Gas tank problem on 1987 with two tanks

[weider1717]

I you have duel pumps and it does not make any noise check the conection at the pump good clean contacts and grounds. if all is good then the pump could be no good.

thanks,

but I just assumed it had a pump per each tank..is that not always the case in these trucks?

when I have it turned to the pump that don't work I don't hear it I also tried beating on the tank some no luck.

 

[royrey]

no spark now?

Say everything has been fine till yesterday morning. It cranked over and over and not a hint of wanting to start. I tried to add some starting fluid and did nothing at all. Had to do to work so put the battery on charge and got home and no difference. Dont think I have any spark. I check the fuse block for bad fuses, looked good there. I know this TBI stuff has relays and all. Dont know what to do next. Sure hope some one out there can stear me in the right direction to fix this truck.
thanks Roy

 

[royrey]

will not start now?

This truck will not even try to start now. I even add some gas to the carb throttle boddy and nothing at all. Can you tell me what to look for? Acts like no sprak is getting to the plugs. These relays have me up against a wall.
Thanks Roy

On an 87 with fuel injection the fuel tank selector valve switches four things, supply line, return line, pump electrical feed, and the gauge lead. Guam52 stated that when he switches to the left tank the engine stumbles and misses. Based on this statement I think the power for the left pump is getting switched. If the pump power didn’t switch, the engine would die immediately. Stumbling and missing are signs of low fuel pressure.

It seems to be common problem with these selector valves that when they fail they will continue to switch the supply, pump power, and the gauge lead, but the return port hangs up blocking the return path to either tank. The electric pump is capable of putting out over 30 pounds of pressure and with the return path blocked off that stresses all of the elements in the supply line. Typically the weakest link in the supply line is that small hose that connects the output of the pump to the metal line that exits the tank because it is submerged in gas all the time. That hose will split causing a low pressure condition. You can elimate the selector valve by bypassing it.

Replacing the selector valve will correct the return blockage problem, but you will also have to replace the hose in order the get the fuel pressure up where it should be.

I may be all wet here, could be a weak pump or flakey valve, but I have seen this problem on a couple of trucks I have messed with.

GonicGM,

I have never messed with a duel tank system on a carbureted truck but base on what you have stated, it sounds to me like the selector valve or the switch is bad. I would try the switch first; it’s less expensive and pretty easy to change.

Hope I don’t sound like a smarta__ or a know-it-all, I’m just trying to help you guys fight the battles that I have already fought.

Don

 

[GonicGM]

Get a second person to help. Grab a spare spark plug or pull one if you have no extras. Crank it over, meanwhile have someone hold a plug wire, spark plug end with a plug in it and place near good ground. Do you have spark? If no, pull distributor cap, check for obvious parts problems(damage) If no, crank again and verify rotor movement. If yes, your choices probably are:

bad coil
bad ignition module
no 12v to coil
distributor not grounding

pull 12v lead to coil (large red wire) with ignition on, check for voltage.

 

[royrey]

Ok found that the distributor pick modual was bad , went to Napa Auto and ended up replacing the whole distributor, cap rotor and pickup coil. It was cheaper to buy it as a package deal and fix it all. Fired right up.
But now I am not sure how to correctly set the timing. I can't get the timing mark to line up on the the indicator on the block unless the motor stumbles. So I have it set to just where it runs good, but I have no idea of the setting it is on. Could use some good advice and outline on how to set it. Is there some sort of wire to disconnect to get the timing set and then re-hook it up?
Thanks for advice you have.
Roy

 

[GonicGM]

Ok found that the distributor pick modual was bad , went to Napa Auto and ended up replacing the whole distributor, cap rotor and pickup coil. It was cheaper to buy it as a package deal and fix it all. Fired right up.
But now I am not sure how to correctly set the timing. I can't get the timing mark to line up on the the indicator on the block unless the motor stumbles. So I have it set to just where it runs good, but I have no idea of the setting it is on. Could use some good advice and outline on how to set it. Is there some sort of wire to disconnect to get the timing set and then re-hook it up?
Thanks for advice you have.
Roy

There is probably a wire you need to disconnect to deactivate the ESC. I'm not sure on the R/V truck, but on my 90 S10, it is a single tan or tan/white wire sticking out of the harness with a dedicated one wire plug and is located just behind the carpet under the dash at the passengers toes. Once again, not sure where or what color on R/V

 

[Jeffrey]

I had plenty of problems also, so I decided to take everything loose from one tank and just use one tank only. unless you take long trips and really need a second tank. Eliminate all the switches and valves this way..

