Understanding the fuel system
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5th Wheeling
Joined: Aug 2024
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I'm a bit disappointed in myself because I did not test the new fuel sender before putting the tank back in. Whenever I turn the key the fuel gauge goes to full which it is not. Could I have put the connector on wrong or is this most likely a bad sender? BTW the truck starts right up with the manual choke, happy about that. Thank again.
Moderator
Joined: Jan 2001
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From: Virginia
If you get under there and carefully squeeze your head between the tank and the driveshaft, you can see the sending unit on the front tank. Unplug the connector. Then go up and turn the key to run, you do not have to start the engine. The fuel gauge should go to empty. You can then take a jumper wire and jump the two terminals in the connector(if you have a two wire connector) and then go up and turn the key to run. The fuel gauge should swing to full. If it passes this test, the wiring and the fuel gauge are working, there is something wrong with the sending unit.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
I dont get what he is saying 
When you turn on the key the fuel gauge (and others) do not do a sweep and back to what the reading is and it also moves slowly.
Now if the tank is full and you turn the key on yes it should go to full but will take time to get there.
If tank is empty then it will stay at empty.
If you do the test Dave posted will tell you if there is a problem or not.
Remember this is old school and things were a lot different back then.
Gauges took their time to move from 0 to normal once motor was started.
Dave ----
When you turn on the key the fuel gauge (and others) do not do a sweep and back to what the reading is and it also moves slowly.
Now if the tank is full and you turn the key on yes it should go to full but will take time to get there.
If tank is empty then it will stay at empty.
If you do the test Dave posted will tell you if there is a problem or not.
Remember this is old school and things were a lot different back then.
Gauges took their time to move from 0 to normal once motor was started.
Dave ----
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5th Wheeling
Joined: Aug 2024
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For now i'm going to have to estimate my mileage and carry some extra gas on the truck since I leave tomorrow. I have run into another quandary that i hope someone can shed some light on. Today I went to install a 4-pin flat type connector for the u-haul trailer i'll be renting. The problems I ran into is that 4 pins only gives you left, right, running and ground, there's nothing for brake. On my truck there is a separate wire for the brake light. How do people get around this?
FTE Legend
Joined: Nov 2015
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From: Angier, NC
First I hope you got one of the Tee pig tails with the flat 4 so you dont use them 3M blue wire taps.
It fits between the tail light and frame harness. You unplug the trucks harnesses and plug the Tee between them and you now have a weather tight flat 4.
The 3M are not weather tight and will break down the wire over time and cause problems.
https://www.etrailer.com/Custom-Fit-...yABEgKnu_D_BwE
I run the Tee on my truck but cut the flat 4 off and took the wires to wire up a 7 flat blade round connector for the trailers I pull.
I also ran electric trailer brake and a trailer battery change wires to the 7 blade.
I was going to say unless you are from someplace that has to have a brake light and a turn light on at the same time you have everything needed to wire in the plug.
For others that dont know the turn & brake light is in the same bulb so it uses the same wire to the rear.
The "turning off" of the brake light for the side the turn signal is on for is done thru the turn signal switch.
Dave ----
It fits between the tail light and frame harness. You unplug the trucks harnesses and plug the Tee between them and you now have a weather tight flat 4.
The 3M are not weather tight and will break down the wire over time and cause problems.
https://www.etrailer.com/Custom-Fit-...yABEgKnu_D_BwE
I run the Tee on my truck but cut the flat 4 off and took the wires to wire up a 7 flat blade round connector for the trailers I pull.
I also ran electric trailer brake and a trailer battery change wires to the 7 blade.
I was going to say unless you are from someplace that has to have a brake light and a turn light on at the same time you have everything needed to wire in the plug.
For others that dont know the turn & brake light is in the same bulb so it uses the same wire to the rear.
The "turning off" of the brake light for the side the turn signal is on for is done thru the turn signal switch.
Dave ----
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5th Wheeling
Joined: Aug 2024
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Thanks..got the lights working. Took the truck to the Oregon dunes towing my sandrail. While the truck performed flawlessly the engine power was not what I was hoping for. I was the slowest vehicle on I-5 and found myself dropping down to 45mph on the long uphill climbs. It would run at 55-60 mph on flat roads but any faster would heat up the engine. I wonder if that cheap amazon carb has any affect on this. I didn't see the need to make any adjustments to it since the truck seems to run fine. I was pulling around 3500 lbs I guess. 7 hour trip took me 10 hours. Thinking it's v-8 time. Anyone looking for a old f-150?
