Fuel Selector valve Troubleshoot

[bwilhite1]

Guys,
Please double check my thinking here. I've reviewed the service manual and done a search here. Thinking I might have a bad Pollack valve.

Here's the background:
My 86 K10 won't feed from the left tank, but works fine from the aux tank. It doesn't quit when you switch tanks, it just seems like it doesn't switch tanks. The tank selector switch is new, and I can hear the motor on the selector valve being actuated when I switch from L/R tank and vice versa. The electric motor does sound different depending on which tank you choose. I've just swapped the sending unit in the left tank and fuel indications seem to be accurate when I flip the switch. The left tank is empty and the aux tank is full.

Yesterday, I ran the truck using the aux tank and had the left fuel hoses unplugged, but sending unit plugged in and grounded. I switched to the left tank and nothing happened. The truck kept running for about 2-3 minutes until I turned off the key. I revved it lightly to help it burn the fuel in the line and also put my finger over the disconnected fuel lines and didn't feel any suction. I would have let it go longer, but didn't want things to get too hot with me crawling around underneath it.

My question is....does it sound like a bad selector valve or did I just not let it run long enough to quit? I assumed it would starve itself of fuel pretty quickly. I took the cover off of the selector valve, but haven't checked the power supply, although I assume it's good since I can hear the electric motor with the truck off. That selector valve looks like a bear to change and I wanted to get someone's opinion that has a little more experience.

Thanks.

 

[gmachinz]

Sounds like the selector valve itself is weak/bad or it has debris clogging it up @ the valve.

 

[bwilhite1]

That seemed logical to me, but without knowing exactly how that valve works internally, I wasn't 100% sure. I will go out and double check power supplies today. Short of taking it out, is there any way to troubleshoot the valve itself? I found the trouble shooting chart, and the last decision point on the first page directs you to check the selector valve side of the harness if power to the harness is good, but there's no second page of the chart. Any advice?

http://www.turboimagehost.com/p/20383255/2.jpg.html

 

[bwilhite1]

I let the truck run for a little bit just to make sure that valve isn't switching to the empty tank. It idled for just under 10 minutes, but DID starve out and quit. Not sure if that's normal timing, but I gave up on it much earlier yesterday.

 

[gmachinz]

Did you inspect the tank inside when you swapped sending units out? I had that same problem-turned out there was a lot of debris at the bottom which would clog up the suction screen of the pickup assembly-causing it to starve for fuel.

 

[bwilhite1]

Did you inspect the tank inside when you swapped sending units out? I had that same problem-turned out there was a lot of debris at the bottom which would clog up the suction screen of the pickup assembly-causing it to starve for fuel.

Yes. There wasn't really any debris, but the old fuel strainer sock was pretty rusty looking. The inside of the tank wasn't too rusty, in my uneducated opinion, so I just dumped the old gas out and put a new sock on with the new sender. Got everything hooked up, bolted the tank back on, and put half a tank of gas in it to test drive.

I guess at idle, the fuel consumption must be even lower than I realized, because it quit running less than a minute after being switched over to the left tank while running down the highway. I guess that narrows it down to the valve, but I'm just really not looking forward to changing it.

 

[Handy Andy]

Changing the selector valve out is a major pain in the arse. I just did it in my 86 gmc sierra 1/2 ton. The first thing I would recommend doing before you remove the valve is disconnect the hoses that go to the problematic tank 1 by 1 and use an air compressor to blow air through them. I messed up on mine because I replaced the fuel selector valve only to find out it wasn't the problem. The tank I was having problems with was bottoming out when I tried to switch to it, so I assumed the sending unit was bad and the selector valve was also bad. Turns out there was a hole in the front of the tank that you could have put a fricken volleyball through. So, new tank and sending unit got everything working for me again...

 

[bwilhite1]

Changing the selector valve out is a major pain in the arse. I just did it in my 86 gmc sierra 1/2 ton. The first thing I would recommend doing before you remove the valve is disconnect the hoses that go to the problematic tank 1 by 1 and use an air compressor to blow air through them. I messed up on mine because I replaced the fuel selector valve only to find out it wasn't the problem. The tank I was having problems with was bottoming out when I tried to switch to it, so I assumed the sending unit was bad and the selector valve was also bad. Turns out there was a hole in the front of the tank that you could have put a fricken volleyball through. So, new tank and sending unit got everything working for me again...

Say what now? You had a hole in the gas tank itself, or it was grounding out? I already removed the tank and replaced the sending unit.

 

[bwilhite1]

Also, do you remember the part number for the valve you used? I got the old one off. It was a pain in the rear. Went to put the new one on and the smaller holes aren't the same size as the pump I took off. I'm using AC Delco 7001, but the knock off pumps from Autozone have the same, wrong sized, holes. Autozone shows only one pump available, but AC Delco also sells part number 14029228, which I'm hoping is correct.

 

[Handy Andy]

Mine actually had pretty much the entire front of the tank rusted out. I don't remember the part number one the one I used. I got it from napa. I remember the ports seemed a little big so I ended up using some some silicone lubricant to get thone hoses to slip on.

 

[bwilhite1]

Just finished swapping out the fuel tank selector valve today and thought I'd pass on what I learned and close out the thread.

All of the parts stores show AC Delco U7001 (or a knock-off) as the only 6-port fuel tank selector valve available. For me, the fuel return line hookups were too large, and didn't match the old valve that I took off. Not a huge deal, but that thing is a PITA to change out, so I didn't want to make it anymore difficult than it already was.

If you have to do this repair, AC Delco #14029228 was the part that I needed, and was only available online for about $110.

Also, unless you've got the special pliers to deal with the hose clamps, use the screw-on type hose clamps instead of the ones you've taken off. IMO, using those and a 5mm socket made it much easier than fooling with a pair of pliers. Probably common knowledge to most, but just thought it was worth mentioning.

 

[bwilhite1]

So much for closing out the thread......

I let the truck idle for 20 minutes to make sure it was burning out of the production tank, which it did with no issue. Took it down the road and it stumbled and died. Switched to the Aux tank and it ran like normal again. Came home and let it idle on the production tank again....died after 10 minutes.

Not sure what the problem is, but not real happy to learn I swapped that valve out for nothing.

To me, it seems like it'd have to be something blocking the fuel line between the production tank and the valve. I blew the supply line out with an air compressor. I had a helper blow the supply line out while I felt the air come out at the selector valve, so I don't think that the hoses were crossed or anything simple like that. I didn't blow out the vent or return line. Any chance of a vacuum lock or something? I'm stumped.

 

[74 Shortbed]

Tank has to vent so need to check that, could be sucking air somewhere too.

 

[chengny]

Tank has to vent so need to check that, could be sucking air somewhere too.

I am going with the second part of 74 Shortbed's suggestion.

Carefully check the integrity of both the LH side rubber supply line hoses - the one that connects the sender nipple to the metal tubing & the one between the metal tubing and the tank transfer valve.

As for the first part of his suggestion, just try running off the production tank with the fill cap removed.

 

[bwilhite1]

Thanks for the advice. Found the problem.

Not sure what the normal length is supposed to be for the rubber fuel lines at the tank, but mine were about 36" long. The supply line was long enough that it kinked when the tank was bolted on. It obviously worked fine while the tank was sitting on the ground, which was what I couldn't figure out.

The PO drove it for years and sold it to me thinking the left tank didn't work. I changed the sending unit...and that $*@$%^# selector valve....for nothing. I learned something, but damn.

Thanks again. I wouldn't have thought about it without your suggestions.