 

[GonicGM]

I had plenty of problems also, so I decided to take everything loose from one tank and just use one tank only. unless you take long trips and really need a second tank. Eliminate all the switches and valves this way..

I take long trips in my K30. Dual tanks really work for me for these reasons:

1) I take trips to states that have much higher gas prices than others, If I fill 40 gallons, this worries me less.

2) Sometimes I travel at hours when gas stations aren't open.

3) It's not convenient to pull into busy gas stations towing a loaded trailer sometimes.

4) I fill both tanks for plowing, extra weight.

5) I can put different octanes in each tank. If I'm towing empty one way, I select one tank for regular. On return trip loaded, I'll select the other for premium. Not that I do, but I could get really fancy. Select the tank with regular for level and downhill grades, select the tank with premium for uphill grades.

6) At a busy gas station, I don't care which lane or side of the pump I pull up to.

7) When towing, I get single digit mileage, so all of the above becomes that much more important for dual tanks.

Dual tanks rule!

 

[smz1919]

fuel gauge reading issues

I have an 87 gmc 1500 with dual tanks. Both of them will stop in between 1/4 and half. The tank will not let me put anymore gas in. I replaced the sending unit, float, screen etc. in my driver side tank and It is still having the same problem. when I had the tank dropped I tested the gauge and grounded it out and it went all the way to full so I know the gauge works. also tested the new sending unit and float and it works. could I have a bad ground somewhere that's stopping the gauge from reading full? and why will it not allow me to put anymore fuel in my tank when I know for a fact it is not full?

Getting very frustrated with this issue

 

[Pontiac1976]

Has this problem just started, or have you been able to fully fill it up before.
If yes. Then check your tank vent lines to the charcoal can & (filter on the can) to make sure it not blocked.
Other things is the tank dented.
Could be gas gauge not reading right.


Could be the way your filling up the tank, if this is a new buy and it has been like this since you got the truck.


Another place to check is the vent bye pass tube make sure it not blocked.


A lot of gas pump, Pump to fast for these trucks. You may have to pull out the tip out a bit turn it a little one way or the other try to pump slower to get it filled up.


Another thing test your tank is fill up as you do, and fill up gas can get hand pump filler put the can in box above the gas tank door and then hand up the gas in see. After you get primed it will flow by it self. See how much gas goes in the tank. The main tank should be as much as 20 gallon or 16 gallons and same for the #2 tank mostly a 16gallon but check your manual. To see what option you had. Two 20G or 20G & 16G that the most common but check.


If start to run out the neck because it to full then check the gauge see if it show full or a little over full. then your Gauge is bad.

 

[smz1919]

Has this problem just started, or have you been able to fully fill it up before.
If yes. Then check your tank vent lines to the charcoal can & (filter on the can) to make sure it not blocked.
Other things is the tank dented.
Could be gas gauge not reading right.


Could be the way your filling up the tank, if this is a new buy and it has been like this since you got the truck.


Another place to check is the vent bye pass tube make sure it not blocked.


A lot of gas pump, Pump to fast for these trucks. You may have to pull out the tip out a bit turn it a little one way or the other try to pump slower to get it filled up.


Another thing test your tank is fill up as you do, and fill up gas can get hand pump filler put the can in box above the gas tank door and then hand up the gas in see. After you get primed it will flow by it self. See how much gas goes in the tank. The main tank should be as much as 20 gallon or 16 gallons and same for the #2 tank mostly a 16gallon but check your manual. To see what option you had. Two 20G or 20G & 16G that the most common but check.


If start to run out the neck because it to full then check the gauge see if it show full or a little over full. then your Gauge is bad.

No it's had this problem since I bought it. Nothing is blocked. Just took the bed off and dropped the driver side tank this past weekend to install a new sending unit. It's not the way it is being filled up because it will shoot the gas back out like its full but I know for a fact its not.

