Time To Pull The Pump (again)

Big_Jim59

Big_Jim59

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Joined
Jul 20, 2024
Messages
249
Age
65
Location
Sherman, Texas
Bike
2006 ST-1300
Yep, it's that time to get the fuel pump back out and deal with blinking fuel gauge. The thermistor I ordered as a replacement (it was a Honda item) was wrong. I have the chip, from the inside of the old unit, and in hind sight I am sure it would have worked fine except that the housing was deteriorated badly. The values can be measured by attaching an Ohmmeter and then spraying the chip with carb cleaner and watching the resistance value rise. I ordered the correct value thermistors and and they operate in the desired range. I will open the replacement unit and use the information from this site to swap it out.

In lead up to this job I manage to empty the top fuel tank naturally by putting 190 miles on it. I have now emptied the lower tank with a siphon through the return fuel line port. Tomorrow the pump comes out. I am really freaky about petrol in the garage.

After this I hope to fix the #9 error code. I plan on pulling the windshield and front fairing cover to check the continuity of the wiring from the air box sensor. (yes I checked and made sure it was plugged in the last time I was in there.) I hate that red IF warning light that's on all the time.

I may be wrong but I guess it's running a generic map, because of the air sensor fault, and it has effected the fuel mileage. It also pops and farts on over run like it's a bit rich.
 
Yep. Right there with you on my 99k 2006. Was gonna pull tank sender and clean with alcohol first before measuring the lower tank resistor.
 
Igofar said:
Sounds like someone should call the white courtesy phone tomorrow before he starts ripping stuff apart.
You are over thinking this repair.
:WCP1:
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If the unit was stock and if the unit was not damaged previously and if the thermistor had not been replaced with an item of unknown value I might agree, As it stands I need to run some tests.
 
I went out today and measured the resistance value of the thermistor with the tank empty. The value = 1.1 Ohms. Then I poured the two gallons back into the tank and measured the resistance value again and it still showed 1.1 Ohms. That's not good. The thermistor that came out of the bike tests at 2.0 Ohms when it's wet so it has to come out.
 
It seems that my project ends in failure. I pulled the pump, dismantled the thermistor can, installed the correct value thermistor, reinstalled the pump and added two gallons of gas, enough to submerge the reworked thermistor can. So far nothing. The fuel light still blinks. It's not a huge deal. I can ride it with the trip mileage keeping track of my fuel usage but it's a bit of an irritant.
 
Still wondering if you’re looking in the wrong area?
If you give a man a hammer, every problem is a nail.
Have you removed the assembly from the upper tank and taken a soft eraser and cleaned the film of varnish off the face of the dial?
This is what often times causes the issues your describing.
 
My understanding is that the low fuel warning is solely activated/deactivated by the thermistor in the lower tank. I thought that this function is independent of the sending unit in the upper tank. i.e. If the thermistor is working properly, and there is sufficient fuel in the tank for the thermistor to be completely submerged, there can't be a low fuel warning regardless of what the upper tank sending unit is doing. If you find out otherwise do report back as this would be good to know.
 
I am ABSOLUTELY not the guy you want me doing electrical repairs on anything, the OP sent me a picture of the pump assembly, and to be honest, it looked like it spent most of its life on the ocean floor!
In my opinion, trying to “rebuild” something this bad was a complete waste of time.
I would have replaced everything if I wanted it to work correctly.
With that said, in response to Andrew’s comments, I don’t know anything about your understanding of how they work, all I know is when the flashing lights skip to almost empty, and have those type of issues, cleaning the film off the upper assembly always corrected the problem….again, don’t know why, but that has always worked for the ones I’ve repaired, or suggested to be repaired over the phone.
It was always reported back to me that that is what fixes their issues as well.
When folks start searching, testing, and using electrical tools to search for issues, reminds me of sling blade….”it ain’t got no gas in it”
I guess he would be like me :rofl1:
 
The wiring diagram is not all that helpful but I would expect the thermistor is connected back to earth through the pump flange. If the earth is poor the resistance of the sensor will be high (or infinite) and (I assume) trigger the "we're empty down here!" flashing. So maybe a test of the earth wire might be helpful?
 
