I read a thread here some time ago (can't find it now) about installing two bulkhead fitting and connecting a tube across the "two" tanks - as close to the bottom as possible. This would let the gas equalize easier - not just when the tanks were filled up to near the top and it "spills" across?

Was curious if any other folks had tried that and did it cure the problem of the fuel gauge cutting out when the two tanks are not equal because the tiny "jet nozzle" keeps getting clogged and won't equalize the two sides etc ?

If you have experience with this - is there some "downside" issues - that may surface - because of the change?

Thanks in advance

 

Bad idea in my opinion. The cross-connecting tube would have to be located below the drive line and in close vicinity of the exhaust system. Not to mention installing bulkhead type fitting on plastic tanks that are not desinged to have them.

 

I have had the idea of taking out the jet pump in the passenger tank, and put a regular pump in there, have a switch to start out on the passenger tank, then when it gets low, switch to driver tank.

Like some of the pickups.

Obviously more trouble than just fixing/replacing the plugged jet pump, but it's fun to dream stuff up!

Of course there are details I left out, like running a 2nd fuel line from the passenger tank, with a 2nd pressure regulator, and removing the lines from the driver to passenger tank to transfer the fuel from the passenger tank to the driver's, etc.

 

1stGlance, if I understand correctly, the way GM designed these cars was to have the passenger tank's fuel consumed 1st, then when it's empty, the driver's side tank starts going down.

So, when your passenger tank is empty, the fuel gauge reads 1/2, because the driver's tank is full, there are fuel sender units in each tank.

Now, when the jet pump in the passenger tank gets plugged, fuel from that tank cannot be "sucked" out and transferred into the driver's tank, then as the driver's tank fuel level goes down, as the passenger tank is full, and the sequence of operation is out of whack, and the ECM will either make the gauge go to empty, or act erratic, because it's getting the incorrect resistance readings.

Kind of a weird setup, I would think they would want both tanks to be drawn from at a equal rate, to keep the cars weight more balanced, but it's probably not feasible to do that, so that's why the passenger tank is consumed first, then the driver's tank.

Passenger tank=1/2 tank, driver's tank the other 1/2 tank.

Both tanks full, the gauge reads full, the passenger tank half full, and the driver's tank still full, gauge reads 3/4, etc.

 

If I understand this system correctly, the passenger tank drains completely before fuel is used from the driver's side tank. If this is true, the info from the fuel senders has to be interpreted in a very specific way. If the two tanks are modified to draw down together equally, the fuel gauge will be way off...just creating another problem to fix, no?

 

Well, the idea I had was to consume the fuel in the passenger tank first, then when the tank reads near 1/2, indicating the passenger tank is nearly drained, you have a switch somewhere in the car to cut that fuel pump off, and turn the driver's side pump on.

Yes, this would create another problem, because then you would have to manually switch between fuel tanks, like some of the pickup trucks.

So when it's all said and done, fixing/replacing the jet pump is the most efficient way to go.

I (probably like a lot of people on here) like to think up "what if" on ideas/situations, or question why something was designed a certain way.

Most of the time it's a waste of time, but once in a while it has benefited a situation.

I guess it's a way to keep from getting bored.

 

Its not a big deal running a line from bottom rear of each tank connecting the two. A fitting such as used by A&A Corvette in left picture for their external fuel pump setups would be screwed into both tanks connecting the two very easily or could use the ECS tank setup feed fitting right picture like I use for both tanks.

There is plenty of room to do it and the line wouldnt hang down lower than both tanks metal protection covers either. If you dont like the idea of braided line between the 2 tanks run a hard line. There are hard lines running up the tunnel to the engine anyway so its not a safety issue having a line next to or under the drive line areas. The tanks dont need to be dropped or opened up to install either of these vendors fittings.
If my passenger jet siphon design ever clogs up ill be doing exactly this.
I wouldn't expect the fuel gauge to read properly though after doing this.

 

When I first read about how these tanks worked several years ago I thought the idea was backwards.

Seems like the drivers tank would empty first, given no passenger, that would keep the car blanced better, you think?

Sorry to highjack the tread but I also agree the tanks should equalize throughout their use if not the way I mentioned above, IMO.

 

I would not recommend doing that Burk. Especially if it is to try and fix an intermittent fuel gauge as you said, because it wont. If your syphon tube is getting clogged you need to remove the tanks and clean them out. Replace your fuel gauge sending unit/s after properly diagnosing the problem, assuming that is the problem.

 

I read this and wasn't sure i understood it yet

OK, a little info may help you here .....

* There are two tanks .... each tank has a fuel sender that reports the fuel level to the PCM. The PCM calculates the fuel level based on the info from the two senders and reports that calculated "single tank" level to the IPC which displays it on the fuel gauge.

* The right tank has a "jet siphon" pump in it, the left tank has an electric pump. When the engine is running, the fuel rail is fed by the left tank electric pump. Just after the left pump pressurizes the fuel, there is a line that feeds some of that pressurized fuel into the right siphon pump. The siphon pump has a line that carries the siphoned fuel to the left tank. Both tanks are connected, at the tops of the tanks, by a large diameter "fuel crossover" line which is how the right tank gets fueled ... once the left tank is full during fueling the fuel then crosses over to the right tank, filling it.

* With the engine running more fuel is fed from the right tank than is being taken out of the left tank, so the excess fuel flows back to the right tank via the crossover pipe.

* The "normal" behaviour the PCM expects to see after the tanks are filled is as follows .... the right tank should drain while the left tank remains full. Once the right tank is empty then the left tank should drain. The PCM also knows that the fuel level in either tank should drop as the car is driven a certain distance ..... say 150 miles.

* If the PCM does not see "normal" behaviour (such as the car driving 150 miles and neither sender has moved) then it will set DTC for things like a stuck sender (no movement in 150 miles) or a bad siphon jet pump (the left tank is draining before the right tank) .... or whatever. A P1431 is an example of the codes than can be set.

Check again for any DTC, the PCM should have recognized a problem ..... if it sees fuel still in the right tank and the left tank is draining then a P1431 SHOULD set ... only way it would not set is if you are using fuel in many short haul trips .....it gets hard for the PCM to measure meaningful fuel changes within short trips (a few minutes/miles of driving).

Try running some Techron through your fuel system. If the problem persists the next step will have to be determining which tank holds the "hidden" three gallons. If it is the right tank you have a siphon jet problem ... if the left taank you have a fuel pick up problem.

If I had to bet ... given the lack of a DTC .... you aren't picking up all the fuel in the left tank.