 

[Pontiac1976]

Ok is your a box or a flat bed??
If you have the flat bed you might not have the right angle on the filler neck
the neck must be higher then the tank you will have to play with angle to get it right. Same thing goes for a box if it does not have the right hose or a better angle.


The fuel has to down hill. The vent tube must be at the higher side to vent gases & air.


clocking of the filler pipe vent up ward some where 10 or 11 o-clock


Only other thing is the tank sitting at a angel to the back.


Because it does not matter what the gauge says if the tank will not fill up.


I hope this helps from what you say.
Oh is it carb or fuel injection.

 

[Pontiac1976]

AS I know for sure if the neck is higher not enough the fuel fills the neck then wash back run all over the ground the only way fill is with a had pump
like I said before. I friend helped with the new flat bed dropped the angel straighten neck out a bit. Now that how I fill it to move it in out of the shop.
As I work on the truck frame cab.

 

[smz1919]

Ok is your a box or a flat bed??
If you have the flat bed you might not have the right angle on the filler neck
the neck must be higher then the tank you will have to play with angle to get it right. Same thing goes for a box if it does not have the right hose or a better angle.


The fuel has to down hill. The vent tube must be at the higher side to vent gases & air.


clocking of the filler pipe vent up ward some where 10 or 11 o-clock


Only other thing is the tank sitting at a angel to the back.


Because it does not matter what the gauge says if the tank will not fill up.


I hope this helps from what you say.
Oh is it carb or fuel injection.

its fuel injected. neck is flowing downhill. tank seems to be in line. not sagging in the rear. vent line seems fine. my only thought is there's a bad ground somewhere from the tank to the gauge. I guess I can try to splice a ground in and ground somewhere else and see if it works. On an 87 dual fuel tank, are there two different grounds? one from each tank that lead to the selector switch then to the gauge or is it one ground just spliced?

 

[Pontiac1976]

If the ground to frame from the sender is bad or broken the fuel gauge will read way over full.

 

[Nate]

Guys I am experiencing the same problem the original poster was facing. Mt truck only runs on one tank. I have gotten waist deep in trying to fix it already. I am almost certain that the fuel switching valve has gone bad. I have one question for you all. When I disconected the electric plug from the switching valve some gasoline poured out (onto my face). Is that normal? I don't believe gas is supposed to be there. Is this a tale tell sign that the valve needs replacing?

 

[GonicGM]

Guys I am experiencing the same problem the original poster was facing. Mt truck only runs on one tank. I have gotten waist deep in trying to fix it already. I am almost certain that the fuel switching valve has gone bad. I have one question for you all. When I disconected the electric plug from the switching valve some gasoline poured out (onto my face). Is that normal? I don't believe gas is supposed to be there. Is this a tale tell sign that the valve needs replacing?

Should be no fuel at electric plug. Sounds very dangerous. In the meanwhile of changing valve, I would bypass the valve for feed and vapor line with hoses from good tank feed to main chassis lines then loop hose from now open inlets to outlets on valve to ensure no leak-by from other tank or residual fuel.

 

[vwnate1]

Fire warning

Nate ;

Get rid of that transfer valve RIGHT NOW before it kills you .

Lots and lots of tank valves on junked trucks .

older one only have a few hose nipples , the newer ones also have the vapor hose nipples , just ignore those and use the newer valve on your older truck .

Unless of course , you're a pedantic fool like , er , well me who took the time t replace and connect every single hose on my old '76 GMC as it had to pass smog testing here in California , land of Fruits , Nuts and Flakes ~ I even rustled up a million (or so) spring typ hose clamps as they're required , even on the vacuum hoses and I like to sweat the details....

 

[mbyoung424]

I'm having the same problem as the OP with the addition of the fuel pump running continuously with ignition off. Right now I just pull the fuse to turn them off. This is my Grandpa's old truck that was given to my sister. While she had it I was told the wiring harness to the fuel tank was replaced. I assume this was done wrong and that's why the fuel pumps run continuously. I have the wiring diagram and plan on working on this tomorrow. As for the left tank not working, when the fuel tank selector switch is on the left tank you can hear the fuel pump running and the gauge works, but the engine dies immediately. Is it possible to test the selector valve for proper functionality or is it just best to swap out?