Goofy Gas Gauge or Pesky Space Aliens!!

KilgoreTrout said:

I've been probed.

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Way to much info and did it hurt?

Well, the truck did it again.
Started out this morning with both tanks full (20 gallons each) and drove to the big city.
Driving home, the driver's side tank ran out at the same place on the highway as it it did the other day, and I am willing to bet there is still 10 gallons (give or take a little) of gas in the tank.
My normal fuel usage is about a quarter tank (5 gallons) each way.
Any ideas??
I'm thinking build a framework with lumber, use my come-along and chains, and remove the truck bed and then remove the driver's side sending unit and peek inside the tank.
I want to replace all the rubber fuel lines that are a bitch to get to anyway, and that will be the perfect time to do that task.

Maybe the pickup came off the pump , raising the empty level?

It's not an in-tank pump.
It's still the original mechanical unit from 82/83.
I don't think I have ever seen a two piece fuel pickup from back then.

possible vapor lock?? before you pull anything try to run it on that tank again. see if it starts and runs . and when you take it apart might as well change the in tank screens on the pickups.

IF it's a vapor lock issue, it would have to be at the switchover solenoid.
As soon as the engine sputters, I switch the solenoid over to the passenger tank and all is fine.
So I would probably rule out vapor lock, but thanks for the suggestion.
Then again, if anything weird is going to happen, I always get it.

Did you try opening the gas cap when the problem occurred? Maybe it's not venting properly and you're pulling vacuum.

It quit drawing fuel from that tank two city trips in a row, fairly level road, temperature about the same.
And within a quarter mile of each event.
So the mileage is the same.
I would think vapor lock might occur anywhere along that highway if it's going to.

Blue Ox said:

Did you try opening the gas cap when the problem occurred? Maybe it's not venting properly and you're pulling vacuum.

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Thanks, I forgot that can sometimes happen.
Usually on later model emission control heavy cars, but possible on most anything.
I will take everybody's suggestions and test for restart after having used the other tank and will unscrew the gas cap and see if it runs right on that tank.
I still want to replace rubber lines and check all connections and grounds.

Okay, I unscrewed gas cap, but since it's been a couple hours since the incident, there's a good chance the pressure has equalized.
Started the engine and switched to the driver's side tank.
Runs fine !!!
I'm thinking if it was vapor lock, it should occur at the switching solenoid vicinity, in which case most likely would also affect the line to the other tank.

I'm wondering since it always happens on the same stretch of road where they are replacing a highway bridge, that there might be a spirit of a dead bridge builder on site from the old days, or maybe a native indian spirit messing with me,
We do have spirits of long dead indians in my area.
And being daylight and the highway crew was working, no space aliens could be involved.

mtnmankev said:

And being daylight and the highway crew was working, no space aliens could be involved.

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You never saw "They Live" did you?

I will have to see if Hulu has it.

And to answer the question, no I did not stop and unscrew the gas cap as soon as it happens.
I was on my home from a long tiring city trip and I don't stop for anything.
I just want to get home.

Try swapping the caps before your next trip.

Blue Ox said:

Try swapping the caps before your next trip.

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I will try that, it will be a few days though.

I will top off both gas tanks before leaving, as usual, giving me the same reference point to work from too.

You may want to check:

1) Your returns lines are going to the correct tank. I had a shop change the dual tank switch and they swapped the return lines by mistake. Then I filled up both tanks after leaving the shop. Next thing I know, I'm spewing gas out of the passenger side tank (it looked like the airplane scene from Die Hard 2, but without the explosion).

2) The fuel gauge ground on the instrument cluster. The fuel levels kept changing, would never show full, etc. The positive and negative from the sending unit were OK, but the gauge ground (on the bottom in the middle of the cluster) was loose, causing the funky readings. (Thanks to Mike's Speedo Repair for finding this one).

3) Your sending units are working correctly. The float mechanism could be getting hung up in the tank and not dropping down all the way, making you think you have fuel. Or it could be the sending unit is faulty.

4) You could have too much resistance (pinched or broken wire?) on the line from that tank.

I hope this helps.

P.S. - It's not that I'm smart, I just break a lot of things.