Can fuel sending unit be calibrated?

[Brain75]

another data point on the ohms resistance range:
"
Pre-1989 Fords, Empty 73 Ohms - Full 10 Ohms
Most '89-up Fords, Empty 16 Ohms - Full 158 Ohms
"

2.0L Fuel Gauge Question

I wanted to know if any knew the factory OHM range for a 1988 Ford Ranger 2.0L which is carbureted? I recently had my fuel sending unit rebuilt since they are discontinued and impossible to find. The company that rebuilt it said the unit is now calibrated for 16 ohms empty to 165 ohms full...

www.therangerstation.com

 

[flyin-lowe]

So I guess I will give the long story. When I bought the truck the PO told me the fuel gauge was not accurate and he just used the trip to drive about 350 miles between fill ups. The gauge would work but sometimes not get below half tank, sometimes stay on full etc. After a month or two of driving it one day it dropped to empty, the fuel light and CEL both came on. It stayed like this for a day or two. I can't remember the code but it was something about no voltage from fuel sending unit (paraphrasing). I ordered the Bosch unit (full assembly) from Rock Auto and replaced it. After a couple days driving with the new assembly unit the CEL came on and it was showing an EVAP leak. I filled the tank completely full and it was leaking around the seal so I assumed I didn't have it seated correctly. Of note the fuel gauge appeared to be accurate with the Bosch assembly. Took the bed back off to check the seal and in doing so managed to crack one of the inlets on top going to the vent line. So I went to Oreilly and bought the one linked above. Truck runs perfectly but the gauge is off. It was stuck on full for almost 175 miles and since then it has gone from full to 3/4 full over the last 50 miles or so.

 

[Brain75]

Yeah, my guess is that either A) the wiper arm is bent wrong, either packaging, shipping, or installation or B) just a dud unit (that oreilly one seems to be pretty crappy all around).

With the float at the highest point it should be like 1/2" below the same level as the top plate (scraping the top of the tank inside), and the lowest point should be like even with the pickup strainer bag... if it is bent wonky it will go too far one side or the other... no point going below the strainer as even if you have an inch of gas you can't suck it up so you are still "on empty".

Sounds like the PO already had you on an aftermarket, so you have no OEM to repair.

JB weld the bosch unit back together?

 

[flyin-lowe]

I may try to see if Oreilly will just give me a refund and if so order another Bosch. Friend of mine told me I should send the Bosch back to Rock Auto but since I knew I cracked it I am not that type of guy so I just trashed it. Didn't want to have to worry about trusting it with a piece "glued" back together, especially in the fuel system. Before I ordered the one from Rock Auto I called Bosch Tech support to make sure it was the correct part number and he told me they made the OEM ones for Ford and it was basically the exact same as OEM...

 

[Brain75]

Even though all these stores carry their own house brand they also can order the real deal.. if you go in with the bosch part number they can order it - might be cheaper than paying rock auto's shipping, might be holy insane expensive... once you got a real bosch part number you could look everywhere for it too partsgeek, amazon, even directly from bosch...

 

[flyin-lowe]

On the Bosch I originally bought Rock Auto was the cheapest. I might check with Oreilly to see what they can get the Bosch for, I assume if their house brand is over 200, they will want more than that for the Bosch.

 

[Brain75]

might take a print/sceenshot of the bosch on rockauto/geek/etc - whatever is cheapest in case you need to see if they will price match it... they might not give you a cash refund, instead store credit, then turn around and use that for the bosch.

 

[pjtoledo]

the replacement pump unit in my 2000 does the same thing. 100+ miles on full then it drops unpredictably.
I use the odometer method.

by the way, the instrument panel has an electronic "slosh module" that slows the fuel gauge response so it doesn't get crazy during sloshing.
testing the sender will not give accurate results unless it sits at the same level for a while.

 

[flyin-lowe]

I was finally able to stop into Oreilly today and they said they will take the fuel pump back and give me a refund. So I have ordered a Bosch from Parts Geek and once it arrived I will hopefully be messing with it for the last time....

 

[JoshT]

The wiper arm is bent wrong. Bending the arm is how you "Calibrate" it. It's not uncommon on float style fuel senders, and is part of setup when using a "universal" float style sender.

It's at full for the first 150 miles of travel because the float has reached max up travel and is submerged until the tank drains down that low. With what you are saying, I imagine the gauge would never get to empty. The float probably hits the bottom of tank before it maxes down travel. The arm needs to be bent up.

If your gauge starts reading late (like it is) AND hits empty before the you run out of gas, then the float arm is too short. Straighten it out some to make it effectively longer and go from there.

If the original is available, and accurate, adjust the arm on the new sender so that it matches the top and bottom range of travel. If the original is not available, and what ever is there is inaccurate, then it's careful measuring and/or trial and error.

