Fuel gauge failing
11-02-2009, 08:16 PM
#23
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My gas gauge works till half tank, my engine temp gauge is pegged in the red at all times, and my speedo reads 11% slow.. my gauge cluster is useless..
11-03-2009, 07:11 AM
#25
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i guess im the only one with a base model? i have no trip, so i would have to go by the odo kinda a pain and i dont think i have a low fuel light either? never seen it, i just keep 2 gallons of gas in the bed if i run out 
11-15-2009, 09:29 PM
#26
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I emailed Toyota of Dallas about getting a new sending unit... they told me Toyota stopped producing them. I'll definitely check Autozone now though. My gauge doesn't work at all.
09-16-2014, 12:05 PM
#28
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I don't know; do they?
Oh, you wanted someone here to check for you?
If by "them" you mean the Fuel Sender, I've never heard that Autozone carried such a specific part. But you can easily check online.
To get the correct part number you can check here: http://www.toyotapartsoverstock.com/...modelYear=1987
The sender varies with the size of the fuel tank, so you'll need to look up your model.
Oh, you wanted someone here to check for you?
If by "them" you mean the Fuel Sender, I've never heard that Autozone carried such a specific part. But you can easily check online.
To get the correct part number you can check here: http://www.toyotapartsoverstock.com/...modelYear=1987
The sender varies with the size of the fuel tank, so you'll need to look up your model.
09-17-2014, 02:00 AM
#29
I've a similar issue, happy to check with Autozone for y'all.
Not sure though if it's because I seem to have a GM fuel pump. I guess it's possible I have a different fuel tank as well (PO had even installed a second tank but it was removed during the sale due to rust).
Either way I'm going to get to the bottom of it, it is on my list
Not sure though if it's because I seem to have a GM fuel pump. I guess it's possible I have a different fuel tank as well (PO had even installed a second tank but it was removed during the sale due to rust).
Either way I'm going to get to the bottom of it, it is on my list
09-17-2014, 02:20 AM
#30
'88 FSM specifies:
So, the resistance should go from about 110ohms empty to 3ohms full
The "universal" one that autozone lists for a 1987 4runner goes from 240ohm at E to 33ohm at F.
This might explain my symptom exactly... which is that the gauge just goes down too fast- it reads E with only 7gal out of the tank!
I'm actually quite certain the PO of my vehicle tried this "universal" replacement and never got it working quite right, well how could he/she when the sender is outputting the wrong value scale? I'm so certain because there are numerous other replacement parts on the car from autozone.
I'm going to start taking multimeter readings at different points during the tank. If it is simply outputting properly and just the wrong scale, it would be easy to hack with a small adc microprocessor and adapt it to OEM spec output.
And either way, I am positive I could get this autozone universal replacement scaled just like OEM.
Perhaps they do have a 110-3 (or close) sender from a different car. It's worth asking them to save the hacking work. But then again, I always love a good hack.
I'm on it
So, the resistance should go from about 110ohms empty to 3ohms full
The "universal" one that autozone lists for a 1987 4runner goes from 240ohm at E to 33ohm at F.
This might explain my symptom exactly... which is that the gauge just goes down too fast- it reads E with only 7gal out of the tank!
I'm actually quite certain the PO of my vehicle tried this "universal" replacement and never got it working quite right, well how could he/she when the sender is outputting the wrong value scale? I'm so certain because there are numerous other replacement parts on the car from autozone.
I'm going to start taking multimeter readings at different points during the tank. If it is simply outputting properly and just the wrong scale, it would be easy to hack with a small adc microprocessor and adapt it to OEM spec output.
And either way, I am positive I could get this autozone universal replacement scaled just like OEM.
Perhaps they do have a 110-3 (or close) sender from a different car. It's worth asking them to save the hacking work. But then again, I always love a good hack.
I'm on it
09-17-2014, 06:37 AM
#31
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Rather than trying to adapt a "universal" sender to your gauge, think what you could do with a Digital gauge!
Since the fuel gauge is essential an ohmmeter, it needs a "constant current" source. According to this extensive post, the gauge has a '60s era mechanical "switching regulator" providing a very slow PWM signal.
Why mess with that? Using a current regulator and a cheap digital voltmeter, you could set up it up to read tenths or even hundredths of a gallon. Since the sender swings an arc it's not perfectly linear, and the tank doesn't have a perfectly uniform cross-section anyway. But if you're willing to do a tiny bit of uController work (and we know you are!), you could use an accurate gas pump to calibrate your sender/tank at, say, each gallon. Then interpolate for a super-accurate gauge.
Since the fuel gauge is essential an ohmmeter, it needs a "constant current" source. According to this extensive post, the gauge has a '60s era mechanical "switching regulator" providing a very slow PWM signal.
Why mess with that? Using a current regulator and a cheap digital voltmeter, you could set up it up to read tenths or even hundredths of a gallon. Since the sender swings an arc it's not perfectly linear, and the tank doesn't have a perfectly uniform cross-section anyway. But if you're willing to do a tiny bit of uController work (and we know you are!), you could use an accurate gas pump to calibrate your sender/tank at, say, each gallon. Then interpolate for a super-accurate gauge.
