Fast Intentions Stage 2 TT build by MA-Motorsports.

phunk · 03-04-2022, 04:01 PM

I am going to guess that the fuel level sensor is on its way out. When mine was going out several years ago, it would intermittently shift between 2 positions about 1/4 tank worth apart. Sometimes hours apart, sometimes not long at all. Sometimes it would read full tank when I filled it, sometimes it would read less than full.

There are those fill valves on the bottom of the canister.. on level ground it would only take maybe 1", if even, of fuel depth to get to the fuel pumps. So if the tank was quite low, it would be no surprise to have fuel pickup issues on a steep hill since the fuel pump mounting flange is about in the middle of the tank (front to rear) and so is the venturi pickup on the driver side. But since it sounds like it didnt want to run even on level ground until you added fuel, I have to assume that either the tank was legit empty (level sensor reading optimistic), the check valves are blocked (unlikely with such a new installation), or perhaps the fuel pumps are too high (i have seen people slide them all the way up in the pump holder rather than setting them so the pickups are as low as possible)

redondoaveb · 03-04-2022, 04:59 PM

Quote:

Originally Posted by phunk

I am going to guess that the fuel level sensor is on its way out. When mine was going out several years ago, it would intermittently shift between 2 positions about 1/4 tank worth apart. Sometimes hours apart, sometimes not long at all. Sometimes it would read full tank when I filled it, sometimes it would read less than full.

There are those fill valves on the bottom of the canister.. on level ground it would only take maybe 1", if even, of fuel depth to get to the fuel pumps. So if the tank was quite low, it would be no surprise to have fuel pickup issues on a steep hill since the fuel pump mounting flange is about in the middle of the tank (front to rear) and so is the venturi pickup on the driver side. But since it sounds like it didnt want to run even on level ground until you added fuel, I have to assume that either the tank was legit empty (level sensor reading optimistic), the check valves are blocked (unlikely with such a new installation), or perhaps the fuel pumps are too high (i have seen people slide them all the way up in the pump holder rather than setting them so the pickups are as low as possible)

Here's where my pumps are set

Spooler · 04-04-2022, 07:22 PM

Quote:

Originally Posted by phunk

I am going to guess that the fuel level sensor is on its way out. When mine was going out several years ago, it would intermittently shift between 2 positions about 1/4 tank worth apart. Sometimes hours apart, sometimes not long at all. Sometimes it would read full tank when I filled it, sometimes it would read less than full.

There are those fill valves on the bottom of the canister.. on level ground it would only take maybe 1", if even, of fuel depth to get to the fuel pumps. So if the tank was quite low, it would be no surprise to have fuel pickup issues on a steep hill since the fuel pump mounting flange is about in the middle of the tank (front to rear) and so is the venturi pickup on the driver side. But since it sounds like it didnt want to run even on level ground until you added fuel, I have to assume that either the tank was legit empty (level sensor reading optimistic), the check valves are blocked (unlikely with such a new installation), or perhaps the fuel pumps are too high (i have seen people slide them all the way up in the pump holder rather than setting them so the pickups are as low as possible)

It is one of the fuel sendors. One of them is bad. I had a full tank. Went for a quick drive. 1/2 tank. Put 6 gallons of fuel in it and it still reads 1/2 tank. LOL, There done.

phunk · 04-04-2022, 11:25 PM

Quote:

Originally Posted by Spooler

It is one of the fuel sendors. One of them is bad. I had a full tank. Went for a quick drive. 1/2 tank. Put 6 gallons of fuel in it and it still reads 1/2 tank. LOL, There done.

That is a large amount to lose. So the sensors are wired in series, out one into the other and out again to the gauge. If either of them had a broken wire or crimp that came out, the gauge would entirely die.

Ive attached a page from the service manual for determining which sensor is bad. If you fill the tank again, without having to open the tank at all, you can just unplug the tophat on both sides of the tank and test resistance across the sensor terminals. Both should read about 3.0ohm full... whichever one is way out, is your culprit. I will bet its the passenger side, since its been handled more.

Also, dont open the tank until you think its more than halfway empty, or it will make a big mess.

Spooler · 04-05-2022, 12:05 AM

Quote:

Originally Posted by phunk

That is a large amount to lose. So the sensors are wired in series, out one into the other and out again to the gauge. If either of them had a broken wire or crimp that came out, the gauge would entirely die.

Ive attached a page from the service manual for determining which sensor is bad. If you fill the tank again, without having to open the tank at all, you can just unplug the tophat on both sides of the tank and test resistance across the sensor terminals. Both should read about 3.0ohm full... whichever one is way out, is your culprit. I will bet its the passenger side, since its been handled more.

Also, dont open the tank until you think its more than halfway empty, or it will make a big mess.

I will worry about it later and just giggle about it for now. Fuel pumps are 4 years old with about 20k miles on them. Will probably put 2 new ones in it when I do whatever I do.

03-04-2022, 04:01 PM	#1 (permalink)
phunk A True Z Fanatic Join Date: Mar 2009 Location: Chicago Posts: 3,669 Drives: 370 Rep Power: 974724	I am going to guess that the fuel level sensor is on its way out. When mine was going out several years ago, it would intermittently shift between 2 positions about 1/4 tank worth apart. Sometimes hours apart, sometimes not long at all. Sometimes it would read full tank when I filled it, sometimes it would read less than full. There are those fill valves on the bottom of the canister.. on level ground it would only take maybe 1", if even, of fuel depth to get to the fuel pumps. So if the tank was quite low, it would be no surprise to have fuel pickup issues on a steep hill since the fuel pump mounting flange is about in the middle of the tank (front to rear) and so is the venturi pickup on the driver side. But since it sounds like it didnt want to run even on level ground until you added fuel, I have to assume that either the tank was legit empty (level sensor reading optimistic), the check valves are blocked (unlikely with such a new installation), or perhaps the fuel pumps are too high (i have seen people slide them all the way up in the pump holder rather than setting them so the pickups are as low as possible) __________________ Charles @ CJ Motorsports : Website \| Facebook \| Instagram \| YouTube Home of the 9 second, stock longblock, stock drivetrain 6MT 370z. 9.91 @ 142mph

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