If I didn't know how it needed to be set I'd measure the inside depth of the tank and draw parallel lines that far apart on a a flat surface (cardboard, poster bord, etc). I'd line up the sender like it was installed into the top of the tank (plate sitting on the top line). Then I'd proceed to bend the arm until the full mark got to the point I wanted it. Since there's not much to be done about the length of some arms, I'd let empty land where ever it did and consider the remaining space as built in reserve.

If I were setting it up from scratch, I'd probably aim for the float to be 0.5" - 1" below the top of the tank when reading full, and probably 1.5" - 2" above the bottom when reading empty. That would leave some reserve in the bottom of the tank when the gauge shows empty. I'd rather who ever is driving it to think it's about to be empty and fill up before they run out.

I'd say that you got lucky with the Bosch you had in that the sender was it was bent right enough. The Bosch I put in my 99 years ago wasn't right, also wasn't so far off that I've bothered to fix it. I'm usually about 50 miles when it starts dropping from full, and I measured it out to be right about 30 miles from empty to out of gas. Ideally I'd get it the other way around, but not worth pulling the sender to do it. Maybe someday in the future when I need to install a larger fuel pump.

 

[JoshT]

Also due to the float traveling in an arc, the gauge may not drop perfectly linear. Through some portions of the gauge the level may appear to drop faster than through other portions.

 

[flyin-lowe]

Josh T, thanks for the info. I have some questions, not doubting what you say, just genuinely trying to learn. I have now driven almost 300 miles on this tank and the gauge is still just over 3/4 full. I can't imagine that this issue could be caused by the arm not being bent right. At three hundred plus miles there can't be more then a few inches of fuel in the tank, so no way the float/arm could be that out of whack is there. From the time I drove the first 175 miles before it started moving I imagine it would have had to drop close to half way down, so it doesn't seem logical to me that the arm could be that far off could it?

 

[JoshT]

I would have to say yes, it could. I wasn't there to see what you installed and we can't see what's inside the tank unless you take it out. Hell maybe it was even the wrong float arm in the box.

You asked about calibrating the fuel sender, that is what I was trying to explain. You calibrate it by bending the arm, but for that to work, it has to fuindtion properly in the first place. It could be that the OHM range of the rheostat is that far off, but if that is the case you aren't going to calibrate it, it's just bad. It could be that the unit was built wrong and the Rheostat is in the wrong location, but again, it's just bad.

 

[lil_Blue_Ford]

I would have to say yes, it could. I wasn't there to see what you installed and we can't see what's inside the tank unless you take it out. Hell maybe it was even the wrong float arm in the box.

You asked about calibrating the fuel sender, that is what I was trying to explain. You calibrate it by bending the arm, but for that to work, it has to fuindtion properly in the first place. It could be that the OHM range of the rheostat is that far off, but if that is the case you aren't going to calibrate it, it's just bad. It could be that the unit was built wrong and the Rheostat is in the wrong location, but again, it's just bad.

I’m gonna say this is probably it, quality of parts isn’t what it used to be, I couldn’t tell you how many times I’ve gotten a brand new bad part. I put two or three brand new bad fuel pumps in mom’s Explorer. I remember one being completely DOA and one that worked for like a month. There may have been a third because I remember spending a bunch of time fighting with it.

 

[flyin-lowe]

So here is an update, I was going to start a new thread but since this one has some of the background info I'll keep it going. Today we had to drive about 60 miles and since we had already gone about 320 on this tank I put 5 gallons in it. I didn't want to fill it up as I plan on putting the new fuel pump in as soon as it gets delivered and didn't want to mess with a full tank. When I shut the truck off to pump the fuel, it was just below 3/4 full. After I put 5 gallon in it and started it back up the gauge dropped to about 1/4 full, which is about where I thought it should be. I made the first leg (30 miles) and during that time the fuel gauge actually went up a little, from 1/4 to almost half. Once I shut the truck off it set for about an hour and then when I started it back up it was at 1/4 full again for about 2 minutes then the gauge went all the way to E and the fuel light came on. This is what happened the very first time I decided to change the unit only that time the CEL also came on and the code said there was no power from the sending unit (can't remember the exact code/wording). I was expecting the CEL to come back on but after a few miles the gauge went from E back to 3/4 full and then over the next 20 miles it went from 3/4 full to 1/4 full.

I am curious if this type of issue has to be in the sending unit or is there something else I should be checking. Since I have the Bosch unit already ordered I am going to go ahead an swap it out and see what happens. Can anyone tell me where the wire harness that goes from the tank to the front of the truck ends up at? I didn't know if that harness is something that is easy to replace, or if that would not be the problem. Would love to hear what everyone's thoughts are and what my next step should be, other than replacing the O'reilly unit with the Bosch unit.