09-17-2014, 09:30 AM
#32
That's exactly what I aim to do. I would bet too that it is a rather linear response curve. Mapping the voltage from E to F would then be easy peasy. Even if it is an exponential curve, it shouldn't be too hard to match with a good amount of data
That is good to know that the sender outputs PWM, sometimes arduino has trouble reading that as an analog voltage. A filter might be necessary, but if it is a very slow PWM perhaps it is kind of filtering innately.
That is good to know that the sender outputs PWM, sometimes arduino has trouble reading that as an analog voltage. A filter might be necessary, but if it is a very slow PWM perhaps it is kind of filtering innately.
Last edited by jennygirl; 09-17-2014 at 09:31 AM.
09-17-2014, 10:30 AM
#33
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The "sender" is just a rheostat. The gauge has a very inefficient "current" source, and the indicator is (traditionally) a hot-wire ammeter. Hot wire ammeters are not only extremely rugged, but inherently damping, with a time-constant measured in seconds.
If it were me, I'd bypass the OEM gauge altogether. As a first cut, I'd just use a current source (LM138 or maybe a current regulator diode) and a simple panel meter (e.g., http://www.futurlec.com/Panel_Meters.shtml). A voltage divider might be enough to scale it.
Since the tank doesn't have a uniform cross-section, I suspect the sender response is linear to within about 10-20%. I'm not sure I would need anything more precise (a gauge that reads in "tenths of a tank" would still be an improvement), but it would be nice if the measurement of "zero" were close.
Good luck!
If it were me, I'd bypass the OEM gauge altogether. As a first cut, I'd just use a current source (LM138 or maybe a current regulator diode) and a simple panel meter (e.g., http://www.futurlec.com/Panel_Meters.shtml). A voltage divider might be enough to scale it.
Since the tank doesn't have a uniform cross-section, I suspect the sender response is linear to within about 10-20%. I'm not sure I would need anything more precise (a gauge that reads in "tenths of a tank" would still be an improvement), but it would be nice if the measurement of "zero" were close.
Good luck!
09-17-2014, 10:55 AM
#34
Can you access the sending unit in a Toyota 4Runner by removing the access panel under the pass. seat? I know you can see the fuel pump, but was wondering about the sending unit. From what I can remember the access panel is pretty small.
I'm hoping this thing has a gas light in it. The last 4Runner I had with the gauge problem had the gas light. This would not make this a priority to fix IMO.
I'm hoping this thing has a gas light in it. The last 4Runner I had with the gauge problem had the gas light. This would not make this a priority to fix IMO.
Last edited by 77lubr; 09-17-2014 at 10:57 AM.
09-18-2014, 05:51 AM
#36
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Ok I just read the recent posts and I've gone cross eyed. I have an 89 pickup with broken has guage. I've actually seen it work once, it was weird.
Bottom line, what's the easiest way to fix it? In retard terms.
Bottom line, what's the easiest way to fix it? In retard terms.
09-18-2014, 07:15 AM
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Take it to the dealer. (Hey, you asked the question.)
The most likely cause is a break in the fine wire of the rheostat in the in-tank sender. For those with a gauge that works part time, the "wiper" is probably lifting off the wire at some point in the swing. So you pull the sender and put in a new one.
BUT: the part isn't cheap and it's not easy to get to, so you should do the basic FSM test to confirm the indicator is working. http://personal.utulsa.edu/~nathan-b.../6combinat.pdf
The most likely cause is a break in the fine wire of the rheostat in the in-tank sender. For those with a gauge that works part time, the "wiper" is probably lifting off the wire at some point in the swing. So you pull the sender and put in a new one.
BUT: the part isn't cheap and it's not easy to get to, so you should do the basic FSM test to confirm the indicator is working. http://personal.utulsa.edu/~nathan-b.../6combinat.pdf
09-18-2014, 07:43 AM
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Haha thanks scope. Getting to it really isn't an issue.I have several inches to work with as I have a custom built flatbed. Just looking for a quick fix so i don't have to guess.
10-05-2014, 12:25 PM
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So is it safe to say that if the sending unit has gone bad then the best way to fix it is to REPLACE IT? Also that being said after a few weeks of searching online is it safe to say that there aren't to many vendors out there selling direct replacements for the 89/ GEN1 4Runner era Fuel Sending Units? If one of you GURUS knows of a vendor that still stocks them could you direct me to it?
10-05-2014, 01:13 PM
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Did you try http://www.toyotapartsoverstock.com/...ssembly=512422 ?
Note that the correct part depends on, at least, the size of your fuel tank. That fact alone should steer you away from some sort of aftermarket guess! You can use your VIN to eliminate all doubt. The part is 3-4 times the price of the universal part from autozone http://www.autozone.com/autozone/acc...er=131481_0_0_ , but there's a lot to be said for guaranteed-to-fit-and-work.
Note that the correct part depends on, at least, the size of your fuel tank. That fact alone should steer you away from some sort of aftermarket guess! You can use your VIN to eliminate all doubt. The part is 3-4 times the price of the universal part from autozone http://www.autozone.com/autozone/acc...er=131481_0_0_ , but there's a lot to be said for guaranteed-to-fit-and-work.
