUGE. As for the light not coming on at start up, must be other problem in your system. There is a low fuel relay somewhere under the dash with a 45 ohm ballast resister in parallel with the relay coil. Thanks for the intrest. And if I do get a number you will see it on this site. Ragtopragtop said:
ahh sorry ragtop. I was asking if the one xr7g428 posted on was that the wire was hooked up wrong on solenoid on apron by reg (69/70).
I got up a minute ago to look something up.... then I forgot but now I remeber Iw as going to read up on the operation of the low fuel T mister. I didn't think it as temp replated but hey I am no electronics expert. How does any of that stuff work anyway,lol?
Anyway I'll do a read and see if I can help shed any lite on this matter.
In past $30 and NPD has been the answer. Never seen one work right yet,myself. I know when its time to get gas.... always,,
OKay a read indicates it is temp related. See page 15-03-03 of the 69 manual set.
I got up a minute ago to look something up.... then I forgot but now I remeber Iw as going to read up on the operation of the low fuel T mister. I didn't think it as temp replated but hey I am no electronics expert. How does any of that stuff work anyway,lol?
Anyway I'll do a read and see if I can help shed any lite on this matter.
In past $30 and NPD has been the answer. Never seen one work right yet,myself. I know when its time to get gas.... always,,
OKay a read indicates it is temp related. See page 15-03-03 of the 69 manual set.
Well guys, I am and EE, as in Electronics Engineer, with extensive circuit design experience, I should be able to get this resolved (and I am a XR7 owner myself) when the time comes. Even if it means devising a new means to get the CORRECT indication under the correct condition. A promise, that is all I can offer at this time...
Hopefully we can reverse engineer the thermistor part number. As an ME, I am glad an EE has adopted this problem.
As for work-arounds, I am told that later model low fuel warning lights operate based on the position of the gas gauge (actually the voltage across the gauge). I hear '86 Mustangs are done this way and that there is a black box adjacent to the fuel gauge that can be retrofitted into our cars. Perhaps the next time I am in a wrecking yard and come across one, I'll take a look see.
As for work-arounds, I am told that later model low fuel warning lights operate based on the position of the gas gauge (actually the voltage across the gauge). I hear '86 Mustangs are done this way and that there is a black box adjacent to the fuel gauge that can be retrofitted into our cars. Perhaps the next time I am in a wrecking yard and come across one, I'll take a look see.
See the light
I was just a dumb S*** kid of 18 years old, working for an EE when I figured it out.
Like Ray, I try to make an honest living and help finace my hobby while helping others. I support Ray keeping his trade secrets just as I need to keep mine.
It really makes me mad to hear the word "Gouge" when trying to offer a part or service in order to help someone. Like Medicine......If you're too cheap to invest in the cure, then live with the problem.
I guess I should have gone into a less Gouging carreer of selling petrolium products.
Wow ...imagine that.....you could fix the light for less than the cost of a fill up !
I was just a dumb S*** kid of 18 years old, working for an EE when I figured it out.
Like Ray, I try to make an honest living and help finace my hobby while helping others. I support Ray keeping his trade secrets just as I need to keep mine.
It really makes me mad to hear the word "Gouge" when trying to offer a part or service in order to help someone. Like Medicine......If you're too cheap to invest in the cure, then live with the problem.
I guess I should have gone into a less Gouging carreer of selling petrolium products.
Wow ...imagine that.....you could fix the light for less than the cost of a fill up !
I just found out that my low fuel light actually works- sort of. After cleaning and re-installing the sending unit in my 68, I drove around in the red zone for a while to see if the light came on. It did, and about 1/2 second later, the car died of fuel starvation. I guess when it says "low" it means "really low".
Lugnut,
You have made a lot of great contributions to this board. You have brought a lot to the party. I know that these threads touch a nerve. Remember the movie Risky Business? "Never "F" with another mans livelihood". I think we understand how you feel.
The problem is that the purpose of the board is to share our specialized knowledge in the hope that someone else with different specialized knowledge will help us out in the future. Since this is a hobby, everyone is always trying to find ways to enjoy it without going broke. The problem with the thermistor is that everyone percieves this as a $1 part at Radio Shack. So folks are willing to spend some time to figure out which part it is. I bought the $35 part from NPD and it doesn't work. No returns on electrical parts.
