Some of you may recall I used a tank from a 91 that had no set up for to put the sensor. So I’ve been going without it. It runs great starts good. Basically no problem but a slight annoyance.
It runs out of fuel at a half tank. In other words when tank is half full it will not pump fuel. How and why would the sensor case this?
The sensor wouldn’t,
But a weak fuel pump would.
Check the fuel pressure.
Tester
Has it been doing this from the beginning of the tank swap??
Possible fuel pump assembly depth (at pick up (sock)) is not deep enough for whatever reason…
Yes from the very start of the tank change. Never with the old tank.
Tanks are shaped exactly the same. Only diff is old one had the spot for sensor.
Possibly a problem with the fuel gauge level unit. The 1998 sending unit might not have proper clearance in the 1991 tank.
The 1991 has the level unit float on the right side, the 1998 has the float on the left.
Those old fuel tanks use a “bowl” in the bottom of the tank for the fuel pump reservoir, the different location of the sending unit might not clear the reservoir. If this is the case, the float cannot drop to the bottom of the tank as the fuel level drops.
Fuel Tank Pressure sensor has nothing to do with the fuel gauge, fuel level, or fuel pump or pressure. All it does is measure the vapor pressure in the tank for emissions monitoring.
Sounds like the fuel pump hanger/sender assy is different. Well, I know they are different, one has a mounting for the tank pressure sensor and one doesn’t.
Replace the fuel pump assembly with the correct one for the car (if it will fit in the wrong tank).
I just looked on Rockauto and I think @knocksensor is out of luck, as far as the fuel tank pressure sensor is concerned
The correct tank has the provision for the fuel tank pressure sensor and the incorrect one doesn’t . . . and it’s on the tank itself, not the sending unit assembly
According to the rockauto pictures I looked at, the 2 fuel tanks only have one difference . . . the newer one has the provision for the fuel tank pressure sensor and it looks as if the correct fuel pump/sender should drop in, imo
fwiw . . . I would have just installed the correct tank from the get-go and avoided the MIL
Is it really running out at 1/2 a tank, meaning, are you getting 1/2 the miles fill up to fill up (150 miles down from 300 miles between fill ups) OR are you getting the same 300 miles (just an example) and the gauge is just showing 1/2 a tank??..
I did use the sending unit that was with the car. If I recall both sending units looked exactly the same.
Before I changed the tank I’d get a little over 400 miles on a tank. After 210 is about the tops.
Before you installed it in the tank, did you connect the fuel gauge sender to the harness & manually move the float ass’y up and down to make sure the movement matches what the gauge says? Or is that even possible given the configuration?
The reason I ask is b/c if the problem is just the sender’s resistance isn’t what the gauge is expecting, there are aftermarket electronic gadgets to pretty easily solve that. If the sender’s float is obstructed by something in the tank, that’s going to be harder to solve.
It was a choice of using a like new tank for a winter beater that I had no other use for a pay money for one. It runs perfectly starts good. It’s not the end of the world to fill it up every 200 miles. Was the right choice.
I just don’t understand why it started doing it as soon as the tank was put in. Every aspect of both tanks are designed exactly the same. But the sensor. Besides I used the sender unit that was originally in the car. It was in better condition than the 91.
If it was me, I would:
A) live with it…
B) drop the tank and pull the fuel pump assembly and see if there is something broken now or a hole in the tube that isn’t supposed to be there, or whatever, just check to see why it is doing this, it is NOT the sending unit level/gas (electrical part) gauge if your gas mileage has gone from 400 down to 200 miles on a full tank of gas, it is something with the pickup assembly… You are going to have to pull the tank and pump assembly to see what is broken/miss adjusted… You may have pushed the pump up on the sending unit tube while installing it in the tank…
My memory must be failing. I’m remembering the GM sending units that had a mounting for the FTP sensor.
I’m with tester on this one. I’d be ready for a new pump, especially on a Gm. Pulling it out and putting it back in can’t be good for it. But sure if you still have half a tank but just won’t push it through.
Could this be a case of no air being let into the tank, so increasing vacuum being developed as more fuel is pumped out, eventually vacuum too strong for the fuel pump to overcome it?
A quick test is to unscrew the gas tank cap.
The other day I dropped the tank. Pulled out the sending unit. Seen nothing wrong. Reinstalled it. Today I filled up the tank after driving for a while. It took almost 17 gallons to fill it. There was probably about a gallon or 2 in it.
So it’s sucking up the entire tank now. When I reinstalled the 3 lines going to the sender. The main line is thicker. The other 2 are the same. Would it matter if those where switched? I wasn’t sure which went to which so I guessed. It’s very weird it’s working properly now.
Of course when u fix one thing something else happens. Not sure what’s going on but I’m hearing a light clunking sound. Like perhaps a pulley going but they all seem solid. When it’s in idle it goes away mostly. Haven’t done much investigation yet. I’ll have a buddy try to pinpoint it while I hold it in gear. Might be a new topic.
Remove the drive belt and see if the noise is still there or gone, that will eliminate or confirm a few parts…
Usually with three lines it’s; main output, return and vapor
If you swapped return and vapor, a lot would depend on the construction of the fuel pump assembly. Looking at the images davesmopar included, it might as there appears to be a vapor separator at the inlet end of one of the smaller pipes…and the return pipe usually extends down further into the tank with the vapor line being higher up…