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Joined: Jan 2001
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From: Virginia
That is the six. It should not have overheated, but running hotter while towing is normal. I hope you are not looking at the factory gauge and worrying about what it says. The six is just like my old diesel. It won't win any races but it will get you there reliably.
If it truly has overheating problems, you might have radiator problems or you might need a different fan setup.
If it truly has overheating problems, you might have radiator problems or you might need a different fan setup.
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FTE Legend
Joined: Nov 2015
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From: Angier, NC
With out going back over 8 pages what transmission, rear axle ratio and tire size.
My 1981 F100 4x2 Flare Side - 4.9 / NP435 w/ Advance Adaptor over drive, 2.75 gear and 235 / 75 / 15 tires also will not win any races but dose get the job done.
It is even slower when I pull a 20' enclosed trailer but the roads I am on the speed limit is 55 MPH so I dont use over drive.
There is 1 hill I hit that I got to drop down to 3rd from 4th and that is about 40 to 45 MPH also. It is what it is and I will live with it.
Do you know what the RPM is when running at 55 - 60?
I know mine is 1800 - 2100. Thye 300 power is at 1800 so if you can get the RPM higher when you hit the hills and let it drop down to the 2100 RPM you would be better but the RPM would be higher on the flat.
It is all a trade off. What was the MPG when pulling?
Oh if that carb is running lean it can get the temp up a little but I cant see going faster making it rise?
Heck last weekend I was running 75 to 80 MPH, even hitting 85 MPH, for miles to catch up to a my clubs group and the temp never wend up.
Dave ----
My 1981 F100 4x2 Flare Side - 4.9 / NP435 w/ Advance Adaptor over drive, 2.75 gear and 235 / 75 / 15 tires also will not win any races but dose get the job done.
It is even slower when I pull a 20' enclosed trailer but the roads I am on the speed limit is 55 MPH so I dont use over drive.
There is 1 hill I hit that I got to drop down to 3rd from 4th and that is about 40 to 45 MPH also. It is what it is and I will live with it.
Do you know what the RPM is when running at 55 - 60?
I know mine is 1800 - 2100. Thye 300 power is at 1800 so if you can get the RPM higher when you hit the hills and let it drop down to the 2100 RPM you would be better but the RPM would be higher on the flat.
It is all a trade off. What was the MPG when pulling?
Oh if that carb is running lean it can get the temp up a little but I cant see going faster making it rise?
Heck last weekend I was running 75 to 80 MPH, even hitting 85 MPH, for miles to catch up to a my clubs group and the temp never wend up.
Dave ----
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5th Wheeling
Joined: Aug 2024
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The factory temp gauge was doing some weird stuff. It may not have been hot at all . The temp would show real high then go down and up and all around. The second half of the drive it finally settled down and showed ok temps for the last 4 hours of driving. Whenever it showed as hot I pulled over , waited 15 min then checked the water which was always fine. One time the gauge actually pegged out. I suppose I'll have to get a better gauge. thx.
Lead Driver
Joined: Jun 2013
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From: Tolland, CT
FWIW, I found corroded terminals on some of the connectors on my 86, when my temp gauge would go from normal to pegged in a few seconds. Then drop back down at times. It was obvious to me, the engine wasn't overheating.
FTE Legend
Joined: Nov 2015
Posts: 30,912
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From: Angier, NC
I would look into the temp gauge thing.
I would also make sure the radiator cap was in good shape and holds psi and make sure you have a radiator recovery tank not just a puke tank as it needs to pull coolant back into the radiator.
I would also like to know the gear ratio, trans and tire size you got for pulling that trailer.
Dave ----
I would also make sure the radiator cap was in good shape and holds psi and make sure you have a radiator recovery tank not just a puke tank as it needs to pull coolant back into the radiator.
I would also like to know the gear ratio, trans and tire size you got for pulling that trailer.
Dave ----
Lead Driver
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An infrared thermometer is a handy tool to have when diagnosing a temp sensor issue or suspected overheating. Point the laser at your thermostat cover for gas engines seems to work well. I found on my 6.9l diesel that the thermostat cover it too heavy and the diesel engine block and heads are heavy too making an effective heat sink. So on diesel I recommend shooting right at the temp sending unit. There I get actual engine temp. Also make sure your connecting wire is good and the connection is clean and tight to the sender.
These things are pretty cheap starting at about 10 bucks and you can use them to check your BBQ temps too.
These things are pretty cheap starting at about 10 bucks and you can use them to check your BBQ temps too.
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