I have seen where you offer to rebuild senders, and having tried to unsolder one of these things, I know that having somebody with skill rebuild the thing is a real service. Many electronic components are easily damaged by being overheated. Seems like a thermistor might be on that list. Maybe if you shared with us what you have to do to rebuild these things, people would be more responsive to what you have to offer. Ray will tell you how he reworks trim, just practice for about 20 years and you too will be able to do what he does. LOL. I bet that it is pretty much the same when you are rebuilding senders.
You are under no obligation to share the part number with the group. But don't be surprised when it pops up here. Please don't take it personally, information is just a lot cheaper than it used to be.
You have made a lot of great contributions to this board. You have brought a lot to the party. I know that these threads touch a nerve. Remember the movie Risky Business? "Never "F" with another mans livelihood". I think we understand how you feel.
The problem is that the purpose of the board is to share our specialized knowledge in the hope that someone else with different specialized knowledge will help us out in the future. Since this is a hobby, everyone is always trying to find ways to enjoy it without going broke. The problem with the thermistor is that everyone percieves this as a $1 part at Radio Shack. So folks are willing to spend some time to figure out which part it is. I bought the $35 part from NPD and it doesn't work. No returns on electrical parts.
I have seen where you offer to rebuild senders, and having tried to unsolder one of these things, I know that having somebody with skill rebuild the thing is a real service. Many electronic components are easily damaged by being overheated. Seems like a thermistor might be on that list. Maybe if you shared with us what you have to do to rebuild these things, people would be more responsive to what you have to offer. Ray will tell you how he reworks trim, just practice for about 20 years and you too will be able to do what he does. LOL. I bet that it is pretty much the same when you are rebuilding senders.
You are under no obligation to share the part number with the group. But don't be surprised when it pops up here. Please don't take it personally, information is just a lot cheaper than it used to be.
Hey 1969XR7Vert,
Since your are an exalted EE, please check me on this schematic (no fair laughing at the ME). It is my interpretation of the shop manual's description.
As for diagnostics, I think we can check the function of the relay by grounding the low fuel warning light lead at the tank connector. The light should come on since resistance will low (short circuit), simulating a low-fuel condition.
As for thermistor selection, all we have to do is balance the relay coil's resistance+thermistor against the 45ohm ballast resistor. Don't know what the coil resistance is yet, I still need to locate it.
In fact, it would seem that given a functioning thermistor, we could replace the ballast resistor with a potentiometer and "tune" the function of the light.
Since your are an exalted EE, please check me on this schematic (no fair laughing at the ME). It is my interpretation of the shop manual's description.
As for diagnostics, I think we can check the function of the relay by grounding the low fuel warning light lead at the tank connector. The light should come on since resistance will low (short circuit), simulating a low-fuel condition.
As for thermistor selection, all we have to do is balance the relay coil's resistance+thermistor against the 45ohm ballast resistor. Don't know what the coil resistance is yet, I still need to locate it.
In fact, it would seem that given a functioning thermistor, we could replace the ballast resistor with a potentiometer and "tune" the function of the light.
Excellent thread on fixing a low fuel light.
This thread tells in detail how to fix the low fuel light, and how all the parts of the fuel sender work.
:wave: http://www.lonestar.texas.net/~eoverton/cougars/lowfuel/lowfuel1.htm
This thread tells in detail how to fix the low fuel light, and how all the parts of the fuel sender work.
:wave: http://www.lonestar.texas.net/~eoverton/cougars/lowfuel/lowfuel1.htm
Todd, sorry for the delay in responding, just saw this post (happened to have found my way back here). I wouldn't say "exalted", I put my pants on one leg at a time like most people (although the third one sometimes wants it's own pant leg too so I got that going for me ;-). Anyway, per usual, I am responding to your email before I looked at the subsequent post info (i.e. the link to some info.), but wanted to respond. Will read after that and probably realize I have opened mouth and inserted foot...ntgregory said:
You are correct as to how to test the light and relay, grounding the wire will light the light if that stuff is working, no great revalation there.
