Fuel Tank Problems

[PPOIII]

I have a 91 Lexus LS400. It will only hold about 6-8 gallons. It will often stop running at idle after putting fuel in it. And lately it burbed a ton of fuel out when my wife went to fill up. I think it is a vent valve problem.

My qustion how do you drop the tank on this car and get to the vent valve.

PLEASE HELP

Manuals are 186-200 bucks. I can do the repairs just need to have good material or instructions.

Thanks Paul.

[landar]

I have a 91 Lexus LS400. It will only hold about 6-8 gallons. It will often stop running at idle after putting fuel in it. And lately it burbed a ton of fuel out when my wife went to fill up. I think it is a vent valve problem.

My qustion how do you drop the tank on this car and get to the vent valve.

PLEASE HELP

Manuals are 186-200 bucks. I can do the repairs just need to have good material or instructions.

Thanks Paul.

You mean you cant even fill it full if you slowly pump gas into the tank?

[PPOIII]

I have a 91 Lexus LS400. It will only hold about 6-8 gallons. It will often stop running at idle after putting fuel in it. And lately it burbed a ton of fuel out when my wife went to fill up. I think it is a vent valve problem.

My qustion how do you drop the tank on this car and get to the vent valve.

PLEASE HELP

Manuals are 186-200 bucks. I can do the repairs just need to have good material or instructions.

Thanks Paul.

You mean you cant even fill it full if you slowly pump gas into the tank?

Nope we have tried everything. Pumping slow, turning the handle around. You cant fill it up. Then it dies after fueling and the gas gauge is not accurate.

[landar]

Interesting. It sure does sound like a venting issue of some sort. The tank is vented to a canister up front.

I believe you need to remove the rear seat to get at the tank though I have never had to work on the tank myself.

I found this site which shows how to replace the pump. Not sure how helpful it will be. Let us know what you find -> http://www.lextreme.com/fp.htm

[curiousB]

You can go here and join club for 2 days ($15) and download the exact model and year service manual which is much better than a generic one. I'd try a few other things before dropping the tank though. Try to inspect the vent line. Maybe disconnect it from the canister mentioned. If its plugged it won't vent. Also how about pushing a piece of hose down filler port into tank. Is there something blocking the passageway? Maybe someone pulled a prank on your car and stuffed something down there....

...https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti;TISESSIONID=ZJ1lMgvSvvNLRNXs6LhT97n3QWSkMZbkr2qY5XH11TZPhzPLhj6L!622306424?_nfpb=true&_pageLabel=ti_home_page....

[RDM]

You can easily pull the tank fill pipe and vent hose from inside the car, since that's where it's located.

[GDixon]

Before you go to the labor and expense you are indicating you might try a simple diagnostic procedure.

Pull back the rubber collar on the gas pump's fill lever so there is a gap between it and the fill tube. It will allow the tank to fill with no back pressure or vacuum. This is how people fill gas cans.

If that solves the problem then trying a different gas station may be indicated.

If the same problem occurs then it can't be a venting or vacuum problem since there will be none with the rubber collar out of sealing contact. Good luck.

[VBdenny]

Do you get a big cacuum whoosh when you take the gas cap off?

[LA1]

Every once in a while I will have a similar problem with burping fuel when filling my land rover. When it does this I will rock it back and forth a few times and then it will work; evidently it removes some back pressure. The problem does seem to occur more at older pumps though.

[AndyLowe]

I once bought a truck that would indicate it was low on fuel.

The gauge made me think it needed to be filled up, when all the while, it was tricking me!

I suspect your Fuel Gauge is indicating incorrectly, and you "think" you need to fill up, and when the overflow occurs, you "think" your tank is unable to vent.

Because you have a 1991, I highly suspect your Fuel Pump SENDING UNIT, the variable resistor which is attached to a swing arm with a float on the end, is defective.

My 1994 LS400 has access to this pump and sending unit, by removing the rear seat cushion first, followed by the rear seat back.

Next you will see an access panel, with screws holding it onto the sheet metal where the seat back was. Removing it will allow access to the pump and sending unit.

Because I think your tank is VERY full, I would first drive it at least 200 miles, and then gain access.

You can purchase a subscription to www.alldatadiy.com, for a 1 year period, and have access to all kinds of good service manual info.

My 1994 LS400 has a solenoid valve, that is located on the driver's side, inner fender, down low. A single vacuum hose connects to this valve, and this rubber hose then attaches to the front top edge of the Intake Manifold. Only when the Computer commands this valve, does gasoline vapors from the tank, enter the Intake Manifold.

A blocked vent line, under the car on the driver's side would NOT cause the engine to die at idle. You should look for other causes of poor idle. It's likely a coincidence that filling up, and dying at idle occur.