Igofar said:
Still wondering if you’re looking in the wrong area?
If you give a man a hammer, every problem is a nail.
Have you removed the assembly from the upper tank and taken a soft eraser and cleaned the film of varnish off the face of the dial?
This is what often times causes the issues your describing.
Click to expand...
After further consideration you may be correct. When I replaced the pump I went to the service station to fill the tank. The low fuel was flashing at the time and the gauge showed maybe 2/3 i a tank. When I filled the bike the gauge still flashed but I noticed that the fuel gauge had moved to full. It has stayed at full and continued to blink. I did order a new seal for the fuel sending unit so I will pull it out and clean the contacts at a minimum.
 
Good luck, let us know what happens.
The sending unit is sealed with a simple large O-ring, you could probably get away using it twice if you’re careful.
At least you would have your answer simply by draining and raising the tank.
No need to drain the lower tank.
 
Igofar said:
Good luck, let us know what happens.
The sending unit is sealed with a simple large O-ring, you could probably get away using it twice if you’re careful.
At least you would have your answer simply by draining and raising the tank.
No need to drain the lower tank.
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The lower tank is well below the top tank level so I should be able to pull it without any issues. I did also buy a replacement upper tank to lower tank hose just in case it was hard or I needed to pull the tank.
 
I think I'm confused about what the failure really is.

Based on information that you provided in another thread I thought that what you were working on was a malfunctioning the low fuel warning system and why you were replacing the thermistor. From what you wrote above I am not sure if you are having an issue with the low fuel warning or if the problem is that all of the guage segments are flashing. If it is the latter than then I agree with Larry that the upper tank sending unit is the suspect.
 
Andrew Shadow said:
I think I'm confused about what the failure really is.

Based on information that you provided in another thread I thought that what you were working on was a malfunctioning the low fuel warning system and why you were replacing the thermistor. From what you wrote above I am not sure if you are having an issue with the low fuel warning or if the problem is that all of the guage segments are flashing. If it is the latter than then I agree with Larry that the upper tank sending unit is the suspect.
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To be clear, the thermistor was messed up or at least the can that contains the thermistor was corroded. The fuel gauge and all its functions flashes. It has always just flashed ever since I got it running again. The only time it seemed to work was at the first fill up when the bars showed full but as I used fuel the bars never showed less than full. I have rebuilt the thermistor and I know it has the correct values. Pulling the fuel sending unit from the upper tank and cleaning the contacts gently seems the obvious next step.
 
Big_Jim59 said:
To be clear, the thermistor was messed up or at least the can that contains the thermistor was corroded. The fuel gauge and all its functions flashes. It has always just flashed ever since I got it running again. The only time it seemed to work was at the first fill up when the bars showed full but as I used fuel the bars never showed less than full. I have rebuilt the thermistor and I know it has the correct values. Pulling the fuel sending unit from the upper tank and cleaning the contacts gently seems the obvious next step.
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That is almost always a failure of the sending unit in the upper tank. If you want to try cleaning it as Larry suggested you might want to introduce a little fuel system cleaner of your choice to the process. I had a fuel gauge problem and fixed it by cleaning it with SeaFoam.

You have a service manual so you are aware of the tests and the results to look for. The only thing that I will add to that is with older or neglected ST1300's there have been a couple of failures of the terminal block on the top of the lower tank where the exterior wires connect to. The exterior of that block looks fine but it was found that there is either no connection or a bad connection between the exterior and the interior portions of that block. This resulted in poor, intermittent, or no continuity between the exterior wires and the interior wires. If you open it up again you might give that a good going over.
 
+1 for the SeaFoam - I have been using it a couple of times a year for many years and I'm sure it helps the fuel system/injectors stay clean.

We can't get it here in the UK (probably contains something the EU doesn't like) so have to smuggle it over....
 
canada_67 said:
+1 for the SeaFoam - I have been using it a couple of times a year for many years and I'm sure it helps the fuel system/injectors stay clean.

We can't get it here in the UK (probably contains something the EU doesn't like) so have to smuggle it over....
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Should I try the SeaFoam before pulling the sending unit?
 
With what you’re dealing with, probably would not help until you ran several tanks through it.
Clean it with a soft white pencil eraser, the run some sea foam and mmo through the system.
let us know how it turns out.
 
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canada_67 said:
We can't get it here in the UK (probably contains something the EU doesn't like) so have to smuggle it over....
Click to expand...
There is nothing magical about SeaFoam. There are many similar products available and there must be some in the UK.
 
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