As for thermistor selection, it is a little more complicated than "balancing" as you suggest. (BTW, I believe the relay in question sits on a plate behind the dash pad and instrument cluster on the left side near the door jamb, I expect to have trouble with mine as these parts have been wet...). Many things to take into account, here are some:
1. Based on the diagram, I surmise that the thermistor sits in gas when there is gas, the gas keeps it cool. When the gas gets below the thermistor, it begins to heat up (hopefully not too hot, can you say "boom"?!). The thermistor would need to be a negative temperature coefficient type, that is the resistance needs to go down as the temperature of of the device goes up. Other important parameters are: a. Nominal resistance of the device (to your "balance" statement) and a. Rate of resistance change over temperature, expressed as a resistance ratio 25C to 50C or "B constant" and c. Power rating (which is very important so that the device does not become a gas tank explosion initiation device!!!, see "boom" above).
2. The relay characteristics are import as well. What the pull-in current or voltage needs to be known. What is the coil voltage of the relay, it is not likely to be 12V b/c the thermistor is going to have resistance (and therefore voltage drop) regardless of where it operates, determining the voltage at the thermistor side of the relay coil.
Are you sure about the connection of your ballast resistor? I am having trouble seeing where it does anything except draw .267A (12V/45 ohms). It would make more sense for that to be in series with the 12V supply to limit current to a maximum of .267A for safety reasons (again see "boom" above!). I may be slow this morning, but I fail to see any reason, effect or benefit by having a resistor off 12V to ground. Maybe the + is actually instrumentation voltage (which as I recall is 5V?). If so maybe there is some impedance in that supply and the 45 ohms drops the voltage further for this low fuel function.
More on this as it unfolds, will check the link in the posts that follow.
Regards,
Bob
Interesting...
Read the info on the page from the link. Is the author a member here? If so, I can help them with what they are seeing. I know what the pulsing is about.
I like the approach and it may be viable, gets rid of the original circuit altogether and is (attempting to) using the fuel gauge rheostat as the sensor.
Anyone know who the author is? Is it the person who posted the link?
Bob
Read the info on the page from the link. Is the author a member here? If so, I can help them with what they are seeing. I know what the pulsing is about.
I like the approach and it may be viable, gets rid of the original circuit altogether and is (attempting to) using the fuel gauge rheostat as the sensor.
Anyone know who the author is? Is it the person who posted the link?
Bob
Actually, if I understand correctly, I agree. If someone (you) has identified a replacement device that actually works (sounds like a sample of (1) NPD one did not, wonder about the MU one) in the original application, it would be well worth the money (and which looks to be in line with the price of others that may not work). And getting a "royalty" (i.e. markup) for the work that led to its identification, etc... is not out of line either, it's called "business"!lugnut said:
Why reinvent the wheel?
That said, I still like the fuel gauge idea and it may worth looking into, it would eliminate the need for the thermistor altogether and although it would not be original, it could work. Not sure about the "test" function though, I understand it blinks the light when starting the car? My car is apart and don't know that it works or worked anyhow.
Bob
'69 XR7 LF light, Dick Hertzler says:
"If the low fuel warning lamp on your '69 doesn't work, relax! Most of them were disabled at the factory (referenced in bulletins) by rotating the connector on the sending unit or pulling the relay. The reasoning was that with less than a half tank of gas, they blink every time the car is in a turn--very annoying. Fix it if you must, but remember: I warned you! I truly believe that is what is really happening in the James Bond film, "On Her Majesty's Secret Service." Diana Rigg is driving a very early production '69 XR-7 convertible and there are good close up shots of the dashboard during the escape chase scene. The light is blinking all the time. You become worried she and Bond are out of fuel, but rest assured, the producers do not set up for a night chase scene like that with low fuel! Nor did they rig the car to make the light flash! Mine never worked from the day I took delivery; the dealer service manager told me it was disabled and that I would be the happier for it. I later fixed it, but it soon drove me crazy, so I pulled the relay."
Don't know if this is also true for earlier cars, but is noteworthy. Anyone have one that works and if so, what is your experience? Dick has had his '69 XR7 since new.
Just a data point...