Gas Caps are bi-directional and SHOULD allow air to enter the tank, when displacement is necessary; ie,,, you're using gas out of the tank, air needs to enter.

Does your tank suck air in when you open the cap? Replace it.

It would be nice to know your tank is not the problem, rather your Sending Unit, the item that tells your Fuel Gauge what to indicate.

When I worked on Audi's, it WAS the tank.........! I don't have nice things to say about Audis.

Best of luck,

Andy

[PPOIII]

I once bought a truck that would indicate it was low on fuel.

The gauge made me think it needed to be filled up, when all the while, it was tricking me!

I suspect your Fuel Gauge is indicating incorrectly, and you "think" you need to fill up, and when the overflow occurs, you "think" your tank is unable to vent.

Because you have a 1991, I highly suspect your Fuel Pump SENDING UNIT, the variable resistor which is attached to a swing arm with a float on the end, is defective.

My 1994 LS400 has access to this pump and sending unit, by removing the rear seat cushion first, followed by the rear seat back.

Next you will see an access panel, with screws holding it onto the sheet metal where the seat back was. Removing it will allow access to the pump and sending unit.

Because I think your tank is VERY full, I would first drive it at least 200 miles, and then gain access.

You can purchase a subscription to www.alldatadiy.com, for a 1 year period, and have access to all kinds of good service manual info.

My 1994 LS400 has a solenoid valve, that is located on the driver's side, inner fender, down low. A single vacuum hose connects to this valve, and this rubber hose then attaches to the front top edge of the Intake Manifold. Only when the Computer commands this valve, does gasoline vapors from the tank, enter the Intake Manifold.

A blocked vent line, under the car on the driver's side would NOT cause the engine to die at idle. You should look for other causes of poor idle. It's likely a coincidence that filling up, and dying at idle occur.

Gas Caps are bi-directional and SHOULD allow air to enter the tank, when displacement is necessary; ie,,, you're using gas out of the tank, air needs to enter.

Does your tank suck air in when you open the cap? Replace it.

It would be nice to know your tank is not the problem, rather your Sending Unit, the item that tells your Fuel Gauge what to indicate.

When I worked on Audi's, it WAS the tank.........! I don't have nice things to say about Audis.

Best of luck,

Andy

Andy well you have been just about dead on. Turns out there was alot of gas in the tank. I pulled the rear cap off the tank and it was over half full. There is a float that we tapped a bit an reinstalled and my gauge came back up to about 3/4 after filling the tank. Now the idle problem was the idle air control motor. Just a coincidence it was dying after fueling.

I took it apart cleaned it up now its running perfect.

Now I have a problem with my radio air and mirrors not working . There is one fuse for this, but it is hot. So now I have no idea where the problem is.

What do you think?

Thanks, Paul

[AndyLowe]

Andy well you have been just about dead on. Turns out there was alot of gas in the tank. I pulled the rear cap off the tank and it was over half full. There is a float that we tapped a bit an reinstalled and my gauge came back up to about 3/4 after filling the tank. Now the idle problem was the idle air control motor. Just a coincidence it was dying after fueling.

I took it apart cleaned it up now its running perfect.

Now I have a problem with my radio air and mirrors not working . There is one fuse for this, but it is hot. So now I have no idea where the problem is.

What do you think?

Thanks, Paul

Paul,

Glad to hear you've made great progress on the fuel and idle problems!

I think your current opinion of a particular fuse as being good, has made you think that no other fuse is at fault. If I were at your house, I would help you by buying a subscription to www.alldatadiy.com and we would look at wiring diagrams together. In these diagrams we would find the source of battery voltage and its path to a large fuse first, say 40amp.

Next we would find branches off this 40 amp fuse (source) to many components and I'm confident you would see the NEXT fuse in line for Radio, A/C Control Head, and Mirrors. There may be one accessory relay / circuit breaker for these, or another fuse.

Have you had a aftermarket Radio, Alarm, GPS or Cell Phone installed recently? (Has someone cut, modified, spliced, jumpered in, any wiring?)

If so, gain access to where they last worked and visually inspect like a surgeon.

Yes, AllDataDIY is a great investment and gives you the birds eye view of how the +12 is sent to each device. It also shows you wire color and connector locations and pinouts.

It's the fastest way to understand and correct these problems and then you're off to problem free driving again!

Let us know?

Thanks,

Andy

I don't always check this site so you can have my email: andylowe@sbcglobal.net

[DouglasHood]

On 9/29/2010 at 10:20 PM, VBdenny said:

Do you get a big cacuum whoosh when you take the gas cap off?

What would that indicate? I'm curious because my cap seems to be doing this.