"If the low fuel warning lamp on your '69 doesn't work, relax! Most of them were disabled at the factory (referenced in bulletins) by rotating the connector on the sending unit or pulling the relay. The reasoning was that with less than a half tank of gas, they blink every time the car is in a turn--very annoying. Fix it if you must, but remember: I warned you! I truly believe that is what is really happening in the James Bond film, "On Her Majesty's Secret Service." Diana Rigg is driving a very early production '69 XR-7 convertible and there are good close up shots of the dashboard during the escape chase scene. The light is blinking all the time. You become worried she and Bond are out of fuel, but rest assured, the producers do not set up for a night chase scene like that with low fuel! Nor did they rig the car to make the light flash! Mine never worked from the day I took delivery; the dealer service manager told me it was disabled and that I would be the happier for it. I later fixed it, but it soon drove me crazy, so I pulled the relay."
Don't know if this is also true for earlier cars, but is noteworthy. Anyone have one that works and if so, what is your experience? Dick has had his '69 XR7 since new.
Just a data point...
UPDATE: Thermistor-less solution nearing completion
I wanted to give an update and ask a question of the group:
1. Update
Decided against pursuing (yet another) thermistor solution, apparently they did not work well (light flashing, etc...) to begin with and there are already replacements available out there as most of us know. The fuel gauge telemetry approach makes a lot of sense and eliminates the thermistor altogether, not to mention the possibility of using a standard, available, tank sender and still getting low fuel functionality.
Picking up where Eric Overton left off, I am putting the finishing touches on a circuit which will go in place of the low fuel relay (possibly along with one additional connection to the fuel gauge, this would eliminate the need to futz with the sender at all if the gauge is working). At first I made a solid state replacement for the instrument regulator to eliminate the gauge signal(s) pulsing, not a bad idea, but complicates the solution (P.S. is there any interest or need for replacement instrument voltage regulators out there?). Today I decided to try and work with the original regulators pulsing and not require a solution to include replacement of the regulator. I succeeded in doing that this morning. The circuit accepts the pulsing gauge telemetry signal and includes the "start" position lamp test functionality. The trip level is adjustable, but I anticipate fixing this in the final version (unless there is differences in the implementation 69-70 to 67-68), which leads me to my question:
2. 67-68 (and any others?) model year low fuel implementation?
Can anyone tell me if the low fuel relay is the same on 67-68 as 69-70? Is the circuit for low fuel the same? Want the solution to work for as many cars as possible and need to consider any differences up front.
I plan on adding a little hysteresis into the circuit as well so that the solution will not have the flickering low fuel lamp problem the original had. Don't want people hating the "new" function, I understand that the original was known to be troublesome and/or annoying.
More later.
Bob
I wanted to give an update and ask a question of the group:
1. Update
Decided against pursuing (yet another) thermistor solution, apparently they did not work well (light flashing, etc...) to begin with and there are already replacements available out there as most of us know. The fuel gauge telemetry approach makes a lot of sense and eliminates the thermistor altogether, not to mention the possibility of using a standard, available, tank sender and still getting low fuel functionality.
Picking up where Eric Overton left off, I am putting the finishing touches on a circuit which will go in place of the low fuel relay (possibly along with one additional connection to the fuel gauge, this would eliminate the need to futz with the sender at all if the gauge is working). At first I made a solid state replacement for the instrument regulator to eliminate the gauge signal(s) pulsing, not a bad idea, but complicates the solution (P.S. is there any interest or need for replacement instrument voltage regulators out there?). Today I decided to try and work with the original regulators pulsing and not require a solution to include replacement of the regulator. I succeeded in doing that this morning. The circuit accepts the pulsing gauge telemetry signal and includes the "start" position lamp test functionality. The trip level is adjustable, but I anticipate fixing this in the final version (unless there is differences in the implementation 69-70 to 67-68), which leads me to my question:
2. 67-68 (and any others?) model year low fuel implementation?
Can anyone tell me if the low fuel relay is the same on 67-68 as 69-70? Is the circuit for low fuel the same? Want the solution to work for as many cars as possible and need to consider any differences up front.
I plan on adding a little hysteresis into the circuit as well so that the solution will not have the flickering low fuel lamp problem the original had. Don't want people hating the "new" function, I understand that the original was known to be troublesome and/or annoying.
More later.
Bob
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
